Mars Rovers Break Driving Records, Examine Salty Soil

By Guy Webster and Dolores Beasley

(JPL/NASA) On three consecutive days, NASA’s Mars Exploration Rover Opportunity accomplished unprecedented feats of martian motion, covering more total ground in that period than either Opportunity or its twin, Spirit, did in their first 70 days on Mars.

Spirit, meanwhile, has uncovered soil that is more than half salt, adding to the evidence for Mars’ wet past. The golf-cart-size robots successfully completed their three-month primary missions in April 2004 and are continuing extended mission operations.

NASA’s Mars Exploration Rover Spirit used its navigation camera to take the images combined into this 360-degree view of the rover’s surroundings on Spirit’s 409th martian day, or sol (Feb. 26, 2005). Spirit had driven 2 meters (7 feet) on this sol to get in position on "Cumberland Ridge" for looking into "Tennessee Valley" to the east. This location is catalogued as Spirit’s Site 108. Rover-wheel tracks from climbing the ridge are visible on the right. The summit of "Husband Hill" is at the center, to the south. This view is presented in a cylindrical projection with geometric and brightness seam correction.

Photo by NASA/JPL

Opportunity set a one-day distance record for martian driving, 177.5 meters (582 feet), on Feb. 19. That was the first day of a three-day plan transmitted to the rover as a combined set of weekend instructions. During the preceding week, engineers at NASA’s Jet Propulsion Laboratory had sent Opportunity and Spirit an upgrade of the rovers’ software, onboard intelligence the rovers use for carrying out day-to-day commands.

The new record exceeded a two-week old former best by 13 percent. As on all previous long drives by either rover, the traverse began with "blind" driving, in which the rover followed a route determined in advance by rover planners at JPL using stereo images. That portion lasted an hour and covered most of the day’s distance. Then Opportunity switched to "autonomous" driving for two and a half hours, pausing every 2 meters (6.6 feet) to look ahead for obstacles as it chose its own route ahead.

The next day, Opportunity used its new software to start another drive navigating for itself. "This is the first time either rover has picked up on a second day with continued autonomous driving," said Dr. Mark Maimone, rover mobility software engineer at JPL. "It’s good to sit back and let the rover do the driving for us."

Not only did Opportunity avoid obstacles for four hours of driving, it covered more ground than a football field. Opportunity has a favorable power situation, due to relatively clean solar panels and increasing minutes of daylight each day as spring approaches in Mars’ southern hemisphere. This allows several hours of operations daily.

On the third day of the three-day plan, the robotic geologist continued navigating itself and drove even farther, 109 meters (357 feet), pushing the three-day total to 390 meters (nearly a quarter mile). In one long weekend, Opportunity covered a distance equivalent to more than half of the 600 meters that had been part of each rover’s original mission-success criteria during their first three months on Mars.

Opportunity has now driven 3,014 meters (1.87 miles) since landing; Spirit even farther, 4,157 meters (2.58 miles). Opportunity is heading south toward a rugged landscape called "etched terrain," where it might find exposures of deeper layers of bedrock than it has seen so far. Spirit is climbing "Husband Hill," with a pause on a ridge overlooking a valley north of the summit to see whether any potential targets below warrant a side trip.

As Spirit struggled up the slope approaching the ridgeline, the rover’s wheels churned up soil that grabbed scientists’ attention. "This was an absolutely serendipitous discovery," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers’ science instruments. "We said, ‘My gosh, that soil looks very bright. Before we go away, we should at least take a taste."

The bright patch of disturbed soil, dubbed "Paso Robles," has the highest salt concentration of any rock or soil ever examined on Mars. Combined information gained from inspecting it with Spirit’s three spectrometers and panoramic camera suggests its main ingredient is an iron sulfate salt with water molecules bound into the mineral. The soil patch is also rich in phosphorus, but not otherwise like a high-phosphorus rock, called "Wishstone," that Spirit examined in December. "We’re still trying to work out what this means, but clearly, with this much salt around, water had a hand here," Squyres said.

