LESS: The Lunar Escape System

LESS-CM docking

The final moments of the open-to-space LESS rescuing two astronauts stranded on the lunar surface by a faulty lunar module. Getting to this point would have been difficult, but the alternative was death by suffocation within a few hours. Image from the NASA document Lunar Escape Systems, Volume I: Summary Report. Click for a larger view.

What it was: A proposed emergency booster from North American Rockwell that could be used by Apollo astronauts in the case that they were stranded on the Moon. It was built around the assumption that the stricken crew would be safe on the ground but with an LM that couldn’t take them back to the Command/Service Module in lunar orbit. Using fuel siphoned from the ascent stage of the lunar lander they would sit in open space, using their space suits for life support, and manually guide themselves into orbit for a rendezvous with the CSM.

Details: Under the influence of the USAF, NASA studied various ways of escaping a stranded ship in orbit. The Apollo program took a different tack, partly because of the difficulty of coming up with an escape system that would work to return the astronauts from such a distance and partly because weight on the lander was at such a premium. Serious work didn’t begin until NASA started planning for the long-duration missions that would lead up to an Apollo-technology lunar base.

The Apollo landings were divided into two phases. Apollos 11 through 14 were of relatively short duration, while Apollo 15, 16, and 17 were “J-Class” missions using the Extended LM to allow longer stays. The Extended LM also had a higher cargo capacity (which is why the final three Moon missions had a Lunar Rover to drive around in). Once the J-Class missions were done, later missions were to use two LMs, one of which (the “LM Truck”) launched unmanned from Earth solely to carry more equipment. With that in mind NASA looked into equipment that could be carried to make landing on the Moon safer.

Neil Armstrong said later in life that he’d had nightmares for two years prior to launch that he’d get back into the LM to begin the trip home and the engines would fail to start; apparently he wasn’t the only one, because one of NASA’s suggestions for the extra equipment tried to deal with the issue. In June 1970 North American Rockwell sent a first-stage feasibility report to NASA for the Lunar Escape System (LESS), based on a flying rover they’d already been working on (the Lunar Flying Vehicle, or LFV). By September of the same year they’d fleshed it out further, including some initial lab and engineering work.

The LESS was very bare-bones, but bear in mind that until something like it was added to the lunar lander the astronauts were facing certain death by suffocation if the LM failed on them. In that dire situation, the stranded men would take two hours to unload the LESS from the side of the LM (where it had been stored in a configuration looking for all the world like an IKEA flat pack) and then siphon fuel from the lander’s ascent stage tanks; the theory here was that if the LM was dysfunctional due to a landing hard enough to crack those, the astronauts weren’t going to be in any shape to rescue themselves anyway.

LESS Schematic

A schematic diagram of the LESS from Lunar Escape Systems, Volume II: Final Technical Report. Click for a larger view.

Having fuelled the LESS, the astronauts would not get in it, but rather sit on it, exposed to open space. The pilot would give them an initial kick skywards to 3000 meters (a trip that would take about sixty seconds), then heel the LESS over to thirty degrees so that they’d continue rising while also starting to make headway horizontally. At about 6 minutes they’d be high enough and have enough vertical velocity that they’d then turn over the rest of the way and head for the CSM completely horizontally. The LESS was to be equipped with three gyros to help determine the attitude of the ship.

Once they were in what they hoped was a 110 kilometer orbit, the LESS crew would make observations of the sun angle and (if launching during the day) the angle to the lunar horizon and their apparent speed over passing landmarks below. Using these they could calculate their actual orbit–by hand, as the LESS had no on-board computing ability and the astronauts spacesuits didn’t have enough air for ground control back on Earth to give them the figures they needed. While too high was obviously a problem, as the orbit was very likely to be elliptical rather than the ideal circular, too low at perilune was the main issue. After testing with simulators, Northern Rockwell blandly states that LESS rescues would obtain “marginally acceptable orbital accuracies in terms of avoiding lunar impact.”

