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ZL2VAL > ROVERS 29.05.04 13:55l 135 Lines 6414 Bytes #999 (0) @ WW
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Subj: Press release, 26th May
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From: ZL2VAL@ZL2AB.#46.NZL.OC
To : ROVERS@WW
NEWS RELEASE: 2004-132
May 26, 2004
Mars Exploration Rover Mission Status
NASA's Mars Exploration Rover Opportunity is beginning on Thursday what
controllers expect to be frequent use of an overnight "deep sleep" mode
to conserve energy.
Opportunity has managed only one to two hours of activity on many recent
days while it has been examining a stadium-sized impact crater from
vantage points around the rim. Shutting down more completely overnight
will conserve enough battery charge to add several hours of science
operations during the day, according to Jim Erickson, Mars Exploration
Rover deputy project manager at NASA's Jet Propulsion Laboratory,
Pasadena, Calif.
There is a calculated tradeoff: an increased risk that, without an
overnight heater running, one of the six scientific instruments might be
disabled by the cold. The susceptible instrument is Opportunity's
miniature thermal emission spectrometer, called the Mini-TES. It makes
infrared observations used for identifying minerals from afar to help
the science team decide where to send the rover. Its observations also
provide close-up evaluation of rock and soil targets, and thermal
information about surface materials and the atmosphere. "The Mini-TES
gives us insight into the minerals in rocks and the role of liquid water
in their formation, so this choice is a carefully considered decision to
weigh the risk of losing this capability against the benefit of
continuing and increasing Opportunity's ability to continue to do
science and exploration in the long run," said Dr. Jim Garvin, lead
scientist for Mars and lunar exploration at NASA Headquarters,
Washington, D.C.
Both Opportunity and its twin rover, Spirit, have already provided
several weeks of bonus operations after successfully completing their
primary missions: three months of examining geological evidence about
past environments at their landing sites.
As the Mars' southern-hemisphere winter advances and dust accumulates on
the solar panels, the amount of electricity the rovers can generate is
decreasing. The decline is more serious for Opportunity because the
robotic arm of that rover has a heater with a malfunctioning switch. The
switch cannot be turned off. A properly functioning thermostat turns the
heater off during the day, but the heater stays on overnight even when
it's not needed. The amount of energy wasted was not enough to hinder
Opportunity from succeeding in its primary mission, but is now sapping
about one-third of the rover's diminished amount of solar-generated
electricity.
"Deep sleep gives us a way to turn that heater off overnight," said
Opportunity Mission Manager Matt Wallace of JPL. The capability to do so
results from a software upgrade transmitted to both rovers in April. The
first use of deep sleep, on Opportunity on May 6, verified its benefit
to the useful power supply.
Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal
investigator for the rovers' science instruments, said, "Deep sleep is
going to buy us back a huge amount of capability to drive farther, take
more pictures, use the arm more." The deep sleep mode turns off a heater
for the miniature thermal emission spectrometer as well as the
troublesome heater in the arm. The spectrometer's heater uses less power
but provides important protection. Scientists and engineers decided not
to use deep sleep again after May 6 until the spectrometer had completed
high-priority observations from two different overlook points of the
crater informally named "Endurance." Those observations were completed
Tuesday.
Tests on Earth indicate the spectrometer's beam splitter, a disc of
potassium bromide salt about the size of a four-coin stack of quarters,
would become ruined somewhere in the temperature range of minus 50 to
minus 60 degrees Celsius (minus 58 to minus 76 degrees Fahrenheit).
Dr. Phil Christensen of Arizona State University, Tempe, lead scientist
for the instrument, said, "The thermal models predict that with deep
sleep, we'll go to about minus 48 Celsius. That has me concerned because
it's getting close." The May 6 deep sleep did no damage, but next time
the temperature could go lower, and it probably will drop lower during
deep sleep later in the martian winter. Christensen concurs with the
decision to take that risk in order for the rover to have adequate power
for its other activities. "We always knew that as dust built up and we
ran low on power, eventually there would come a time when we couldn't
use the Mini-TES heater," he said. "We're getting to that point sooner
because of the stuck heater on the arm."
Meanwhile, engineers and scientists are assessing how well Opportunity
would be able to climb out of Endurance Crater. The assessment will aid
in deciding whether to send the rover into the crater for up-close
examination of rock layers there. Opportunity may complete a circuit
around the crater's rim by mid-June and be ready for a decision about
entering the crater.
Spirit, halfway around Mars, resumed normal operations May 23 after
engineers diagnosed a software glitch that halted the rover's activities
on May 21. The symptoms resembled a problem seen about a week earlier,
where again the computer encountered a conflict between two onboard
tasks. However the errors are understood and the two incidents are
unrelated. If they recur, neither pose a threat to the rovers' health.
Spirit is now less than 700 meters (0.4 miles) from the base of the
"Columbia Hills," having traveled more than 2.5 kilometers (1.5 miles)
since landing. Controllers are optimistic that Spirit will reach the
base of the hills by mid-June.
JPL, a division of the California Institute of Technology, manages the
Mars Exploration Rover project for NASA's Office of Space Science,
Washington, D.C. Additional information about the project is available
from JPL at http://mars.jpl.nasa.gov/mer and from Cornell University at
http://athena.cornell.edu .
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73 de Alan, (Sysop ZL2AB).
AX25:ZL2VAL@ZL2AB.#46.NZL.OC
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Message timed: 22:51 on 2004-May-29 (NZT)
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Points to ponder
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Rural wisdom
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When you wallow with pigs, expect to get dirty.
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