[meteorite-list] Looming Martian Winter Threatens Spirit Rover

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 25 Jan 2010 16:22:52 -0800 (PST)
Message-ID: <201001260022.o0Q0MqhK017096_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n1001/24spirit/

Looming Martian winter threatens Spirit rover
BY CRAIG COVAULT
SPACEFLIGHT NOW
January 24, 2010

NASA Headquarters managers face an imminent decision to formally halt
further extraction maneuvers by the Mars rover Spirit to conserve
electricity and to save the rover's life while it remains stuck in a
sand trap 61 million miles from Earth.

After six years of roving, Spirit's continued survival on Mars is now an
open question as this marvel of robotics, human affection and ingenuity
now risks freezing to death in the weeks ahead.

"Right now there is no assurance we will get through the winter because
power predictions are looking quite challenging for the rover sitting at
its current attitude," says John Callas, rover project manager at the
Jet Propulsion Laboratory, Pasadena Calif.

"The reality is we are running out of time," Callas tells Spaceflight Now.

"There is less and less power for the vehicle every day that goes by
because we are getting closer and closer to low winter Sun angles,"
Callas says. Without that power we can not run the heaters positioned in
the rover's body beside critical electronics.

"We are very close to saying that we have tried everything that we could
have possibly tried to drive out of the sand trap," says rover principal
investigator Steve Squyres of Cornell University.

In reality, the issue has changed from whether the rover can be freed
ever to rove again. The issue now is whether it can generate enough
electric power while stuck to keep from freezing to death in the coming
months -- an increasingly dire situation.

This critical juncture in the historic dual Mars Exploration Rover (MER)
mission to Mars will evoke strong emotions and memories among the
hundreds of scientists and engineers who have worked on Spirit and
millions of members of the public worldwide. They have followed the
adventures of the 384-pound robot and its sister Opportunity as if they
were human.

If Spirit does survive, the science strategy for the rover as a fixed
station should provide extremely important additional discoveries.
Spirit can still perform major science that "holds the potential of for
revealing major details about Mars that would add to Spirit's scientific
legacy in a very meaningful and important way," Squyres tells
Spaceflight Now.

It is as if the now-fixed stationary Spirit has just touched down at
another new Mars landing site.

Squyres says these include major new data on whether Mars has a solid or
liquid core and the acquisition of significantly more high resolution
multispectral imagery of the Columbia Hills region of the giant Gusev
crater area. Such data have not been obtained previously because it
simply takes so long to acquire. But Spirit, if it can survive the
coming winter power crisis, is now in a position to obtain such new data.

Months of simulation and analysis at JPL, Lockheed Martin and other NASA
centers and companies could not solve the unsolvable, how to escape the
sand pit with only four rather than six operational wheels. A third
wheel is also in question.

"Spirit has achieved so much and become such a significant vehicle in
the history of Mars exploration we owe it to the rover and to ourselves
that we are satisfied that we did everything we could possibly have done
to get the thing out," says Squyres.

But with the onset of Martian winter, a looming power crisis, and a
worsening wheel capability it was too risky to trade the benefit of a
fixed science lander against trying to drive Spirit out of the bizarre
silica powder that overwhelmed its three left wheels last April.

Ironically, the discovery of this silica is Spirit's greatest scientific
achievement, Squyres tells Spaceflight Now.

That is because for such extensive deposits of silica (90 percent pure
opaline dioxide) there had to have been lengthy and abundant
volcanically-warmed water at the Home Plate location. That cinched
conclusions that the Home Plate site where Spirit is stuck was a
volcanic fumeral not unlike those at Yellowstone or Lassen National
Parks. And some of this water could have been hospitable to Martian life.

Spirit's right front wheel, unable to roll for most of the mission,
complicated any hope of getting out, but the stuck wheel also made the
initial silica discovery. Like a pioneer farmer with a single bottom
plow to bust sod, the wheel dragging behind Spirit acted like that
pioneer's plow, to turn over the bright white silica material under much
darker topsoil.

The bad news was months later Spirit's three left wheels fell through a
camouflaged crust that concealed a pit of the slick powdery substance
that entrapped Spirit. JPL rover drivers would have powered it out of
the trap long ago had it been possible to do so. But both of Spirit's
front and aft right wheels are inoperable now -- and even the right
center may be acting up.

