Mars orbiter relies on ‘science friction’

Sweat factor
Onboard MRO is a periapsis timing estimator, or PTE. Using very precise accelerometers and a computer algorithm, the spacecraft can predict orbit period changes from one orbit to the next. Trial-running this think-for-itself, auto-navigation approach may lead to wider adoption of the PTE in the future.

PTE number-crunching is being gauged against the output from the traditional work on navigation prediction, done by the team here on Earth, with very favorable results, Sidney said. "We kind of have our own little navigator onboard MRO ... the two methods line up very, very well."

Sidney said a daily round of collision avoidance analysis pinpoints the whereabouts of MRO relative to other Mars orbiters now busy at work — Mars Global Surveyor, Mars Odyssey, and Europe’s Mars Express. There has been an "interesting little dance" with Mars Odyssey in particular, he added.

While having a fleet of orbiters circuiting Mars has relayed a bonanza of data, precise knowledge of MRO’s orbit, given its aerobraking aerobics, is top priority.

But there’s more of a sweat factor when you mix in the orbits of the Mars moons — Phobos and Deimos — and the unknown locations of two Viking orbiters from the 1970s that are thought to be still zipping around Mars.

All orbiters are supposed to be in Quarantine Safe Orbits, which requires a minimum lifetime of 50 years circling Mars. So it’s believed that both Viking orbiters are swinging around Mars too — silent sentinels that ran out of attitude control gas early on in their missions.

Desired time-of-day
With each loop around the Red Planet, the $750 million MRO mission draws closer to the day when its science gathering tasks can begin. Following months of aerobraking — 512 dips through the atmosphere — MRO will be locked into the desired time-of-day pattern for the mission’s science phase.

"It all has to come together," Sidney observed.

The orbit will remain at a fixed angle to the sun; every time the spacecraft passes northbound over the equator, it will see midafternoon lighting on the ground. A complete orbit will then take about one hour and 52 minutes. By the next time MRO loops around and crosses the equator again, Mars will have rotated just enough that the spacecraft sees the same time-of-day on the ground beneath it.

A key objective of MRO is to search for evidence that water persisted on the surface of Mars for a long period of time. While other Mars missions have shown that water flowed across the surface in the planet’s past, it remains a mystery whether water was ever around long enough to provide a habitat for life.

"It’s going extremely well ... it really is," Sidney concluded. "We’re on the glide slope ... right on track to keep moving forward."

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