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https://www.jpl.nasa.gov/news/news.php?feature=6764

NASA Orbiter Steers Clear of Mars Moon Phobos
Jet Propulsion Laboratory
March 2, 2017

NASA's MAVEN spacecraft performed a previously unscheduled maneuver this
week to avoid a collision in the near future with Mars' moon Phobos.

The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has been orbiting Mars for just over two years, studying the Red Planet's upper atmosphere, ionosphere and interactions with the sun and solar wind. On Tuesday, Feb. 28, the spacecraft carried out a rocket motor burn that
boosted its velocity by 0.4 meters per second (less than 1 mile per hour). Although a small correction, it was enough that -- projected to one week
later when the collision would otherwise have occurred -- MAVEN would
miss the lumpy, crater-filled moon by about 2.5 minutes.

This is the first collision avoidance maneuver that the MAVEN spacecraft
has performed at Mars to steer clear of Phobos. The orbits of both MAVEN
and Phobos are known well enough that this timing difference ensures that
they will not collide.

MAVEN, with an elliptical orbit around Mars, has an orbit that crosses
those of other spacecraft and the moon Phobos many times over the course
of a year. When the orbits cross, the objects have the possibility of colliding if they arrive at that intersection at the same time. These scenarios are known well in advance and are carefully monitored by NASA's
Jet Propulsion Laboratory in Pasadena, California, which sounded the alert regarding the possibility of a collision.

With one week's advance notice, it looked like MAVEN and Phobos had a
good chance of hitting each other on Monday, March 6, arriving at their
orbit crossing point within about 7 seconds of each other. Given Phobos'
size (modeled for simplicity as a 30-kilometer sphere, a bit larger than
the actual moon in order to be conservative), they had a high probability
of colliding if no action were taken.

Said MAVEN Principal Investigator Bruce Jakosky of the University of Colorado in Boulder, "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."

MAVEN's principal investigator is based at the University of Colorado's Laboratory for Atmospheric and Space Physics, Boulder. The university
provided two science instruments and leads science operations, as well
as education and public outreach, for the mission. NASA's Goddard Space
Flight Center in Greenbelt, Maryland, manages the MAVEN project and provided two science instruments for the mission. Lockheed Martin built the spacecraft and is responsible for mission operations. The University of California
at Berkeley's Space Sciences Laboratory also provided four science instruments for the mission. NASA's Jet Propulsion Laboratory in Pasadena, California, provides navigation and Deep Space Network support, as well as the Electra telecommunications relay hardware and operations.

News Media Contact
By Nancy Neal Jones
NASA's Goddard Space Flight Center in Greenbelt, Maryland
301-286-0039
nancy.n.jones@nasa.gov

Laurie Cantillo
NASA Headquarters, Washington

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster@jpl.nasa.gov

2017-057

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