Spirit rover's first drive expected mid-week
Posted: January 10, 2004

The Spirit Mars rover completed its multi-part "stand-up" sequence today, the most complex set of mechanical deployments ever attempted by a robotic spacecraft. Resting on its now unfolded, locked-in-place undercarriage and its six ridged wheels, Spirit should be ready to roll off its lander and onto the martian surface by early Wednesday morning East Coast time to begin its long-await exploration of Gusev Crater.

On any other day, that would be a major milestone. But Wednesday morning also is the day President Bush is expected to announce a new space initiative that would end shuttle operations by 2010 and send astronauts to the moon by the middle of the next decade. The ultimate goal is to expand humanity's exploration of the solar system to Mars.

But for the Spirit team, the rover's short drive off its lander is the central focus and today's completion of the four-part stand-up sequence was a major milestone in its own right.

An artist's concept of Spirit driving off its lander. Credit: NASA/JPL
"After seven months of our rover being folded up in a small lander, today is the day the Spirit rover finished its final unfolding on the surface of Mars," said mission manager Jennifer Trosper. "So it now stands full height and all six wheels are in the final position and ready drive onto the surface So it's a very big day for the Spirit rover."

Chris Voorhees, the engineer credited with designing the ingenious collapsible mechanisms that allowed the rover to be folded up for its trip to Mars, said "it's been a very, very exciting couple of days for the spacecraft team."

"Spirit has spent most of the last seven months crunched up inside of a tetrahedran-shaped lander," he said. "And it is not the shape a lander wants to be in. Over the last couple of days, Spirit has performed what really, I think is reverse robotic origami as it unfolded itself and really turned itself from a lander into a rover."

Early Friday, a screw jack mechanism elevated Spirit's body so its two front wheels, stowed against the front of the craft for launch and landing, could be unfolded. The jack then lowered the body to allow its now extended rocker-bogey linkage suspension to lock in its unfolded position. Today, after verifying the linkages were, in fact, latched securely, engineers released two cables holding the rover's two back wheels in place and then extended them to give the vehicle the desired wheelbase length.

To carry out the stand-up sequence, Voorhees said, 12 explosive pyrotechnic devices had to fire, nine motorized mechanisms had to work and six structural latches had to engage. Along the way, two navigation cameras and numerous sensors had to relay data back to Earth to help engineers verify each step had been successfully completed.

"The only other number is the scores of engineers, designers, analysts, technicians, machinists, not just here at JPL but across the country, that in each their own way allowed Spirit to perform what really is one of the most complex sequence of deployments that's ever been done on a robotic spacecraft," he said.

"Being successful in that sequence, we've left Spirit in a very, very comfortable position. She's asleep right now and she's resting on all sixes, comfortably supporting herself on all six wheels and is ready and raring to go, ready for final releases to get onto the surface."

The next step in the procedure, Trosper said, is to fire cables holding Spirit's two central wheels to the lander and to move the rover's instrument-laden mechanical arm from its launch-and-landing position to its normal roving position. That work will be carried out overnight. Then, overnight Sunday, a final cable will be severed by an explosive cutter.

Engineers originally hoped to drive Spirit straight off its lander. But partially collapsed airbags to the front left and right of the lander could pose problems. Efforts to retract the bags further have not been successful and engineers are concerned that Spirit's left-side solar array could brush up against one as the rover rolls off.

"Some of our engineers spent some time in the test bed today, in our little Mars landing sandbox at JPL, and simulated the rover driving down the front ramp with the airbags in the positions that you see," Trosper said. "What we discovered was, there is a possibility, as the rover drives down the front ramp, that the rear left part of the rover's solar panel could possibly brush against the airbag that's on the left side of the lander. It's not very close, there's a little bit of margin, but it's not really a place we want to be in. We don't necessarily want to get the solar panels caught on the airbags or even to brush against the airbags.

"So we made a decision today that the egress path that we're choosing ... is to turn the rover 120 degrees to facing the right rear of the (lander) and we will drive down the egress aids."

With six independently-steerable wheels, Spirit can literally turn on a dime, rotating as required without moving laterally. The 120-degree "turn-in-place" maneuver is expected overnight Monday and if all goes well, Spirit will roll off its lander a few hours past midnight Tuesday, East Coast time.

"We are very excited about being in the final parts of moving the rover onto the surface of," Trosper said.

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