Lunar escape systems

Lunar escape systems (LESS) were a series of emergency vehicles designed for never-flown long-duration Apollo missions. Because these missions were more hypothetical than the planned cancelled Apollo missions, the designs were never constructed. This concept was an outgrowth of the Lunar Flying Vehicle by Bell Aerospace (a lunar surface mobility design that was cancelled in favor of the less risky Lunar Rover).

Details

As NASA planned for longer stays on the Moon after the first few Apollo flights, they had to consider new issues, one of which was what to do if the astronauts cannot get back. Typically the longer a spacecraft is idle the less reliable it becomes, so after a stay of two weeks on the Moon the Lunar Module ascent engine or other essential systems might fail to function, leaving the astronauts stranded on the Moon without enough supplies to survive until a rescue mission could arrive from Earth.

For one possible solution, NASA studied a number of low-cost, low-mass lunar escape systems (LESS) which could be carried on the lunar module as a backup, like a lifeboat on a ship.

'KISS' was the order of the day, with a few basic assumptions about any operational LESS system:

The LESS would use fuel from the LM ascent stage tanks, so no extra fuel would be carried on the mission.

Rather than the multiple redundant systems used elsewhere in the Apollo program, the LESS would be as simple as possible while still achieving its mission.

All life support would come from the astronauts' space-suit backpacks. This greatly reduced the mass and complexity of the LESS, but required that the astronauts could rendezvous with the orbiting CSM within the four-hour backpack oxygen supply.