Mars Global Surveyor
Mars Orbiter Camera

MGS Finds Viking Lander 2 and Mars Polar Lander (Maybe)

MGS MOC Release No. MOC2-1082, 5 May 2005

MGS Finds Viking Lander 2

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Enlargement of MOC image and Schematic Drawing of Viking 2

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Viking Lander 2

One of the more interesting and appealing activities of the Mars Orbiter Camera (MOC) observational objectives identified in the original 1985 Mars Observer proposal was to image landers on the martian surface. The scientific goal of this objective is to place the landers into their geologic context, which in turn helps the science community to better understand the results from the landers. In addition to this, the MOC team believed that it would be "really neat" to see the landers sitting on the surface. In previous releases, we have shown images of Viking Lander 1, Mars Pathfinder, and the two Mars Exploration Rovers, Spirit and Opportunity. To this group of landers we can now add with certainty Viking Lander 2 (VL-2), the location of which has been uncertain by many kilometers for nearly 30 years. We also believe that we have found a candidate for the location of the Mars Polar Lander, which failed without a trace on 3 December 1999.

The first figure (above) shows: (A) a mosaic of Viking Orbiter images obtained in the 1970s at a resolution of 75 m/pixel, (B) a typical Mars Global Surveyor (MGS) MOC narrow angle camera view at about 3 meters/pixel (25x higher resolution than the Viking images), and (C, D) sections of a cPROTO image at 0.5 m/pixel. The second figure (above) shows an extreme enlargement of the feature identified as Viking Lander 2, compared to a schematic drawing of the lander in the orientation determined during the Viking mission.

Finding Viking 2 has been a challenge owing to the extreme subtlety of horizon features visible in the lander panoramas and relatively inaccurate radio tracking data. Without the diligent work of Timothy J. Parker of the Jet Propulsion Laboratory and Philip Stooke of the University of Western Ontario, we wouldn't really have known where to point the MOC. Using the best estimated locations based on sightline studies to guide our targeting, we finally located the lander amid the remarkably homogenous terrain. Viking Lander 2 touched down on Utopia Planitia on 3 September 1976.

MOC Image of Candidate Mars Polar Lander Landing Site

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Mars Polar Lander

The loss of Mars Polar Lander in December 1999 was a traumatic experience not only for those of us intimately involved in the mission, but also for the U. S. Mars Exploration Program. Following the failure, exhaustive reviews of what happened and why led to major shifts in the way planetary exploration was implemented. Without telemetry, the cause of the failure could only be surmised. It would be extremely important if, through some observation, it were possible to confirm the failure mode.

Shortly after the loss of Mars Polar Lander (MPL), the Mars Global Surveyor MOC was employed to acquire dozens of 1.5 m/pixel images of the landing uncertainty ellipses, looking for any evidence of the lander and its fate. The criteria we used in searching for MPL required a bright feature of irregular or elongated shape (the parachute) within about 1 kilometer (0.62 miles) of a location that included a dark area (rocket-disturbed martian dirt) and a small, bright spot near its center (the lander). In 2000, we found one example (see figure) that met these criteria, but in the absence of any substantive, corroborating evidence, the interpretation that this was MPL and its parachute were considered to be extremely speculative.

Observations by MGS MOC in 2004 of the Mars Exploration Rover (MER) landing sites provided guidance for a re-examination of the previously identified MPL candidate. For example, the material from which the MPL and MER parachutes are made is similar, and its brightness in MOC images can be calculated, at least in a relative sense, as a function of sun angle. The brightness of the candidate "parachute" in the MPL candidate location image turns out to be consistent with it being the same material. The brightness difference of the ground disturbed by rocket blast at the MER sites is similar to the brightness difference seen in the MPL candidate image, again adjusted for the difference in illumination and viewing angles. These consistencies lend credibility to this tentative identification.

If these features really are related to the MPL landing, what can we surmise about that landing from the image? First, we can tell that MPL's descent proceeded more-or-less successfully through parachute jettison and terminal rocket firing. The relative location of the candidate parachute and lander is consistent with the slight west-to-east wind seen in dust cloud motion in the area around the date of landing. The blast-disturbed area is consistent with the engines continuing to fire until the vehicle was close to the ground. How close is not known. The larger MER retrorockets fired at about 100 m altitude and continued firing until the engines were about 20-25 m above the surface; the candidate MPL disturbance is roughly the same size, but whether this means the engines were firing as close to the ground as the MER rockets cannot be determined. These interpretations are consistent with the proposed MPL mode of failure: the engines fired at the correct time and altitude and continued firing until the flight software checked to see if an electronic message indicated that the landing leg contact switch had been set. Since the initial leg deployment several kilometers above the surface apparently induced sufficient motion to trigger this message, the software stopped the engines as soon as the check was made, about 28-30 seconds into the 36-40 second burn. MPL was probably at an altitude of about 40 m, from which it freely fell. This is equivalent to a fall on Earth from a height of about 40 feet. The observation of a single, small "dot" at the center of the disturbed location would indicate that the vehicle remained more-or-less intact after its fall.

What is important about having a candidate for the Mars Polar Lander site? It gives the MOC team a place to target for a closer look, using the compensated pitch and roll technique known as "cPROTO." Examples of cPROTO images and a description of this capability, developed by the MGS team in 2003 and 2004, were discussed in a MOC release on 27 September 2004. Without a candidate for targeting a cPROTO image, it would take more than 60 Earth years to cover the entire Mars Polar Lander landing ellipse with cPROTO images, because the region spends the better part of each Mars year covered with carbon dioxide frost, part of each winter is spent in darkness, and, because of several uncertainties involved with the technique, it often takes two, three, or more tries before a cPROTO image hits a specific target. Now that a candidate site for Mars Polar Lander has been identified, we have a cPROTO target, which may permit us to obtain an image of about 0.5 meters per pixel (allowing objects approximately 1.5-2.5 meters in size to be resolved) during southern summer this year. At the present time (May 2005), the landing site is just beginning to lose its cover of seasonal carbon dioxide frost.

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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 Astronautics, from facilities in Pasadena, California, and Denver, Colorado.

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