NASA repositions Mars orbiters to avoid comet flyby

Robotic orbiters being sent behind the Red Planet to protect them from comet debris

With a comet rushing toward Mars, NASA scientists are working to protect their robotic orbiters from being damaged or destroyed by comet debris.

The object, dubbed Comet C/2013 A1 Siding Spring, is on a path to make what NASA is calling a close flyby of Mars on Oct 19. Scientists' trajectory has the comet's nucleus coming within about 82,000 miles of the Red Planet.

Though 82,000 miles seems like a great distance, its proximity to Mars is expected to be less than one-tenth the distance of any known comet flyby to Earth.

While the nucleus will miss the orbiters working around Mars, the comet will be shedding material as it goes by. The debris is expected to hurtle toward Mars at 35 miles per second.

NASA noted that at that velocity, even a particle only one-fiftieth of an inch across could cause significant damage to a spacecraft and could be disastrous for the Mars orbiters.

The period of greatest risk will start about 90 minutes after the comet passes Mars and should last about 20 minutes.

Even though Mars' atmosphere is thinner than the one on Earth, it's thought to be thick enough to protect NASA's robotic rovers working on the ground.

Right now, there are two orbiters -- the Mars Reconnaissance Orbiter and the Odyssey -- working there. However, a third -- the Mars Atmosphere and Volatile Evolution (MAVEN) -- spacecraft already has been launched and is expected to rendezvous with Mars and enter its orbit just a month before the comet's flyby.

To protect the three orbiters, NASA engineers plan to make sure they are on the opposite side of the planet when the comet passes.

NASA reported that engineers sent the Mars Reconnaissance Orbiter directions to make an orbit-adjustment maneuver on July 2 as the first move to safely reposition the orbiter in time for the Oct 19 flyby. A second maneuver is planned for Aug. 27.

The team operating NASA's Mars Odyssey is planning a similar maneuver for Aug. 5.

MAVEN, the orbiter still on its way to Mars, is expected to reach the Red Planet on Sept. 21. The MAVEN team is scheduled to make a repositioning maneuver for it on Oct. 9, prior to the start of the mission's main science phase in early November.

"Three expert teams have modeled this comet for NASA and provided forecasts for its flyby of Mars," said Rich Zurek, chief scientist for the Mars Exploration Program at NASA's Jet Propulsion Laboratory. "The hazard is not an impact of the comet nucleus, but the trail of debris coming from it. Mars will be right at the edge of the debris cloud, so it might encounter some of the particles -- or it might not."

Mars Reconnaissance Orbiter and Odyssey have been working in conjunction with the Mars rovers Curiosity and Opportunity to study the planet. The orbiters also relay data and images from the rovers back to Earth, and relay commands from Earth to the rovers.

As the comet approaches Mars, scientists plan to use several instruments on the three orbiters to study the nucleus, the coma surrounding the nucleus and gases coming off it, as well as the comet's tail. They also will study the possible effects the comet will have on the Martian atmosphere.

According to NASA, this particular comet has never before entered the inner solar system, so scientists are hoping it will provide a fresh source of information about the solar system's earliest days.

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This graphic depicts the orbit of comet C/2013 A1 Siding Spring as it swings around the sun this year. On Oct. 19, the comet is expected to make a close flyby of Mars, putting NASAs orbiters in jeopardy. (Image: NASA

Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at  @sgaudin, on Google+ or subscribe to Sharon's RSS feed . Her email address is sgaudin@computerworld.com.

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