An artist's impression of the Mars Odyssey spacecraft in orbit around the Red Planet.
Odyssey changes orbit to study Mars
27 Jun 2009
NASA's long-lived Mars Odyssey spacecraft has completed an eight-month adjustment of its orbit, positioning itself to look down at the dayside 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 5:00pm, 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, and project scientist for Mars Odyssey.
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 maximise science benefits from the spacecraft in coming years.
< Odyssey's instruments study Mars from orbit.
Odyssey's orbit is synchronised 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 5:00pm whenever Odyssey was overhead. (Likewise, the local time was about 5:00am under the track of the spacecraft during the south-to-north leg of each orbit, on the night side of Mars.)
On September 30, 2008, Odyssey fired its thrusters for six minutes, putting the orbiter into a "drift" pattern that gradually changed the time-of-day of its overpasses during the following 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.
Discoveries
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.
Odyssey's new orbit means an instrument on the end of the long boom will get overheated. That's the trade-off for a better view for the main instrument, THEMIS.
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 of 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.
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 orbit helps prepare the mission to be a relay for NASA's Mars Science Laboratory mission, scheduled to put the rover Curiosity on Mars in 2012.
More information: Mars Odyssey mission
Adapted from information issued by NASA JPL news.
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