Hours before NASA's Opportunity rover reaches Mars,
engineers have found a way to communicate reliably with its
twin, Spirit.
Engineers are working to get Spirit's computer out of a cycle
of rebooting many times a day. Spirit's responses to commands
sent Saturday morning confirmed a theory the problem is related
to the rover's two "flash" memories or software controlling
those memories.
"The rover has been upgraded from critical to serious," said
Mars Exploration Rover Project Manager Peter Theisinger at
NASA's Jet Propulsion Laboratory, Pasadena, Calif. He predicted
significant work is still ahead for restoring Spirit.
Opportunity is on course for landing in the Meridiani Planum
region of Mars. That point was selected months ago. Mission
managers chose not to use an option for making a final
adjustment to the flight path. " We managed to target
Opportunity to the desired atmospheric entry point, which will
bring us to the target landing site, in only three maneuvers,"
said JPL's Dr. Louis D'Amario, navigation team chief for the
rovers.
Opportunity will reach Mars at 12:05 a.m. Sunday EST. From the
time Opportunity hits the top of Mars' atmosphere at about 5.4
kilometers per second (12,000 miles per hour) to the time it
hits the surface six minutes later, then bounces, the rover
will be going through the riskiest part of its mission. Based
on analysis of Spirit's descent and on weather reports about
the atmosphere above Meridiani Planum, mission controllers have
decided to program Opportunity to open its parachute slightly
earlier than Spirit did.
Mars is more than 10 percent farther from Earth than it was
when Spirit landed. That means radio signals from Opportunity,
during its descent and after rolling to a stop, have a lower
chance of being detected on Earth. About four hours after the
landing, news from the spacecraft may arrive by relay from
NASA's Mars Odyssey orbiter. However, that will depend on
Opportunity finishing critical activities, such as opening the
lander petals and unfolding the rover's solar panels, before
Odyssey flies overhead.
Spirit has 256 megabytes of flash memory, a type commonly used
on gear such as digital cameras for holding data even when the
power is off. Engineers confirmed Spirit's recent symptoms are
related to the flash memory, when they commanded the rover to
boot up and use random-access memory instead of flash memory.
The rover obeyed commands about communicating and going into
sleep mode. Spirit communicated successfully at 120 bits per
second for nearly an hour.
"We have a vehicle that is stable in power and thermal, and we
have a working hypothesis we have confirmed," Theisinger said.
By commanding Spirit into a mode that avoids using flash
memory, engineers plan to get it to communicate at a higher
data rate, diagnose the cause of the problem and develop ways
to restore as much function as possible.
The work on restoring Spirit is not expected to slow the steps
in getting Opportunity ready to roll off its lander platform.
For Spirit, those steps took 12 days. The rovers' main task is
to explore landing sites for evidence in the rocks and soil to
determine if past environments were watery and possibly
suitable for sustaining life.
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. Images and additional
information about the project are available from JPL at:
http://marsrovers.jpl.nasa.gov
Information is also available from Cornell University, Ithaca,
N.Y., at:
http://athena.cornell.edu