Since Spirit is nearing electrical power limits to maneuver at all, it
is likely virtually all future maneuvers will be devoted to further
improving the attitude of Spirit's top solar array relative to the Sun.

The new objective will be to shift to maneuvers to increase solar array
power to survive the winter in the few days left where Sun angles will
still provide enough power to ensure it can even do that minimal
maneuvering in place.

Until it eventually dies at this spot, this will help Spirit obtain more
electricity to survive nighttime winter temperatures dipping to around
minus 100 degrees F.

Both Spirit and Opportunity have lasted 6 years compared with their
specification lifetime of about 90 days. Extremely complex mechanically,
their robotic mechanisms had a specification travel distance of about
900 feet.

Since landing late January 3, 2004, Pasadena time, Spirit has driven 4.8
miles. Its airbag landing was followed on January 24, 2004 by
Opportunity, which has logged more than 12 miles. They have had
substantially different missions on opposite sides of Mars. Both found
important evidence of lengthily localized episodes of surface or
underground water capable of sustaining life during early Martian
history. And Opportunity continues to race its own lifetime (at a
turtle's pace), toward massive Endeavour crater still more than a year
of roving ahead.

Spirit has had a much harder "blue collar" but amazing life even for
geology-tuned Mars rover that built upon the airbag landing system
pioneered in 1997 by the Mars Pathfinder lander and rover Sojourner.

During landing, the Martian atmospheric density was somewhat less than
programmed into Spirit's computer. This pushed its descent rocket firing
to the latter part of the flight envelope, meaning the 10-foot-tall
airbag system with Spirit inside descended far closer to the surface --
within a few feet of crashing before being yanked by its lanyard system
to a neutral velocity state for release for the airbags to work.

Two weeks after landing and finishing measurements on Adirondack, its
first rock target, Spirit nearly died of a flash memory problem.

It was solved in the end by JPL software engineer Glenn Reeves who
during the software design had the foresight to include a INIT_CRIPPLED
command in the system that fixed the flash memory problem after four
days of no contact between Spirit and Earth.

It saved the mission from software failure. But Spirit was still in
scientific trouble because the expected riverbed or lakebed deposits
were totally buried under uninteresting lava -- a heartbreaking find.

The rover that was ostensibly specified for only about 900 feet of
travel was then quickly dispatched on a scientific Hail Mary. She was
aimed across difficult volcanic rubble toward the Columbia Hills two
miles distant in search of water evidence on higher ground. The gamble
worked and Spirit found increasing water evidence the higher it went.

Spirit climbed her mountain, Husband Hill, reaching the top in late
October 2005, dragging the frozen wheel behind it. It then carefully
descended the mountain's backside to explore the mysterious baseball
diamond-sized feature named "Home Plate." It was the extinct volcanic
fumeral where she made her most important discovery, the silica deposits
indicative of abundant volcanic-related water.

Over the last several weeks, the rover team, using techniques developed
by heavy work at JPL using two ground test rovers, have undertaken a
systematic set of maneuvers on Mars in an attempt to drive out of the
sand trap. None of it has worked, just like it never worked during all
that grueling simulation work at JPL. But nobody can say it was not for
a lack of trying both at JPL and on Mars.

Since mid-January, Callas says they have tried driving backwards, south
out of the trap instead of forward. That too provided minimal progress,
except for one very significant benefit -- the back wheels tended to
climb, elevating the solar array deck more directly north.

This is a critical finding because the Sun will be low on the northern
Martian horizon during the most dangerous part of winter. Any array
elevation gain pointed north is more electricity in the bank for the
winter.

The climbing motion, however, means that the team may be able to park
the rover in a somewhat better attitude for solar array power generation.

"The other thing we might try once in optimum position is activate the
right front wheel just to steer it back and fourth to literally try and
grind it into the ground. That will tend to dip the right front side of
Spirit and also pointing the deck more toward the north," Callas tells
Spaceflight Now.

The right front wheel will not rotate but it can be steered, meaning
this technique could burrow it deeper elevating the solar array deck.

