Microwaves used to locate moving, missing satellites around the Moon
This afternoon, I managed to lose track of my car in a parking lot, spending a few bumbling minutes trying to remember where I had left the 14- by 5.5-foot object. Last week, NASA announced that they had found a two lost satellites, one measuring no more than five cubic feet, as they raced around the Moon 237,000 miles away. It’s not a flattering comparison, especially considering my search range for an immobile object was less than a full city block, but perhaps if I’d had access to a 230-foot radar antenna to help out, I’d have had slightly more impressive results.
The two satellites NASA tracked down obviously presented different challenges than a forgotten car, although there were a few, very generalized, similarities. In both scenarios, the targets were slightly camouflaged in their environments— my car among an abundance of similar, silver vehicles, and the satellites that are so small optical telescopes lose them in the glare of light reflected off the Moon’s surface. I had a general sense of where I’d last seen my car, and the search team the from Jet Propulsion Laboratory (JPL) also had some coordinates for one of the satellites, the Lunar Reconnaissance Orbiter (LRO), based on its last transmitted position.
Tracked down in just over two hours
The challenge to find the second satellite, the Indian Space Research Organization’s Chandrayaan-1 spacecraft, was a bit more complicated. Contact with Chandrayaan-1 had been lost in August of 2009, giving the orbiting probe over nine years to get nudged off course by variations in the Moon’s gravity. The only starting point was that it was expected to still be crossing over the Moon’s poles every two hours and eight minutes around 124 miles above the surface, which is where the microwave signal from the Goldstone Deep Space Communications Complex was focused.
The concept was very similar to what a police officer’s radar gun does to catch a speeding driver, only scaled up. A beam of microwave energy is sent out, and then monitored to see how long it takes to be bounced back if it hits an object. Since the Moon, and the Chandrayaan-1 were obviously out of range for a standard radar gun, the Goldstone antenna was used to send the signal out. Appropriately, a 330-foot dish at the Green Bank Telescope in West Virginia was used to receive the return signal, which did match the signature of a five-cubic-foot object orbiting the in just over two hours a trip two times in row.
Testing the technique
It’s great to know the whereabouts of these two missing satellites, but not necessarily because they’ll be pressed back into service. The Chandrayaan-1, for instance, managed to complete all of its primary science missions before losing contact, so nobody really missed out on anything essential. The real gain of these searches is that they allowed JPL scientists to test out this new method for finding lost objects on the Moon. The the possibility of new missions to (or around) the Moon on the horizon, it may prove very useful to have a terrestrial method for finding small satellites, probes, robots and maybe even crewed vehicles. Better to have plan B in place before we know we need it.
Source: New NASA radar technique finds lost lunar spacecraft, Science Daily