Figure 1: Why There are Two Images of Odyssey
NASA's Mars Odyssey spacecraft appears twice in the same frame in this
image from the Mars Orbiter Camera aboard NASA's Mars Global Surveyor.
The camera's successful imaging of Odyssey and of the European Space
Agency's Mars Express in April 2005 produced the first pictures of any
spacecraft orbiting Mars taken by another spacecraft orbiting
Mars.
Mars Global Surveyor and Mars Odyssey are both in nearly circular,
near-polar orbits. Odyssey is in an orbit slightly higher than that of Global
Surveyor in order to preclude the possibility of a collision. However, the
two spacecraft occasionally come as close together as 15 kilometers (9
miles).
The images were obtained by the Mars Global Surveyor operations teams
at Lockheed Martin Space System, Denver; JPL and Malin Space Science
Systems.
The two views of Mars Odyssey in this image were acquired a little under
7.5 seconds apart as Odyssey receded from a close flyby of Mars Global
Surveyor. The geometry of the flyby (see Figure 1) and the camera's way
of acquiring an image line-by-line resulted in the two views of Odyssey
in the same frame. The first view (right) was taken when Odyssey was
about 90 kilometers (56 miles) from Global Surveyor and moving more
rapidly than Global Surveyor was rotating, as seen from Global Surveyor.
A few seconds later, Odyssey was farther away -- about 135 kilometers (84
miles) -- and appeared to be moving more slowly. In this second view of
Odyssey (left), the Mars Orbiter Camera's field-of-view overtook Odyssey.
The Mars Orbiter Camera can resolve features on the surface of Mars as
small as a few meters or yards across from Mars Global Surveyor's orbital
altitude of 350 to 405 kilometers (217 to 252 miles). From a distance of
100 kilometers (62 miles), the camera would be able to resolve features
substantially smaller than 1 meter or yard across.
Mars Odyssey was launched on April 7, 2001, and reached Mars on Oct. 24,
2001. Mars Global Surveyor left Earth on Nov. 7, 1996, and arrived in Mars
orbit on Sept. 12, 1997. Both orbiters are in an extended mission phase,
both have relayed data from the Mars Exploration Rovers, and both are
continuing to return exciting new results from Mars. JPL, a division of
the California Institute of Technology, Pasadena, manages both missions
for NASA's Science Mission Directorate, Washington, D.C.
