Environmental Control and Life Support System
The Environmental Control and Life Support System (ECLSS) maintains the thermal stability of the orbiter and provides a pressurized, habitable environment in the crew compartment for the crew and onboard avionics. ECLSS also stores water and crew liquid waste.
ECLSS may be functionally divided into four systems as shown in Figure 1-1. Each system is described in detail later in this book.
a. Pressure Control System (PCS) - The PCS pressurizes the crew compartment with a breathable mixture of oxygen (O2) and nitrogen (N2). N2 also is used to pressurize the supply and wastewater tanks.
b. Atmospheric Revitalization System (ARS) - The ARS circulates air and water through the crew compartment to remove heat, control humidity, and maintain carbon dioxide (CO2) concentrations within tolerable levels.
c. Active Thermal Control System (ATCS) - Two Freon loops collect waste heat from orbiter systems and transfer that heat overboard.
d. Supply and wastewater system - The supply water system stores water produced by the fuel cells for drinking, personal hygiene, and orbiter cooling. The wastewater system stores crew liquid waste and wastewater from the humidity separator.
Additionally, the external airlock of the orbiter is considered part of ECLSS, but it is covered in a separate section of this document.
ECLSS overview Environmental Control and Life Support System Interfaces
PRESSURE CONTROL SYSTEM INTERFACES
a. Fuel cell Power Reactant Storage and Distribution (PRSD) system - The PRSD system supplies cryogenic O2 to the PCS.
b. Supply and wastewater system - The water tanks are pressurized by N2.
c. ATCS - The cryogenic O2 is warmed by the ATCS Freon loops in the O2 restrictors.
d. ARS - The PCS provides air circulation necessary for O2 and N2 control and to prevent localized concentrations of O2 or N2.
e. Crew - The crew breathes O2 and N2. The crew also controls cabin pressure to meet mission requirements such as Extravehicular Activity (EVA) and International Space Station (ISS) docked operation.
f. Caution and Warning (C/W) - Sensor outputs are continuously checked for out-of- limits conditions.
g. Instrumentation (INST) - Sensor outputs are conditioned for display and telemetry.
h. Data Processing System (DPS) - Sensor outputs are provided for Systems Management (SM) conditioning, monitoring, and display of PCS parameters on Cathode-Ray Tube (CRT) displays (or the equivalent Multifunction Display Unit (MDU) if upgraded to the Multifunction Electronic Display System (MEDS)) and dedicated display meters.
i. Onboard Display and Control (D&C) - Dedicated meters provide the crew with system information. Switches, circuit breakers, and talkbacks allow the crewmembers to monitor and control system configurations.
j. Electrical Power Distribution and Control (EPDC) - The EPDC distributes electrical power to operate the PCS controls and equipment.
ECLSS interfaces Diagram
ATMOSPHERIC REVITALIZATION SYSTEM INTERFACES
a. Supply and wastewater system - Humidity condensate removed from the cabin air is stored in the wastewater tank. Supply water (drinking water) is chilled by the ARS.
b. ATCS - The ATCS takes the waste heat collected by the ARS water loops and transfers the heat overboard.
c. PCS - The PCS maintains a controlled cabin pressure at a density adequate for heat transfer (minimum of 8 psi) from air-cooled equipment to the water loops.
d. Crew - The crewmembers’ presence in the cabin produces humidity, CO2, and heat that must be removed.
e. INST - Sensor outputs are conditioned for display and telemetry.
f. C/W - Sensor outputs are continuously checked for out-of-limits conditions.
g. DPS - Sensor outputs are provided for SM conditioning, monitoring, and display of ARS parameters on CRT displays and dedicated display meters.
h. D&C - Dedicated meters provide the crew with system information. Switches and circuit breakers allow the crewmembers to monitor and control the system and verify system configuration.
i. EDPC - The EDPC distributes electrical power to operate the ARS controls and equipment.
ACTIVE THERMAL CONTROL SYSTEM INTERFACES
a. ARS - The ARS collects waste heat from inside the crew compartment and passes the heat to the ATCS in the water/Freon interchanger.
b. Supply and wastewater system - Supply water is used by the Flash Evaporator System (FES) to cool the Freon loops.
c. PCS - The ATCS Freon loops warm the PCS cryogenic O2 in the O2 restrictors.
d. Hydraulics - The ATCS Freon loops warm the orbiter hydraulic fluid.
e. Fuel cells - The fuel cell O2/H2 reaction produces heat. This heat is transferred to the Freon loops in the fuel cell Heat Exchanger (HX).
f. Payloads - The ATCS Freon loops provide cooling for payloads (e.g., SpaceHab).
g. C/W - Sensor outputs are continuously checked for out-of-limits conditions.
h. INST - Sensor outputs are conditioned for display and telemetry.
i. DPS - Sensor outputs are provided for SM conditioning, monitoring, and display of ATCS parameters on CRT displays and dedicated display meters.
j. D&C - Dedicated meters provide the crew with system information. Switches, circuit breakers, and talkbacks allow the crewmembers to monitor and control system configurations.
k. EPDC - The EPDC distributes electrical power to operate the ATCS controls and equipment.
SUPPLY AND WASTEWATER SYSTEM INTERFACES
a. ARS - Humidity condensate removed from the cabin air is stored in the wastewater tank. The ARS chills supply water to provide cold drinking water for crew consumption.
b. PCS - The water tanks are pressurized by N2.
c. ATCS - Supply water is used by the FES to cool the Freon loops.
d. Fuel cells - The fuel cell O2/H2 chemical reaction produces water, which is stored in the supply water tanks.
e. Crew - The crewmembers use supply water for drinking and personal hygiene. The crewmembers’ liquid waste is stored in the wastewater tanks.
f. Extravehicular Mobility Unit (EMU) - Supply water is used to recharge the EMU in the airlock.
g. C/W - Sensor outputs are continuously checked for out-of-limits conditions.
h. INST - Sensor outputs are conditioned for display and telemetry.
i. DPS - Sensor outputs are provided for SM conditioning, monitoring, and display of supply and wastewater system parameters on CRT displays and dedicated display meters.
j. D&C - Dedicated meters provide the crew with system information. Switches, circuit breakers, and talkbacks allow the crewmembers to monitor and control system configuration.
k. EPDC - The EPDC distributes electrical power to operate the supply and wastewater system controls and equipment.
PRESSURE CONTROL SYSTEM
The crew compartment (cabin) is normally pressurized to 14.7 psia to provide the crew with a habitable O2/N2 environment. This pressurization also provides the cabin atmosphere necessary to cool the cabin air-cooled equipment. Positive and negative pressure relief valves protect the structural integrity of the cabin from over- and underpressurization. The PCS N2 is used to pressurize the supply and wastewater tanks. The PCS also supplies breathing O2 directly to the Launch and Entry Suit (LES) helmets.
The 14.7 psia cabin atmosphere is maintained by either of the two PCS systems. These O2/N2 systems are commonly referred to as PCS system 1 and PCS system 2. At 14.7 psia, the crew compartment is normally pressurized with approximately 40 pounds of O2 and 130 pounds of N2. This 20 percent O2 and 80 percent N2 atmosphere closely resembles the atmosphere at sea level on Earth. Each PCS system can be broken down into three functional components: the O2 system, the N2 system, and the O2/N2 manifold.
The fuel cell PRSD system supplies the PCS with O2 from the same cryogenic tanks used to supply the fuel cells. The O2 is maintained at a pressure of 811 to 875 psia by heaters in the O2 tanks. The high-pressure O2 enters the PCS through the O2 supply valves (Figure 2-1). These valves are latching solenoid valves. If power to an O2 supply valve is lost, it will remain in its present position.
After passing through the O2 supply valve, the O2 flow is then limited by an O2 restrictor. Freon warms the O2 in the restrictor to a comfortable temperature before it flows into the cabin. PCS system 1 has one 23.9 ± 1 lb/hr flow restrictor, while PCS system 2 has two parallel 12.0 ± 0.5 lb/hr flow restrictors. The flow restrictors protect the fuel cell cryogenic system pressure from being depleted by an excessive demand from the PCS. Freon loop 1 warms the PCS system 1 O2, and Freon loop 2 warms the PCS system 2 O2.
Next, the O2 piping penetrates the 576 bulkhead and enters the crew compartment. Check valves inside the cabin prevent the reverse flow of O2 in both PCS systems. Downstream of the check valves, O2 system 1 and O2 system 2 are connected by an O2 crossover line. This O2 crossover line allows both O2 systems to supply O2 to the crossover manifold. O2 systems 1 and 2 can be separated by closing either of the two O2 crossover valves (Figure 2-1). The O2 crossover manifold supplies oxygen to the LES helmet regulators, the direct O2 valve, and the airlock EMU O2 supply lines (Figure 2-2).
Oxygen system Diagram
The O2 crossover valves are solenoid-powered valves that close if power is lost. Two parallel Launch and Entry Helmet (LEH) regulators step the high-pressure (∼840 psia) O2 pressure down to 100 psig. The two LEH regulator inlet valves on Panel C7 isolate the LEH regulators when they are not in use. Check valves downstream of the LEH regulators prevent the reverse flow of O2. O2 is supplied to the LES during ascent and entry by connecting the LES O2 supply hose to the LEH Quick Disconnects (QDs). These QDs are located on Panel C6 on the flight deck and on Panels MO32M and MO69M on the ceiling of the middeck. Once the QD connection is made, the O2 flow is initiated by opening the associated LEH O2 valve. A direct O2 valve allows approximately 20 lb/hr of O2 flow into the middeck. The direct O2 valve is located on the center console aft of the pilot’s left leg on Panel C5.
The airlock EMU O2 supply valves send high-pressure O2 to the airlock for EMU servicing and to the ISS during O2 transfer operations.
The emergency O2 kit has been removed from all of the orbiters. The line has been capped to protect the integrity of the piping. The manual O2 emergency valve and an auto O2 emergency valve are kept closed to isolate the nonfunctioning regulator outside the cabin (Figure 2-1).
Downstream of the O2 crossover line, there is an O2 regulator inlet valve (Figure 2-2). When the O2 regulator inlet valve is open, the 100-psig O2 regulator steps the O2 pressure down to 100 psia. The 100 psia O2 then flows through a check valve and into the O2/N2 manifold. This 100 psia O2 can only fill the O2/N2 manifold when the higher pressure N2 (200 psia) is shut off from the manifold. The capability also exists to supply 100 psia O2 to payloads by opening the payload O2 valves.
Associated with the 100 psig O2 regulator is a relief valve that cracks at 245 psig and reseats at 215 psig. The relief valve relieves into the cabin to protect the PCS from an O2 regulator failure. The O2 regulator is a psig regulator that controls the O2 pressure to 100 ± 10 psig above cabin pressure.
The PCS nitrogen supply is nominally provided by four tanks located in the payload bay, but all orbiters are capable of carrying additional N2 tanks. As mission duration increases, the amount of N2 lost to normal vehicle leakage and wet trash venting also increases. In addition, operation of the Regenerable Carbon Dioxide Removal System (RCRS) (see Appendix C) consumes N2 in the overboard vent cycle. Since longer missions provide additional opportunities for extravehicular activities, a large volume of N2 is required for cabin and airlock repressurization.
Recent enhancements have increased the N2 capacity to eight tanks (see Figure 2-3). The additional tanks are identical to the N2 tank hardware currently in use.
O2 Crossover Manifold Diagram
At least four N2 tanks are permanently installed on all vehicles. The permanent tanks for PCS 1 have been relocated to the aft payload bay. The tanks are designated as system 1, tanks 3 and 4. This move was necessary to adjust the vehicle center of gravity to a more favorable position. PCS 2 tanks 1 and 2 are also permanent and are located in the forward right side of the payload bay. Up to four additional tanks may be installed as mission kits. These extra tanks are not permanently installed in the vehicles; they are installed when needed on a flight-specific basis.
Location of N2 Tanks Diagrams
The 3300 psia N2 flows out of the tanks, through the N2 supply valves, and into the N2 supply manifold (Figure 2-4). After passing through the N2 regulator inlet valve, the 200 psig N2 regulator steps the N2 pressure down to 200 psia. The N2 regulator inlet valve can be manually closed to isolate the N2 regulator.
The N2 supply and N2 regulator inlet valves are motor-driven valves. If power to the valves is lost, the valves will remain in their present position. There are no heaters in the N2 tanks; the feed is driven by pressure only. Associated with the 200 psig N2 regulator is a relief valve that cracks at 275 psig and reseats at 245 psig. The relief valve relieves overboard through the vacuum vent line to protect the N2 system from overpressurization due to an N2 regulator failure. The N2 regulator controls the N2 pressure to 200 ± 15 psig above ambient pressure. High-pressure N2 can be supplied to the Manned Maneuvering Unit (MMU) by opening the MMU gaseous nitrogen (GN2) isolation valve. This valve is located between the N2 tanks and the N2 supply valves (Figure 2-4). N2 can be transferred to the ISS through PCS N2 System 1 only.
Next, the 200-psig N2 piping penetrates the 576 bulkhead and enters the crew compartment. A check valve inside the cabin prevents reverse flow of N2. The 200- psig N2 pressure is then stepped down again by the water tank N2 regulator and is used to pressurize the supply and wastewater tanks. An N2 crossover valve makes it possible to connect PCS system 1 N2 to PCS system 2, and vice versa. The flow of 200-psig N2 into the O2/N2 manifold is controlled by the O2/N2 controller. The capability also exists to supply 200 psig N2 to a payload by opening the payload N2 valves.
The 14.7 psia cabin regulator controls the cabin pressure to 14.7 psia when the 14.7 regulator inlet valve is open (Figure 2-5). The O2/N2 control valve controls the flow of N2 into the O2/N2 manifold. Whatever gas (O2 or N2) is in the O2/N2 manifold will flow into the cabin when the cabin pressure drops below 14.7 psia. This “makeup” flow will continue as long as the cabin pressure is less than 14.7 psia and the 14.7 cabin regulator inlet valve is open. An 8-psia emergency regulator provides flow to maintain a cabin pressure of 8 psia in the event of a large cabin leak. There is no regulator inlet valve to isolate the 8 psia emergency regulator; therefore, it is always configured to provide makeup flow.
The 14.7-psi regulator cabin regulator regulates the cabin pressure to 14.7 ± 0.2 psia and is capable of a maximum flow of at least 75 lb/hr per specifications. The 8-psi emergency regulator is designed to regulate to 8 ± 0.2 psia and is capable of a maximum flow of at least 75 lb/hr per specifications. Both the 14.7- and 8-psi regulators flow into the cabin through ports on Panel MO10W, located in the Waste Collection System (WCS) compartment. The crewmembers can hear the regulators when they flow if they are in the vicinity.
