The orbiter will loop around the planet, firing onboard rockets to slow its speed enough to be gravitationally captured by Mars. If the attempt fails, the spacecraft could crash after dipping too low into the atmosphere, or fly right past the planet it was meant to investigate. "Orbiters seem like they might be the easiest thing to do," says McCuistion.

"But in reality, (NASA) only has about a 65 percent success rate of getting orbiters into orbit. Whereas landers, we have about an 80 percent success rate of getting them on the surface." He adds that, if you factor in the attempts made by other countries, the success rate for Mars orbiters is even lower, about 40 percent.

MRO will approach the southern pole of Mars and then fire its thrusters at 1:25 Pacific Standard Time Friday, March 10. After 21 minutes, MRO will go behind the planet and mission scientists will lose contact with the spacecraft for 30 minutes. Six minutes after this loss of contact, the rockets should stop firing automatically, having decreased the speed of the spacecraft by 18 percent.

The spacecraft should swing back around Mars and re-establish Earth contact at 2:16 pm PST. Mission scientists will need an additional 30 minutes to determine whether the spacecraft has been captured by Mars gravity.

"We're getting into the dangerous portion of the mission," says Jim Graf, Mars Reconnaissance Orbiter Project Manager from the Jet Propulsion Laboratory. "Now we're starting to enter into the realm where we've lost two spacecraft in the last 15 years."

If MRO does begin to orbit Mars as planned, it will take six months for the spacecraft to decrease its 35-hour, highly elongated orbit to a more circular, 2-hour one. The spacecraft will use an aerobraking technique to get into this final orbit, dragging its body against the martian atmosphere so that the resulting friction slows the spacecraft down.

If successful, MRO will join the three other spacecraft currently orbiting the Red Planet: NASA's Mars Global Surveyor (MGS) and Mars Odyssey, and the European Space Agency's Mars Express.

MRO's 10-foot diameter dish antenna can transmit data to Earth at approximately 10 times the rate of any previous Mars mission. Ultimately, MRO is expected to send 34 terabits of data to Earth. In addition to its communications system, MRO has six science instruments. The HiRISE camera will provide extremely detailed images of the martian surface.

"If you had HiRISE in New York, you could look over at Washington and count the number of people visiting the Mall," says Michael Meyer, Mars Lead Scientist at NASA Headquarters.

MRO also has a radar sounder to peek beneath the surface and look for water ice or even liquid water. Scouting out hidden water reservoirs will help us better understand if Mars could ever have harbored life.

"Since Mariner 4, we've learned that Mars was once warmer and wetter," says Meyer, "but when and for how long remains to be the central question in understanding the biological potential of Mars."

MRO will provide information about the polar landing site for the Phoenix lander, which is scheduled to head to Mars next year. In addition, MRO will help look for the best possible sites for the next mars rover: the Mars Science Laboratory, scheduled for launch in 2009.

Besides the radar and high-resolution camera, the other science instruments onboard MRO include a spectrometer to identify minerals and water-related deposits, a weather camera, and an infrared sounder to monitor atmospheric temperatures and the movement of water vapor.

"MRO will be multi-tasking," says Meyer. "It's going to be a weather satellite, it's going to be a surveyor - able to identify geological features, minerals, the subsurface structure - it's going to be a communications relay, and a guide to the next decade of exploration."

The two little rovers Spirit and Opportunity are still exploring Mars today, and MRO potentially can help transmit some of their data. MRO also could help the rovers figure out where to go next by providing detailed maps. The HiRISE camera on MRO could not only help the rovers navigate unfamiliar terrain, it may even be able to snap photos of the rovers themselves.

MRO will start operating its scientific instruments in November, and will gather science data for two years. After that, the spacecraft will be used primarily as a communications relay to support other missions. It has enough fuel in the tank to orbit Mars for nearly ten years.

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