NASA's Mars Reconnaissance Craft Begins Adjusting Orbit

http://www.jpl.nasa.gov/news/news.cfm?release=2006-048

Guy Webster (818) 354-6278
Jet Propulsion Laboratory, Pasadena, Calif.

Erica Hupp (202) 358-1237
NASA Headquarters, Washington

2006-048

NASA's Mars Reconnaissance Craft Begins Adjusting Orbit
March 31, 2006

NASA's Mars Reconnaissance Orbiter yesterday began a crucial six-month
campaign to gradually shrink its orbit into the best geometry for the
mission's science work.

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

The orbiter has been flying about 426 kilometers (265 miles) above
Mars'
surface at the nearest point of each loop since March 10, then swinging
more than 43,000 kilometers (27,000 miles) away before heading in
again.
While preparing for aerobraking, the flight team tested several
instruments, obtaining 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.

On Thursday, Mars Reconnaissance Orbiter fired its intermediate
thrusters for 58 seconds at the far point of the orbit. That maneuver
lowered its altitude to 333 kilometers (207 miles) when the spacecraft
next passed the near point of its orbit, at 6:46 a.m. Pacific time
today
(9:46 a.m. Eastern Time).

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

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 per day.

"We have to be sure we don't dive too deep, because that could overheat
parts of the orbiter," Kubitschek said. "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.
"We
demonstrated that we're ready to support aerobraking, should we be
needed," JPL's Dr. Daniel McCleese, principal investigator for the Mars
Climate Sounder, said of new test observations.

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. "There is risk every time we
enter
the atmosphere, 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," said JPL's Jim Graf, project
manager 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. "It allows
you to fly more science payload to Mars instead of more fuel,"
Kubitschek said.

Once in its science orbit, Mars Reconnaissance 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.
It
will also 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
additional information about Mars Reconnaissance Orbiter are available
online at http://www.nasa.gov/mro and at
http://marsprogram.jpl.nasa.gov/mro
javascriptpenNASAWindow('http://marsprogram.jpl.nasa.gov/mro') .

For information about NASA and agency programs on the Web, visit
http://www.nasa.gov .

JPL, a division of the California Institute of Technology in Pasadena,
manages the Mars Reconnaissance Orbiter for NASA's Science Mission
Directorate, Washington. Lockheed Martin Space Systems, Denver, is the
prime contractor for the project and built the spacecraft.