NASA probe narrowly avoids collision with Martian moon Phobos
by Ryan Whitwam
NASA’s MAVEN spacecraft is orbiting Mars to study the planet’s atmosphere and how it interacts with the solar winds. Also high on its list of mission-critical goals is not crashing into things. That one almost went out the window recently, as MAVEN was found to be on a collision course with the Martian moon Phobos. NASA managed to prevent the impact, though.
MAVEN stands for Mars Atmosphere and Volatile EvolutioN — yes, it’s pretty clunky by NASA acronym standards. It arrives in orbit of Mars two years ago and set itself up in an elliptical orbit. It is equipped with instruments to analyze the state of Mars’ atmosphere, which will allows scientists to extrapolate the evolution of Mars over time. It is believed that Mars once had substantial liquid water on its surface and a much thicker atmosphere.
Phobos isn’t particularly big as far as moons go — it’s essentially a large asteroid with a diameter of 22 kilometers (13.6 miles). The highly elliptical nature of MAVEN’s orbit means it crossed the orbits of many other probes as well as Phobos. There’s always a possibility that two objects with crossing orbits will be in the same place at the same time, but space it really big. It’s not a particularly big possibility. However, after two years of operation, Phobos was coming up fast.
NASA calculated earlier this week that MAVEN had a chance of running into Phobos on March 6th. The orbital intersection of the two was only off by seven seconds. Even with Phobos’ weak gravity, it could easily pull the probe off course and smash it to bits. The team had just a week to get MAVEN on a different course, so a course correction was sent. In the interest of expediency, NASA modeled the orbit with a 30-kilometer sphere standing in for Phobos. That’s slightly larger than the moon, allowing for more certainty the maneuver would put the probe clear of impact.
On February 28th, MAVEN fired its maneuvering engine to increase its velocity by 0.4 meters per second. This small change means the intersection of MAVEN and Phobos will now be separated by 2.5 minutes. That should put the probe out of harm’s way. MAVEN should not have any further encounters with Phobos and will continue making observations of Mars through at least 2018. After that, it may still be used as a communication relay for other missions.
Originally published at www.extremetech.com on March 6, 2017.