The O2/N2 control valve position can be controlled manually by the crew or automatically by the O2/N2 controller. What follows is a discussion of O2/N2 control valve operation.
Nitrogen system Diagram
Pressure Control System Diagram
Oxygen/Nitrogen Control Valve Manually
Open With the O2/N2 control valve open, 200 psi N2 fills the O2/N2 manifold and forces the O2 check valve to close. If the cabin pressure drops below 14.7 psia, the gas in the O2/N2 manifold will flow into the cabin, and N2 will flow into the O2/N2 manifold to replenish it
O2/N2 Control Valve Open Diagram
Oxygen/Nitrogen Control Valve Manually Open
With the O2/N2 control valve open, 200 psi N2 fills the O2/N2 manifold and forces the O2 check valve to close. If the cabin pressure drops below 14.7 psia, the gas in the O2/N2 manifold will flow into the cabin, and N2 will flow into the O2/N2 manifold to replenish it (Figure 2-6).
O2/N2 Control Valve Manually Open Diagram
Oxygen/Nitrogen Control Valve Manually Closed
With the O2/N2 control valve closed, no N2 is available to replenish the O2/N2 manifold. If the cabin pressure drops below 14.7 psia, the gas in the O2/N2 manifold will flow into the cabin. Once the pressure in the O2/N2 manifold drops below 100 psi, the O2 check valve will open and 100 psi O2 will flow into the O2/N2 manifold to replenish it
O2/N2 Control Valve Closed Diagram
Auto Control of the Oxygen/Nitrogen Control Valve
On orbit, the O2/N2 control valve on the active PCS is placed in AUTO. This position enables automatic management of the O2/N2 control valve by the O2/N2 controller. The valve will be opened or closed to maintain the correct amount of O2 in the atmosphere based on the partial pressure of oxygen (PPO2) in the cabin. At PPO2 less than 2.95 psia, the valve is closed to enable O2 to flow through the 14.7 cabin regulators if the cabin pressure drops below 14.7 psia. If PPO2 is greater than 3.45 psia, the valve opens and allows N2 to flow through the system. At PPO2 levels between 2.95 and 3.45 psia, the valve remains in its previous position until the upper or lower PPO2 limit is reached and the valve changes position. (Note: Historical data show that actual control is maintained at 3.1 ± 0.05. The 2.95 to 3.45 range is the original specification requirement.)
PPO2 sensor A data are used by O2/N2 controller 1 to determine when to open and close the system 1 O2/N2 control valve. Likewise, PPO2 data from sensor B are used by O2/N2 controller 2. The PPO2 SNSR/VLV switch is used to determine which controller drives which control valve. When the switch is in NORMAL, O2/N2 controller 1 manages the position of O2/N2 control valve on PCS 1, while controller 2 governs the position of the valve on system 2.
This configuration can be reversed, however, so that controller 1 controls the PCS 2 O2/N2 control valve, and controller 2 manages the PCS 1 valve by taking the PPO2 SNSR/VLV switch to REVERSE. This capability prevents the loss of a PPO2 sensor from resulting in the loss of automatic control of one of the two PCSs.
The structural integrity of the orbiter crew compartment is maintained by positive and negative pressure relief valves. The two positive pressure relief valves protect the crew compartment from overpressurization. These positive pressure relief valves will crack at 15.5 psid, reach full flow by 16.0 psid, and reseat again below 15.5 psid. Motor- driven cabin relief isolation valves are located in series with the relief valves (Figure 2-8). Should a relief valve fail open, it can be isolated, and the alternate relief valve will still provide overpressurization protection. The positive pressure relief valves are located behind the back wall of the WCS compartment and relieve into the payload bay (Figure 2-8).
The two negative pressure relief valves protect the crew compartment from being crushed if ambient pressure rises above the pressure in the cabin. These negative pressure relief valves will crack when ambient pressure is 0.2 psid greater than cabin pressure. The negative pressure relief valves are located below the side hatch. Caps are provided as a redundant seal to prevent leakage overboard (Figure 2-8). When the pressure outside the cabin increases above cabin pressure, the relief valves will crack, the caps will pop off, and air will flow into the cabin to equalize the pressure.
The cabin vent isolation and cabin vent valves are used to vent the cabin to the payload bay while the orbiter is on the ground. These two motor-controlled valves are in series. They are located behind the back wall of the WCS compartment and vent into the payload bay (Figure 2-9). Prelaunch cabin pressure integrity checks ensure that there are no leaks in the cabin prior to lift-off. During this cabin leak check, the cabin pressure is increased to 16.7 psia by ground support personnel. The cabin pressure is then monitored for 35 minutes to verify that no pressure decay is occurring. During this time, the cabin vent and cabin vent isolation valves are alternately opened and closed to verify that each valve holds pressure. At the end of the leak check, both valves are opened to allow the cabin pressure to bleed back down to ambient pressure. Once the pressure has equalized, both valves are closed. The cabin vent line has a very high flow capability, 1080 lb/hr at 2 psid; therefore, it is very important that these valves never be opened after lift-off. One of the actions in the Post Insertion Checklist procedures is to disable power to the cabin vent and cabin vent isolation valves to safe them.
Cabin Vent/Negative and Positive Pressure Relief Valves Diagram
Cabin Vent/Positive Pressure Relief Valves Diagram
PRESSURE CONTROL SYSTEM CONTROLS
The switches that control PCS systems 1 and 2 are located primarily on Panel L2 and Panel MO10W. The switches on Panel L2 (Figure 2-10) operate the electrically controlled PCS valves. The valves themselves are actually located outside the crew compartment. The layout of the atmosphere pressure control portion of Panel L2 is a schematic of the PCS. The switches and associated talkbacks indicate the position of the valves. The manual valves located on Panel MO10W are drawn on the schematic for completeness but are denoted by a circle with an X in the middle, which represents a switch on another panel.
Panel MO10W is located on the ceiling of the WCS compartment (Figure 2-11). All the manual valves, the 14.7-psi regulators, the 8-psi regulators, the 100-psig O2 regulators, the water tank regulators, and some sensors are physically located behind Panel MO10W. The toggle switches on Panel MO10W control the valves located directly behind the panel. Any N2 or O2 flowing into the cabin through the 14.7 or 8-psi regulators flows through Panel MO10W. All the O2/N2 switches control manual isolation valves; the valves are either open or closed. Panel MO10W has a schematic drawn on it, but it is not easily understood because of the layout of the valves.
Panel C5, located by the pilot’s left leg, contains the direct O2 valve switch (Figure 2-10). The direct O2 valve allows direct O2 flow into the middeck through an orifice on Panel MO69M. Direct O2 flow is used for 10.2 psia cabin maintenance (see Section 2.7.3) and configuring the crew cabin in response to several failure scenarios. Isolation valve switches and hose connections for LES helmets are labeled as LEH O2 and are located on Panels C6, MO69M, and MO32M (Figure 2-12). This labeling is a remnant from early in the shuttle program when the LEH was used, rather than the complete LES in use today. The two LEH O2 SUPPLY switches on Panel C7 allow the LEH regulators to be isolated from the O2 crossover manifold.
The top portion of Panel L2 contains the CABIN VENT ISOL and CABIN VENT switches and talkbacks (Figure 2-12). The CABIN RELIEF A and CABIN RELIEF B switches and talkbacks are also located on Panel L2.
ECLSS pressurization controls are listed in Table 2-1.
The circuit breakers that power the motor-driven valves are located on Panels MNA O14, MNB O15, and MNC O16 (Figure 2-13). Some of these circuit breakers also power PCS instrumentation.
The MANNED MANUV UNIT GN2 SPLY ISOL VLV A and B switches supply high- pressure N2 to service the MMU and through system B only, to the ISS. These switches and their talkbacks are located on Panel R13L (Figure 2-14). If power is lost, the valve will retain its present position, and the talkback will go barberpole. The circuit breakers that power the valves are located on Panel ML86B (Figure 2-14).
Panel L2 - PCS Diagram
Panel MO10W - PCS Diagram
Overview Panels - PCS Diagram
Overhead panels - PCS Diagram
MMU - PCS Diagram
PRESSURE CONTROL SYSTEM INSTRUMENTATION/DISPLAYS
Crew insight into PCS performance is provided by ECLSS instrumentation and Dedicated Signal Conditioners (DSCs). In addition to powering the O2/N2 controllers, the O2/N2 CNTLR circuit breakers on overhead Panels MNA O14 and MNB O15 (Figure 2-13) power the following transducers:
Backup dP/dT is available only with the Backup Flight Software (BFS) during Operational Sequence (OPS) 1, OPS 3, and OPS 0. It is a calculated value based on the rate of change of cabin pressure over time (psia/min). The computation is updated every 5 seconds. The current cabin pressure is compared to the pressure 30 seconds earlier. The backup dP/dT computation is fed by the cabin pressure transducer; therefore, if it fails, the backup dP/dT computation data are no good. The PPO2 C/CABIN dP/dT circuit breaker on overhead Panel MNB O15 powers PPO2 sensor C and the cabin dP/dT sensor. The cabin dP/dT sensor is a hardware dP/dT sensor; it is available in all OPS modes in Primary Avionics Software System (PASS) or BFS.
The O2 concentration computation takes the average of PPO2 sensors A, B, and C and divides the result by cabin pressure. If one of the PPO2 sensors fails, it can be removed from the computation. If the cabin pressure sensor fails, the alarms generated by the computation can be inhibited. The O2 concentration computation is available only in the PASS SM flight software, on SM SYS SUMM 1.
The equivalent dP/dT computation is available in both the PASS and BFS flight software on SM SYS SUMM 1. The cabin dP/dT sensor and the cabin pressure sensor provide the inputs to the calculation. The computation multiplies the cabin dP/dT by 14.7 and divides the result by the cabin pressure. This way, if the leak rate remains constant, the equivalent dP/dT will remain constant because it is adjusted to a reference pressure of 14.7 psia. The cabin dP/dT will decrease as the pressure in the cabin drops.
The N2 systems 1 and 2 tank quantities and the emergency O2 tank quantity are derived from a Pressure/Volume/Temperature (PVT) computation performed by the PASS SM computer. The rest of the PCS instrumentation is powered by DSCs. Figure 2-15 shows where some of the PCS instrumentation is located.
PCS instrumentation Schematic
PCS Status CRT Displays
The crew has insight into PCS status on the following CRT displays, dependent on mission phase. Backup dP/dT appears only on BFS SM SYS SUMM 1. PASS SM SPEC 66 is the main display for PCS information during orbit operations.
Crew-dedicated displays (meters) located on Panel O1 (Figure 2-19) enable the crew to monitor critical PCS parameters at all times. The CABIN dP/dT meter enables the crew to monitor the pressure integrity of the cabin. An increase in cabin pressure will result in a positive dP/dT. A leak out of the cabin will result in a negative dP/dT.
The O2/N2 FLOW meter rotary switch enables the crew to monitor system 1 or 2, O2 or N2 flow. The CABIN PRESSURE is also displayed on a meter. A toggle switch enables the crew to view either PPO2 SENSOR A or B on a single meter. These meters are all driven by the same sensors that are shown on the CRT displays.
PASS SM SPEC 66 Display
The ENVIRONMENT display is an SM display (DISP 66) available in SM OPS 2 and 4; the display provides data on the pressure control system.
BFS SM SYS SUMM 1 Display
The SM SYS SUMM 1 display is an SM display (DISP 78) available in the BFS; the display provides summary data on the pressure control system.
PASS SM SYS SUMM 1 Display
The SM SYS SUMM 1 display is an SM display (DISP 78) available in SM OPS 2 and 4; the display provides summary data on the pressure control system.
PCS meters - Panel O1 Display
Caution and Warning
The CABIN ATM light on the Panel F7 matrix (Figure 2-20) will illuminate if one of the following parameters is out of limits: (Default values for a 14.7 psi cabin configuration only are shown in the table.)
Panel F7 C/W matrix
PRESSURE CONTROL SYSTEM NOMINAL OPERATION
For ascent, both 14.7 psia cabin regulator inlet valves are closed to isolate the 14.7-psia cabin regulators. If a cabin leak develops, this configuration conserves N2 by not allowing any makeup flow into the cabin until the cabin pressure drops below 8 psia. The O2 regulator inlet valves are closed, directing all the O2 to the O2 crossover manifold to supply the LES helmets. The O2/N2 control valve on PCS system 1 is open to allow N2 to pressurize the O2/N2 manifold. The O2/N2 control valve on PCS system 2 is closed. Nothing is configured to flow through the emergency 8-psia regulators on PCS system 2. The crew will close the visor of their LES helmet shortly before lift-off and breathe 100 percent O2 until shortly after Solid Rocket Booster Separation (SRB SEP).
system remains in the ascent configuration until early in the flight plan
when the orbit PCS configuration is performed. The PCS configuration to
system 1 is typically called for on Flight Day (FD)-1. The 14.7-psia cabin
regulator inlet valve on the selected PCS is opened. This enables the cabin
regulator to automatically maintain the cabin pressure at 14.7 psia. The O2
regulator inlet valve is opened, and the selected system O2/N2 control valve
is taken to AUTO. This enables the O2/N2 controller to control whether O2 or
N2 flows into the O2/N2 manifold based on cabin PPO2 level. An O2 bleed
orifice is installed in LEH QD-8 (Figure 2-21) during the presleep
activities on FD-1 or postsleep activities on FD-2 (depending on current
PPO2 levels). The O2 bleed orifice is sized based on crew size and
compensates for the crew’s metabolic O2 usage by flowing O2 directly into
the cabin. This helps keep the PPO2 level stable when the cabin pressure is
greater than 14.7 psia and the cabin regulators are not flowing. The PCS is
reconfigured to PCS system 2 halfway through the mission.
O2 bleed orifice assembly Display
10.2 psia Cabin
The 10.2-psia cabin protocol was developed by the flight surgeons to minimize the risk of decompression sickness (bends) for the crewmembers preparing for an EVA. The EVA crewmembers must prebreathe pure O2 before they go EVA to help flush the N2 out of their body tissue. The following 10.2 cabin protocol options have been developed:
a. Option 1
1. 60-minute initial prebreathe on Quick
Don Mask (QDM)
2. 12 hours at 10.2 psia cabin pressure
3. 75-minute final prebreathe in suit
b. Option 2
1. 60-minute initial prebreathe
2. 24 hours at 10.2 psia cabin pressure
3. 40-minute final prebreathe in suit
c. Option 3 - 4-hour prebreathe in suit
For scheduled EVAs, option 1 or 2 is chosen to minimize the in-suit prebreathe just prior to the EVA. The cabin is depressurized to 10.2 psia using the airlock depressurization valve located in the airlock. Since there is no 10.2 psia cabin regulator, the cabin pressure and the PPO2 levels must be manually managed during 10.2 psia cabin operations.
The PCS configuration is the same for entry as it was for ascent.
