Cryogenic Apollo

In 1966, Lockheed Missiles & Space Company reported to NASA on the thermal protection systems to be developed for a cryogenic Apollo Service Module propulsion system. This new SM would be a very different beast for the baseline SM… 192 inches in diameter, it had a single spherical liquid hydrogen tank containing 5500 pounds of LH2, and four smaller spherical tanks containing 27,500 pounds of liquid oxygen. These fed into a single RL-10 rocket engine.

The insulation system was to be sufficient to keep boiloff of the hydrogen to less than 5% over a standard 8-day lunar mission. Performance would be improved over the standard SM; instead of the 26,000 pound lunar excursion module that the standard Apollo CSM would be able to put into lunar orbit, this cryogenic propulsion module would be able to handle 41,000 pounds of lunar orbit payload.