Encyclopedia Astronautica
1965.07.16 - Apollo LEM as backup for the service propulsion system

In order to use the LEM as a backup for the service propulsion system (SPS) to abort the mission during the 15-hour period following translunar injection, Grumman informed North American that some redesign of the spacecraft's helium system would likely be required. This information prompted North American designers to undertake their own analysis of the situation. On the basis of their own findings, this latter group disagreed with the LEM manufacturer.

NAA's analysis indicated:

- Before transposition and docking, the two spacecraft would already be on a confirmed free-return trajectory.
- During the 15-hour interval, moreover, LEM propulsion would be required only in the event of failures in the SPS and some time- dependent, mission-critical system.

The probability of two such failures during the abort period, North American concluded, was not sufficient to warrant redesigning the helium system.

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