Table 2-1 lists the ECLSS pressurization controls.
ECLSS pressurization controls
PRESSURIZATION SYSTEM PERFORMANCE, LIMITATIONS, AND CAPABILITIES
a. Crew cabin volume with external airlock 2475 ft3
b. External airlock volume 185 ft3
c. Cabin pressure regulators flow capacity at 100 psid (SPEC) 75 lb/hr
1. Regulated pressure 14.7 psia
2. Minimum emergency pressure 8.0 psia d. N2 tank volume 8181 in3
e. N2 tank operating range 285 to 3300 psig
f. N2 tank burst pressure 4950 psig
g. N2 tank operating temp range −65° to 200° F
h. Emergency O2 tank (identical to N2 tanks) No longer installed; line capped
i. Cryo O2 tanks maximum operating pressure 1035 psig
j. Cryo O2 tanks proof pressure 1138.5 psig
k. Cryo O2 tanks burst pressure 1552 psig
l. Cryo O2 tanks operating range 811 to 875 psig
m. ECLSS O2 budget 2.08 lb/man-day
ATMOSPHERIC REVITALIZATION SYSTEM
The ARS circulates air and water through the crew compartment to remove heat, control humidity, and condition the cabin air. The cabin air picks up heat, moisture, CO2, odor, dust, debris, and particles of skin and hair from the crew. The Avionics (Av) and electronic equipment located in the cabin also generate heat that is picked up by the air. The ARS air system consists of a network of fans that circulates the air through the cabin, the Av Bays, and the Inertial Measurement Units (IMUs).
The ARS water coolant loops collect heat from the air at the air/water heat exchanger (HX). The water coolant loops also provide conductive cooling for electronic equipment mounted directly on water-cooled coldplates. The crew compartment is kept thermally stable because the waste heat collected by the water coolant loops is passed outside the cabin to the ATCS Freon coolant loops.
ARS AIR SYSTEM
The ARS air system is functionally divided into three separate air circulation systems. The cabin fans circulate the cabin air, the Av Bay fans circulate air in Av Bays 1, 2, and 3A, and the IMU fans draw air in from the cabin to cool the IMUs. A fourth air system circulates air into the external airlock via booster fans. This system is discussed later.
The cabin fan draws warm air into the cabin fan ducting where filters remove particles suspended in the air. The cabin fan blows a portion of the air through the lithium hydroxide (LiOH) canisters where CO2 and odor are removed. On extended duration flights, LiOH may be replaced with the Regenerable Carbon Dioxide Removal System (RCRS). See Appendix C for a discussion of the RCRS. Just upstream of the cabin HX, the cabin temperature control valve bypasses some of the warm air around the cabin HX to maintain a comfortable cabin temperature. The warm cabin air is then routed through the cabin HX where the air is cooled by the water coolant loops. The humidity in the cabin air is condensed out on a slurper bar in the cabin HX. The humidity separator creates a suction that draws the condensate away from the HX and drives it to the wastewater tank. An Ambient Temperature Catalytic Oxidizer (ATCO) removes carbon monoxide (CO) from the air. The cool conditioned cabin air and the warm bypassed air then come together again and flow back into the cabin through the return air ducts.
Cabin Air System Diagram
One of two cabin fans is used at all times. The cabin fan draws air past electronic equipment to provide that equipment with forced air cooling (Table 3-1 at the end of Section 3). The cabin fans are located below the middeck floor in the ECLSS bay (Figure 3-2). Access to the fans is provided by Panel MD79G. The cabin fan filter is also accessible through Panel MD79G. Each fan is powered by a three-phase, 115-volt Alternating Current (AC) motor. These 495-watt motors produce a nominal flow rate of 1400 lb/hr through the cabin air ducting. A check valve located at the outlet of each fan (Figure 3-1) prevents air from backflowing through the non-operating fan. This flapper-type check valve will open if there is a 2 psi differential pressure across the valve. A cabin fan will not start on two phases of AC. However, if the cabin fan is already operating when a phase of AC is lost, the fan will continue to run on two phases of AC. A cabin fan can be started on “2-1/2 phases” of AC, with the extra half phase being provided by the induced voltage generated by other rotating equipment (that is, fans and pumps) running on that AC bus. If a phase of AC is lost with a short, then the induced voltage will not be usable and starting the cabin fan will not be possible.
Odor and CO2 are removed from the cabin air by the
LiOH canisters. A flow orifice directs approximately 120 lb/hr of air
through each of the two LiOH canisters (Figure 3-1). Activated charcoal in
the canister controls odor; CO2 is removed from the air when the CO2 reacts
with the LiOH to produce lithium carbonate. The LiOH canisters are changed
out periodically during the mission on a predetermined schedule, generally
one or two times per day based on the number of crewmembers. The LiOH
canisters are located in the ECLSS bay and are accessible through the MD54G
opening in the middeck floor (Figure 3-2). Up to 30 spare LiOH canisters are
located in the ECLSS bay below Panel MD52M.
CAUTION - During LiOH canister change out, both cabin
fans should be turned off. Dust from the LiOH canisters kicked up by the
cabin fan has caused eye and nose irritation on previous missions. LiOH dust
may also be a contributing factor to the humidity separator failures.
Cabin Temperature Control Valve
The cabin temperature control valve is a variable position valve that controls the flow of air that bypasses the cabin HX (Figure 3-1). The ratio of warm bypassed air and cool air from the cabin HX determines the cabin temperature. The cabin temperature control valve may be positioned manually by the crew or automatically by one of the two cabin temperature controllers. The cabin temperature controller is a motor-driven actuator that adjusts the cabin temperature control valve to achieve the temperature selected on the cabin temperature rotary knob located on Panel L1. The cabin temperature control valve and the two cabin temperature controllers are located in the ECLSS bay below Panel MD44F (Figure 3-2).
ECLSS bay Diagram– View looking down through middeck floor
ECLSS bay Display – View looking down through middeck floor
ECLSS bay Display – View looking down through middeck floor
In manual mode, the crew can position the cabin temperature control valve in one of four positions by pinning the valve arm to one of the four fixed holes (FULL COOL, FULL HEAT, etc.) (Figure 3-3). To use the auto mode, the valve arm must be pinned to the valve arm linkage, and the valve arm linkage must be pinned to either the primary or secondary cabin temperature controller actuator. Once this is completed and the cabin temperature controller is powered, the rotary switch can be adjusted to increase or decrease the cabin air temperature. If the active cabin temperature controller malfunctions, the valve arm linkage must be physically disconnected and pinned to the alternate cabin temperature controller actuator before the alternate controller can be selected. The total travel time from full cool to full hot is a maximum of 4 minutes in the auto mode.
Cabin temperature controller Display
Cabin Heat Exchanger
The cabin HX transfers heat that has been picked up by the cabin air to the ARS water coolant loop. The cabin fan blows warm cabin air through the air/water HX, and the air is cooled (Figure 3-1). The humidity in the cabin air condenses out on a slurper bar in the cabin HX. The condensate is drawn away from the cabin HX and into the humidity separator.
Two humidity separators are located adjacent to the cabin HX in the ECLSS bay below the middeck floor (Figure 3-2). One humidity separator is used at all times. Each humidity separator is powered by a three-phase, 115-volt AC motor. The humidity separator fan develops a suction that draws water-laden air away from the cabin HX. The air/condensate mixture is separated by a centrifugal rotating drum. The condensate is drawn off and stored in the wastewater tank. For ISS missions, the condensate is stored in a CWC (Contingency Water Container). This reduces the number of wastewater dumps required while docked. The dehumidified air is returned to the ECLSS bay at the rate of 37 lb/hr (Figure 3-4).
Humidity separator Diagram
Ambient Temperature Catalytic Oxidizer
The ATCO removes CO generated by the crew and from the off-gassing of nonmetallic materials in the cabin. The ATCO is located just past the cabin HX (Figure 3-1). The CO is converted to CO2 by catalytic oxidation, and the CO2 is then removed by the LiOH canisters. The catalyst is 2 percent platinum on carbon.
Avionics Bay Fans
Since convective cooling requires the presence of gravity to create air currents, which then carry off heat, no convection occurs in microgravity. The Av Bay fans circulate air through the Av Bays to replace convective cooling with continual forced air cooling. Av Bays 1, 2, and 3A each have two fans, one of which is used at all times. Each Av Bay functions as an enclosed air circulation system but is not completely airtight. The Av Bay fans are located in the ECLSS bay below the middeck floor level under their respective Av Bays (Figure 3-2). The fans draw air across the avionics equipment. The air picks up the heat generated by this equipment and is blown through the Av Bay HX, where the heat picked up from the Av Bay is transferred to the ARS H2O loop (Figure 3-5).
Av Bay fans Display
Each fan in Av Bays 1 and 2 is powered by a three-phase, 115-volt AC motor. These 111-watt motors produce a normal flow rate of 875 lb/hr through the Av Bays. The Av Bay fans will start and run on two phases of AC. A check valve located at the outlet of each fan prevents air from backflowing through the non-operating fan. The flapper-type check valve will open when the fan develops 1 psi of differential pressure across the valve. Current plans involve replacing Av Bay 3A fans with three-phase, 115-volt, 495-watt cabin fans. The replacement fans are capable of flowing 1400 lb/hr through the Av Bay for additional middeck cooling for payloads that will be stowed in middeck lockers. Each of the orbiters will continue to use a standard Av Bay fan in Av Bay 3 until it is upgraded. A list of the air-cooled equipment for each Av Bay is contained in Tables 3-2, 3-3, 3-4, and 3-5 located at the end of Section 3.
Inertial Measurement Unit Fans
The IMU fans provide cooling by drawing cabin air over the IMUs that picks up the heat generated by the IMUs (Figure 3-6). There are three fans, one of which is normally on. The warm air is then blown through the IMU HX where the heat is transferred to the ARS water coolant loops. The cool air is then returned to the cabin.
IMU fans Display
Each fan is powered by a three-phase, 115-volt AC motor. These 50-watt motors produce a nominal flow rate of 144 lb/hr. The IMU fans will start and run on two AC phases. A check valve located at the outlet of each fan prevents air from back flowing through the non-operating fans. The flapper-type check valve will open when the fan develops 1 psi of differential pressure across the valves.
ATMOSPHERIC REVITALIZATION SYSTEM WATER
The ARS water coolant loops circulate water through the crew compartment to collect excess heat and transfer it to the ATCS Freon coolant loops. There are two water coolant loops, only one of which is active at a time. Both of the water loops flow side by side through all of the HXs and coldplates that they service. Downstream of the pump package, the water flow splits into three legs to cool the Av Bays (Figure 3-7). The water loops also provide thermal conditioning for the seals around all the windows.
H2O coolant loop 1 Display
The warm water then either flows through the water/Freon interchanger where it is cooled or bypasses the interchanger and returns to the pump package. The water bypass valve determines the amount of water that will flow through or bypass the interchanger. The water cooled in the interchanger then flows through the liquid-cooled garment HX, the galley water chiller, the cabin HX, and the IMU HX before it joins the bypass flow and returns to the pump package.
Water loop 1, the backup water loop, has two pumps. Water loop 2, the normally active loop, has only one pump. The water pumps are located in the ECLSS bay below the forward lockers (Figure 3-2). These centrifugal pumps are powered by three-phase, 115-volt AC motors. A ball-type check valve on water loop 1 prevents water from backflowing through the non-operating pump (Figure 3-7). The pump outlet pressure from the active pump positions a check ball against a seal to close off the inactive pump outlet. An accumulator on each loop compensates for any thermally induced volume changes and maintains the head pressure on the pump to prevent cavitation. The accumulator is pressurized with N2. When the accumulator bellows is fully extended, the accumulator has 1.81 pounds of water. When the accumulator is bottomed out, 0.19 pounds of water remain in the accumulator.
Av Bay 1 Leg
The water flows through the Av Bay 1 air/water heat HX (Figure 3-7). Heat is picked up from the air in Av Bay 1. The water then flows through 25 ft2 of coldplates. Water-cooled equipment is mounted directly on metal plates with water flowing through them to provide direct conductive cooling. (Table 3-2 at the end of the section contains a list of the coldplated equipment in Av Bay 1.)
Av Bay 2 Leg
The flow through the Av Bay 2 leg is similar to the flow through Av Bay 1. In addition to cooling the Av Bay HX and 30 ft2 of coldplates, the water loop thermally conditions the seals around all of the orbiter windows (Figure 3-7). (Table 3-3 at the end of the section contains a list of the coldplated equipment in Av Bay 2.)
Av Bay 3 Leg
A small portion of this leg provides cooling to the Multiplexer/Demultiplexer (MDM) coldplate, while the majority of the flow bypasses this coldplate (Figure 3-7). The flow splits again for Av Bays 3A and 3B. The Av Bay 3A leg cools the Av Bay HX and 32 ft2 of coldplates. Av Bay 3B is a separate compartment that contains only water-cooled equipment. The Av Bay 3B leg cools 5 ft2 of coldplates. (Tables 3-4 and 3-5 at the end of the section contain a list of the coldplated equipment in Av Bay 3.)
The heat collected by the water coolant loop is transferred to the ATCS Freon coolant loops in the water/Freon interchanger (Figure 3-8). The interchanger is located outside the crew compartment to keep the toxic Freon 21 outside the cabin. The water bypass valve is a variable position diverter valve that determines the amount of water that will flow through the interchanger. The water bypass valve has two modes of operation, manual and auto. The manual mode of operation enables the crew to increase or decrease the bypass flow by means of an increase/decrease switch. Normally, the water bypass valve is preset on the ground to allow 950 lb/hr of water flow through the interchanger. If the crew takes the H2O LOOP BYPASS switch to INCR, the amount of flow bypassing the interchanger will increase, and the interchanger flow will decrease. Likewise, by taking the switch to DECR, the crew can decrease bypass flow and increase interchanger flow. In auto mode, the water loop bypass controller governs the position of the bypass valve. The bypass valve will be actuated to maintain the temperature at the exit of the water loop pump at 63° F.
H2O/Freon interchanger Display
For normal operations, only one water loop is active. Running two water loops for long periods of time is undesirable. Two operating loops will flow too much water through the water/Freon interchanger and result in a significant increase in the cabin temperature. This occurs because two active water loops are capable of picking up more heat than the HX can transfer to the Freon loops. Over time, the water loops will accumulate heat, and cooling efficiency will decrease. The water/Freon interchanger will begin to rise as soon as the thermal transfer rate of the interchanger is exceeded. This will affect the interchanger leg of the water loop causing reduction in cooling capability of the liquid cooling and ventilation garment (LCVG), H2O chiller, cabin and IMU HX. When the interchanger out leg approaches 63° F, cooling capability will also be lost on the Av Bay legs of the water loops.
