mpl_canyonThe finger-pointing has begun between NASA and Lockheed Martin Astronautics over the ill-fated Mars Polar Lander. The loss of a second spacecraft within three months seems to be stressing the relationship of the once-cozy marriage between the space agency and the aerospace giant.
Scientists inside Lockheed Martin made the first accusations, quoted in newspaper reports, accusing NASA of covering up knowledge that a huge canyon lay at the northern end of the landing site. The scientists at the company, which built the spacecraft and issued its commands, said that the craft most likely set down in the canyon and tumbled down steep slopes that it was not designed to land on.
Such a mishap would appear to absolve the company from blame for any faulty spacecraft design, but a Lockheed Martin spokeswoman said there is still no consensus about the fate of the craft, and any of 1,001 problems are still possible causes.
Scientists at NASA have fired back, though, saying that the so-called "canyon" is nothing more than a very gradual depression. Still, operators at mission control were alarmed when they first noticed -- just hours before the craft was to set down -- that the lander appeared to be heading for the broad dip, said David Smith of NASA's Goddard Space Center.
Smith, who leads the team that gathers topographical information from the Mars Global Surveyor was analyzing maps of the landing site at the Jet Propulsion Laboratory's mission control as the Polar Lander closed in on the Red Planet last month. Engineers were giving Smith the latest tracking data that from the spacecraft. He and his colleague, Maria Zuber, a geophysist at the Massachusetts Institute of Technology, were analyzing maps of the landing site as the craft approached the atmosphere and its target became more and more precise.
"To our surprise, when they gave us the new coordinates, it is true that it looked very much like a gully there," Smith said. "But when we sat and actually looked at the contours and the amount of depression around this sort of trough, we were talking about less than a few hundred meters (a few hundred yards) and the horizontal scale was many many kilometers (several miles)."
Such a gradual slope is well within the scope of surfaces the lander was designed to accommodate, Smith said.
"Canyon is a bad word because it gives the impression that you've got deep near-vertical sides and a flat bottom and so on," Smith said. "This -- if you were walking on it you may barely realize the slope."
The team was initially less worried about a crash than how the depression might interfere with communications. Controllers were concerned that the area might be sufficiently deep that it would stop signals from getting out to Earth or to a spacecraft, Smith said, but a further look at the topography showed that that there was no cause for worry.
"This thing probably has a horizon of 5 or 10 degrees, its not a lot," Smith said.
Engineers at NASA's Jet Propulsion Laboratory now think the Mars Polar Lander came down near 76.5 degrees south latitude and 165.2 degrees east. That region is lies in a low basin, seen here in dark maroon just above and to the right of the blue spot in this map. The blue spot is a crater that controllers at JPL were trying to avoid. The color scale at the right shows the elevation in meters above an average "zero" elevation. The dark shadowing was applied to emphasize the existence of a gradual depression. The map was produced with data from the Mars Orbiter Laser Altimeter aboard the Mars Global Surveyor.
Smith said he understands how somebody might misread the maps and jump to the conclusion that the low valley is a canyon. "There is a sort of vertical exaggeration associated with the colors" on the maps, he said.
A close look at the topography reveals the very gradual slopes of the region, he said.
This contour map shows the area where the Mars Polar Lander would be if it did land on the surface. The closely-spaced vertical lines near the center (above the dark spotty area) show the change in elevation associated with the shallow surface depression. The left line traces an elevation of 2,000 meters (6,700 feet) and the right-hand line indicates 2,400 meters (8,000 feet). The two lines are separated by several kilometers.
"There is a kind of a gully there, but I have to point out, we're only talking about a few hundred meters over a handful of kilometers," Smith said.
During the past month since the lander disappeared, the Mars Global Surveyor has collected more information about the target landing site, and there is still nothing that shows the controversial area was particularly dangerous, said Joseph Boyce, the Program Scientists for the Mars Polar Lander.
"We knew what was there," he said. "The assessment was, and still is, that there were no unacceptable risks in the area, including valleys and slopes and the rest of it. We didn't see anything in there that should have disrupted the lander -- at a scale that we could see."
"Now once you get down below those resolutions you can always hit a rock or you can always hit a ledge or a crack that's a meter wide or something, just like you can go and stub your toe on a sidewalk." Boyce said.
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