ISRO-NASA in joint experiment with lunar probes

Mumbai: A few minutes before midnight, India's lunar mission Chandrayaan-1 would have crossed another milestone conducting an extremely complicated joint experiment with NASA's recently launched Lunar Reconnaissance Orbiter (LRO). The experiment is intended to look at the possibility of water ice existing at the bottom of a massive crater on the moon's surface.

The Bi-Static radar experiment, as it is called, will search for water ice in a crater on the Moon's north pole. At approximately five minutes before midnight on 20 August both spacecraft would have been in close proximity approximately 200 km above the lunar surface.

As both the probes are equipped with radar instruments, the two instruments will look at the same location from different angles, with Chandrayaan-1's radar transmitting a signal which will be reflected off the interior of the Erlanger crater, and then be picked up by NASA's LRO.

The signal that bounces straight back to Chandrayaan will be compared with the signal that bounces at a slight angle to the LRO in a bid to garner unique information, particularly about any water ice that may be present inside the crater.

Both spacecraft are equipped with a 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 advantage of a Bi-Static experiment is that you're looking at echoes that are being reflected off the Moon at an angle other than zero," said Paul Spudis, principal investigator for Chandrayaan-1's Mini-SAR. "Mono-static radar sends a pulse, and you are looking in the same phase or incident angle. But with Bi-Static, you can look at it from a different angle. The significance of that is ice has a very unique bi-static response."