GRAIL Mission Video Released

SchrodingerZ writes "A new video was released yesterday by NASA from the GRAIL mission probes, which ended their mission last month as they impacted the lunar surface. 'Dramatic' footage was captured by the probe Ebb on December 14th. The video was taken from the 'MoonKAM (Moon Knowledge Acquired by Middle school Students) cameras. It shows the view of Ebb flying at an altitude of 6 miles (10 km) above the Moon's northern hemisphere in the vicinity of Jackson crater (22.4N 163.1W).' Two videos were released, one from the fore and one from the aft of the probe, showing a forwards and backwards time lapse containing 931 and 1,489 pictures each of the lunar terrain. The footage was part of the probes' final systems check before they shut down and were sent into a controlled impact to a predetermined location."

Re:Ask Slashdot question in the making...

[tjp]

The whole purpose of this mission was to measure the variations in the moon's gravity by flying at a very low altitude. Consequently, those gravitational variations introduced changes in the orbit requiring relatively frequent corrections. It follows that the closer you orbit, the more actively you'll have to work to maintain that orbit. When you fly low over a mountain, the extra mass in that area will pull you down, and you'll have to correct for that with upward thrust.

The moon's uneven gravity field presents a challenge to ground controllers planning trajectories for low-altitude lunar orbiters. The tug of lunar gravity can alter a satellite's orbit, requiring frequent rocket burns to adjust the spacecraft's path around the moon.

Spaceflight Now, March 21, 2012 [spaceflightnow.com]