As weight was a problem from the beginning (launch) of an Apollo mission, was the LM water tank already filled, or were they filled during the trip to the moon from fuel-cell byproduct water?

  • $\begingroup$ I suspect the LM water tank was filled partially. I think cooling water was necessary when they activated the electronics of the LM. But what about the LM computer, was it powered up before launch from ground or before the separation of LM and CM? $\endgroup$
    – Uwe
    Mar 18, 2017 at 9:02

1 Answer 1


In the Command Module, water was generated by fuel cell operation; in the Lunar Module, all water supplies were loaded in storage tanks before lift-off.


The LEM did not have fuel cells, it was battery powered only.

enter image description here

If you were asking about product water from the Command Module fuel cells, there was no interface from the CM->LM to transfer that water. Notice in the water schematic below that the tank fill ports (below each tank) are all labeled "GSE" - Ground Support Equipment. And, the check valves in the tank outlet lines prevent any water from flowing into the tanks.

All water was, therefore, stored on board prelaunch and not generated. (With the exception of condensed water from the Atmospheric Revitalization System water separators, which entered the system at the middle bottom, and was used for cooling only).

The GSE device used to fill the tanks is described in the 1965 Apollo LEM Familiarization Manual LM790-1. (Which I am not finding on the internet right now, except for sale on Amazon...)

5-62. WATER SUPPLY UNIT, PART NO. 430-94119. The Water Supply Unit is a mobile unit that contains a pump, a reservoir, starters, tubing, valving and controls, remote and manual controls, explosion-proofing and instrumentation. It is used in the LEM Environmental Control Subsystem to fill the water management section with triple-distilled water. This unit is an item of common usage GSE modified for LEM use.

enter image description here

Diagrams from the LM Orientation, Course No. 30005-012, April 12, 1966

  • $\begingroup$ Interesting, was there any risk of freezing the water in those tanks whilst coasting to the moon? $\endgroup$ Dec 4, 2019 at 8:03

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