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New Mexico State University

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NMSU astronomer helps guide Mars spacecraft into desired orbit

NASA's newest Mars spacecraft, the Mars Reconnaissance Orbiter, completed its aerobraking phase last week, settling into an orbit that takes it around the red planet in just under two hours instead of the 36-hour circuit it started with.

five months to maneuver it into this desired orbit using the tricky technique known as aerobraking - dipping into the planet's atmosphere to slow the spacecraft and reshape its orbit - but it saved about $15 million, said Jim Murphy, head of the astronomy department at New Mexico State University.

That's about what it would have cost to carry enough fuel to use the spacecraft's rocket engines to maneuver it into the desired orbit, he said.

Murphy is a member of the Mars Reconnaissance Orbiter mission's Atmospheric Advisory Group, a dozen or so scientists who have met daily in lunchtime teleconferences over the past five months to assess the planet's atmospheric conditions. Their daily reports guided mission managers on the critical question of how far to push the spacecraft into the upper atmosphere as it passed closest to Mars in its elliptical orbit.

With each "dip," the spacecraft's orbit became a little shorter and more circular. But each encounter with the atmosphere generates heat, so the spacecraft's handlers had to balance the need to get into the desired orbit on schedule with the risk of overheating.

"It's a little like the Goldilocks story," Murphy said. "If the density of the atmospheric gas encountered by the spacecraft is too great it could cause damage, but if there's not enough density the orbit doesn't change enough. It has to be just right."

Predicting the changing conditions the spacecraft would encounter was the responsibility of the Atmospheric Advisory Group. Murphy and two other members rotated the leadership role so that each could take some days off during the five months of daily conference calls.

Mars' famous dust storms were not a major issue for the team because the mission was timed so that aerobraking took place during a cycle of low storm activity, Murphy said.

The Mars Reconnaissance Orbiter is NASA's third Mars orbiter to use the aerobraking method and Murphy has been involved each time. It's a major commitment of his time, "but I have a much better appreciation of the big picture as a result of my involvement," he said. "And this is a fun group of people. Some of them, I know their voices very well, but we've never met in person."

Except for a University of Michigan researcher, all the team members besides Murphy are scientists from various NASA centers.

The orbiter gathered some data on the Martian atmosphere during the aerobraking process, Murphy said. That data will be archived at NASA's Planetary Atmospheres Node, which is located at NMSU and managed by NMSU astronomer Reta Beebe.

The orbiter's main science observations are scheduled to begin in November, after Mars passes behind the sun.

"The main science mission is to get a very nice characterization of the surface and atmosphere of Mars," Murphy said. "The spacecraft has a high-resolution camera on board that can see objects of about a foot in size. It also has a camera that operates at the near-infrared part of the spectrum, just beyond what the human eye can see."

The cameras will provide close-up photography of the Martian surface, analyze minerals, look for subsurface water, trace how much dust and water are distributed in the atmosphere, and monitor daily global weather.