Looking for a job as a celestial traffic cop? Consider giving NASA a call. With the arrival last summer of two additional orbiters at Mars, there are now five active satellites with their eyes on the Red Planet. NASA tracks those and the approximate location of its Mars Global Surveyor, a 1997 orbiter that’s not longer working, to make sure they don’t thump together like bumper cars anytime soon.
NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) and India’s Mars Orbiter Mission joined the 2003 Mars Express from ESA (the European Space Agency) and two from NASA — the 2001 Mars Odyssey and the 2006 Mars Reconnaissance Orbiter (MRO) to form the quintet.
While the total number of spacecraft is important, consider that each conducts its own science mission from a different orbit, which can be lowered or raised depending on the needs of the mission. MAVEN studies the upper atmosphere and loops around Mars in an elongated orbit that climbs higher than any other probe but also dips below them on the opposite side of its orbit, crossing the altitudes of their orbits.
To be on the safe side, NASA not only monitors its own but also the Indian and European satellites with the aim of avoiding potential collisions:
“MAVEN’s highly elliptical orbit, crossing the altitudes of other orbits, changes the probability that someone will need to do a collision-avoidance maneuver. 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,” said Robert Shotwell, Mars Program chief engineer at the Jet Propulsion Lab (JPL) in California.
Despite the increased focus on safety at Mars, there’s far less concern there than closer to home, where more than 1,000 active orbiters plus lots of inactive hardware add to trackers’ headaches. Still, more missions to the Red Planet are in the planning stages including NASA’s InSight, slated to launch in 2016, and the Mars 2020 rover. And that’s just what the U.S. has in its back pocket. China and the European Space Agency are working on their own Mars missions as you read this.
All five active Mars orbiters use the communication and tracking services of NASA’s Deep Space Network, which is managed at JPL. The amount of uncertainty in the predicted location of a Mars orbiter a few days ahead is more than a mile (~2 km). Calculating projections for weeks ahead multiplies the uncertainty to dozens of miles, or kilometers.
“When two spacecraft are predicted to come too close to one another, we give people a heads-up in advance so the project teams can start coordinating about whether any maneuvers are needed,” said Joseph Guinn, manager of JPL’s Mission Design and Navigation Section.
On Jan. 3 this year, automated monitoring determined that two weeks down the road, MAVEN and MRO could come within about two miles (3 km) of each other. Before an avoidance maneuver was planned, uncertainties in the calculations shrank to within safe parameters and nothing untoward happened.
Although two spacecraft approaching within a few hundred yards of each other would be a bad thing, it could also serve as a tool to simultaneously observe the same features with complementary instruments at the same time. A brilliant idea!