Meanwhile, scientists are re-calibrating data from both rovers’ alpha particle X-ray spectrometers. These instruments are used to assess targets’ elemental composition. The sensor heads for the two instruments were switched before launch. Therefore, data that Opportunity’s spectrometer has collected have been analyzed using calibration files for Spirit’s, and vice-versa. Fortunately, because the sensor heads are nearly identical, the effect on the elemental abundances determined by the instruments was very small. The scientists have taken this opportunity to go back and review the results for the mission so far and re-compute using correct calibration files. "The effect in all cases was less than the uncertainties in results, so none of our science conclusions are affected," Squyres said.

Articles Related to the Spirit and Opportunity Rovers:

** Mars Craft Spirit Taking in ‘Tennessee Valley’
** Opportunity Gets New Flight Software

Mars Craft Spirit Taking in ‘Tennessee Valley’

Spirit has spent the last 70 sols climbing up the "Columbia Hills" to reach "Larry’s Lookout," a point on "Cumberland Ridge." Having accomplished the trek up to Larry’s Lookout, Spirit is getting into position to shoot a panorama of the "Tennessee Valley" located below. Spirit is still in excellent health.

Sol-by-sol (Day-by-day) summaries:

Sols 401 and 402 were planned in a single planning cycle. On sol 401, Spirit placed the Mössbauer spectrometer on a target of disturbed soil called "Paso Robles" and collected data for most of sols 401 and 402. Spirit also performed about three hours of remote-sensing observations, including imaging of Phobos, one of the moons of Mars.

Sols 403 through 405 were planned in another single planning cycle, to allow the Earthlings to take President’s Day holiday off. Sol 403 was spent continuing the very long Mössbauer spectrometer integration on Paso Robles. Spirit stowed the rover arm, and then moved back about a meter (3 feet) to allow imaging of Paso Robles with the miniature thermal emission spectrometer and panoramic camera. Spirit then began moving closer to Larry’s Lookout, covering 16 meters (52 feet). On sol 405, Spirit spent over two hours performing remote-sensing observations and recharging the batteries.

Spirit moved still closer to Larry’s Lookout on sol 406, driving another 14 meters (46 feet) uphill. By the end of the drive, Spirit was within 5 meters (16 meters) of the crest. Spirit also performed another Phobos observation.

On sol 407, Spirit reached Larry’s Lookout, driving another 3.5 meters (11 feet). Spirit performed an hour of post-drive imaging and was ready to begin observations of Tennessee Valley.

Total odometry as of sol 407 is 4,157 meters (2.58 miles).

Opportunity Gets New Flight Software

Opportunity received a software tuneup that should improve its mobility capabilities. With the new load on board, Opportunity booted into it and began an initial checkout. After a short test drive with promising results, there remains more checkout to do before blessing the load and having the rover’s sister craft, Spirit, boot up the new software. Atmospheric opacity has been stable, with tau around 0.9. Solar power is still relatively plentiful and Opportunity continues to be in excellent health.

Sol-by-sol (Day-by-day) summaries:

Sols 374 through 376 were used to load the files for the new flight software, so Opportunity did not move during this operation. There were a few hours of remote-sensing observations on sols 374 and 375. Opportunity successfully booted into the new flight software on sol 376.

Starting out slowly, Opportunity performed three hours of remote-sensing activities on sol 377.

Sol 378 was the first driving sol using the improved flight software. The drive employed various methods, such as blind driving, auto-navigation, and visual-odometry driving to exercise the rover’s new software. Opportunity traversed approximately 25 meters (82 feet) this sol.

After completing the drive on sol 378, Opportunity had a very nice rock target just outside its front right wheel. On sol 379, Opportunity performed two hours of remote sensing and then turned to 170 degrees, putting the rock target "Russet" perfectly in the rover’s work volume. Sol 379 ended on Feb. 16, with Opportunity’s total odometry at 2,559.88 meters (1.59 miles).