SPIRIT UPDATE: The quest for the top of the hills continues – sol 201-204, August 03, 2004

Mars has seasons like the Earth does, but the seasons are twice as long
due to Mars’ larger orbit around the Sun. Right now, Mars is approaching
northern summer. That also means that it’s approaching southern martian
winter at the same time. So Spirit is headed for winter, being 14
degrees south of the equator. Because martian winter is setting in,
solar array energy continues to be a concern for Spirit. If Spirit parks
with a northerly tilt, the rover will see between 350 and 380 watt-hours
of energy, but if Spirit stops on flat ground or with a southerly tilt,
solar energy is as low as 280 watt-hours. So engineers make a concerted
effort to find the north-facing islands along Spirit’s path.

On Sol 201, Spirit was commanded to drive 98 feet (30 meters) across
terrain that was pretty steep. Spirit accomplished 8.2 feet (2.5 meters)
then stopped due to an excessive tilt angle of 25.6 degrees. Engineers
had set the maximum tilt angle limit at 25 degrees. Spirit did complete
pre-drive science observations and post-drive imaging.

On sol 202, Spirit repeated the drive plan from sol 201 with the maximum
tilt angle set to 32 degrees. This time the rover completed the drive as
planned, traveling 83.6 feet (25.5) meters up the hill. Spirit then
performed post-drive imaging.

On sol 203, scientists’ hope was to find rock outcropping in this
location, but none were found. So the decision was made to continue the
drive up the hill to find a better rock outcrop. Spirit performed
another six-wheel, 62-foot (19-meter) drive. This drive was completed
successfully; however, at the end of the drive, Spirit drove into a
small hollow. As a result, Spirit was pitched 15 degrees toward the
southwest, and ended up with a southerly tilt.

Planning for sol 204 was very exciting due to the late downlink of
information from sol 203. Very late in the planning cycle, available
power on sol 204 was reduced from 370 watt-hours to 288 watt-hours.
Ouch! Pre-drive observations were cut back to 17 minutes, during which
the motors were heated for driving. Spirit drove only 0.82 feet (0.25
meters). Because the drive was so short, the power situation is not as
bad as it could have been.

Total odometry after sol 204, which ended on July 30, is 2.21 miles
(3,565.57 meters). Total elevation above the plains of Gusev Crater is
estimated to be 30 feet (9 meters).

Over the next few sols, scientists and engineers hope to make it to
“Clovis” rock outcrop and to recharge the batteries.

OPPORTUNITY UPDATE: Opportunity Finishing Up at ‘Karatepe’ – sol 181-185, August 03, 2004

Opportunity is completing an intensive survey of the “Karatepe” region
that began 50 sols ago when the rover first ventured into “Endurance
Crater.” The rover currently sits about 20 meters (about 66 feet) inside
the stadium-sized crater. The investigation at an area dubbed “Inuvik”
at a target called “Tuktoyuktuk” (named for a small village in the
Canadian arctic) will likely be the rover’s last in this region. The
rover planning team is contemplating the next traverse which will move
Opportunity around the interior of the crater, first to some
outcroppings dubbed the “Arctic Islands,” then possibly to “Burns
Cliff,” roughly 80 meters (about 262 feet) from the rover’s current
position. Opportunity continues to perform very well, a testament to all
those who worked so hard to get it to Mars and to those who operate it
daily.

Some concerns that are being addressed are slippage, an error message
from the microscopic imager and pointing errors with the front
hazard-avoidance cameras.

The drive on sol 185 included a short backup, during which the rover
experienced a 40 percent slip. Typical slips when driving uphill have
been in the 15- to 20-percent range. More evaluation of what happened on
this and other drives will be needed before any general conclusions can
be made about traversability in this region. The overall slope in this
area is 15 degrees, which is 10 degrees below the general threshold of
concern for rocky terrain. Sol 185 ended on Aug. 1.

There have been four instances of a warning message in the last ten sols
that indicate a problem getting data from the microscopic imager. The
messages indicate that the data was corrupted, and that a retry was
necessary to receive the data without error. In all cases, the retry
succeeded in transferring the data. This problem has not been seen
before on either vehicle.

The new front hazard-avoidance camera models may need some more
tweaking. Pointing errors were greater than expected on two recent
placements of the instrument deployment device (robotic arm). The error
is such that rover planners can still confidently place the instruments,
provided that a 2-centimeter (0.8-inch) offset can be safely tolerated.
If more precision is needed, planners must first use the microscopic
imager to survey the target, then wait one sol before placing any
instruments.

Sol highlights:

181 – A very accurate drive placed the target “Mackenzie” squarely in
Opportunity’s work volume.

182 – A two-hour hour rock abrasion tool (RAT) operation at Mackenzie
was followed by an observation with the Mˆssbauer spectrometer. On this
sol, Opportunity took panoramic camera images during the abrasion tool
operation for the first time. The images were normal. Being able to use
the panoramic camera and abrasion tool in parallel is one of the items
on the “teach your dog new tricks” list, an effort to help the rover
multi-task. The rover went into deep sleep this sol.

183 – Opportunity completed the Mˆssbauer observation of the RAT hole at
Mackenzie, then placed the alpha particle X-ray spectrometer on the hole
for an observation to start at 4 a.m. the next morning. (This instrument
works best when very cold).

184 – The rover took microscopic imager pictures of the Mackenzie RAT
hole, stowed the arm, then backed up to observe the hole with the
panoramic camera and the miniature thermal emission spectrometer. The
rover drove forward roughly 8 meters (26 feet) to Inuvik, using visual
odometry to gauge the amount of slip. The drive left Opportunity to the
right of the intended location because the rover slipped towards the
fall line of the crater, causing the vehicle to effectively arc to the
right. Deep sleep was invoked.

185 – Opportunity performed a short maneuver to get Tuktoyuktuk into the
arm’s work volume. Slippage was greater than expected during the uphill
part of that move, so Opportunity ended up with only the upper part of
the target in the work volume. That turned out to be good enough to
perform a full set of arm work, which is planned for sols 186 through
188. The rover took panoramic camera images of the area between Inuvik
and the Arctic Islands for the purposes of evaluating that drive. It
turned the inertial measurement unit on again during the afternoon
communications relay. This is another item on the “new tricks” list
that, if successful, will allow rover planners to turn the vehicle
during communication passes to optimize the data return. The rover again
used deep sleep.