February 24, 2006
NASA Mars Orbiter to Arrive at Red Planet March 10
By Deborah Zabarenko
WASHINGTON -- NASA's Mars Reconnaissance Orbiter is headed into a perilous phase after a seven-month journey from Earth, aiming to start looping around the Red Planet on March 10, space agency officials said on Friday.If it manages to reach its planned orbit, a process that will take another seven months, the spacecraft could collect unprecedented data about Earth's next-door planetary neighbor, which could help scientists determine where to land the next Mars rovers and even to make preliminary plans for a human landing site.
"It's going to be difficult to get it into orbit," Doug McCuistion, who heads the NASA Mars Exploration Program, said at a briefing. "Mars is hard, Mars can be unpredictable, but we've got a good team here."
NASA has only a 65 percent success rate in getting space probes to orbit Mars, as opposed to a more than 80 percent success rate in managing to land spacecrafts on its surface, he said.
The tricky part is getting the orbiter to slow down enough to be captured by the planet's gravity.
"We're getting into the dangerous portion of the mission," said James Graf, the project's manager.
At just 15 million miles from Mars, the orbiter has cruised for nearly 300 million miles (483 million km) since its launch on August 12, 2005.
GOING BEHIND MARS
As it approaches the planet, controllers on Earth expect a signal from the spacecraft indicating a 27-minute engine burn meant to slow it down and let martian gravity capture it.
At 21 minutes after the engine burn begins, the spacecraft will go behind Mars and be out of radio contact with Earth, and stay that way for another half hour, Graf said.
If this procedure -- known as aerobraking -- works, the spacecraft will be in an extremely elliptical orbit around Mars, about 200 miles at the closest point and about 35,000 miles at the farthest.
Over the next six months, the spacecraft will use aerobraking and the drag of the martian atmosphere to reel itself in from an elongated 35-hour orbit to a nearly circular two-hour orbit. When that is accomplished, scientific operations can begin.
The orbiter's six scientific instruments are designed to collect more data than all previous Mars probes combined, including information on the planet's weather, color images and even radar to look about half a mile (1km) below the martian surface.
Since NASA's exploration of Mars has consistently focused on the search for signs of water, the orbiter's instruments will be able to look for any sub-surface clues to this as well, which could give future rovers a place to start looking. Water is seen as a requirement for Earth-type life.
Further information and images are available online at http://www.nasa.gov/mission_pages/MRO/main/index.html