Liquid-Cooled Garment Heat Exchanger
The LCVG HX is used to cool the water loops that cool the LCVG before and after an EVA. The LCVG HX is in the airlock.
The water chiller is used to cool the crew’s potable water from the supply water tanks.
The cabin HX and the IMU HX have already been discussed in this section under the heading, Cabin Air.
ATMOSPHERIC REVITALIZATION SYSTEM CONTROLS
The switches that control the ARS air and ARS water systems are located on the left- hand side of Panel L1 (Figure 3-9). The layout of Panel L1 is a schematic of the cabin air ducting and the water coolant loops. With this in mind, it should be much easier to locate switches on the panel.
The circuit breakers that provide the AC power to operate the fans, pumps, controllers, and signal conditioners are located in the center of Panel L4 (Figure 3-10).
The circuit breakers that provide DC power to the H2O BYP LOOP ½ SNSR are located on Panels MNA O14 and MNB O15 (Figure 3-11).
A detailed listing of the ARS controls is in Table 3-6.
Panel L1 – ARS
Panel L4 – ARS
Overhead/Panels 014 with H2O BYP LOOP 1 SNSR and O15 with H2O BYP LOOP 2 SNSR circuit breakers
ATMOSPHERIC REVITALIZATION SYSTEM INSTRUMENTATION AND DISPLAYS
Crew insight into ARS performance is provided by ECLSS instrumentation and DSCs (Figure 3-12). The CABIN AIR signal conditioner powers the cabin fan delta pressure, cabin humidity (Mission Control Center (MCC) insight only), and CO2 partial pressure transducers. The three Av Bay signal conditioners power Av Bay temperature and Av Bay fan delta pressure sensors in each Av Bay (Figure 3-13). The HUM SEP and IMU FAN signal conditioners power speed sensors that check to be sure that the IMU fan and humidity separator are operating normally. In addition to powering the cabin temperature controller, the CABIN CNTLR 1 circuit breaker powers the cabin HX air outlet temperature and cabin temperature sensors. The H2O BYP LOOP 1 SNSR signal conditioner powers the water loop 1 interchanger flow sensor and the IMU fan delta pressure sensor (Figures 3-14 and 3-15). The H2O BYP LOOP 2 SNSR signal conditioner just powers the interchanger flow sensor on water loop 2. In addition to providing the power to drive the water bypass valve, the H2O CNTLR powers all of the instrumentation on the water loop pump package. The accumulator quantity, pump outlet pressure, pump outlet temperature, and pump delta pressure sensors are all powered by the H2O CNTLR.
ARS data are available to the crew on the following CRT displays (see Figures 3-16 to 3-20), dependent on mission phase.
Cabin air system instrumentation Diagram
IMU fan instrumentation Diagram
BFS SM SYS SUMM 1 Display 78
The SM SYS SUMM 1 display is an SM display (DISP 78) available in the BFS; the display provides summary data on the ARS.
PASS SM SYS SUMM 1
The PASS SM SYS SUMM 1 display is an SM display (DISP 78) available in the SM OPS 2 and 4; the display provides summary data on the ARS.
SM SYS SUMM 2
The SM SYS SUMM 2 display is an SM display (DISP 79) available in the BFS and in PASS SM OPS 2 and 4; the display provides summary data on the ARS.
SPEC 66 ENVIRONMENT
The ENVIRONMENT display is an SM display (DISP 66) available in SM OPS 2 and 4; the display provides data on the ARS.
SPEC 88 APU/ENVIRON THERMAL
The APU/ENVIRON THERM display is an SM display (DISP 88) available in SM OPS 2 and 4; the display provides data on the ARS H2O loops.
Crew dedicated displays (meters) on Panel O1 (Figure 3-21) enable the crew to monitor critical ARS parameters at all times. The air temperature meter allows the crew to monitor the temperature in Av Bays 1, 2, and 3 and the cabin HX air outlet temp. The water loop 1 and 2 pump outlet pressure can also be monitored. The meters are driven by the same sensors that are shown on the CRT displays.
Caution and Warning
The H2O LOOP light on Panel F7 (Figure 3-22) will illuminate if one of the following parameters is out of limits:
Since water loop 2 is nominally the operating loop, its C&W limits are set higher to annunciate a degraded loop. Water loop 1 is normally deactivated; therefore, its C&W limits are set to bracket the expected pressure of a non-operating loop.
The AV BAY/CABIN AIR light will illuminate if one of the following ARS air parameters is out of limits:
ARS meters – Panel O1
Panel F7 caution and warning matrix
ATMOSPHERIC REVITALIZATION SYSTEM NOMINAL OPERATION
The ARS is already configured for ascent at crew ingress. One cabin fan, one humidity separator, one IMU fan, and one fan in each Av Bay are already operating. The cabin temperature controller is off, the cabin temperature control valve arm is pinned to the valve arm linkage, and the valve arm linkage is pinned to the actuator on cabin temperature controller 1. The cabin temperature control valve is positioned in the FULL COOL position by powering the controller and adjusting the rotary switch to the COOL position. Once the FULL COOL position is reached, cabin temperature controller 1 is unpowered. The HUM SEP and the IMU FAN signal conditioners are unpowered to protect against an AC to AC bus short causing loss of a main engine. (The wire bundle that carries power to these signal conditioners did short on STS-6.) Water loop 2 is on, and water loop 1 is off during ascent. Water loop 1 pump A control buses (cb’s) are opened to preclude an AC3 bus to AC1 bus short due to a relay failure on water loop 2, which would cause the loss of a main engine during powered flight. The circuit breakers are kept open for all phases of flight. Both water bypass valves are positioned to flow ∼950 lb/hr through the water/Freon interchanger. If no failures occur during ascent, then no actions are required to manage the ARS.
The orbit air and water configuration is largely the same on orbit as for ascent. However, cabin temperature controller 1 is activated, water loop 1 is set to the GPC position, and water loop bypass mode 2 is set to AUTO.
For ISS missions, condensate from the humidity separator is stored in a CWC. This reduces the number of wastewater dumps needed while docked.
While in SM OPS 2, the General Purpose Computer (GPC) position causes the inactive water loop to be cycled on periodically. This periodic cycling thermally conditions the inactive water loop and prevents large temperature differences from forming throughout the loop. The cycling sequence is initiated any time an OPS transition is made into SM OPS 2. When an OPS transition is made, the pump will receive a 6-minute ON command, then remain off for 240 minutes (4 hours). The pump will cycle on for 6 minutes every 4 hours.
By using auto mode for control of the water loop 2 bypass valve, the water loop pump out temperature will be maintained at a constant value. This process greatly assists in stabilizing the cabin temperature.
The pump on water loop 2 is powered by AC3 when its switch is in the ON position and by AC1 when in the GPC position. AC1 power, however, is supplied by the same circuit breakers that have been pulled to protect against the relay failure mentioned earlier.
Therefore, to power either water loop 1 pump A by means of the ON or GPC switch position, or to power loop 2 by means of the GPC position, the circuit breakers must be in the closed position. In this case, if both loops are in the GPC position while there is an ON command present from the GPC, both loops will be running. The GPC position creates a path for the SM GPC to command water loop 1 pumps through PL MDM 1 and to command the water loop 2 pump through PL MDM 2. During ascent and entry, the BFS provides a continuous on command so AC1 becomes a readily available alternate power source for the water loop 2 pump. On orbit, the SM GPC provides a 6 minute ON command followed by a 4 hour OFF command to provide loop conditioning. This cycle can be converted to a continual ON command by changing the length of the “on cycle” via SM SPEC 60 or TMBU.
If the situation arises where no PASS SM or BFS computers are available, the water loop pumps can still be commanded in the GPC position using Real-Time Commands (RTCs). The RTCs can be issued by way of a ground uplink or by way of crew inputs on DPS UTILITY SPEC 1. The RTCs must be issued through the computer that has control of the payload Multiplexer/Demultiplexers (MDMs). It would take a severe loss of system redundancy for the use of RTCs to ever be required.
Atmospheric Revitalization System Cooling Tables
Refer to Tables 3-1 through
3-5 for methods of cooling equipment in the cabin, Av Bay 1, Av Bay 2, Av
Bay 3A, and Av Bay 3B. Table 3-6 lists the ECLSS controls (ARS). These
tables may be found in the Pocket Checklists at the beginning of the ECLSS
Cabin air-cooled equipment cooling matrix
Av Bay 1 equipment-cooling matrix
Av Bay 2 equipment-cooling matrix
Av Bay 3A equipment-cooling matrix
Av Bay 3B equipment-cooling matrix
ECLSS controls (ARS)
ARS Systems Performance, Limitations, and Capabilities
a. Cabin air velocity range 15 to 40 ft/min
b. Nominal air velocity 25 ft/min
c. Cabin air flow 1400 lb/hr
d. Avionics bay air flow 875 lb/hr/bay
e. Nominal dew point range 39° to 61° F
f. H2O separator inlet flow (air and H2O) 37 to 41 lb/hr
1. Outlet flow (air) 37 lb/hr
2. (H2O) 0 to 4 lb/hr
g. CO2 removed by LiOH 2.11 lb/man/day
h. H2O centrifugal pumps design pressure 90 psig
i. H2O centrifugal pumps proof pressure 135 psig
j. H2O centrifugal pumps flow range 970 ± 15 lb/hr
k. H2O centrifugal pumps inlet pressure 18 to 35 psig
l. H2O centrifugal pumps pressure rise 46.5 ± 1.2 psid m. H2O accumulator volume 56 in3
n. H2O accumulator capacity 1.81 lb o. H2O loop volume (without accumulator) 1810 in3
p. H2O loop capacity 65.3 lb
ACTIVE THERMAL CONTROL SYSTEM
The ATCS performs three basic functions:
a. Transfers heat from
heat sources to heat sinks using the Freon coolant loops
b. Cools or heats orbiter subsystems through HXs and coldplate interfaces
c. Rejects waste heat by various means dependent on mission phase
Heat Sinks and Heat Sources
Heat sinks Heat sources
Fuel cell HX
Ground Support Equipment (GSE) HX
Water/Freon Interchanger (ICH)
O 2 restrictor
Figure 4-1 shows the Freon coolant loops; Figure 4-2 shows the locations of ATCS components.
ATCS Freon coolant loop (typical)
ATCS components locations
Each Freon loop has two pumps known as A and B. Both loops have a pump running at all times, typically the B pump. The Freon pump package is located in the midbody of the orbiter below the payload bay liner (Figure 4-2). These centrifugal pumps are powered by three-phase, 115-volt AC motors. A ball-type check valve prevents Freon from backflowing through the non-operating pump (Figure 4-1). An accumulator on each loop compensates for any thermally induced volume changes in the loop, as well as maintains the head pressure on the pump to prevent cavitation. Freon 21 will boil at 100° F and 40 psia. The accumulator is pressurized with N2. When the accumulator bellows is fully extended, approximately 80 lb of Freon are in the accumulator.
If the B pump is unable to be turned on by the crew, the pump may be commanded on by using RTCs. The RTCs can be issued by way of a ground uplink or by way of crew inputs on DPS UTILITY SPEC 1. The RTCs must be issued through the computer that has control of the payload MDMs.
4.3 AFT COLDPLATES The avionics in aft Av Bays 4, 5, and 6 and the Rate Gyro Assemblies (RGAs) are mounted on Freon-cooled coldplates. A typical coldplate assembly is shown in Figure 4-3. Both Freon loops flow through each coldplate, one above the other. The avionics in the Av Bays are arranged on parallel cooling shelves (Figure 4-4 and Table 4-1). Approximately 12 percent of the total Freon loop flow is routed through the aft coldplates, while the remaining flow goes through the O2 restrictor, the H2O/Freon ICH, and the payload HXs (Figure 4-1).
Typical coldplate assembly
Aft Av Bay coldplate configuration
Aft coldplate-cooling matrix
Aft coldplate-cooling matrix
GROUND SUPPORT EQUIPMENT HEAT EXCHANGER
The GSE HX acts as the heat sink for the Freon loops prelaunch and postlanding. Prelaunch cooling is provided by a ground servicing system that interfaces with the GSE HX through the Time-Zero (T – 0) umbilical panel (Figure 4-5). During launch, the ground servicing coolant flow will be terminated at T minus 6 seconds, and the GSE plumbing will disconnect by T minus 0. Postlanding, GSE cooling is provided through a portable cooling cart located at the nominal end of the mission landing site. Cooling cart hookup to the T – 0 umbilical panel usually occurs within 30 minutes of landing. The GSE HX also can be used for payload heat rejection. The GSE HX has more heat rejection capability than the Payload (PL) HX. It has been used as a heat sink for the Radioisotope Thermoelectric Generator (RTG) cooling loops on the Galileo and Ulysses missions.
The port and starboard midbody coldplates act as a heat source for the Freon loops. The avionics, power distribution, and control equipment mounted on the coldplates receive cooling from both Freon loops. (See Table 4-2 and Figure 4-6.)
Midbody coldplate-cooling matrix
HYDRAULIC HEAT EXCHANGER
The hydraulic system acts as a heat sink for the Freon loops. The hydraulic HX utilizes the Freon heat to keep the orbiter’s idle hydraulic systems warm while on orbit.
FUEL CELL HEAT EXCHANGER
The fuel cell coolant loops act as a heat source for the Freon loops. Fuel cell waste heat is transferred to the Freon loops in the fuel cell HX (see Figure 4-6).
Fuel cell HX/midbody coldplates
CARGO HEAT EXCHANGER
The cargo heat exchanger has be added as an interface for active Multipurpose Logistics Module (MPLM) missions where environmental control is required in the MPLM for its payloads. The Heat exchanger is a FREON/WATER interchanger. Freon from the shuttle runs through the heat exchanger whether an MPLM is present or not. The MPLM information will be displayed on SPEC 168 CRYO PALLET/CARGO in both BFS and PASS. More information will be provided as MPLM information is made available. OV103 has been modified and OV105 is being modified in 2004. OV104 will not be modified until after STS114 and STS117.
Cargo Heat Exchanger Diagram
Pressure control system 1 oxygen is warmed by Freon loop 1 as it flows through a 23.9 lb/hr O2 restrictor. (See Figure 4-8) Freon loop 2 warms the PCS system 2 oxygen as it flows through two parallel 12.0 lb/hr O2 restrictors. If either Freon loop fails or is turned off, the associated PCS O2 supply valve must be closed. Closing this valve prevents an O2 leak at the O2 restrictor. An O2 leak will result when no heating is provided by the Freon loop to the Viton seals of the restrictor.
The heat collected by the active H2O coolant loop is transferred to the Freon coolant loops in the water/Freon ICH (Figure 4-2). The water/Freon ICH is a heat source for the Freon loops. Both water loops and both Freon loops pass over one another in the counterflow plate-fin HX. The water/Freon ICH is located outside the crew compartment to keep the toxic Freon 21 outside the cabin (Figure 4-1).
