Extraterrestrial

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NASA's Mars Reconnaissance Orbiter (MRO) is a multipurpose spacecraft, launched August 12, 2005 to advance knowledge of Mars through detailed observation, to examine potential landing sites for future surface missions, and to provide a high-data-rate communications relay for those missions. MRO closely approached Mars and began orbital insertion on March 10, 2006. It is intended to orbit for four or more years, and to become Mars' fourth active artificial satellite (joining Mars Express, Mars Odyssey, and Mars Global Surveyor), and its sixth active probe (the satellites plus the two Mars Exploration Rovers), in a historic scientific focus on Mars.

The Mars Reconnaissance Orbiter will lay the groundwork for NASA's planned surface missions: a lander called Phoenix selected in a competition for a 2007 launch opportunity, and the Mars Science Laboratory, a highly capable rover being developed for a 2009 launch opportunity. The MRO's high-resolution instruments will help planners evaluate possible landing sites for these missions both in terms of science potential for further discoveries and in terms of landing risks. The MRO's communications capabilities will provide a critical transmission relay for the surface missions; MRO will even be able to provide critical navigation data to these probes during their landing. Also it may provide evidence which could help to uncover the reasons behind the failure of past Mars missions such as NASA's Mars Polar Lander, and the British Beagle lander.[1]

Orbital insertion and aerobraking

The start of the orbital insertion occurred as MRO approached Mars for the first time on March 10, 2006, passing above the Martian southern hemisphere at an altitude of about 370–400 km (190 mi). All six of the orbiter’s main engines burned for 27 minutes reducing the speed of the probe (relative to Mars at closest approach) from 2900 m/s (6500 mph) to 1900 m/s (4250 mph).

Orbital insertion has placed the orbiter in a highly elliptical polar orbit. The periapsis, the closest point in the orbit to Mars will be 3709 km (about 329 km from the surface). The apoapsis, farthest away from Mars will be 47,972 km. The orbital period will be approximately 35 hours.

Aerobraking will be conducted soon after orbital insertion to bring the orbiter to a lower, quicker orbit. Aerobraking cuts the fuel needed to reach the desired orbit roughly in half, and consists of three steps:

1. MRO will drop the periapsis of its orbit to aerobraking altitude using its thrusters. Aerobraking altitude will be determined at that time depending on the thickness of the Martian atmosphere (Martian atmospheric density changes over the seasons on Mars). This step will take about five orbits or one Earth week.

2. MRO will remain in aerobraking altitude for 5½ Earth months, or less than 500 orbits. Correct aerobraking altitude will have to be maintained with occasional corrections in periapsis altitude using its thrusters. Through aerobraking the apoapsis of the orbit will be reduced to 450 km (280 mi).

3. To end aerobraking, the MRO will use its thrusters to move its periapsis out of the edge of the Martian atmosphere.

After aerobraking another week or two will be spent to make additional adjustments in the orbit with thrusters. These corrections will likely occur before solar conjunction when Mars will appear to pass behind the Sun from Earth perspective, between October 7 and November 8, 2006. After this, science operations will begin. Final or science operations orbit will be at approximately 255 km (160 statute miles) to 320 km (200 mi) above the Martian surface. After reaching science operational orbit the SHARAD will be deployed.

Orbital insertion timeline

On March 10, 2006, Mars Reconnaissance Orbiter successfully completed orbital insertion.
In the next few weeks MRO's controllers will begin the "walk in" phase of aerobraking, where the periapsis is lowered into Mars' atmosphere. [2]

http://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiter