Spirit Is Ailing But Still Plodding
Scientists Unsure How Rover's Stint On Mars Will End

By Joel Achenbach
Washington Post Staff Writer
Sunday, April 19, 2009 6:49 PM

The old rover was supposed to work for only 90 days, enough time to 
crawl two-thirds of a mile across the Martian desert. More than five 
years later, Spirit has put five miles on its odometer and is still 
rolling along -- but getting mighty cranky.

The rover, one of two NASA vehicles operating on Mars, has a broken 
right wheel. It has dust on its solar panels. It's operating at about 
30 percent of normal power. Various sensors and software programs 
have gone screwy.

Then, on April 9, Spirit refused to wake up. The rover is designed to 
sleep at night, when there is no sunlight hitting the solar panels. 
But Spirit snoozed right through its wake-up call. It happened three 
times in succession. Finally a backup timer got Spirit up and moving 
again after a 27-hour slumber.

John Callas, project manager for the Mars rovers at the Jet 
Propulsion Laboratory in Pasadena, Calif., said he doesn't have an 
explanation for what ailed Spirit. Nor can he explain why the rover 
repeatedly rebooted itself when engineers at JPL tried to send it 
commands. The engineers found a fix -- they relayed commands via a 
spacecraft that orbits Mars -- but the incidents suggest that Spirit 
is getting erratic. Or maybe just old.

By any measure, Spirit and its sister rover, Opportunity, which is a 
good bit healthier, have been triumphs of the civilian space program. 
Spirit may yet operate for several more years, or it may be on its 
last leg. In any event, it is providing a tutorial on how even the 
most exquisitely designed machines eventually die.

"I don't think anyone can tell you how these rovers will eventually 
end on Mars," Callas said. "Will they gradually degrade until their 
mechanical functionality goes or will they have a catastrophic end, 
where something inside the rover breaks?"

When the rovers were designed, the presumption was that dust would 
blanket the solar panels within a few months of being on Mars and 
that the rovers would grind to a halt. Martian winds blew to the 
rescue, cleaning the panels periodically and letting the rovers 
extend their missions for many years.

Spirit is now driving around a plateau called Home Plate in a valley 
known as the Inner Basin. Opportunity, on the other side of Mars, has 
left Victoria Crater and is rambling toward a large crater named Endeavour.

Day-to-day life on Mars can be rocky. The temperature can swing 150 
degrees Fahrenheit between night and day because of the thin 
atmosphere. That heating and cooling cycle puts stress on metal.

"Metal parts and glass parts expand and contract as the temperature 
changes," explains John Casani, who has worked on robotic space 
missions for decades at JPL. "If you take a piece of metal and keep 
bending it back and forth, pretty soon it's going to break."

Casani said spacecraft -- the ones that stick to space and don't try 
to land on a planet or some such feat -- exist in a much more stable 
environment. Thus JPL is still getting data from the two Voyager 
craft launched in 1977. According to JPL, the oldest functioning 
spacecraft is Voyager 2 (launched slightly earlier, strangely enough, 
than Voyager 1), which is zipping toward interstellar space far 
beyond Neptune's orbit.

There's not much to see out there, and, in any event, no operational 
camera to see it with, as the spacecraft's batteries, powered by 
radioisotope decay, slowly become enfeebled. But a few instruments 
still function, and scientists have rebuffed efforts to shut down the 
Voyager program.

Spacecraft can also be sent to their deaths. Casani was the project 
manager on Galileo, a probe to the Jupiter system. When Galileo ran 
low on propellant, engineers knew that eventually it would lose 
attitude control and start tumbling. That raised the fear that 
Galileo would crash into one of Jupiter's moons, which potentially 
harbor life, and might be contaminated by stowaway Earth microbes. So 
Casani and his colleagues used the last bit of propellant to send 
Galileo into Jupiter, where it burned up in the thick atmosphere.

When things go wrong, scientists and engineers often have a 
workaround. Sometimes they just get lucky, which is what happened 
when Spirit's right-front wheel broke three years ago.

The other five wheels on the rover were functional and were capable 
of dragging the broken wheel across the surface. The inoperative 
wheel, locked, gouged a trench as it went along. By examining that 
trench, Spirit was able to detect a certain kind of silica that 
offered evidence of ancient hot springs on Mars.

"When life hands you lemons, you make lemonade," Callas said.

So that's not really a broken wheel on Spirit -- it's a scientific instrument.


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