Standing on the shoulders of Apollo


The Apollo 15 Laser Ranging Retroreflector (Source: NASA)

When ‘open source’ Google Lunar X PRIZE contestant Team FREDNET attempts, if all goes well, to land a rover on the face of the Moon in a few years time, the mission may ingenuously rely on retroreflector mirrors left by the Apollo missions back in the 1970’s to guide the team’s craft safely to the lunar surface, according to a draft mission plan published by the team in late July. A laser range-finder (LRF) will scan the surface of the Moon until a reflected beam is detected and the craft will then steer towards the source of the reflection.

Using the retroreflector arrays as beacons for a lunar touchdown has so many advantages to Team FREDNET’s mission that one may wonder if the Apollo missions left the arrays those 40 years ago just for the sake of Team FREDNET’s navigational needs (the actual purpose of the arrays is for use in high-precision ranging experiments on Earth measuring the distance between our planet and the Moon).

First of all, because it took a manned mission to put the arrays where they are now, in the first place, Team FREDNET have hard proof that the retroreflectors are situated in areas that are generally suited for landing a lunar spacecraft – the retroreflectors basically designate areas that are good, proven landing sites. Hence, by steering towards and landing near one of the retroreflectors, the team may have a better chance of landing their craft safely than if they were to pick a landing site from the Moon’s 37 million km² surface area by themselves.

Secondly, the team will use data from the LRF to establish how fast the lander is approaching the lunar surface during its descent – a highly critical piece of information when using retrorockets to slow down the lander just sufficiently to make a soft touchdown not crashing the craft into the Moon, nor thrusting it back into space. Laser ranging is a textbook way of determining velocity, also used in, for instance, some ‘speed guns‘ used by law enforcement to detect vehicles traveling over the legal speed limit.

And finally, the Google Lunar X PRIZE contest offers the team a bonus prize if it is able to send back images of remains from the Apollo landings. Landing the rover close enough to an Apollo site for it to capture any such images would likely be impossible without the retroreflector ‘beacon’. For the sake of comparison, NASA’s recent mission to Mars, Phoenix, which touched down in May and did not use any form of beacon, operated with a landing accuracy in the range of hundreds of kilometers.

To minimize the time needed for scanning the lunar surface, Team FREDNET’s spacecraft will enter a lunar orbit particularly favorable for locating the Apollo landing sites this way:

“Since we already have a good idea of where ‘historical’ places like the Apollo 15 landing site are, we can narrow down the scanning range, so we don’t have to scan the entire surface of the Moon searching for retroreflectors. That would take way too long,” said Ryan Weed, team leader of FREDNET’s Propulsion System group.

Other uses of the Apollo program’s remains on the lunar surface are also being explored. For instance, an alternative guidance method relying on the heat signature of the RTG‘s (nuclear power sources) placed on the lunar surface by Apollo missions for power supply, which could be imaged from orbit with a sufficiently high-resolution infrared camera, has been suggested. There has even been proposals for the rover to, once deployed, drive up to one of these RTG’s (which remain the property of NASA according to international treaties) during its mission and use the RTG as an energy source to survive the cold lunar nights. This robotic romance could multiply the lifetime of FREDNET’s rover and give it enough energy to e.g. attempt to take photos with its camera at night.

If the team is successful in building on the Apollo program’s lunar heritage, any other private group with the sufficient resources may, due to Team FREDNET’s unique open approach, attempt to copy FREDNET’s methodology for landing other rovers, or perhaps even equipment which could subsequently facilitate a private manned mission, which in turn could one day lead to private colonization of the Moon.

So who said the Apollo missions were a complete waste of public funds?

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