NASA / JPL-Caltech
Rover team members Matt Van Kirk, Julie Townsend and Tam Nguyen set up a test
rover and sandbox at NASA's Jet Propulsion Laboratory to rehearse maneuvers
aimed at extracting a Mars rover from a similar sand trap on the Red Planet.
As NASA's Spirit rover marks its 2,000th workday on Mars, team members back on Earth are conducting the final rehearsals for a long-range operation they hope will free the plucky robot from its Red Planet sand trap.
The rover team keeps track of Spirit's timeline in Martian days, or "sols," which are slightly longer than Earth days. The result is that even though the rover passed the 2,000-day milestone a few weeks ago, as measured on Earth, the Sol 2000 mark didn't come around until Tuesday.
"We had a little celebration," John Callas, project manager for the Mars rover missions at NASA's Jet Propulsion Laboratory, told me. "We had a Sol 2000 cake."
This morning, yawning as I woke
From another Troy-trapped night
I watched Sol rise for the 2,000th time
And wondered: "Was it all a dream?" ...
The reference to the "Troy-trapped night" recognizes that Spirit is currently mired in a sandpit nicknamed Troy, facing a trial worthy of the Divine Comedy. The poetic parallel is doubly apt - considering that Dante posted half-buried villains around Hell's central pit in his "Inferno," and that NASA's Opportunity rover escaped from being buried in a Martian sand dune called "Purgatory" more than four years ago.
It took weeks for NASA to get Opportunity unstuck back then - and if anything, Spirit's situation is even stickier. The six-wheeled rover rolled into a sloping patch of loose soil more than three months ago, and its downhill wheels have spun deeply into the stuff. But wait ... there's more: A rock appears to be sticking up toward Spirit's underbelly, and one of the rover's wheels doesn't work.
To simulate Spirit's predicament, rover team members set up a sandbox at the Jet Propulsion Laboratory and tried out a variety of maneuvers, using a test rover that's a clone of Spirit and Opportunity. The maneuvers included many of the tricks you'd use to free your car from a snowdrift, ranging from plowing ahead powerfully to backing out slowly.
During a series of one-day and two-day tests, engineers determined that the best escape strategy was to cycle through all those maneuvers. But how to begin? JPL's Callas said that's the last big choice facing the rover team.
"It comes down to whether we go forward initially, or go backward initially," he told me. Eventually, mission managers want Spirit to go forward. But the rover generally does a better job rolling backward, because it can pull its locked wheel behind rather than having to push it ahead.
To gain more insight into the forward vs. backward question, the team is planning a couple of additional kinds of test drives: One experiment calls for maneuvering a reduced-weight rover (known as SSTB-Lite) through the sandbox, to see how much difference Mars' weaker gravity might make. The team also want to drive both of the test rovers through a bed of crushed aggregate, just to see how Spirit would be affected if the soil isn't as soft as the simulated Mars dirt at JPL.
"The soil we're testing it in is the worst-case scenario," Callas explained. "We think it's better on Mars than it is on Earth."
Once the rescue plan is fully in place, mission managers plan to conduct a weeklong dress rehearsal and see how things turn out. The upshot is that the actual command sequences may not be radioed up to Spirit until late September or early October, Callas said.
NASA / JPL-Caltech
|A picture sent back by Spirit on Sol 1984 (Aug. 2) shows the rover's shadow on Martian terrain. Click on the image for a QuickTime 360-degree view from Unmanned Spaceflight.
Fortunately, Martian winds have swept the dust off Spirit's power-generating solar arrays several times, which has helped keep the rover's energy levels high. There's no need to rush toward a winter haven, as team members had feared when Spirit got stuck.
"She could ride out the winter where she is right now," said Callas, using the feminine pronoun to refer to the rover. "There's no problem."
If Spirit has to stay stuck where it is, that won't necessarily end the odyssey. And when Spirit finally gives up the ghost, the rover team will be able to look back with pride on a years-long mission that was originally scheduled to last just 90 Martian days. But it's way too early to write the obituary: There's still a good chance that Spirit will rise out of the mire and move on to its next scientific paradise.
Although he's wary about "counting our rovers before they hatch," Callas has his eye on the duration record for Mars surface operations, set by the Viking 1 lander (1976-1982). "We want to beat that record," he said.
He figures that will happen on April 29, 2010 - which translates to Sol 2247.
To keep up with the countdown, check out NASA's "Free Spirit" Web page as well as the Mars rovers' Twitter updates. And don't forget our own archive on Mars missions, titled "Return to the Red Planet."
Update for 8:40 p.m. ET Aug. 19: I revised and added to this item after hearing back from JPL's John Callas.
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