Scaled View, Computer Drawing of Mars Odyssey MOC2-1096d; NASA/JPL/MSSS
Combined MOC Images of Mars Express MOC2-1096g; NASA/JPL/MSSS
The Mars Orbiter Camera (MOC) images shown here are the first pictures of a spacecraft orbiting Mars taken by another spacecraft orbiting Mars. In April 2005, the MOC aboard Mars Global Surveyor (MGS) was used to take pictures of the other two spacecraft currently operating in orbit around Mars: NASA's Mars Odyssey and the European Space Agency's (ESA) Mars Express.
The MGS MOC is able to resolve features on the surface of Mars as small as a few meters across from its nominal 350 to 405 kilometers (217 to 252 miles) altitude. From a distance of 100 kilometers (62 miles), MOC would be able to resolve features substantially smaller than 1 meter across. Engineers at the Jet Propulsion Laboratory (JPL; Pasadena, California), Lockheed Martin Space Systems Company (LMSSC, Denver, Colorado), and Malin Space Science Systems (MSSS; San Diego, California) worked very closely together to acquire images of Mars Express and Mars Odyssey.
Mars Global Surveyor and Mars Odyssey are both in nearly circular, near-polar orbits. Odyssey is in an orbit slightly higher than that of MGS, in order to preclude the possibility that the two orbiters would collide. However, the two spacecraft occasionally come as close to one another as 15 kilometers (9 miles).
The first figure (above, MOC2-1096a) shows two views of Mars Odyssey acquired less than 7.5 seconds apart on 21 April 2005 as Odyssey receded from a close flyby of MGS. The second figure (MOC2-1096b) shows schematically the geometry of the flyby. Two views of Odyssey were acquired: the first was taken when Odyssey was close to MGS and moving more rapidly than MGS was rotating, as seen from MGS. A few seconds later, Odyssey was farther away and appeared to be moving more slowly. In this second view of Odyssey, the MOC field-of-view overtook Odyssey.
The third figure (MOC2-1096c) shows an extreme enlargement of the best MOC view of Odyssey; the fourth figure (MOC2-1096d) is a computer-generated drawing scaled to the same size. Below these images is a labeled enlargement of the computer drawing (MOC2-1096e). The MOC image clearly shows the Gamma Ray Spectrometer (GRS) and its 6 meters-long boom, the high gain antenna used to transmit not only the science data from Odyssey's own instruments, but also to relay data from the two Mars Exploration Rovers (Spirit and Opportunity), and its solar array panel.
It is possible to synthesize a stereoscopic (3-D) anaglyph from the two observations of Odyssey, owing to the different viewing angles between the two views. The sixth figure (MOC2-1096f) shows this stereoscopic composite; for proper viewing, the user needs "3-D" glasses with red over the left eye and blue over the right eye.
Mars Odyssey was launched on 7 April 2001, and reached Mars on 24 October 2001. Mars Global Surveyor left Earth on 7 November 1996, and arrived in Mars orbit on 12 September 1997. Both spacecraft 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.
The first image taken by one spacecraft orbiting Mars of another orbiting Mars was acquired less than one day before the Mars Odyssey image. On 20 April 2005, Mars Global Surveyor acquired an image of the European Space Agency's Mars Express orbiter. Mars Express is in a highly elliptical orbit, which is also highly inclined relative to the equator of Mars. Although the Mars Express orbit's periapsis (closest point to the planet) is lower than that of MGS, permitting close encounters, such encounters occur more rarely than for Odyssey because the orbit of Mars Express is more elliptical and has a longer period.
Three views of Mars Express are shown here. The first (MOC2-1096g) is a composite of the two MOC images acquired on 20 April 2005. The second (MOC2-1096h) is an artist's rendition of the orientation of Mars Express relative to the view from MGS when MOC acquired its images; and the third picture (MOC2-1096i) is a view of Mars express with its key features labeled. Owing to the larger distance between MGS and Mars Express when the image could be taken (two views were acquired by MOC, again as the target spacecraft moved away from MGS), and a substantial cross-track component of apparent motion for which no correction could be made, Mars Express appears in the 20 April 2005 image as a narrow blur rather than as a well-defined spacecraft. Seen from about 250 kilometers (155 mi) away, Mars Express appeared to be about 1.5 meters in the small dimension and 15 meters in the long dimension, consistent with the viewing distance, pixel scale, and encounter geometry. Closer encounters later in the year may permit a better MOC image of Mars Express to be acquired. The newest of the three active Mars orbiters, Mars Express was launched on 2 June 2003, and reached the red planet on 25 December 2003.
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Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, California. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Space Systems Company, from facilities in Pasadena, California and Denver, Colorado.
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