PAYLOAD HEAT EXCHANGER
Payloads that require supplemental cooling can be cooled by the Freon coolant loops through the payload HX interface (Figure 4-2). When used, the payload HX is a heat source for the Freon loops. The payload HX can accommodate two payload coolant loops. The payload coolant can be either Freon or water. The payload HX has been used as a heat sink for Spacelab and SpaceHab missions.
FLOW PROPORTIONING VALVE
The flow-proportioning valve proportions the amount of Freon flowing through the water/Freon ICH and the payload HX (Figure 4-1). In the ICH position, approximately 90 percent of the flow goes through the water/Freon ICH and 10 percent through the payload HX. In the Payload (PL) position, approximately 43 percent goes through the payload HX, and 57 percent flows through the water/Freon ICH.
The radiators act as a heat sink for the Freon coolant loops. The radiators are mounted on the inside of the payload bay doors. When the payload bay doors are open, during orbit operations, the radiators are the primary source of cooling for the Freon loops. Each radiator consists of four panels, with the forward two mechanically deployable should the need for an increased cooling capacity arise. (See Figure 4-9.) Deploying the radiators results in approximately a 10 percent increase in cooling efficiency. During deorbit prep, the Freon in the radiators is “cold soaked” by positioning the orbiter in a “cold” attitude. This “cold soak” is saved for use as a heat sink during the latter stages of entry. Radiator cooling efficiency is extremely dependent on vehicle attitude. Freon loop 1 flows through the radiator panels located on the port payload bay door; loop 2 flows through the panels on the starboard door. The flow through each radiator is controlled by a flow control assembly. Each flow control assembly consists of two radiator controllers, a flow control valve, a rad/bypass valve, and four temperature sensors (see Figure 4-10).
Two electronic radiator controllers are provided for each loop for redundancy. The radiator controllers are commonly referred to as Auto A and Auto B. The radiator controller logic is functionally divided into two areas. One part of the logic controls commands to the flow control valve, while the other controls commands to the rad/bypass valve (see Figure 4-10).
The flow control valve is a mixing valve that mixes cold Freon from the radiator panels with hot Freon from the Freon loop. The active radiator controller adjusts the flow control valve to maintain the desired radiator out temperature. The radiator out temperature control point is selectable to either 38° ± 2° F or 57° ± 2° F by means of the radiator out temperature switch. A dedicated temperature sensor provides the input to the radiator controller logic, and the controller adjusts the flow control valve accordingly to achieve the desired radiator outlet temperature. The position of the flow control valve cannot be adjusted manually.
The rad/bypass valve is a
two-position valve. The BYPASS position bypasses the radiators so that they
are not used as a source of cooling. The RAD position allows the Freon to
flow through the radiators and into the Freon loop. When operating in the
auto mode, the rad/bypass valve position is controlled by the radiator
controller. The crew can position the rad/bypass valve manually by using the
manual select switch when operating in manual mode.
The rad/bypass valve portion of the rad controller logic is continually monitoring for an undertemp condition. If the radiator out temperature drops below 33° ± 0.5° F, the undertemp logic will command the rad/bypass valve to BYPASS. This undertemp protection will keep the water in the stagnant water loop from freezing in the water/Freon ICH. When either radiator controller is active, backup undertemp protection is provided by the alternate radiator controller. If either radiator controller detects an undertemp condition, it can command the rad/bypass valve to bypass the radiator (See Figure 4-11).
Even when the rad/bypass valve is in the bypass position, there is still a very small amount of Freon that flows through the radiators to prevent the Freon from freezing.
In the event of a Freon loop leak, capability exists to divert the Freon flow from the radiators through the radiator isolation leg by means of the radiator isolation hardware. The radiator isolation leg redirects the flow past the radiator through the flow control valve. A check valve keeps Freon from back flowing into the radiator and leaking out. A likely place for a leak on orbit in a Freon loop would be in the radiators since they are large panels that are exposed to micrometeor hits. When operating in the auto mode on orbit, if the accumulator quantity drops for more than 5 seconds below the preset lower limit of 12 percent (or as manually set) but is greater than zero and does not have an “M” due to loss of data, then a command is sent to isolate the radiator. If an OPS transition is requested while the commands are being issued, the OPS transition will be held out until the commands are terminated. (USA001547, Space Shuttle Computer Program Development Specification, OI-30 CPN-2, 27 Feb 03) The crew can manually control the radiator isolation hardware by using the manual select switch when operating in manual mode.
Each radiator controller receives inputs from two dedicated temperature sensors. One sensor feeds the temperature data to the flow control valve logic. The other sensor provides the temperature data used by undertemp protection logic. The radiator controller logic is powered by the MNA and MNB overhead panel buses. The rad/bypass valve is driven with single-phase AC power. The flow control valve is powered by the MNA and MNB overhead panel buses. The rad isol valve is also driven with single-phase AC power. The rad isol controller is powered by the MNA overhead panel bus.
Freon radiator panels
Radiator/flow control assembly overview
Radiator controller detailed
During the deorbit prep timeframe, a radiator coldsoak is performed to store cool Freon in the radiators for use as a heat sink later during entry. The coldsoak process begins 4 hours before the deorbit burn. The orbiter is maneuvered to a tail-sun attitude to enhance the radiator cooling. The coldsoak is initiated by shifting the radiator out temperature control point from 38° to 57° F. The topping FES is restarted to keep the Freon evap out temperature stable at 39° F. The fact that the radiators are only cooling the Freon to 57° F instead of 38° F provides the coldsoak. Much less radiator Freon is required to achieve a 57° F radiator out temperature. Consequently, the reduced flow through the radiator causes the Freon to stay in the radiators longer and become cooler. An hour after the coldsoak is initiated, the radiators are manually bypassed to store the cool Freon for entry.
During entry, the radiator auto startup sequence is performed when V = 12k (vehicle relative velocity of 12,000 ft/s) which corresponds to roughly 176,000 feet. Radiator flow is initiated approximately 11 minutes before touchdown. The radiators provide the cooling until the coldsoak runs out 10 to 15 minutes after touchdown. NH3 cooling is then initiated upon MCC request. The NH3 provides the cooling until the GSE hookup is complete 30 to 45 minutes after touchdown.
Radiator Controller Auto Startup Sequence
The radiator controller auto startup sequence prevents a cold slug of radiator Freon from freezing the water loop interfaces during radiator activation. The sequence is described below and in Figure 4-12.
The rad/bypass valve mode switch must have auto mode selected. Auto mode enables the radiator controller logic to control the position of the rad/bypass valve.
T = 0
Selecting radiator controller A auto (B auto) initiates the auto startup sequence. The rad controller issues a command to drive the rad/bypass valve to bypass. At the same time, commands are issued to bypass the radiators with the flow control valve.
T = 5 seconds
The rad/bypass valve
command is terminated because the valve should be in the bypass position
after 5 seconds. The Flow Control Valve (FCV) continues to be commanded to
the bypass position for 85 more seconds. The time it takes to reach the
bypass position depends on the initial position of the FCV.
T = 90 seconds
The commands to the FCV are terminated. The rad/bypass valve is commanded to rad flow now that the FCV has the radiators bypassed.
T = 95 seconds
The rad/bypass valve open command is terminated since the valve should now be in radiator flow. The flow control valve begins to open up and allows the cool radiator Freon to mix with the hot bypass Freon to achieve the control point temperature (38° For 57° F).
Radiator controller auto startup sequence
AMMONIA BOILER SYSTEM
The ammonia (NH3) boiler system acts as a heat sink by evaporating liquid anhydrous NH3 on both Freon loops in the NH3 boiler HX. The resultant superheated vapor is vented overboard. The Freon loops are cooled by NH3 during the latter stages of ascent abort entries and postlanding. The NH3 boiler system consists of two parallel systems (systems A and B) that supply NH3 to the NH3 boiler. Each system is made up of an NH3 storage tank, an isolation valve, an overboard relief valve, two flow control valves, a controller, three temperature sensors, and a feedline to the NH3 boiler (Figure 4-13).
The system utilizes the low boiling point of NH3 to cool the Freon loops at relatively low altitudes. When NH3 is sprayed on the Freon loops in the NH3 boiler, it immediately vaporizes and carries the Freon heat away. The NH3 controller adjusts the NH3 spray to control the Freon temperature exiting the NH3 boiler to 34° ± 3° F.
An NH3 controller is functionally divided into three sections:
a. Primary controller
b. Secondary controller
c. Undertemp switchover logic
Each of these sections receives data from a dedicated temperature sensor on the Freon loop at the NH3 boiler outlet. The undertemp switchover logic will cause switchover from the primary to secondary controller if the primary controller controls below 31.25° F for more than 10 seconds. Switchover from the secondary to the primary controller does not occur.
The two switches that control NH3 systems A and B are located on the lower right of Panel L1 (Figure 4-14). The PRI/GPC position allows the BFS software to initiate NH3 cooling below 120,000 feet by enabling the primary controller. The SEC/ON position manually initiates NH3 cooling, using the secondary controller.
In case of an ascent abort, the NH3 B select switch is placed in the PRI/GPC position prelaunch. This switch position enables the BFS SM software to initiate NH3 cooling. During a Transoceanic Abort Landing (TAL) or Abort Once Around (AOA), NH3 cooling is initiated at either Major Mode (MM) 304 and <120,000 feet or MM305. During a Return to Launch Site (RTLS), the MM602 transition causes NH3 cooling to be initiated. The NH3 cooling is not required for a normal end of mission entry. The radiator coldsoak will provide the Freon cooling until the coldsoak runs out postlanding. If NH3 cooling is desired for a normal entry, it can be manually selected (SEC/ON) below Entry Interface (EI), 400,000 feet. Gravity is required to keep the NH3 at the tank outlet. No bladder separates the NH3 from its helium (He) pressurant. If an NH3 controller is manually activated (SEC/ON) while in zero g, the He pressurant could leak out, making that system unusable (Figure 4-15).
NH3 system: functional diagram
NH3 tank orientation
Requirements for Ammonia Controller Operation The power/MDM requirements for NH3 controller operation are shown in the following chart.
No NH3 system telemetry is visible on crew displays. The crew can indirectly monitor an active NH3 system by watching the Freon evap out temperature on the Panel O1 meter or on SM SYS SUMM 2 crew display.
The flight controllers have additional insight and can monitor the telemetry parameters as shown in Table below.
FLASH EVAPORATOR SYSTEM
The FES acts as a heat sink for the Freon loops. Water from the supply water tanks is sprayed onto the Freon loops in the high load and topping heat exchangers. This water “flashes” to steam at low ambient pressure and carries heat away from the Freon loops. The resultant steam is vented overboard (Figure 4-16). The FES is used as a primary source of cooling during ascent and entry and is also used as a supplement to radiator cooling during orbit operations.
The FES consists of two evaporators, three electronic logic controllers, two water feedlines with pulser valves, and two overboard steam ducts.
The high load and topping evaporators are located in the aft of the vehicle (Figure 4-16). Both evaporators are identically sized cylindrical heat exchangers about the size of an office wastebasket. The spray nozzles on the hi load evaporator are larger, giving the high load a larger heat rejection capacity (Table below).
FES heat rejection capacity***
The FES water feedlines provide the FES with water from the supply water tanks. Their 100-foot long feedlines are commonly referred to as the A supply and B supply feedlines. The FES feedlines are routed beneath the payload bay envelope and into the aft fuselage. Thermostatically controlled heaters are wrapped around the FES feedlines to keep them warm. Each FES feedline has two sets of heaters.
Flash evaporator system overview
Utilizing inputs from dedicated temperature sensors, each of the three electronic FES controllers can control the operation of the FES (Figure 4-17). Only one controller is selected at a time. The controllers are commonly referred to as the primary A (PRI A), primary B (PRI B), and secondary (SEC) controllers. PRI A and PRI B control the spray of A supply and B supply water (respectively) into the evaporators. The PRI A and PRI B controllers control to 39° ± 1° F, while the secondary controller controls to 62° ± 2° F.
The primary controllers have two modes of operation: high load enabled and topping only. If the high load evaporator is enabled, the primary controller will spray water into both the high load and the topping evaporators to achieve the 39° F control point. If the high load is off, the primary controller will spray water only into the topping evaporator in an attempt to control to 39° F.
The secondary controller also has two modes of operation: high load only and topping only. If the high load evaporator is enabled, the secondary controller will spray water into the high load evaporator only. The source of the water is selectable with the SEC A SPLY/B SPLY switch. If the high load is off, the secondary controller will spray water into the topping evaporator only from both the A and B supply feedlines in an alternate pulsing fashion that may have overlapping pulse at high heat loads.
The overboard steam ducts provide the path for the steam to vent overboard. The evaporator duct and nozzle temperatures are maintained by thermostatically controlled heaters. The topping evaporator duct vents to both sides of the orbiter so that it is essentially a nonpropulsive vent. The high load evaporator vents in the orbiter –Y axis and is propulsive.
The PRI A and PRI B FES controllers have undertemp and overtemp shutdown logic that will turn off the FES if it is not controlling to the 39° ± 1° F control point. The undertemp and overtemp shutdown logic receives its input from a dedicated temperature sensor (Figure 4-17). The SEC controller does not utilize this undertemp or overtemp protection. The secondary controller will attempt to control the evap out temperature to 62° ± 2° F. If the heat load is too great, the secondary controller will just spray as much water as it can and control to a warmer temperature.
The cooling rate shutdown circuits are active only when the Freon shutdown temperature at the evaporator outlet is above 41.5° ± 0.25° F. The rate of change is calculated by holding an initial shutdown temperature sensor reading 5 seconds after turn-on and comparing it to an updated sample 19 to 22 seconds later. The result of this first comparison is ignored, but subsequent sample comparisons at 29- to 32-second intervals can produce a shutdown signal. To avoid a rate shutdown, the cooling rate of change must be greater than 0.082 ± 0.047 deg F/sec. The rate monitor is disabled as soon as the Freon outlet shutdown sensor temperature has decreased to less than 41.5° F. The rate shutdown functions as the overtemp shutdown, and it is how an overtemp shutdown is accomplished.
The undertemperature shutdown logic is activated whenever the Freon outlet shutdown sensor temperature is less than 37° ± 0.25° F with the FES midpoint temperature greater than 41° F (i.e., when the FES is active). To prevent an inadvertent shutdown during startup or a transient condition, the undertemperature condition must be present for greater than 22 ± 3 seconds for the shutdown command to be generated. When the midpoint temperature (Freon temperature inlet to topping evaporator) drops below 40° F and the topping evaporator is in standby, the undertemperature shutdown feature is inhibited. This is necessary because the low temperature shutdown setpoint is within the shuttle radiator outlet temperature control band of 38° ± 2° F.
