Electrical Power System (CSM)

This section provides step-by-step examples and instructions how to use the Electrical Power System (EPS). Hopefully this will help users to get a better understanding and feeling how to work with the spacecraft systems. In these procedures it is assumed that the spacecraft is in a "stable condition" without flying manoeuvers with the systems in "flight configuration", for example during Trans Lunar Coast and you can use time acceleration up to 1000 so that all of the internal systems have reasonable reaction times.

Cryogenic tank and fuel cell check

During normal operations the cryo tanks and fuel cells should operate as descriped in the original Apollo documentationASTP_AOH2.

Fuel cell purging

To keep the fuel cells working properly, it's necessary to do fuel cell purging from time to time. Unlike shown in the original Apollo documentationASTP_AOH2 below in Project Apollo it's not necessary to wait after switching the H₂ PURGE LINE switch to HTR, but to do on H₂ purging it's necessary to turn on the H₂ purge line heater.

H₂ cryogenic tank pressurization

During normal operations cryogenic hydrogen from the cryo tanks is consumed by the fuel cells, so for this procedure it is necessary that the fuel cells are turned on and all cryo tank heaters and fans are switched to AUTO. The cyro tank fans and heaters then maintain the pressure in the tanks.

• Switch to time acceleration 1000. Monitor the H₂ PRESSURE 1/2 meters, they should slowly drop to 225 psi, then increase to 260 psi and so forth.

• Switch the H₂ HEATERS 2 switch and the H₂ FANS 2 switch to OFF (center position). After a couple of hours you can see that the H₂ tank 1 gets still repressurized while the pressure in H₂ tank 2 decreases below 200 psi. You get a CRYO PRESS alarm, push the MASTER ALARM pushbutton/light to turn off the alarm. Furthermore the spacecraft consumes more hydrogen from tank 1 because of the higher pressure so the H₂ QUANTITY 1 meter decreases faster than the H₂ QUANTITY 2 meter.

• Switch the H₂ FANS 2 switch to ON (down position). The pressure in H₂ tank 2 increases continuously without stopping, the CRYO PRESS alarm goes away and comes back to indicate the now too high pressure, push the MASTER ALARM pushbutton/light to turn off the alarm. This way you can overpressure the tank (but it doesn't explode at the moment...). Switch the H₂ FANS 2 switch back to OFF if you have enough pressure.

• Switch the H₂ HEATERS 2 switch and the H₂ FANS 2 switch back to AUTO (up position). Now the tanks are operated automatically again. Please notice that they now doesn't operate "synchronously" as before.

Fuel cell shutdown and restart

During normal operations all fuel cells are running and have a load of about 20 A. Fuel cell 1 and 2 are connected to main bus A, fuel cell 3 to main bus B. Unlike in reality the fuel cells can be shut down and restarted at any time, so let's do that with fuel cell 1.

• Switch the FUEL CELL INDICATOR to position 1. You can monitor a hydrogen and oxygen flow above 0 lb/hr on the FUEL CELL FLOW H₂/O₂ meters and a FUEL CELL MODULE SKIN TEMP of above 400 °F.

• Make sure that the FC REACS VALVES switch is in NORM position, otherwise you cannot operate the fuel cell reactants valves. Switch the FUEL CELL REACTANTS 1 switch to OFF (down position). The switch is spring-loaded and flips back to to center position.

• The FC BUS DISCONNECT alarm is triggered, because fuel cell 1 is disconnected from main bus A. The FC MNA 1 indicator changes to striped-line indication. Push the MASTER ALARM pushbutton/light to turn off the alarm. Switch the FC MNA 1 switch to OFF to turn off the FC BUS DISCONNECT light.

• Now fuel cell 1 is down, the FUEL CELL REACTANTS 1 indicator changes to striped-line indication, both flows are 0 lb/hr, but the fuel cell skin temperature remains almost unchanged because the fuel cell temperature is still maintained by the fuel cell heaters.

• Switch the FUEL CELL HEATERS 1 switch to OFF (down position). The fuel cell skin (and condenser exhaust) temperature decreases slowly. The FC 1 alarm is triggered when the fuel cell temperatures get too low, push the MASTER ALARM pushbutton again. Wait until the skin temperature drops below 300 °F (use time acceleration 100 to 1000, if you are impatient).

• Switch the FUEL CELL REACTANTS 1 switch to ON (up position). Unfortunatly the fuel cell does not start, because the skin temperature is below 300 °F.

• Switch the FUEL CELL HEATERS 1 switch to up position. The fuel cell skin temperature increases slowly (use time acceleration about 100 again). After 300 °F is reached, again switch the FUEL CELL REACTANTS 1 switch to ON (up position). The fuel cell turns on, the skin temperature increases quickly to the old value and the FC 1 alarm is turned off.

• Switch the FC MNA 1 switch to up to connect fuel cell 1 to main bus A again, the switch is spring-loaded and flips back to to center position. The FC MNA 1 indicator changes to gray indication, the flows are increasing and the fuel cell is running normally again.

Fuel cell radiator emergency bypass

During normal operations no fuel cell emergency bypass is necessary. But if only one fuel cell is running at a load of about 20 A, some of the radiators need to bypassed so that the coolant temperature doesn't become too low.

• To maintain power supply during this test switch both MAIN BUS TIE switches to on (up).

• Switch the FUEL CELL INDICATOR to position 1. Make sure that the FC REACS VALVES switch is in NORM position. Switch the FUEL CELL REACTANTS 2 and 3 switches to OFF (down position), the FUEL CELL REACTANTS 2 and 3 indicators change to striped-line indication. The FC BUS DISCONNECT alarm is triggered, push the MASTER ALARM pushbutton/light to turn off the alarm.

• Wait about 20 minutes (use time acceleration 100 to 1000, if you are impatient), then the FC RAD TEMP LOW indicator changes to striped-line indicating a coolant temperature below -30°F. The FC 1/2/3 alarms are triggered because of that, push the MASTER ALARM pushbutton again.

• Switch the FUEL CELL RADIATORS 1 switch to EMER BYPASS (down position). The switch is spring-loaded and flips back to to center position. The FUEL CELL RADIATORS 1 indicator changes to striped-line indication. After a few minutes the FC RAD TEMP LOW indicator changes back to gray indicating a normal coolant temperature, the FC 1 alarm is turned off. You are now in "emergency mode".

• Monitor fuel cell 2 and 3 by switching the FUEL CELL INDICATOR to position 2 and 3. The flows are 0 lb/hr of course and the FC RAD TEMP LOW indicator shows striped-line indication because the radiators of the other fuel cells are not bypassed. Switch the FUEL CELL INDICATOR back to position 1.

• Switch the FUEL CELL REACTANTS 2 and 3 switches to ON (up position). Reconnect the fuel cells to the busses by switching FC MNA 2 and FC MNB 3 to up, the FC DISCONNECT alarm is turned off. Disconnect the batteries by switching both MAIN BUS TIE switches to OFF. After a few minutes the FC 2/3 lights are turned off, the coolant temperatures are fine again.

• Switch the FUEL CELL RADIATORS 1 switch to NORMAL (up position). You are now back in "normal mode". The FC RAD TEMP LOW indicator should show gray indication again.

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1. References

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External Links

• Apollo experience report: Command and service module electrical power distribution subsystem
• Apollo experience report: Battery subsystem