>From an electricity standpoint, the objective is to generate at least
160 watt hours per day during the worst of the winter on Mars, that will
be during May in Earth terms. Spirit is currently running on 220 watt
hours per day but that is decreasing on a daily basis.

"We would like to have at least 160 watt hours available per day. But
the energy predictions now are below that. That is why we want to get as
much northern tilt as we can," says Callas.

"Those predictions mean the rover will get colder and colder. If it gets
too cold, it will damage critical electronics inside the warm
electronics box of the rover," he says. "We would be running a daily
energy deficit," that would likely eventually freeze Spirit.

Hoping Spirit's demise can be at least postponed, a significant fixed
rover science strategy has been built involving geophysics measurements,
the monitoring of atmospheric and surface changes and geology and
geochemistry measurements using the imaging systems and Cornell Athena
science package spectrometers.

Individually they would involve:

o Geophysics: "The geophysics research is the one we are the most
excited about," says Squyres. "By doing two-way X-band tracking of the
rover's position on Mars when stationary, the team can determine the
position of the rotational pole of Mars to extremely high accuracy," he
says. "What that will do is very accurately characterize any wobbles in
the planet's spin state related to whether Mars has a liquid or solid
core,"

Most researchers believe the core is solid or mostly solid because of
the lack of a strong magnetic field, but there is still debate on that.
The rover geophysics measurements could settle the liquid versus solid
Martian core issue.

o Atmospheric and surface changes: Wind blown material transport plays
the primary role in sculpturing Martian terrain. The Cornell Athena
science payload Pancam and Mini-TES thermal emission spectrometer
mounted on the Pancam mast will continue daily monitoring of this
phenomenon as has been done throughout the flight. They will also
continue to monitor opacity and the appearance of clouds and other more
dramatic features like dust storms and dust devils.

That monitoring will continue, but be supplemented for more unique
investigations like parking the microscopic imager over a single spot to
observe how dust grains move. Earlier runs have shown that some Martian
sand grains actually hop from place to place. "Albedo Pans" which are
full 360-degree Pancam images will be continued to show atmospheric
conditions in Gusev crater on a regional basis.

Another fixed rover investigation will be important to understanding
climate change on Mars. It will use the Cornell/Max Planck Institute
Alpha Particle X-ray Spectrometer to measure the argon mixing ratio with
carbon dioxide in the Martian atmosphere.

"That ratio changes seasonally because C02 condenses out at the poles,
but argon does not. So that argon/C02 ratio will change and can be
measured with time based on measurements of the carbon dioxide at the
equator where Spirit is. It will be a technique to quantify the mixing
rate of Martian atmospheric gases," Squyres says.

o Geology and geochemistry: The Pancam and Mini-TES will also be used
for long data takes aimed at the hills around where Spirit sits. There
are several especially interesting volcanic features in the area.

"We can effectively double the resolution of the Pancam by imaging a
target then moving the instrument slightly so the computer can carry out
a technique called high path filtering," says Squyres. It is a time
consuming operation but can result in dramatic imagery. That will be
done more often to study rock strata in nearby hills. In addition
Pancam's extreme high resolution multispectral capabilities will used
more often than time allowed in the past.

"We will now be able to take the time needed to get extremely high
resolution mineralogy data on the features around us, something we have
not had time to do earlier," says Squyres.

Closer to the rover "we have still got a lot of really interesting
churned up soil around us. The reason we got stuck here is that this is
not normal Martian soil. It is a really interesting mix of normal
Martian soil but combined with high purity silica plus ferric sulfates.
How all that came about is a mystery that Spirit will now have more time
to solve. We have also found there is very complex layering to this
stuff related to its water transport properties," says Squyres.

To study it well requires the Mossbauer spectrometer. But the rover has
been operating far longer than planned, given the unit's cobalt 57
atomic source to detect the molecules and atoms it is looking for in the
soil. This is because the atomic half life of the cobalt is only 272
days, a duration exceeded several times already.

The spectrometer still works. It just requires many days of placement on
rock and soil targets to acquire the data it is looking for. With Spirit
now a fixed science station, that Mossbauer capability will be used more
often to unravel the complex geologic and water history of the site that
Spirit has surrendered its roving life to solve.
Received on Mon 25 Jan 2010 07:22:52 PM PST