Temperature sensors at the midpoint in Freon loop flow between the high load and topping evaporators provide inputs to the primary controllers. These sensors are instrumental in FES control and shutdowns.
FES controller functional diagram
ENVIRONMENTAL CONTROL AND LIFE SUPPORT SYSTEM COOLING MANAGEMENT
Depending on the mission phase, the Freon cooling loops are cooled four different ways (see Figure 4-18). Prior to launch, cooling is provided by way of the GSE. After lift-off, there is no active cooling until after SRB SEP. It takes the orbiter slightly more than 2 minutes to reach an altitude where water evaporation provides effective cooling. Until that time, sufficient “thermal inertia’’ is in the Freon loops to limit the temperature increase so that no active heat rejection is required.
At the Major Mode 103 transition (SRB SEP), the FES receives a GPC “ON” command from the BFS and begins providing active cooling. The FES continues to be the primary cooling source through the ascent phase and on into the post insertion timeframe. During the Post Insertion Checklist procedures, flow is initiated through the radiators, the payload bay doors are opened, and the radiators become the primary source of cooling. The FES may be left on to provide supplemental cooling when necessary. If the orbiter is in a warm attitude, radiator cooling efficiency may decrease and the FES may be needed to provide additional cooling to achieve the desired Freon loop temperatures.
During the deorbit prep procedures, the radiators are “coldsoaked” to provide cooling for use later during entry. The radiator coldsoak process lowers the temperature of Freon in the radiators by changing the radiator control temperature from 38° to 57° F. Since less cool Freon from the radiators is required to control to this high temperature, flow through the radiators is slower. As a result, the Freon spends a longer period in the radiators exposed to space and becomes colder than if the flow control valve were controlling for a 38° F radiator out temperature. The FES is used to cool the Freon from 57° to 39° F. After approximately 1 hour of coldsoak, the radiators are bypassed, trapping the cold Freon in the radiators. At this point, the FES provides all the cooling to the Freon loops. The FES supplies cooling during the rest of the deorbit, through EI, and down to V = 12k (approximately 175,000 feet).
At V = 12k, the radiators are activated, since below 100,000 ft the atmospheric pressure is too high for the FES to cool effectively. Radiator flow is reinitiated after the auto startup sequence is complete. The cool Freon stored in the radiators is used as the primary source of cooling from this point through rollout.
Once the orbiter is on the ground and the radiator coldsoak is depleted, the NH3 boiler is activated. The MCC calls the crew to request the NH3 activation. The NH3 boilers are used as the primary cooling source until the GSE cooling cart hookup is complete. Then the NH3 cooling is deactivated, and GSE cooling is initiated.
ECLSS cooling management
For ascent aborts, the thermal management of the Freon cooling is somewhat different (see Figure 4-19). The FES still provides the cooling after SRB SEP. The cooling management during the entry portion is what has changed. The NH3 boilers provide the cooling during the lower stages of the abort entry. The NH3 is used for cooling during the entry phase of an ascent abort because the orbiter lifts off without a radiator coldsoak, and the FES functions normally only at low atmospheric pressure (above 100,000 ft).
For a TAL or an AOA, the NH3 boiler receives a GPC “ON” command from the BFS at MM304 and 120,000 ft. For an RTLS, the NH3 boiler receives a GPC “ON” command from the BFS at External Tank Separation (ET SEP) (MM602). The NH3 boiler will provide the cooling from this point through landing. The NH3 boilers can provide cooling for approximately 1 hour.
ACTIVE THERMAL CONTROL SYSTEM CONTROLS
The switches and circuit breakers that control the ATCS are located on Panels L1, L2, L4, O14, O15, and O17. The majority of the switches are located on Panel L1 (Figure 4-20). The layout of this half of Panel L1 is a schematic of the Freon loops.
The FLASH EVAP FEEDLINE HTR switches are located on Panel L2 (Figure 4-21). There is one switch for the A SUPPLY water line and one for the B SUPPLY water line heaters. The switches have three positions, 1, OFF, and 2.
The circuit breakers that provide power to the radiator controller logic are located on Panels O14 and O15 (Figure 4-22). The FREON RAD CNTLR 1 and 2 circuit breakers on Panel O14 provide MNA power to the AUTO B RAD controllers. The FREON RAD CNTLR 1 and 2 circuit breakers on Panel O15 provide MNB power to the AUTO A RAD controllers. The circuit breakers that provide AC power to the radiator rad/bypass valve motors are located on Panel L4 row P (Figure 4-23). The RAD CNTLR 1B circuit breaker provides AC1 phase A power to drive the RAD/BYPASS valve on Freon loop 1. The circuit breakers that provide AC power to the Freon flow proportioning valve motors are located on Panel L4 row N (Figure 4-23). For example, the FREON FLOW PROP 1 circuit breaker provides phase A power to drive the flow proportioning valve on Freon loop 1. The circuit breakers that provide AC power to the Freon pumps are also located on Panel L4 on rows M and N. The FREON LOOP 1 PUMP A circuit breakers provide three phases of AC1 power to Freon pump 1A.
The circuit breakers that provide AC power to the rad isol valve motors are located on Panel L4 row N (Figure 4-22). The circuit breaker that provides power to the rad isol controller logic is located on Panel O14.
The ATCS controls are listed in Table 4-5.
Ascent/abort thermal management
Panel L1 – ATCS
Panel L2 – ATCS
Overhead panels – ATCS
Panel L4 – ATCS
Active Thermal Control System Instrumentation/Displays
Crew insight into ATCS
system performance is provided by ECLSS instrumentation and DSCs (Figure
4-24). The Freon signal conditioners power the following transducers:
Freon S/C A Freon S/C B Freon loop 1 payload HX flow rate Freon loop 2 payload HX flow rate Freon loop 2 accum quantity Freon loop 1 accum quantity Freon loop 2 interchanger flow rate Freon loop 1 interchanger flow rate.
The crew has insight into ATCS status on the following CRT displays, dependent on mission phase. SPEC 88 is the primary display for ATCS system information during orbit operations.
Freon coolant loop instrumentation
RAD ISOL Display Logic
SPEC 88 APU/environ therm
The APU/ENVIRON THERM display is an SM display (DISP 88), available in SM OPS 2 and 4, which provides the crew with data on the ATCS Freon loops and heaters.
The SM SYS SUMM 2 display is an SM display (DISP 79), available in the BFS and PASS SM OPS 2 and 4, which provides summary data on the ATCS thermal control.
SM SYS SUMM 2
Parameter characteristics of SM SYS SUMM 2
Note: A blank display field denotes normal operation. ‘↑’ and ‘↓’ indicate heater or thermostat failures in a series heater line. Level detection limits are shown on SM displays. “M,’’ “H,’’ and “L’’ denote data transfer or sensor failures unrelated to heater control. CRT titles are aligned to panel switches needed to select different heater circuits.
Crew-dedicated displays (meters) located on Panel O1 (Figure 4-28) enable the crew to monitor critical ATCS system parameters during all mission phases. The FREON FLOW meter permits the crew to monitor the Freon flow to the H2O/Freon ICH (Figure 4-24). The FREON LOOP 1/LOOP 2 switch allows the crew to select between loop 1 and loop 2 on the meter.
The FREON EVAP OUT TEMP meter displays the evap out temperature on the Freon loop selected by the switch.
ATCS meters – Panel O1
Caution and Warning
The FREON LOOP light on the Panel F7 matrix (Figure 4-29) will illuminate if one of the following parameters is out-of-limits.
Panel F7 C/W matrix
ATCS Systems Performance, Limitations, and Capabilities
a. Freon 21 loop
1. Freon 21 boiling point
at 14.7 psi 48° F
2. Freon 21 freezing point -211° F
3. Total flow (2 loops) 5336-5972 lb/hr
4. Net positive suction head 35 psia minimum
5. Accumulator operating pressure 230 psig
6. Accumulator proof pressure 345 psig
7. Accumulator burst pressure 460 psig 8. Accumulator volume 1658.8 in3
1. Basic heat rejection capability 61,100 Btu/hr
2. Operating pressure 320 psia max
c. Ammonia boiler – Heat rejection ability 113,200 Btu/hr
d. Flash evaporator
1. Primary controllers
Max. capability: Topping only 39,000 Btu/hr Topping and Hi load 148,000 Btu/hr
2. Secondary controller
Max. capability: Topping 76,800 Btu/hr Hi load 113,100 Btu/hr
SUPPLY AND WASTEWATER SYSTEM
The supply water storage system stores water generated by the fuel cells for FES cooling and crew consumption. The wastewater storage tank stores crew liquid waste and humidity condensate. The PCS system N2 provides the supply and waste tank pressurization. The vacuum vent line provides a controlled overboard bleed to vacuum from the cabin.
SUPPLY WATER STORAGE SYSTEM
The supply water storage system consists primarily of four water tanks that are pressurized with N2 from the PCS (Figure 5-1). These 165-lb capacity tanks are located below the middeck floor (Figure 5-2). Each tank has a bellows, a quantity sensor, a tank inlet and outlet valve, and a hydrophobic filter. The water stored in the water tanks is generated by the fuel cells. Water tank A is sterile and is reserved for storing potable water. Water tanks A, B, C, and D may all be used to supply water to the FES for cooling. The capability exists to dump excess water overboard to create the necessary ullage in the tanks to store the fuel cell product water. Filtered water is routed to the galley for crew consumption. Water in the supply water tanks can be routed to the airlock and used for EMU reservicing.
Fuel cell product water is transferred to the supply water storage tanks by the pressure difference between the fuel cells and the supply water tanks themselves. The H2- enriched water from the fuel cell flows through the H2 separators. The H2 separator removes any residual H2 from the water as it flows to the supply water tanks. The silver palladium tubes of the H2 separators attract the H2. The H2 passes through the walls of the tubes and is vented overboard through the vacuum vent line.
The water then flows through the microbial filter before entering water tank A. The microbial filter adds iodine to the water, which acts as a disinfectant to prevent microbial growth in tank A. Tank A is sterilized prelaunch and its outlet valve is kept closed to ensure that only filtered water enters the tank. Tank A is used for storing potable water for crew consumption. This filtered potable water is routed to the galley via the galley supply valve. For ISS missions, tanks A and B are used for storing potable water so that there is more water available to transfer to the station via the CWC bags.
If water tank A is full or if the tank A inlet valve is closed, the water pressure will increase, crack the 1.5 psid check valve, and allow water flow into water tank B. If water tank B is full, the next 1.5 psid check valve will crack and the water will fill water tanks C and D. By manipulating the tank inlet and outlet valves, the water tanks can be selectively filled and/or dumped overboard.
Supply water storage system
The outlet side of the four water tanks is plumbed together to form an outlet manifold. As stated earlier, for non-ISS missions the water tank A outlet valve is kept closed to preserve the sterility of the tank A water. The crossover valve between the tank B and C outlets breaks this manifold into two parts, the A-B side and the C-D side. This crossover valve is normally kept closed with tank C isolated from lift-off until post- insertion. When it is open, with tank C isolated, tanks B and D act as a single large tank. The A-B side of the crossover valve supplies water to the FES A supply water feedline and the EMU airlock feedline. The supply water dump line is also on the A-B side of the manifold. The C-D side of the manifold supplies water to the FES B supply water feedline. There is a valve to isolate the FES B supply feedline. The FES A supply feedline cannot be isolated directly. FES PRI A normally uses tank B water during ascent. If FES PRI B is used during ascent, the water is supplied by tank D. The FES H2O feedlines are kept warm outside the cabin by thermostatically controlled electrical resistance wire wrapped heaters.
Once on orbit, the fuel cells produce more water than the crew needs for drinking and FES cooling. The excess water must be dumped overboard periodically to make room for the water the fuel cells are producing. This is accomplished by performing a supply water dump. The supply water dump nozzle heaters are turned on to keep the dump nozzle from freezing during the water dump. Thermostatically controlled line heaters keep the portion of the dump line outside the cabin warm. The dump isolation valve and the dump valve are then opened to dump the water overboard. A supply water dumpline purge device is inserted into the potable water inlet on the contingency crosstie panel in the WCS. This allows air into the dump lines when the dump is complete, allowing a more efficient purge of the lines. Before this device was used, water remaining in the lines would on occasion freeze, forcing the dump valve open and causing a little water to “burp” overboard. When the desired amount has been dumped, the dump isol valve is closed, the dump valve is cycled to remove excess water in the lines then finally left closed, and the dump isol is opened. If the supply water dump does not work or if there are mission-specific payload constraints that prevent the use of the supply water dump line, ullage may be created by using the FES for cooling. In a supply water dump through the FES, the radiators are taken to the higher radiator out temperature control point of 57° F. The FES is then used to cool the Freon to 39° F. This FES operation consumes more water than is produced, resulting in a net reduction of water in the tanks. A supply water dump using the FES is slower than a nominal dump through the supply water dump line. If neither of these methods works, water may be dumped through the wastewater dump line by connecting the contingency crosstie hose and performing the backup water dump In-Flight Maintenance (IFM) procedure.
The normal water management plan is to keep as much water in the water tanks as possible to make it to the next water dump opportunity. See Figure 5-2 for a typical mission water management plan. The top plot shows the total quantity of all four water tanks and the total of tanks C and D. The bottom plot shows the water quantity in tank A and tank B. Normally, water tank C is kept full for contingency purposes. This reserve of supply water is required to provide water for FES cooling in case of a deorbit wave-off (where the payload bay doors remain closed) or a contingency deorbit.
On-orbit water management is accomplished by dumping and filling tanks A and B. Supply water dumps are usually scheduled at 12-hour intervals unless there are mission-specific payload constraints. This allows for performing the supply water dumps during the pre- and postsleep activities. Up to 210 lb of water may be dumped to obtain the required ullage. At least 76 percent (128 lb) of water must remain in tank A. This is the amount of water that is necessary to sustain five crewmembers over a 96-hour Minimum Duration Flight (MDF) time period (128 lb assumes a metabolic requirement of 6 lb/per person per day).
For ISS docking missions, a
supply water transfer may be performed. In this case, the water tank valve
configuration on orbit will be different: tank B inlet and the crossover
valves closed, everything else open. This allows tanks A and B to be used
for potable water storage, and C and D are used for supply water storage.
Instead of dumping the excess water overboard, the water will be transferred
to the ISS either through dedicated transfer lines or through manually
filled water transfer bags filled at the galley. FES Pri B will be used on
orbit so that the potable water in tanks A and B will not be used for the
The supply water tank quantity sensor indicates water quantity by sensing the water tank bellows position. If the tank is full, the gauge will indicate ≈100 percent. If the water tank bellows develops a leak, the bellows will seek its neutral spring rate position and indicate a tank quantity between 60 to 70 percent. The hydrophobic filter prevents water that has leaked past a failed bellows from getting into the water tank N2 manifold (Figure 5-3).
