To the “Arctic Islands,” then possibly to “Burns Cliff”

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 Mössbauer 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 РOpportunity completed the M̦ssbauer 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.