We've already seen water ice on Mars. NASA's Phoenix lander will reach out and touch it.
- By Charles Petit
- Air & Space magazine, August 2007
(Page 3 of 5)
That’s one reason the Phoenix team spent so much time scouting landing sites. The HiRISE pictures on the table show an essentially flat landscape with a pattern of cracks resembling polygons—in many places, polygons within polygons. It’s the kind of terrain seen in Earth’s polar permafrost, which is saturated with (frozen) water. Smith explained that the pattern, which repeats itself for thousands of miles at the northern latitudes where Phoenix will touch down, results from the expansion and contraction of ice.
There was something else in the pictures. Speckled on the polygons were irregular blobs. They looked pretty, like pebbles with a bluish sheen. Those, Smith explained, were boulders. How big? He compared them to the size of SUVs, like the ones in the parking lot outside. The boulders weren’t packed in; the density was more like a stadium parking lot an hour after the game ends. But there were still enough to pose a danger. “You land on one of those, it’s over,” Smith says.
That’s why, after much discussion, the Phoenix team abandoned their first-choice landing site and looked in other places, including a region north of a collapsed volcano called Alba Patera, the broadest mountain on the planet. One promising site—the current top pick for a landing zone—was dubbed Green Valley because the computerized maps were coded by boulder density, and green has the fewest boulders. By comparing the detailed HiRISE images to wider-angle infrared images taken from another orbiter, the scientists found that rocky terrain appeared warmer in infrared images taken in the morning (a boulder’s surface holds heat longer than sandy soil does). That helped speed up the process of scouting landing sites, since the infrared images cover larger areas of ground. The target landing zone is about 100 by 30 miles—the smallest footprint for which the scientists can accurately predict the spacecraft’s aim.
The name Phoenix comes from the mythical bird that periodically dies in fire, then arises reborn from the ashes. It’s an appropriate metaphor for this mission, some of whose parts originated with another spacecraft that died before reaching its goal. Phoenix’s Surface Stereoscopic Imager and the ovens for soil analysis are close copies of gadgets on the Mars Polar Lander, the spacecraft that crashed in 1999. The loss of that lander, which came during a nightmarish stretch of Mars program failures, led NASA to cancel another mission, the 2001 Mars Surveyor Lander, and stash its hardware, which had already been built, in a cold-storage clean room in Colorado. The basic structure of Phoenix, including its robotic arm, the camera on the arm, and the chemistry lab on the main deck, was recycled from the 2001 lander. That spacecraft was to have touched down near the equator in dusty soil. To accommodate the switch to hard permafrost, the Phoenix team put stronger bearings in the robotic arm joints, added the ice-cutting rasp, and beefed up the drive motors.
Thinking back to the failed 1999 mission, Smith is amazed at how close to the wire that project was run. “We literally did not have enough time in those days to track down the reason for every anomaly we might have found during testing,” he says. Those were the days of “faster, better, cheaper,” a speed-it-up, keep-it-cheap philosophy espoused by NASA’s then-administrator Dan Goldin. The 1990s saw a dramatic increase in the rate of space science missions, but even Goldin admitted later that he pushed the agency’s workers and contractors too hard. When the low-cost Scout program was proposed, NASA agreed that the scope of the missions would also be scaled back; scientists and engineers wouldn’t be forced to do more with less.
Phoenix originated with a phone call in early 2002. Chris McKay, a planetary scientist at NASA’s Ames Research Center in California, called Smith to say, “Hey, let’s do something with the Surveyor lander.” NASA was inviting ideas for the first Scout, due to fly in 2007, and McKay and some of his colleagues at Ames had already been studying, with NASA money, ways to take the hardware from the canceled mission out of storage. “The word on the street was that headquarters would never let the 2001 lander fly,” McKay recalls. “Not just ‘No’ but ‘Hell no.’ ”
So, as a way to keep costs down, the scientists adapted the unused lander for their Scout proposal, with the idea that they’d use the equipment to do a detailed analysis of some patch of Martian soil. There was one small problem. “We didn’t know where to go,” Smith says. “We’d have a shovel, a bunch of instruments, and a pretty good general-purpose lab. We just didn’t know where to land it.”
Like an answer to a prayer, another NASA mission provided a solution. The Mars Odyssey entered orbit around Mars just as the space agency was getting ready to decide which Scout mission proposals to fund for further study. Measurements of hydrogen by Odyssey’s gamma-ray spectrometer strongly suggested that at both polar regions, shallow ice exists at or near the surface. Planners would select a launch window for the 2007 mission that would enable the craft to land on Mars during northern spring and summer, when the days would be longest. And because it included instruments from the 2001 spacecraft, Phoenix would have more capabilities than the 1999 lander, and be more economical. Smith, in essence, was asking for a second chance at the mission that broke his heart.