LRO to Perform Bi-Static Radar Experiment with Chandrayaan-1

On Aug. 20, 2009 NASA and the Indian Space Research Organization (ISRO) will attempt a novel joint experiment that could yield more information on whether ice exists in a permanently shadowed crater near the north pole of the moon. Currently the ISRO’s Chandrayaan-1 and NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft are orbiting the moon. While LRO is in its commissioning phase the two spacecraft pass close enough to each other when they are over the lunar north pole to attempt a unique experiment. Both spacecraft are equipped with a NASA Miniature Radio Frequency (RF) instrument that functions as a Synthetic Aperture Radar (SAR), known as Mini-SAR on Chandrayaan-1 and Mini-RF on LRO. The experiment uses both radars to point at Erlanger Crater at the same time.

Normally the Mini-RF Instrument sends radio pulses to the moon and precisely records the radio echoes that bounce straight back from the surface, along with their timing and frequency. From these data scientists can build images of the moon that not only show areas they otherwise couldn’t see, such as the permanently-shadowed areas near the lunar poles, but also contain information on the physical nature of the surface.
For the Bi-Static experiment the Mini-SAR on Chandrayaan-1 performs its normal SAR imaging (transmitting and receiving) while the Mini-RF is set to receive only. The two instruments look at the same location from different angles. Comparing the signal that bounces straight back to Chandrayaan with the signal that bounces at a slight angle to LRO provides unique information about the surface.

While this coordination sounds easy, this experiment is extremely challenging because both spacecraft are traveling at about 1.6 km per second and will be looking at an area on the ground about 18 km across. Due to the extreme speeds and the small point of interest, NASA and ISRO need to obtain and share information about the location and pointing of both spacecraft. The Bi-Static experiment requires extensive tracking by ground stations of NASA’s Deep Space Network, the Applied Physics Laboratory, and ISRO. In addition LRO will perform a 23 second propulsion burn today to adjust LRO orbit phasing to enable the coordinated observations.

The Mini-RF website will be the place to look for the first results of this experiment. The event is illustrated in the simulation below.