[meteorite-list] NASA's Mars Odyssey Alters Orbit to Study Warmer Ground

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.cfm?release=2009-100  

NASA's Mars Odyssey Alters Orbit to Study Warmer Ground
Jet Propulsion Laboratory
June 22, 2009

PASADENA, Calif. -- NASA's long-lived Mars Odyssey spacecraft has
completed an eight-month adjustment of its orbit, positioning itself to
look down at the day side of the planet in mid-afternoon instead of late
afternoon.

This change gains sensitivity for infrared mapping of Martian minerals
by the orbiter's Thermal Emission Imaging System camera. Orbit design
for Odyssey's first seven years of observing Mars used a compromise
between what worked best for the infrared mapping and for another
onboard instrument.

"The orbiter is now overhead at about 3:45 in the afternoon instead of 5
p.m., so the ground is warmer and there is more thermal energy for the
camera's infrared sensors to detect," said Jeffrey Plaut of NASA's Jet
Propulsion Laboratory, Pasadena, Calif., project scientist for Mars
Odyssey.

Some important mineral discoveries by Odyssey stem from mapping done
during six months early in the mission when the orbit geometry provided
mid-afternoon overpasses. One key example: finding salt deposits
apparently left behind when large bodies of water evaporated.

"The new orbit means we can now get the type of high-quality data for
the rest of Mars that we got for 10 or 20 percent of the planet during
those early six months," said Philip Christensen of Arizona State
University, Tempe, principal investigator for the Thermal Emission
Imaging System.

Here's the trade-off: The orbital shift to mid-afternoon will stop the
use of one of three instruments in Odyssey's Gamma Ray Spectrometer
suite. The new orientation will soon result in overheating a critical
component of the suite's gamma ray detector. The suite's neutron
spectrometer and high-energy neutron detector are expected to keep
operating. The Gamma Ray Spectrometer provided a dramatic 2002 discovery
of water-ice near the Martian surface in large areas. The gamma ray
detector has also mapped global distribution of many elements, such as
iron, silicon and potassium.

Last year, before the start of a third two-year extension of the Odyssey
mission, a panel of planetary scientists assembled by NASA recommended
the orbit adjustment to maximize science benefits from the spacecraft in
coming years.

Odyssey's orbit is synchronized with the sun. Picture Mars rotating
beneath the polar-orbiting spacecraft with the sun off to one side. The
orbiter passes from near the north pole to near the south pole over the
day-lit side of Mars. At each point on the Mars surface that turns
beneath Odyssey, the solar time of day when the southbound spacecraft
passes over is the same. During the five years prior to October 2008,
that local solar time was about 5 p.m. whenever Odyssey was overhead.
(Likewise, the local time was about 5 a.m. under the track of the
spacecraft during the south-to-north leg of each orbit, on the night
side of Mars.)

On Sept. 30, 2008, Odyssey fired thrusters for six minutes, putting the
orbiter into a "drift" pattern of gradually changing the time-of-day of
its overpasses during the next several months. On June 9, Odyssey's
operations team at JPL and at Denver-based Lockheed Martin Space Systems
commanded the spacecraft to fire the thrusters again. This
five-and-a-half-minute burn ended the drift pattern and locked the
spacecraft into the mid-afternoon overpass time. "The maneuver went
exactly as planned," said JPL's Gaylon McSmith, Odyssey mission manager.

In another operational change motivated by science benefits, Odyssey has
begun in recent weeks making observations other then straight
downward-looking. This more-flexible targeting allows imaging of some
latitudes near the poles that are never directly underneath the orbiter,
and allows faster filling-in of gaps not covered by previous imaging.

"We are using the spacecraft in a new way," McSmith said.

In addition to extending its own scientific investigations, the Odyssey
mission continues to serve as the radio relay for almost all data from
NASA's Mars Exploration Rovers, Spirit and Opportunity. Odyssey's new
orbital geometry helps prepare the mission to be a relay asset for
NASA's Mars Science Laboratory mission, scheduled to put the rover
Curiosity on Mars in 2012.

Mars Odyssey, launched in 2001, is managed by JPL, a division of the
California Institute of Technology, Pasadena, for NASA's Science Mission
Directorate, Washington. Lockheed Martin Space Systems is the prime
contractor for the project. Investigators at Arizona State University
operate the Thermal Emission Imaging System. Investigators at the
University of Arizona, Tucson, head operation of the Gamma Ray
Spectrometer. Additional science partners are located at the Russian
Aviation and Space Agency, which provided the high-energy neutron
detector, and at Los Alamos National Laboratories, New Mexico, which
provided the neutron spectrometer.

For more about the Mars Odyssey mission, visit:
http://mars.jpl.nasa.gov/odyssey .

Media Contacts: Carolina Martinez/Guy Webster 818-354-9382/6278
Jet Propulsion Laboratory, Pasadena, Calif.
carolina.martinez at jpl.nasa.gov / guy.webster at jpl.nasa.gov

2009-100