WASHINGTON — A NASA Mars orbiter performed a maneuver to avoid a “high probability” of colliding with the Martian moon Phobos next week, the agency said March 2.
The Feb. 28 maneuver came a day after spacecraft controllers identified a potential collision between the Martian Atmosphere and Volatile Evolution, or MAVEN, spacecraft and the moon Phobos on March 6. The orbits of the spacecraft and the moon intersect, and on that day the two would have passed through the same point within seven seconds of each other.
Given the size of Phobos, an irregularly-shaped body 27 kilometers across on its longest axis but modeled by spacecraft controllers as a sphere 30 kilometers across, “they had a high probability of colliding if no action were taken,” NASA’s Jet Propulsion Laboratory said in a statement.
MAVEN fired a thruster Feb. 28 that increased the spacecraft’s velocity by 0.4 meters per second. That maneuver means that MAVEN and Phobos will now pass the same place in their orbits two and a half minutes apart, sufficiently far apart to avoid any chance of a collision.
“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,” said Bruce Jakosky, the principal investigator of the mission, in the statement.
The incident is the first time that MAVEN has had to maneuver to avoid a collision with a moon or other spacecraft. Unlike NASA’s other two Mars orbiters, Mars Odyssey and Mars Reconnaissance Orbiter (MRO), which orbit close to the planet, MAVEN is in an elliptical orbit that goes out beyond the orbit of Phobos.
“MAVEN’s highly elliptical orbit, crossing the altitudes of other orbits, changes the probability that someone will need to do a collision-avoidance maneuver,” said Robert Shotwell, Mars program chief engineer, in a 2015 JPL statement about tracking Mars missions. “We track all the orbiters much more closely now. There’s still a low probability of needing a maneuver, but it’s something we need to manage.”
While still far less crowded than Earth, the increasing number of Mars spacecraft poses a growing challenge to spacecraft controllers. In addition to Mars Odyssey, MRO and MAVEN, NASA tracks the European Mars Express and ExoMars Trace Gas Orbiter spacecraft, and India’s Mars Orbiter Mission, or Mangalyaan, spacecraft. They also track the defunct Mars Global Surveyor spacecraft, which remains in orbit.
That problem will become more difficult by 2021 with the scheduled arrival of several more spacecraft scheduled for launch in the mid-2020 launch window. China, India and the United Arab Emirates are all planning to launch Mars orbiters then. In addition, lander missions are planned by China, ESA and NASA.
SpaceX may also launch its first Red Dragon lander mission in 2020. That mission was scheduled for launch in 2018, but the company last month that it would likely be delayed to 2020 as it focuses on its Falcon Heavy and Crew Dragon programs, as well as a commercial human circumlunar mission SpaceX announced Feb. 27 for launch as soon as late 2018.