Lunar escape systems

Lunar escape systems (LESS) were a series of emergency vehicles designed for never-flown long-duration Apollo missions.

As NASA planned for longer stays on the Moon after the first few Apollo flights, they had to consider a number of new issues, one of which was what to do if the astronauts cannot get back.

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.

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.

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.

Another benefit of the RCS-based designs was that the RCS thrusters could be fired in bursts as short as ten milliseconds, so instead of complex throttling hardware they could simply be pulsed to adjust the average thrust over time.

The CSM had a fuel reserve, and plans would allow it to change velocity by a maximum of around 250 meters per second in order to rendezvous with the LESS after orbit insertion.

This would require some skilled flying on the part of the pilot, as any use of the front-facing RCS jets could present a serious hazard to the astronauts on the LESS if the hot exhaust gases hit them.

Most plans called for the astronauts to use landmarks on the lunar surface to control their heading while the pitch program took care of altitude and velocity.

Ultimately, however, this was considered to be less desirable than hardware control, particularly as it imposed significant constraints on vehicle thrust level and inertia.

This would, for example, allow reconnaissance trips to potential future landing sites, and the LRF could also be used for orbital flight to return the crew to the CSM in an emergency.