NASA has “beefed up” the processes it uses to stop orbiters around Mars from colliding with each other, after two orbiters came within two kilometres of each other in early January.
Humanity currently has five live orbiters around the red planet, namely NASA's MAVEN, Mars Odyssey and the Mars Reconnaissance Orbiter (MRO), plus India's Mars Orbiter Mission (MOM) and the European Space Agency's Mars Express. NASA's Mars Global Surveyor is bricked but is still in orbit.
Many of the orbiters' orbits intersect: the image at the top of this story shows that India's MOM, for example, cuts across the orbit of three other craft and Mars' two moons.
MAVEN's arrival last year complicated matters, because it too intersects other visitors' orbits.
Indeed, MAVEN and the MRO looked like they might get uncomfortably close earlier this year, NASA has revealed.
“On Jan. 3, automated monitoring determined that two weeks later, MAVEN and MRO could come within about two miles (three kilometers) of each other, with large uncertainties remaining in the exact passing distance,” the agency says. NASA's response was automated messages to teams running all Mars missions, to help them prepare for collision-avoidance manoeuvres.
Those messages are a result of a new regime that sees NASA monitor all orbiters for potential collisions. Previously, only the Odyssey and MRO teams chatted about such matters. Now, NASA monitors data non-stop.
Doing so is tricky because the agency says “The amount of uncertainty in the predicted location of a Mars orbiter a few days ahead is more than a mile (more than two kilometers).”
“ Calculating projections for weeks ahead multiplies the uncertainty to dozens of miles, or kilometers. In most cases when a collision cannot be ruled out from projections two weeks ahead, improved precision in the forecasting as the date gets closer will rule out a collision with no need for avoidance action.”
Earth has more than 1,000 orbiting craft, so has a more sophisticated warning system. That Mars needs one at all with its low orbiter population can be attributed to the odd orbits we've selected as we study the red planet. ®