Typical water plan for a mission
Typical water tank
WASTEWATER STORAGE SYSTEM
The wastewater storage system consists of one wastewater tank that is pressurized with N2. The waste tank is physically identical to a supply water tank and also is located below the middeck floor (Figure 5-2). The waste tank stores crew liquid waste (urine) and humidity condensate in a sanitary manner until it can be disposed. The waste tank has an inlet valve and a drain valve (Figure 5-4). The drain valve is used only during ground servicing and is kept closed and unpowered during flight. The inlet valve functions as both the tank inlet and outlet. Wastewater can be dumped overboard by way of the wastewater dump line. The contingency water crosstie enables the supply water dump line to be connected to the wastewater dump line. This allows supply water to be dumped through the waste line or vice versa. The contingency water crosstie QDs are located on the wall of the WCS compartment.
The normal waste tank management plan is to dump the waste tank via the wastewater dump line when the tank quantity reaches 80 percent. The waste dump nozzle heaters are enabled to prevent ice formation on the nozzle. Thermostatically controlled heaters keep the portion of the dump line outside the cabin from freezing. The dump isol valve and dump valve are then opened to allow the wastewater to dump overboard. In case the waste tank cannot be dumped overboard, a collapsible contingency wastewater collection bag known as a CWC (Figure 5-5) is flown to provide additional ullage. The wastewater tank can be dumped into the contingency wastewater collection bag by way of the contingency water crosstie. The production of wastewater on previous flights has been as high as 6.2 lb per person per day. Mission duration and the number of crewmembers flying make wastewater management very mission specific.
For ISS missions, humidity condensate is collected in a CWC to reduce the number of waste dumps needed while docked to the ISS.
Wastewater storage system
Contingency water collection bag
SUPPLY AND WASTEWATER PRESSURIZATION SYSTEM
The supply and wastewater tanks are normally pressurized with PCS system N2. This N2 pressure is controlled to 15.5 to 17.0 psi above cabin pressure and provides the force necessary to move the water through the system; 200 psig N2 from PCS systems 1 and 2 passes through the water tank N2 regulator inlet valves (Figure 5-6) and is stepped down to between 15.5 to 17.0 psig by the H2O tank N2 regulator. The H2O tank N2 regulator is flow limited to 1 lb/hr. To protect against overpressurization, two relief valves are provided that relieve into the cabin at 18.5 ± 1.5 psig. The N2 then passes through the H2O tank N2 isolation valves and pressurizes the H2O tank N2 manifold. This common manifold provides pressurization to the waste tank and all of the supply water tank bellows.
During ascent, water tank A must be vented to the cabin. During launch, the orientation of the orbiter and vehicle acceleration both work against the flow of fuel cell product water into the supply water tanks. If the water tanks were pressurized with N2, the water would not make it into the water tanks. It would relieve overboard since overboard relief offers the path of least resistance (Figure 5-1). This is not desirable since if the overboard relief path fails, the fuel cells will flood and stop producing electricity. To vent water tank A, the tank A supply valve is closed. This isolates tank A from the rest of the H2O tank N2 manifold. Then the tank vent valve is opened (vent) to vent tank A to the cabin (Figure 5-6). Tank A remains vented until post insertion.
Then the tank vent valve is reconfigured to the closed (PRESS) position, and the tank A supply valve is reopened to let N2 pressurize tank A.
The tank A supply and tank vent valves are also used to vent the entire H2O tank N2 manifold. The tank A supply valve is kept open and the tank vent valve is taken to vent in order to vent all the water tanks to cabin pressure. If a water leak is suspected, taking the N2 pressure off the water tanks will stop the leak if the leak is inside the cabin. The water alternate press valve provides a backup method of venting the H2O tank N2 manifold to the cabin.
Water tank N2 pressurization
VACUUM VENT SYSTEM
The vacuum vent system provides the orbiter with a controlled overboard bleed. The vacuum vent line is a pipe with an inside diameter of 1.93 in. The pipe originates inside the cabin and vents outside to space (Figure 5-7). The vacuum vent isolation valve isolates the portion of the vacuum vent line located inside the cabin. Even with the vacuum vent isolation valve closed, an orifice plate in the valve still allows an overboard flow of 3.0 ± 0.25 lb/hr at a cabin pressure of 14.7 psia. The purpose of the orifice plate is to allow the H2 removed by the fuel cell H2 separators to vent overboard even if the vacuum vent isolation valve is closed.
The vacuum vent isolation valve is closed during ascent and entry. The vacuum vent system is activated during orbit operations. When the vacuum vent isol valve is opened, the line and nozzle heaters are activated. The heaters prevent water vapor from freezing in the vacuum vent line. The WCS uses the vacuum vent line to provide the vacuum required for operation. The WCS commode vents overboard during WCS operation. A small amount of cabin air continuously bleeds overboard through the WCS wet trash compartments to help keep WCS odors to a minimum. The RCRS vents CO2 to space if installed (see Appendix C).
Vacuum vent system
SUPPLY AND WASTEWATER SYSTEM CONTROLS
The switches that control the supply and wastewater system are located primarily on Panels R11, ML31C, ML26C, ML86B, L1, and O16. The switches on Panels R11 and ML31C (Figure 5-8 and Figure 5-9) control the electrically controlled supply water system valves. The panel layout is a schematic representation of the supply water system. Talkbacks indicate the position of the valves. The talkbacks will indicate either open, closed, or barberpole. If power to a valve is lost, the valve will remain in its present position, but the talkback will indicate barberpole. All of the valves on Panel R11 are of this same type. The SUPPLY H2O DUMP VLV ENABLE/NOZ HTR switch activates the dump nozzle heaters and powers the SUPPLY H2O DUMP VLV. The supply H2O dump valve cannot be opened unless the nozzle heater is powered.
Panel ML31C also houses the
controls for the wastewater and vacuum vent systems.
The circuit breakers on rows A and B of Panel ML86B provide the power used to drive the valves and heaters on Panels R11 and ML31C (Figure 5-10). The MNA H2O LINE HTR A and MNB H2O LINE HTR B circuit breakers provide power to the supply water dump line, wastewater dump line, and vacuum vent line heaters.
The Panel ML26C (Figure 5-11) switches are used to vent the supply H2O tank N2 manifold to the cabin. The SUPPLY H2O GN2 TK A SPLY valve is a two-position manual valve. If OPEN, tank A is pressurized by the H2O tank N2 manifold. If CLOSED, tank A is isolated from N2 pressurization. The SUPPLY H2O GN2 TK VENT valve is also a two-position manual valve. If in PRESS, tank A is pressurized by the H2O tank N2 manifold. If in VENT, the pipe stub is opened and vents tank A to cabin pressure (Figure 5-6).
The H2O ALTERNATE PRESS
switch on Panel L1 is a remotely powered valve that can also be used to vent
the H2O tank N2 manifold to cabin pressure (Figure 5-11). The power for the
H2O alternate press valve comes from the H2O ALT PRESS circuit breaker
located on Panel O16 row D.
The H2O tank N2 switches were discussed in the pressure control system controls and displays section.
A detailed listing of supply and wastewater system controls is contained in Table 5-1.
Panel R11 – Water
Panel ML31C – Water
Panel ML86B – Water
Water system pressurization controls
SUPPLY AND WASTEWATER SYSTEM INSTRUMENTATION/DISPLAYS
CRT Displays The crew has insight into supply and wastewater system performance on the following CRT displays, dependent on mission phase. SPEC 66 is the primary display for water system information during orbit operations. The supply water pressure data on the BFS thermal display are valid only during MM104-106, MM301-303, and orbit OPS 0.
The EVLSS water supply pressure is available on Panel AW82D in the airlock (Figure 5-14). This shows the supply water pressure on the tank A and B outlet portion of the supply water system (Figure 5-14). This parameter is used during EMU airlock operations.
Instrumentation The instrumentation points visible to the crew are shown on Figure 5-15, Figure 5-16, Figure 5-17, and Figure 5-18.
BFS SM0 THERMAL
The THERMAL display is a BFS display (OPS/0001) that provides the crew data on the supply H2O system.
SPEC 66 ENVIRONMENT
The ENVIRONMENT display is an PASS SM display (DISP 66), available in PASS SM OPS 2 and 4, which provides data on the supply and wastewater system.
EVLSS H2O supply pressure meter
Supply water system instrumentation
Wastewater system instrumentation
Water tank N2 pressurization instrumentation
Vacuum vent system instrumentation
Supply and wastewater system controls
Water and Waste Management Systems Performance, Limitations, and Capabilities
a. Fuel cell – ECLSS
Interface100° to 220° F
b. Maximum flow rate (from fuel cells) 10.7 lb/hr
c. Maximum back pressure 40 psia
d. Minimum back pressure 10 psia
e. Storage usable capacity 165 lb/tank
f. Proof pressure 37.5 psid
g. Burst pressure 50 psid
h. Operating temperature range 60° to 120° F
i. g limit 5.0g
j. Operating pressure range (pressurant side) 15.5 to 20.0 psig
k. Supply temp from tank 75° F
l. Tank flow rate 0 to 165 lb/hr
m. Water dump average flow capacity 2 to 2.3 lb/min
EXTERNAL AIRLOCK SYSTEM
The orbiter airlock is used to allow crewmembers to safely stay in the pressurized crew compartment while doing operations, such as docking or EVA, in vacuum. The external airlock is mounted in the payload bay, in which the hatch at the Xo = 576 bulkhead (middeck hatch) opens to the transfer tunnel, airlock, and tunnel adapter. (See Figure 6-1.)
External airlock with tunnel adapter (fwd), tunnel extension, and vestibule
ASSOCIATED AIRLOCK VOLUMES
The tunnel adapter provides
a method for EVA access with a pressurized module. It is a 130 ft3 volume
with an EVA hatch on top, and the capability to add another hatch at the aft
For the external airlock, the tunnel adapter may be installed either forward or aft of the external airlock, depending on mission requirements; for example, obtaining improved visual clearances for ISS docking missions by moving the tunnel adapter further aft.
The vestibule is located on top of the external airlock and is used only during docking and undocking operations. When docking and undocking, the vestibule is at vacuum, while the external airlock is pressurized; this prevents having to vent the much larger volume of the airlock and allows for more efficient leak checks. The vestibule is a relatively small 50 ft3 in volume; it can be vented to vacuum and can be pressurized from the airlock.
Also known as the transfer tunnel or transition section, this 43 ft3 volume provides access to the external airlock volume itself. The external airlock and the tunnel extension are always flown together and are considered one volume. It has no heaters or controls and is always forward of the airlock.
EQUALIZATION, DEPRESS, AND ISOLATION VALVES
The equalization valves are located on all hatches and are used to equalize the airlock with cabin pressure, or to isolate the airlock from the middeck if the hatch is closed. They also are used as a backup method for airlock depress. Two valves are used for redundancy. Each valve consists of a removable cap and a three-position switch (OFF, NORM, EMER).
The OFF position allows no flow. The NORM position allows 240 lb/hr flow at 14.5 psid, and the EMER position allows 1278 lb/hr of flow at 14.5 psid. (See Figure 6-2.)
Airlock equalization valve
The airlock depressurization valve (also known as the depress valve) and its associated cap are located on Panel AW82B. It is used to depress the cabin to 10.2 psia and to depressurize the airlock to vacuum for EVA. The airlock depressurization line cap is in series with the airlock depress valve and must be removed to perform an airlock depressurization. The airlock depress valve is a three-position rotary switch (CLOSED,5, 0) that must be pushed in to allow rotation. The CLOSED position allows no flow. Position 5 normally is used to depressurize the airlock to 5 psia, hence the name “5,” and is also used in depressurizing the cabin from 14.7 to 10.2 psia. Position 5 opens a 0.59-inch-diameter orifice to vacuum. The zero position is used to depress the airlock from 5 to 0 psia. Position 0 opens a 1.02-inch-diameter orifice to vacuum. The airlock depress valves have been modified for the external airlock to vent overboard directly into the payload bay through a “T” that is designed to be nonpropulsive.
For docking missions, the airlock also has a vestibule on top that mates with the Pressurized Mating Adapter (PMA) on the ISS. Valves on Panel A6L depressurize the vestibule (before undocking), and the equalization valves on the hatch pressurize the vestibule before hatch opening (post-docking).
A cabin purge valve has been installed in the middeck floor. The valve has a number of detent positions to purge the cabin at 8 psi depending on the number of crewmembers wearing QDMs following a fire or toxic spill (see Figure 6-3). The cabin purge system vents overboard through the vacuum vent system.
Cabin purge valve assembly
If the tunnel adapter is flown, a payload isolation valve is installed in the duct on the tunnel adapter side of the aft hatch to provide protection against leaks in volumes aft of the tunnel adapter hatch (see Figure 6-4). This is used when the tunnel is taken to vacuum in support of an EVA. It provides a seal to keep the module from leaking through the duct into the evacuated tunnel adapter.
Payload isolation valve assembly
AIR AND WATER TRANSFER
For various reasons and in various capacities, air and water are transferred either to the ISS or to the EMUs, or both. Oxygen is provided to the EMUs for EVA crewmembers, and is transferred to the ISS along with nitrogen. Supply water is provided for EMU cooling during EVA and for crewmember drinking; wastewater is returned from the EMUs following an EVA.
Water is supplied via the airlock for the EMU feedwater system, used for cooling crewmembers via sublimation during an EVA, and for crewmember consumption. Since the water comes from the supply water system on the A-B outlet leg, it must be purified before flowing to the ISS. The water passes through a filter and a check valve on its way to the airlock in order to prevent contamination from passing from the EMU to the orbiter. To provide an isolation capability against leaks, a water shutoff valve is downstream of the filter/check valve package. After an EMU water recharge, an ullage dump is performed through the wastewater return line back to the waste tank.
Water also flows into and out of the airlock in two closed LCVG coolant loops, one for each EMU, for chilling the LCVG (“long underwear”) while hooked into the Servicing and Cooling Umbilical (SCU). This water is cooled by the orbiter water loops at the LCVG heat exchanger.
The portions of the supply and wastewater lines in the payload bay are wrapped with triply redundant heaters for thermal conditioning. Thermostatically controlled electrical resistance heaters in two zones on the LCVG lines prevent freezing.
An O2 line through the airlock provides 900 psi O2 for EMU servicing; in the case of the external airlock, it provides ISS transfer directly from the orbiter cryo O2 supply. Oxygen flowing into the ISS will come from the EMU supply line, which is fed from the O2 crossover manifold in the PCS. The EMU oxygen switches on Panel AW82B enable PCS systems 1 and 2 O2 to be used to service the EMUs. On the airlock floor is the EMU O2 isol valve, a manual O2 shutoff valve to protect against leaks into the airlock or overboard via the transfer line into the payload bay. The EVLSS O2 P sensor upstream of this valve drives the gauge in the airlock on Panel AW82B.
