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| |  | | | | Latest on the Mars Rovers
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08.04.04
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NASA's Spirit rover has climbed higher into rocky hills on Mars,
and its twin, Opportunity, has descended deeper into a crater,
but both rovers, for the time being, are operating with some
restrictions while team members diagnose unexpected behavior.
Image above: A rock outcrop with a view of the surrounding landscape beckons NASA's Mars Exploration Rover Spirit. This view, taken on July 29, 2004, is a mosaic of images taken by the rover's navigation camera near the top of the "West Spur" portion of the "Columbia Hills." Directly ahead are rock outcrops that scientists will examine for clues that might indicate the presence of water in the past. In the upper right-hand corner is the so-called "sea of basalt," consisting of lava flows that lapped onto the flanks of the hills. + Click for full image Image Credit: NASA/JPL.
Both rovers have successfully operated for more than double the
span of their three-month primary missions. They have been
conducting bonus science in extended missions since April.
While Spirit was executing commands on Aug. 1, a semiconductor
component failed to power on as intended. The component, a
programmable gate array, directly affects usability of the
rover's three spectrometer instruments. Subsequent commands for
using the miniature thermal emission spectrometer in that day's
sequence resulted in repeated error messages.
Engineers on the Mars Exploration Rover team at NASA's Jet
Propulsion Laboratory, Pasadena, Calif., have determined the
most likely cause is a timing issue of one instruction reaching
the gate array microseconds before another that was intended to
precede it. If that diagnosis is confirmed, a repeat could be
avoided by inserting a delay between commands that might
reproduce the problem, engineers expect. Until then, the rover
science team's daily choices for how to use Spirit do not
include using the miniature thermal emission spectrometer, the
Moessbauer spectrometer or the alpha particle X-ray
spectrometer.
"While we're being very cautious in how we operate today and
tomorrow, we expect to verify the problem and resolve this issue
with a relatively easy workaround," said JPL's Jim Erickson,
project manager for the twin rovers.
Spirit has driven to a bedrock exposure near the top of a spur
of the "Columbia Hills." The location sits about nine meters (30
feet) above a plain that the rover crossed for months to get
from its landing site to the hills. Planners intend for Spirit
to spend more than a week at this site, inspecting the rock
exposure, dubbed "Clovis," and recording the panoramic scene
from this viewpoint.
Halfway around Mars, Opportunity has driven about 20 meters (66
feet) into "Endurance Crater," examining increasingly older
layers of bedrock as it advances. If assessments of
traversability continue giving positive indications, the rover
team plans next to send Opportunity counterclockwise across the
inner slope of the crater to study possible targets of dune
tendrils, boulders and the base of a cliff.
Four times in the past two weeks, Opportunity has sent error
messages while successfully taking pictures with its microscopic
imager. One theory for the cause is degradation of flexible
cabling that runs down the rover's robotic arm to the
instrument. As a precaution while undertaking further analysis,
the rover team is treating use of the arm as a consumable
resource, with cable wear each time the arm is moved decreasing
the possible number of future microscopic images.
"We are being very conservative about this because we certainly
don't want to do anything to jeopardize the instruments," said
Dr. Ken Herkenhoff of the U.S. Geological Survey Astrogeology
Team, Flagstaff, Ariz., lead scientist for both rovers'
microscopic imagers. "We are running more diagnostics that we
hope will identify the problem. There are potential explanations
that would mean we do not have to treat arm use as a
consumable."
Erickson said, "We will no doubt have more issues with them in
the future. We'll do everything we can to milk the most value
out of them while they are usable, but they won't last forever."
JPL, a division of the California Institute of Technology
in Pasadena, manages the Mars Exploration Rover project for
NASA's Science Mission Directorate, Washington. Additional
information about the project is available from JPL at
http://marsrovers.jpl.nasa.gov and from Cornell University,
Ithaca, N.Y., at http://athena.cornell.edu.
Guy Webster
NASA's Jet Propulsion Laboratory
Donald Savage
NASA Headquarters, Washington
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