NASA’S robotic Mars geologist, Spirit, embodying
America’s enthusiasm for exploration, must run a grueling
gantlet of challenges before it can start examining the red
planet. Spirit’s twin Mars Exploration Rover, Opportunity,
also faces tough Martian challenges.

“The risk is real, but so is the potential reward of using
these advanced rovers to improve our understanding of how
planets work,” said Dr. Ed Weiler, associate administrator
for space science at NASA Headquarters, Washington.

Spirit is the first of two golf-cart-sized rovers headed for
Mars landings in January. The rovers will seek evidence about
whether the environment in two regions might once have been
capable of supporting life. Engineers at NASA’s Jet
Propulsion Laboratory (JPL), Pasadena, Calif., have navigated
Spirit to arrive during the evening of Jan. 3, 2004, in the
Eastern time zone.

Spirit will land near the center of Gusev Crater, which may
have once held a lake. Three weeks later, Opportunity will
reach the Meridiani Planum, a region containing exposed
deposits of a mineral that usually forms under watery

“We’ve cleared two of the big hurdles, building both
spacecraft and launching them,” said JPL’s Peter Theisinger,
project manager for the Mars Exploration Rover Project. “Now
we’re coming up on a third, getting them safely onto the
ground,” he said.

Since their launches on June 10 and July 7 respectively, each
rover has been flying tucked inside a folded-up lander. The
lander is wrapped in deflated airbags, cocooned within a
protective aeroshell and attached to a cruise stage that
provides solar panels, antennas and steering for the
approximately seven month journey.

Spirit will cast off its cruise stage 15 minutes before
hitting the top of the Martian atmosphere at 5,400 meters per
second (12,000 miles per hour). Atmospheric friction during
the next four minutes will heat part of the aeroshell to
about 1,400 C (2,600 F) and slow the descent to about 430
meters per second (960 mph). Less than two minutes before
landing, the spacecraft will open its parachute.

Twenty seconds later, it will jettison the bottom half of its
aeroshell, exposing the lander. The top half of the shell,
still riding the parachute, will lower the lander on a
tether. In the final six seconds, airbags will inflate, retro
rockets on the upper shell will fire, and the tether will be
cut about 15 meters (49 feet) above the ground.

Several bounces and rolls could take the airbag-cushioned
lander about a kilometer (0.6 mile) from where it initially
lands. If any of the initial few bounces hits a big rock
that’s too sharp, or if the spacecraft doesn’t complete each
task at just the right point during the descent, the mission
could be over. More than half of all the missions launched to
Mars have failed.

JPL Director Dr. Charles Elachi said, “We have done
everything we know that could be humanly done to ensure
success. We have conducted more testing and external reviews
for the Mars Exploration Rovers than for any previous
interplanetary mission.”

Landing safely is the first step for three months of Mars
exploration by each rover. Before rolling off its lander,
each rover will spend a week or more unfolding itself, rising
to full height, and scanning surroundings. Spirit and
Opportunity each weigh about 17 times as much as the
Sojourner rover of the 1997 Mars Pathfinder mission. They are
big enough to roll right over obstacles nearly as tall as

“Think of Spirit and Opportunity as robotic field
geologists,” said Dr. Steve Squyres of Cornell University,
Ithaca, N.Y., principal investigator for the rovers’
identical sets of science instruments. “They look around with
a stereo, color camera and with an infrared instrument that
can classify rock types from a distance. They go to the rocks
that seem most interesting. When they get to one, they reach
out with a robotic arm that has a handful of tools, a
microscope, two instruments for identifying what the rock is
made of, and a grinder for getting to a fresh, unweathered
surface inside the rock,” he said.

JPL, a division of the California Institute of Technology in
Pasadena, manages the Mars Exploration Rover project for
NASA’s Office of Space Science, Washington. For information
about the Mars Exploration Rover project on the Internet,

For Cornell University’s Web site about the science payload,