NASA Mars Picture of the Day: Global With OSM-7

The Mars Orbiter Camera (MOC) team celebrated
a milestone late last week as Mars Global
Surveyor (MGS) completed its 25,000th orbit
since it reached the red planet on 12 September
1997. Also last week,
on 27 May 2004, MGS’s thrusters
were fired briefly to adjust the spacecraft’s
orbit. This Orbit Synchronization Maneuver-7
(OSM-7) was designed to stop the orbital drift in
Mars local mean solar time that MGS had been
experiencing as a result of the OSMs that were
done in late 2003 and early 2004 to move the
spacecraft into position to relay data during the
January landings of the Mars Exploration Rovers.

OSM-7 occurred on
the day side of Mars, and thus the effects of
the maneuver are visible in the MOC wide angle
daily global map image acquired on that orbit,
as shown here. MOC has two wide angle cameras,
one that acquires a red view, the other is
blue. Because Mars has very little that is
green, the green channel in the color image
is synthesized by combining the red and blue
channels by a known ratio. The black
areas in the image are views of outer space.
Black portions of the image were obtained because
MGS was rotated into position for the burn, then
the engines were fired.

The spacecraft moves
from south to north on the day side of the planet.
Thus, the bottom of the image is near the south polar
region of Mars, and the top shows the north polar
cap. Before the black areas appeared near the
bottom of the scene, the spacecraft was moving
along in its normal orientation. Then, where the
black first appears, MGS was being rotated
relative to its normal position. Later, toward
the middle of the image, the thrusters were fired.
The spacecraft returned to its normal operational
orientation before it reached the north polar region.
The white area in the image is saturated by sunlight
glinting off of clouds over the southern high latitudes.
Sunlight illuminates the planet from the left. The
dark region immediately south (below) the north
polar cap is Acidalia Planitia.

The status of MGS is described each week by the
MGS Project at the Jet Propulsion Laboratory’s
web page,
http://marsweb.jpl.nasa.gov/mgs/status/reports/msop-mgs.html.
These reports include additional information about
OSM-7 and the previous OSMs conducted to support
the rover mission.