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NASA's Mars Reconnaissance Orbiter Begins Adjusting Orbit

03 April 2006

Spacecraft scheduled to begin science mission in six months

Washington – NASA's Mars Reconnaissance Orbiter March 30 began a crucial six-month effort to shrink its orbit gradually into the best geometry for the mission's science work.

Three weeks after entering orbit around Mars, the spacecraft is in a phase called aerobraking. This process uses friction with the tenuous Martian upper atmosphere to transform a very elongated 35-hour orbit to the nearly circular two-hour orbit needed for the mission's science observations, according to a March 31 NASA press release.

"We're not low enough to touch Mars' atmosphere yet, but we'll get to that point next week," said Daniel Kubitschek of NASA's Jet Propulsion Laboratory (JPL) in California, deputy leader for the aerobraking phase of the mission.

The orbiter has been flying about 426 kilometers above Mars' surface at the nearest point of each loop since March 10, then swinging more than 43,000 kilometers away before heading in again.

While preparing for aerobraking, the flight team tested several instruments, taking the orbiter's first Mars pictures and demonstrating the ability of its Mars Climate Sounder instrument to track the atmosphere's dust, water vapor and temperatures.

AEROBRAKING MANEUVERS

The orbiter fired its intermediate thrusters March 30 for 58 seconds at the far point of the orbit. That maneuver lowered its altitude to 333 kilometers when the spacecraft next passed the near point of its orbit.

The phase includes about 550 dips into the atmosphere, each carefully planned for the desired amount of braking. At first, the dips will be more than 30 hours apart. By August, there will be four dips per day.

"We have to be sure we don't dive too deep,” Kubitschek said, “because that could overheat parts of the orbiter. The biggest challenge is the variability of the atmosphere."

Readings from accelerometers during the passes through the atmosphere are one way the spacecraft can provide information about upward swelling of the atmosphere due to heating. The Mars Climate Sounder instrument also has the capability to monitor changes in temperature that would affect the atmosphere's thickness.

Infrared-sensing instruments and cameras on two other Mars orbiters are expected to be the main sources of information to the advisory team of atmospheric scientists providing day-to-day assistance to the aerobraking navigators and engineers.

OTHER MARS ORBITERS

"There is risk every time we enter the atmosphere,” said JPL's Jim Graf, project manager for the Mars Reconnaissance Orbiter, “and we are fortunate to have Mars Global Surveyor and Mars Odyssey with their daily global coverage helping us watch for changes that could increase the risk."

NASA's Mars Global Surveyor is the oldest Mars spacecraft still operating. It has been studying the red planet for nearly a decade. Mars Global Surveyor arrived at Mars in 1997 and since has returned more scientific data about the planet’s evolution than all other Mars missions combined.

Mars Odyssey is part of NASA's Mars Exploration Program, a long-term effort of robotic exploration. The primary science mission of Mars Odyssey, which launched in April 2001 and arrived at Mars in October 2001, took place between February 2002 and August 2004. The orbiter began its extended mission on August 24, 2004. For the first time, the mission mapped the amount and distribution of chemical elements and minerals that make up the Martian surface.

SCIENCE ORBIT

For the Mars Reconnaissance Orbiter, using aerobraking to get the spacecraft's orbit to the desired shape, instead of doing the whole job with thruster firings, reduces how much fuel a spacecraft needs to carry when launched from Earth.

Once in its science orbit, the orbiter will return more data about the planet than all previous Mars missions combined. The data will help researchers decipher the processes of change on the planet.

The orbiter also will aid future missions to the surface of Mars by examining potential landing sites and providing a high-data-rate communications relay.

Test observations from the Mars Climate Sounder, other images and more information about the Mars Reconnaissance Orbiter are available at the NASA and JPL Web sites.

(Distributed by the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)