The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft last week made a hasty burn to avoid a likely collision with Martian moon Phobos.
NASA says that without the burn, the probe and the moon stood “a good chance of hitting each other on Monday, March 6th”.
NASA's Jet Propulsion Laboratory (JPL) figured that out about a week ago, noting that the two objects would come within about seven seconds of a collision. NASA says Phobos is “modeled for simplicity as a 30-kilometre sphere, a bit larger than the actual moon in order to be conservative”. But as we lack precise measurements of the Moon, the space agency assumed a close encounter was deemed to “represent a high probability of colliding if no action were taken.”
So action was taken.
A quick squirt of MAVEN's engines gave it an extra 0.4 metres per second of velocity. The probe and Phobos therefore occupied the same volume of space after a far-more-comfortable interval of two-and-a-half minutes.
MAVEN is said to have executed its burn “flawlessly” and, having avoided Phobos and a near-certain mission-ending bonk, continues its atmosphere-sniffing work.
This isn't MAVEN's first near-miss: in January 2015 it came within two kilometres of the Mars Reconnaissance Orbiter, leading NASA to call for a Martian traffic cop to handle the increasing orbital traffic around the red planet. MAVEN's part of the problem, as it became the fifth active human-made satellite at Mars. ExoMars arrived last year, bringing the total to six. Humanity has sent another eight craft to orbit Mars. It's assumed they're still in orbit, but most have broken and can't be contacted. ®
Bootnote While we're covering space news, a quick 38th-anniversary reminder of how awesome the Voyagers are/were/will continue to be for the handful of years their thermoelectric generators remain viable.