Finding a needle in a haystack is tough. Finding the needle when the haystack is orbiting the moon sounds impossible, yet that’s what NASA has done … twice! Two lunar orbiters – one that has been lost for years - were found recently using Earth-based radar and some diligent detective work.
The Lunar Reconnaissance Orbiter (LRO) was launched on June 18, 2009, on a two-year mapping mission that has since been extended and is ongoing. While the robotic craft continues mapping the lunar surface and transmitting images back to Earth, its exact location has been a mystery. India’s first lunar probe, Chandrayaan-1 was launched on October 22, 2008, and successfully dropped a Moon Impact Probe to look for lunar water ice. The lunar satellite was supposed to map the surface for two years but suffered technical problems and stopped sending radio signals on August 28, 2009.
While both spacecrafts are small, the cube-shaped Chandrayaan-1 is the real needle in this search, measuring just five feet (1.5 meters) per side. NASA scientists first had to figure out where they might be so they could narrow the search. Fellow scientists working on the LRO mission provided current orbit data. However, all they had to go on with Chandrayaan-1 was that the craft was in a polar orbit 200 km (120 miles) above the surface. Luckily, that was enough.
The equipment used consisted of the 230-foot antenna at NASA's Goldstone Deep Space Communications Complex in California for sending microwaves to the moon and the 330-foot Green Bank Telescope in West Virginia for picking up the radar echoes. Knowing that the Chandrayaan-1 would pass over each pole every two hours and eight minutes, the scientists pointed the antennas at a spot above the north pole and waited.
The eureka moment occurred when something matching the signature of Chandrayaan-1 was picked up twice in a little over two hours near the orbital path predicted by Ryan Park, the manager of JPL's Solar System Dynamics group.
It turns out that we needed to shift the location of Chandrayaan-1 by about 180 degrees, or half a cycle from the old orbital estimates from 2009. But otherwise, Chandrayaan-1's orbit still had the shape and alignment that we expected.
While this discovery won’t bring Chandrayaan-1 back to life, it proves the capability of the large radar antennas to locate small objects. This will come in handy on future missions for tracking and for helping prevent collisions with other orbiting objects.
With a little more fine-tuning, they could eventually help astronauts who lose the keys to their lunar vehicles.