NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) Mars orbiter was forced to take evasive action this week. On February 28, the space agency ordered the unmanned spacecraft to fire its main engine, boosting its velocity by 0.4 m/s (1.31 ft/s) to prevent a potential collision with the Martian moon Phobos.

Launched on November 18, 2013, MAVEN arrived at Mars on September 22, 2014, where it went into a elliptical 4.5-hour orbit ranging in altitude from 150 km (93 mi) to 6,200 km (3,900 mi) from which it studies the Martian upper atmosphere, ionosphere, and how they interact with the solar wind.

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While it carries out its mission, NASA and other space agencies monitor the orbits of MAVEN, the Martian moons Phobos and Deimos, and other Earth probes orbiting the Red Planet on the lookout for collision threats.

According to NASA, with only a week's notice, orbital projections by the Jet Propulsion Laboratory indicated that MAVEN's orbit would intersect that of Phobos. Such intersections happen on a regular basis, but on March 6 it was calculated that the spacecraft and moon would cross orbits within about seven seconds of one another.

Given the size of Phobos, which is conservatively modeled as a 30-km (18.6-mi) sphere for the sake of simplicity, NASA determined there was a high probability of a collision and ordered an engine burn to widen the gap to about 2.5 minutes. This is the first time MAVEN has had to carry out such a maneuver.

"Kudos to the JPL navigation and tracking teams for watching out for possible collisions every day of the year, and to the MAVEN spacecraft team for carrying out the maneuver flawlessly," says MAVEN Principal Investigator Bruce Jakosky of the University of Colorado in Boulder.

Source: NASA/JPL