How Maven dodged a martian moon

Stuart Clark
Artist’s impression of Maven in orbit around Mars. Photograph: AP

Nasa successfully avoided a possible collision between its Maven spacecraft and the martian moon Phobos this week. The danger was spotted in late February by mission controllers at Nasa’s Jet Propulsion Laboratory (JPL) in Pasadena, California.

Maven studies Mars’s upper atmosphere and has been at the planet for two years. It follows an elliptical orbit that crosses the paths of Phobos and several other Mars spacecraft. This means that controllers are always on the look out for possible collisions.

The alarm was raised when Nasa realised that on 6 March the spacecraft and the moon would reach the same location in space within seven seconds of each other. Given that Phobos is a roughly 30km-wide celestial object, they flagged the possibility of a collision as high.

On 28 February, they commanded the spacecraft to perform an engine burn that boosted its velocity by 0.4 metres per second. Although less that 1 mile an hour extra, this accumulated over the next six days to mean that Maven missed the martian moon by 2.5 minutes.

This is the first collision avoidance manoeuvre that Maven has undertaken to steer clear of Phobos. It is not just the moon that controllers have to keep an eye on. As international attention is turning to Mars, there will be an increasing number of spacecraft around the Red Planet to avoid.

Nasa has three other orbiters around the planet, ESA has two and India one. In the next four years more robotic landers and orbiters will come from Nasa, ESA, China, India and the United Arab Emirates. The private company SpaceX is also planning an uncrewed Mars landing, called Red Dragon, in 2020.




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