In case an EVA is required to perform a contingency undocking, a manual EVA isolation valve is installed on the outside of the airlock to allow crewmembers to vent and cut the O2 line while still maintaining the capability for EMU servicing. This valve is accessible only on EVA on Panel AW64(E) (see Figure 6-5).
Manual EVA isolation valve
Nitrogen transfer to the ISS is connected into the orbiter PCS at the MMU A GN2 supply. In this configuration, the MMU A GN2 supply isol valve on Panel R13L controls the flow of N2. The lines are all completely external to the airlock.
AIRLOCK BOOSTER FANS AND DUCTWORK
Because the airlock does not have vents to circulate orbiter-conditioned air from the cabin fan, ductwork must manually be set up by the crew to provide it. The ductwork for both the airlock has two major functions in circulating air:
a. Humidity control via conditioned air from orbiter ARS
b. Prevention of pockets of CO2, O2, or N2
Additionally, the ductwork provides other functions for the airlock and tunnel adapter:
a. Condensation control of airlock and upper hatch window, where the docking camera is mounted
b. Thermal conditioning of the airlock avionics bay, installed under the floor
c. Supply of orbiter-conditioned air to a docked ISS or a module in the payload bay
Two booster fans (see Figure 6-6), used one at a time, provide supplemental airflow for a module or the ISS. Although the fan filter is not easily accessible on orbit, flight experience has shown that filter cleaning during a mission is not required. The fans, installed in the tunnel adapter (if present) or the tunnel extension (if the tunnel adapter is not present or is mounted in the aft position) are powered by a three-phase, 115-volt AC motor. The 180-watt motors produce a normal flow of 541 to 767 lb/hr. The ARS interface to the fans and ductwork is via a middeck floor fitting; in the airlock configuration, the fitting has been moved closer to the Xo = 576 bulkhead. The fans are controlled via Panel MO13Q. If there is no pressurized module and there are no plans for docking with the ISS, the booster fan is not required to be flown.
The configuration of the ARS ductwork is highly dependent on mission requirements and varies according to the availability of a booster fan or a tunnel adapter. See Figure 6-7 for an example of the airlock ductwork configuration.
Airlock ductwork configuration Diagram
Six fluid lines run outside the pressurized volume to provide servicing capability for the EMUs in the airlock and potable water transfer to the ISS. These six lines are as follows:
a. One LCG supply and one return line (for SCU/EMU 1)
b. One LCG supply and one return line (for SCU/EMU 2)
c. One potable water supply
d. One wastewater return
The six lines are broken up into two zones separated by a QD Panel. The fluid lines in each zone are individually wrapped with three strings of line heaters, used one at a time, and are controlled by thermostats that enable or disable all six heaters in that zone. See Figure 6-8.
Payload bay line routing
Additionally, thermal conditioning of the airlock is provided by a series of structural patch heaters located around the outside shell of the airlock in three zones: the forward and aft halves of the airlock upper bulkhead and the lower bulkhead keel fitting. The heaters are designed to maintain the airlock internal temperature above freezing, especially when the airlock is at vacuum, due to the water lines that run inside the airlock for EMU servicing and ISS water transfer. The heaters are designed also to help prevent the buildup of condensation on the internal walls and hatches and in the docking avionics bay. The structural heaters are dually redundant.
As part of the docking system, the vestibule heaters are technically not considered part of ECLSS, but they are briefly discussed here with the rest of the airlock system for completeness. The vestibule heaters are structural patch heaters of the same type as the airlock structural heaters; they are dually redundant and are broken up into three zones, which are activated via a single circuit breaker.
All heaters are controlled via circuit breakers on Panel ML86B.
Orbiter hatches can be either a “B” type or a “D” type.
a. “B” type – Capable of holding pressure in one direction only, as in the case of the always-pressurized orbiter and the sometimes-depressurized airlock.
b. “D” type – Capable of
holding pressure in either direction; for example, if a pressurized module
aft of the airlock stays pressurized during an EVA when the airlock is
depressurized, it can also protect against a depressurization of that module
while the airlock remains pressurized.
All airlock hatches are essentially identical with respect to their size, structure, gauges, actuators, and valves. The distinctions are in the hinges and number of latches that differentiate them and drive their location in the vehicle. However, the nomenclature of the hatches can be confusing due to the fact that the original naming convention did not evolve with the modifications and additions to the orbiters.
The hatch names (in particular, “B” type and “D” type) generally reflect their capability. See Figures 6-12 and 6-13.
a. Middeck hatch – The middeck hatch is always a “B” type; located between the Xo = 576 bulkhead and the payload bay.
b. Upper hatch – The upper hatch is typically a “B” type for EVA, but may be a “D” type for docking; located at the top of the external airlock or Orbiter Docking System (ODS).
c. Aft hatch – The aft hatch is a “B” type if there is no pressurized module; otherwise, it is a “D” type; located at the aft end of the airlock.
d. Tunnel adapter hatch –
The tunnel adapter hatch is the C-hatch, a “B” type; located on top of the
tunnel adapter for EVA access.
Airlock, no tunnel adapter
Airlock with tunnel adapter (fwd)
The EVA hatch depends on whether or not the shuttle has a pressurized module aft of the airlock (such as a SpaceHab) connected through another tunnel extension. If there is another module, then the EVA hatch is the overhead hatch in the tunnel adapter; otherwise, it is the hatch on the aft of the airlock (which leads to a pressurized module if one is there). While the tunnel adapter can be mounted either forward or aft of the airlock, depending on mission requirements, the nomenclature remains the same.
AIRLOCK SYSTEM CONTROLS
See Figure 6-11, Figure 6-12, Figure 6-13, Figure 6-14, Figure 6-15, Figure 6-16, and Figure 6-17 for the various panels.
Airlock vent valves on AW82B
AIRLOCK INSTRUMENTATION AND DISPLAYS
Crew insight into airlock performance is provided by sensors throughout the airlock and its associated hardware. There are no DSCs. Data are provided to the crew and Mission Control Center on various air and water pressures, water and structure temperatures, and vestibule valve status. It is worth noting that structural temperature sensors, whether internal or external, are located to monitor the automatic thermostat function of the externally mounted heater strings. They are not designed to monitor actual structure temperature or internal airlock temperatures.
The difference in pressure across the various airlock hatches is displayed on a meter on each side of the hatch and thus accommodates the middeck and EVA crewmembers. See Figure 6-18. For a schematic of the airlocks, see Figure 6-19. Note that the tunnel adapter may be forward or aft of the airlock, depending on mission requirements.
Airlock delta pressure gauge
The EXTERNAL AIRLOCK display (DISP 177) is available in SM OPS 2 only (see Figure 6-20). It provides information on airlock atmosphere, vestibule depress valves, water lines, and structural heaters. The associated hardware is present on all vehicles, but the display is present on all flights to keep the software load generic.
Note that on the display, the “Internal Temp” parameters refer to the physical location of the sensor inside the airlock, but their sole function is to monitor the externally mounted thermostat. They can provide no insight into the air temperature of the airlock.
SPEC 177 EXTERNAL AIRLOCK
AIRLOCK NOMINAL OPERATION
The middeck (inner) hatch is generally opened during the post-insertion timeframe to provide the crew with additional stowage for launch and entry suits, seats, and other items that are not usually used on orbit. In deorbit prep, the hatch is closed early to keep it from interfering with stowage locations of middeck stowage bags. On orbit, the inner hatch is always left open except during EVA operations.
Since each heater string (water line, structure, and vestibule) is individually capable of maintaining proper thermal conditioning, only one string is operated at a time. The MNA heater string is activated during post insertion and is swapped with the MNB heater string during the mid-mission heater reconfig. The MNC water line heaters are not normally used.
Airlock depress operations are typically performed for docking/undocking and EVA.
For a mission in which the shuttle will dock with ISS, a set of protocols has been developed that covers the critical time periods before docking, during docking, and immediately after docking and undocking.
a. Before docking – The Airlock/ODS is prepared for crew egress, and the inner airlock hatch and the equalization valves are closed, isolating the airlock. After docking, the crews wait to see whether the airlock pressure decreases, which indicates a leak. Following a successful leak check, the middeck hatch is reopened. Meanwhile, the pressure differential across the ODS hatch to the vestibule is checked to ensure that no leak exists there either. The vestibule is then pressurized and after another leak check, the equalization valves are opened, which may trigger a Dp/Dt klaxon if the two volumes are at different pressure. Finally, the hatch is opened.
b. Before undocking – The PMA hatch and then the ODS hatch are closed, both with all equalization valves closed. The vestibule is depressurized from the orbiter flight deck; after a leak check, the orbiter undocks from the ISS.
For a mission in which crewmembers perform an EVA, the cabin is first depressurized to 10.2 psia (from 14.7) using the airlock depress valve and various PCS valves. While the cabin is depressurizing, the crew manipulates the PCS valves to maintain the proper oxygen content in the atmosphere, and the airlock depress valve is typically opened twice during the procedure. Note that while the cabin is depressurizing, the hardware Dp/Dt sensor annunciates with a klaxon. The “5” position on the depress valve allows the cabin to depress to 10.2 psia in about a half hour.
AIRLOCK SYSTEM CONTROLS
Table - Airlock controls
Airlock System Performance, Limitations, and Capabilities Volume (ft3)
a. Airlock 185
b. Tunnel extension 43
c. Tunnel adapter 130
d. Vestibule 40
e. EMU Subtract 10 ft3 for each suit
APPENDIX A - ACRONYMS AND ABBREVIATIONS
A / B / C / D / E / F / G / H / I / J / K / L / M / N / O / P / R / S / T / V / W
AC - Alternating Current
ACA - Annunciator Control Assembly
ACCUM - Accumulator
ALT - Alternate
AMEU - Aft Master Events Unit
AMI Alpha Mach Indicator
AOA - Abort Once Around
ARS - Atmospheric Revitalization System
ATCO - Ambient Temperature Catalytic Oxidizer
ATCS - Active Thermal Control System
ATM - Atmosphere Av Avionics
AVVI - Ascent Vertical Velocity Indicator
BFC - Backup Flight Controller
BFS - Backup Flight System
C/P - Coldplate
C/W - Caution and Warning
C&W - Caution and Warning
CAB - Cabin
CAM Computer Annunciation Matrix
CAP - Crew Activity Plan
cb - control bus
CCTV - Closed-Circuit Television
CDR - Commander
CIU - Computer Interface Unit
CNTL - Controller
CO - Carbon Monoxide
CO2 - Carbon Dioxide
COMSEC - Communications Security
CRT - Cathode Ray Tube
CWC - Contingency Water Container
D&C - Display and Control
DC - Direct Current
DDU - Digital Display Unit
DEU - Display Electronic Unit
DFI - Developmental Flight Instrumentation
DMP - Dump
dp/dt - delta pressure/delta time
DPS - Data Processing System
DPU - Data Processing Unit
DSC - Dedicated Signal Conditioner
ECLSS - Environmental Control and Life Support System
EDO - Extended Duration Orbiter
EI - Entry Interface
EMER - Emergency
EMU - Extravehicular Mobility Unit
ENA - Enable
EPDC Electrical Power Distribution and Control
EPS - Electrical Power System
ET-SEP - External Tank Separation
EVA - Extravehicular Activity
EVAP - Evaporator
EVLSS - Extravehicular Life Support System
FCL - Freon Coolant Loop
FCV - Flow Control Valve
FD - Flight Day
FE 21 - Freon 21
FES - Flash Evaporator System
FM - Frequency Modulation
FREQ - Frequency
GN2 - Gaseous Nitrogen
GPC - General Purpose Computer
GSE - Ground Support Equipment
H2 - Hydrogen
H2O - Water
He - Helium
HUD - Head Up Display
HX - Heat Exchanger
HYD - Hydraulics
Hz - Hertz
ICH - Interchanger
IDP - Integrated Display Processor
IFM - In-Flight Maintenance
IMU - Inertial Measurement Unit
INST - Instrumentation
INTCHGR - Interchanger
ISOL - Isolation
ISS - International Space Station
JSC Johnson Space Center
KSC - Kennedy Space Center
LCVG - Liquid Cooling and Ventilation Garment
LEH - Launch and Entry Helmet
LES - Launch and Entry Suit
LiOH - lithium hydroxide
MADS - Modular Auxiliary Data System
MCC - Mission Control Center
MCIU - Manipulator Controller Interface Unit
MDF - Minimum Duration Flight
MDM - Multiplexer/Demultiplexer
MDU - Multifunction Display Unit
MECO - Main Engine Cutoff
MEDS - Multifunction Electronic Display System
MLS - Microwave Landing System
MM - Major Mode
MMU - Manned Maneuvering Unit
MOD - Mission Operations Directorate
MPLM - Multipurpose Logistics Module
MS - Mission Specialist
N2 - Nitrogen NEG Negative
NH3 - Ammonia
NOZ - Nozzle
NSP - Network Signal Processor
O2 - Oxygen
ODS - Orbiter Docking System
OFI - Operational Flight Instrumentation
OPS - Operational Sequence
PASS - Primary Avionics Software System
PCMMU Pulse-Code Modulation Master Unit
PCS - Pressure Control System
PEI - Polyethylenimine
PEV - Pressure Equalization Valve
PL - Payload
PMA - Pressurized Mating Adapter
PNL - Panel
POT - Potable
PPCO2 - Partial Pressure Carbon Dioxide
PPO2 - Partial Pressure Oxygen
PRI - Primary
PROP - Proportioning
PRSD - Power Reactant and Storage Distribution System
PS - Payload Specialist
psi - pounds per square inch
psia - pounds per square inch absolute
psid - pounds per square inch differential
psig - pounds per square inch gauge
PVT - Pressure Volume Temperature
PW Pulse Width
QD - Quick Disconnect
QDM - Quick Don Mask
RCRS - Regenerable Carbon Dioxide Removal System
RCU - Remote Control Unit
REG - Regulator
REST - Restrictor
RGA - Rate Gyro Assembly
RJDF - Reaction Jet Driver Forward
rpm - revolutions per minute
RTC - Real-Time Command
RTG - Radioisotope Thermoelectric Generator
RTLS - Return to Launch Site
SCU - Servicing and Cooling Unit
SEC - Secondary
SM Systems Management
SRB SEP Solid Rocket Booster Separation
SSOR Space to Space Orbiter Radio
SW Software SYS System
T - 0 Time-zero
TACAN - Tactical Air Navigation
TAL - Transoceanic Abort Landing
TK - Tank
TM - Telemetry
VCV - Vacuum Cycle Valve
VSU - Video Switching Unit
WCS - Waste Collection System
WMS - Waste Management System