Indian Space Research Organisation (ISRO) and NASA performed a unique joint experiment today (Aug. 21, 2009), that could yield additional information on the possibility of existence of ice in a permanently shadowed crater near the North pole of the moon. Known as Bi-Static Experiment, it involved ISROs Chandrayaan-1 and NASAs Lunar Reconnaissance Orbiter (LRO) spacecraft. Currently, Chandrayaan-1 and LRO are orbiting the Moon. The two spacecraft passed close enough to one another when they were over the lunar North pole to attempt this interesting experiment.
Both Chandrayaan-1 and LRO 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. Chandrayaan-1 in transmit mode transmitted the signals and LRO received the reflected signals. The experiment used both radars to point at Erlanger Crater at the same time.
The Bi-Static observations were made on August 21, 2009 at 00:30 hours (IST). Before the experiment commenced, LRO executed a minor manoeuvre to adjust its orbit to the well-established Chandrayaan-1 orbit. The data was collected for about 4 minutes. MiniSAR of Chandrayaan-1 was fine tuned for making observations in terms of pulse width, range rate sampling as well as its 200 km orbit height. The operations went on as planned.
All Chandrayaan-1 operations related to Bi-Static experiment were executed from Spacecraft Control Centre (SCC) at ISRO Telemetry, Tracking and Command Network (ISTRAC), Peenya. Science Data was immediately downloaded over Johns Hopkins Universitys Applied Physics Laboratory (APL), the ground station that had the visibility. Later today morning (August 21, 2009), during Chandrayaan-1s visibility over Indian Deep Space Networks antennas at Byalalu, near Bangalore, the data was again obtained along with spacecrafts orientation information when Bi-Static observations were performed.
For the Bi-Static experiment, the Mini-SAR on Chandrayaan-1 performed its normal SAR imaging (transmitting and receiving) while the Mini-RF was made to receive only. The two instruments looked at the same location from different angles. Comparing the signal that bounces straight back to Chandrayaan-1 with the signal that bounces at a slight angle to LRO provides unique information about the lunar surface.
Observations from today`s experiment are being analysed by scientists from ISRO and NASA.