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).

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 had to be as light as possible so as not to significantly reduce the cargo capacity of the LEM, and easy to pack into the LM in such a way that it would not interfere with the other cargo. One consequence was that most designs used detachable legs: the legs would be set up on the lunar surface, the LESS assembled on top of them, and the legs then left behind as the LESS launched. This did not directly reduce the mass required, but it did reduce the empty mass of the LESS, which reduced the fuel required to lift it to orbit, which also reduced the thrust required from the engines and the total mass of the design.

The LESS would pack flat in the side of the LM descent stage, and arms and wires would be provided to allow controlled removal of the LESS and ensure it did not harm the astronaut who was removing it. A protective cover also doubled as a sled, so the LESS could be pushed or pulled along the ground to reach a safe launch position prior to assembly. The assembly operations were expected to take at least forty-five minutes, with a further two hours for checkout and fueling before launch. On long-duration missions the crew might assemble the LESS early in the mission as a precaution.

Given the cut-down nature of the LESS compared to a typical spacecraft of its era, the primary differences between designs were in propulsion, guidance, navigation and control.

Typical LESS designs used flexible fuel tanks so that it could fold flat for storage. When the LESS was connected to the LM ascent stage, the flexible tanks would be filled and expand to their full size ready for flight.