Will the Moon mess up a moon-base?Posted: March 4, 2010
If we want to build a permanent base on the Moon – and the question of whether we ever will (or even should) remains very open – we need to have some idea of the effect the lunar environmental conditions will have on our equipment. There’s no point going to all the trouble (and expense) of hauling some fancy LunarThingy™ up there only to have it disintegrate within a year because nobody checked to see what it might have to cope with! Well, a paper out today, led by T. Murphy from the University of California, gives some indication of the sort of degradation such a base might encounter by looking at what’s happened to the lunar equipment we already have in place.
As part of the Eclipse Week we had on this blog back in July I talked about the lunar ranging project, which bounces laser light off retroreflecting arrays left on the Moon by the Apollo astronauts to measure the Earth-Moon distance; the picture at the top of this post shows the array left by the Apollo 11 mission. A retroreflector is a clever device that reflects light falling on it back in the direction it came from via – in this case – total internal reflection using three perpendicular mirrors arranged to form a triangular corner (have a look here if that makes no sense!)
By studying nearly 40 years of lunar ranging data Murphy et al. found that the efficiency with which the arrays return the laser light is ten times less now than it was originally and this loss of efficiency is even worse at full moon. This lunar phase dependency surprised them so they double checked that it wasn’t something to do with the overall increased brightness of the Moon at this time of the month interfering with the result. It wasn’t.
Clearly something has happened to the retroreflector arrays to degrade them over the four decades they’ve been up there, but what? The paper puts forward two suggestions – a build up of lunar dust or scratches from micrometeorite impacts. Both of these could alter the way the light is reflected by allowing light from the Sun to slightly heat up the arrays. The effect is strongest at full moon because that is the time when the arrays are exposed to the most solar energy. The authors lean more towards dust as the cause, but point out that laboratory simulations of the lunar conditions would be the best way to understand what’s going on. It’s important to pin this down as dust can be wiped off, but a scratch could permanently damage a piece of equipment and it’s an awfully long way to go to carry out repairs!
T. W. Murphy, Jr., E. G. Adelberger, J. B. R. Battat, C. D. Hoyle, R. J. McMillan, E. L. Michelsen, R. Samad, C. W. Stubbs, & H. E. Swanson (2010). Long-term degradation of optical devices on the moon Icarus arXiv: 1003.0713v1