[meteorite-list] Mars Rover Spirit's Fate Weighed as Options Dwindle

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun, 20 Sep 2009 20:01:39 -0700 (PDT)
Message-ID: <200909210301.n8L31dRh006321_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n0909/18spirit/

Mars rover Spirit's fate weighed as options dwindle
BY CRAIG COVAULT
SPACEFLIGHT NOW
September 18, 2009

The Mars rover Spirit engineering team trying to free the spacecraft
from the sand trap that halted driving five months ago is becoming more
realistic, if not pessimistic, about whether this marvel of the U.S.
space program will ever rove again.

"Tests on Earth simulating Spirit's predicament on Mars have reinforced
understanding that getting Spirit to rove again will be very difficult,"
says a new rover status report issued by the Jet Propulsion Laboratory.

"There is a very real possibility that Spirit may not be able to get
out," says John Callas, rover project manager.

A remarkable image (below) from the Mars Reconnaissance Orbiter (MRO)
looking down from 185 mi. above shows Spirit with its swept wing solar
arrays sitting at the 9 o'clock position beside the circular 260 ft.
dia. Home Plate volcanic feature were it became mired in early May.

[Image]
This view of Spirit stuck by Home Plate was taken from the Mars
Reconnaissance Orbiter. Credit: NASA/University of Arizona
 
If a drive out strategy fails, this MRO view shows where Spirit will
stay intact for perhaps millions of years, depending upon decisions made
in the course of the human exploration of Mars in coming centuries.

Spirit became embedded in soft soil at this site called "Troy" more than
five years into a mission on Mars that was originally scheduled to last
for three months. The rover team suspended further driving attempts with
Spirit, while evaluating possibilities from tests performed at JPL
simulating the Troy situation.

Rover managers point out that when Spirit originally became stuck they
said then the event could mark the end of roving. This would turn Spirit
into a still scientifically active but fixed spacecraft for local soil
analysis, panoramic imaging and weather data.

But engineers also showed more optimism earlier when beginning the test
of wheel drive and steering scenarios with JPL's primary test rover.
Those tests are being done in specially formulated Martian-like soil.

Callas adds that a new series of ground tests and computer simulations
are designed to give the rover "very best chance" it can have to move
again.

"We are proceeding very cautiously and exploring all reasonable
options," he says in the JPL assessment. A mid summer plan to use the
ground test data acquired to that point for new maneuver commands for a
drive out attempt in August were shelved when a review (see photo below)
found they would have almost no chance of success. Now the earliest such
drive out attempts will be made is well into October.

Two test rovers, instead of just one, are being used for these extended
tests. One weighs about 150 lb. like the two spacecraft on Mars, and
another more realistic one weighing more than 400 lb. -- the flight
rovers' weight on Earth. One oddity of testing is that the heavier rover
earlier seemed to provide better data on drive options than the rover
duplicating the lighter Martian weight.

The Surface System Testbed Lite, weighs about the same on Earth as
Spirit does on Mars. Unlike the primary test rover called simply the
Surface System Testbed.

The lighter model does not carry science instruments or a robotic arm.
An object that weighs 10 pounds on Earth weighs just 3.8 pounds on Mars,
due to the smaller mass of Mars compared to Earth.

New computer modeling using results from both test rovers is now being
compiled to aid the decision process on how to proceed with drive-out
options on Mars. The planet is now about 139 million mi. from Earth and
temporarily growing closer at about 570 mi. per minute as Mars moves in
its orbit around the Sun relative to Earth.

"The computer modeling will allow us to connect the results from tests
performed in Earth gravity with what to expect from the rover in Mars
gravity," says Callas.

An additional round of testing was added to the September schedule to
gain more detailed assessment of how to move Spirit while avoiding
putting the rover's center of gravity directly over a rock that is
touching or nearly touching the rover's underbelly. A complete "dress
rehearsal" test of the extrication strategy judged to hold the best
chance of success is planned in the test setup at JPL before the team
commands Spirit to begin driving. That test and subsequent review of its
results are expected to take several weeks.

However, Spirit has been conducting geology and other science even
though embedded at the Troy location.

For example during one week earlier this month a several hour Mossbauer
spectrometer reading was completed by placing the sensor on a soil
target designated "Olive Leaf." On the next Martian day (or sol), a rock
abrasion tool (RAT) calibration and a RAT diagnostics test were
performed, then the instrument turret rotated to place the Alpha
Particle X-ray Spectrometer (APXS) instrument atop the Olive Leaf target
for an overnight data acquisition period.

On the sol after that, the robotic arm elevated the rover's microscopic
imager to take an image of the Martian dust capture magnet on Spirit's
top deck. The APXS instrument was then placed on that magnet for
multi-sol data acquisition to determine the composition of dust that has
recently collected on the rover from a mild dust storm that recently
blew through the area.

The panoramic camera (Pancam) was busy taking 13-filter images of an
area designated the "Scamander Plains" and documentary images of the
rover deck were also made.

The rover's solar arrays had earlier picked up a slight covering of dust
from the passing storm, but a gust of wind later cleared off the array.
This is enabling Spirit to obtain ample power. It is enough that the
rover is run at night, so the power generation and storage during the
day do not cause heating problems. The ample power means Sprit will be
able to survive the coming Martian winter stuck where it is without the
need to move to a sun facing hillside as was the case when Spirit first
arrived at this site.

Total Spirit odometry remains at 4.80 miles since beginning to rove
after landing in early January 2004. The rover's design life was for
only about 900 ft. of driving over about a 90 day period.

On the opposite side of Mars, the rover Opportunity is completing
inspection and sensor data acquisition on an iron meteorite dubbed Block
Island that analysis indicates has been sitting in that same spot on the
Meridiani plane for 3 billion years.

Opportunity placed its instruments (see photo below) on a number of
locations on the 28 in. dia. meteorite that researchers estimate weighs
nearly half a ton. Following contact data acquisition, Opportunity has
been driving around the meteorite stopping at six planned locations to
take a series of Pancam images at each stop.

The meteorite's impact period of 3 billion years ago has been determined
because it would had to have been slowed by a much thicker Martian
atmosphere than has existed on the Mars since that time, about 1.5
billion years after Mars and Earth were formed along with the rest of
the Solar System.

Nothing on Earth survives intact after 3 billion years, because on Earth
unlike Mars, continents are constantly reprocessed by plate tectonics
and continental drift.

At the same time that meteorite landed in the same spot where
Opportunity discovered it, on Earth the surface had just cooled enough
to for the formation of rocks and an initial solid surface. Only one
giant continent existed as plate tectonics were just beginning to
function. The absorption of carbon dioxide by the oceans, however, had
left a high oxygen content in the atmosphere, factors leading to the
formation if initial extremely simple forms of life here.

Study of the Block Island meteorite, one of the great discoveries of the
rover program, can not determine whether anything similar happened on
Mars. But the object landed in that spot on the planet at the same time
life could possibly have begun there too, if it ever did.
Received on Sun 20 Sep 2009 11:01:39 PM PDT