The CSM pilot would likewise be trying to figure out where the LESS was going to be. The launch of the rescue craft would be timed so that as it reached its height (and assuming it was on target) it would pass within 20 kilometers before they started to diverge. Using a sextant to observe a flashing beacon on the LESS and using a VHF rangefinder, the CSM pilot would use his onboard computer to calculate an intercept with the LESS. Unfortunately the LESS not very visible to the CSM pilot if the LESS was too far from where it should be: only to a maximum 90 kilometers by eye. The North American Rockwell report says “Visibility and acquisition of the target with the CSM optics was found to be a problem” and suggests no solutions. Ultimately it came down to hoping that the LESS astronauts hadn’t missed their correct orbit by too much.

The CSM’s orbit would take it around the Moon, during which he’d execute a burn that would put him at the same place at the same time as the LESS before the end of its first orbit. If absolutely necessary he could bring his craft as low as 80 kilometers above the surface. The stranded astronauts would have at best a couple of hours of air left, so a second chance on the next orbit was out of the question.

It was very likely that the two would miss each other by some distance, anywhere up to one kilometer and with somewhat differing speeds, so as they got close it was necessary for the CSM to start a new maneuver to lessen the gap. Meanwhile the LESS crew would be changing the orientation of their craft so it pointed towards the nose of the CSM. The Command/Service Module actually flown to the Moon had a VHF transponder and flashing light beacon of its own for use with LM docking, and these would be turned on for a LESS flight, giving the astronauts on it a target to aim for.

Assuming all went well the LESS would dock with the Command Module using a special docking attachment on the latter’s nose. Once there was a firm connection, the astronauts could climb onto the CM and enter its hatch, opened from within by the CSM pilot.

At that point the CM’s cabin would be repressurized and the presumably relieved crew could begin the process of returning to Earth used by a regular Apollo mission.

What happened to make it fail: The late dates at which the feasibility studies came back to NASA are a clue. While the space agency was still planning for expanding the United States’ presence on the Moon, Apollo was shrinking quickly. The same month as the second report came out, budget cuts forced NASA down to just three extended LM missions, and there was no sign of funding for the longer missions they wanted after that. In fact it never came, and there was no need for the LESS to rescue astronauts because no-one was going to the Moon anyway.

What was necessary for it to succeed: It was part and parcel of the Apollo program’s continuation according to its initial plan. If Apollo had kept going, or been revived fairly quickly after going into abeyance for a while in the early 1970s, something like it would have been desirable until stranded astronauts had a long-term Moon base to return to in case of emergency. As long as the CSM was the only place to go to, LESS would have been a plausible addition to the astronauts’ equipment.

The difficulty here is that the Apollo program relied on the Saturn V, and the Saturn V stopped production in August 1968. The ability to start it back up again disappeared very quickly, and it’s estimated that NASA would have needed an extra billion dollars to keep it going after 1970. Without Saturn the entire Apollo program falls apart as nothing else is powerful enough to launch the heavy Apollo Lunar CSM/LM combination. Ultimately the success of the LESS comes down to avoiding the US’ budget crunch in the late 1960s, like so much else did in the American space program of the time.


5 thoughts on “LESS: The Lunar Escape System

  1. It seems to me that if you’re potentially sending an unmanned LEM (or similar vehicle) with the mission it would be easier to adapt that to add an emergency reorbiting capacity than to carry an extra piece of kit that’s only going to be used if things go wrong. As with MOOSE/SAFER, the effort going into this was better spent making the primary device really reliable.

    • It’s difficult to argue with your second point, but your first I can explain. The LM Truck wasn’t going to have an ascent stage at all — entirely replaced with a cargo carrier instead. We’ll see it again soon enough.

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  4. The LM ascent engine was one of only a handful of ‘mission critical’ pieces of hardware for which there was no backup – others included the SPS and the CM heat shield. I guess the LESS was practical in that circumstance, but the ‘one shot rendezvous’ while flying gimcrack hardware was always going to count against it. In the post-Apollo Applications environment, as planned – with the longer-stay LM taxis and other hardware – I suspect the better option would be to send a second LEM from Earth (thus killing a future mission, of course) – much the same setup as NASA actually deployed for Skylab with a second ‘rescue’ CSM on the pad.

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