Spirit Is One Of Two
Stop us if this sounds
familiar. Come Saturday morning, if all goes according to plan, a
spacecraft from Earth will speed through the Martian atmosphere in
hopes of deploying its rockets, parachutes and airbags all in
sequence and touching down on the Red Planet. Shortly after landing
the rover vehicle will supposedly deploy and start talking to
another satellite from Earth orbiting overhead.
It's the same script European Space Agency controllers hoped
would unfold without incident in the Beagle 2 mission. So far,
Beagle has failed to bark. European officials now hope that its
mothership, Mars Express, will be able to talk with Beagle once its
in an orbit low enough to facilitate communications.
No, in this case, we're talking about the first of two American
probes to land on Mars this month. Spirit and Opportunity will
explore different sides of the Red Planet for signs of life.
They'll look in areas where geographic data indicates there was a
pretty darned good chance water once existed.
Floating on parachutes, Spirit will come to within eight seconds
of landing before the golf-cart-sized probe deploys a set of
airbags designed to cushion its impact. "It's not the fall that
kills you. It's what you hit at the end," said Pete Theisinger,
NASA's Mars project manager. He says one sharp or canted rock could
doom Spirit to the afterlife that has swallowed about 20 Mars
probes before it.
"Entering into Mars is always very tricky, as everyone knows,
and we can fail. But we want to learn from those failures, so next
time -- of course, we have another rover coming three weeks later,
so we do have our own next time -- we can learn from the experience
so we can correct any problems," said Polly Estabrook,
telecommunications lead for the entry, descent and landing portions
of the joint Mars Exploration Rover mission.
In addition to acknowledging critical commands with a series of
beeps, Spirit is supposed to have a little chat with the Mars
Global Surveyor which has been plotting the Martian surface since
1997. Spirit is supposed to update Surveyor on the function of its
critical systems about a minute before landing. The transmission
will stop as the signal is blocked by those airbags, which will
allow Spirit to bounce around a bit after landing on the surface.
After that, they hope a second orbiter, Mars Odyssey, will pick up
signs of life from Spirit when it passes overhead a couple of hours
later.
If that doesn't work, the pins-and-needles crew at the JPL lab
in Pasadena (CA) will have to wait until Odyssey makes another
orbit.