Dark Days for Spirit

Spirit’s solar panels are receiving limited sunshine due to a regional dust storm on Mars. Dust storms are common on the red planet. NASA’s Hubble Space Telescope snapped this picture of a storm near the middle of Mars on October 28, 2005. This storm was about 930 miles long when measured diagonally.
Credit: NASA, ESA, The Hubble Heritage Team (STScI/AURA), J. Bell (Cornell University) and M. Wolff (Space Science Institute)

The amount of electricity generated by the solar panels on the Mars rover Spirit has been declining for the past several Martian days, or sols, as a regional dust storm moved southward and blocked some of the sunshine at Spirit’s location. The team operating the rover has responsively trimmed Spirit’s daily activities and is keeping an eye on weather reports from observations by NASA’s Mars Reconnaissance Orbiter.

Spirit’s solar panels generated 392 watt-hours during the mission’s Sol 2006 (Aug. 24, 2009), down from 744 watt-hours five sols earlier, but still generous compared with the 240 watt-hours per sol that was typical before a series of panel-cleaning events about four months ago.

"We expect that power will improve again as this storm passes, but we will continue to watch this vigilantly," said JPL’s John Callas, project manager for Spirit and its twin, Opportunity. "Spirit remains power positive with healthy energy margins and charged batteries. The weather prediction from the Mars Color Imager team is that the storm is abating, but skies will remain dusty over Spirit for the next few sols."

Recent images from the Mars Color Imager camera on Mars Reconnaissance Orbiter showed this regional storm becoming less extensive Monday even as it shifted southward so that its southern edge covered the Gusev Crater area where Spirit is working. Malin Space Science Systems in San Diego, which operates that camera, provides frequent weather updates to the rover team. Weekly reports are posted at http://www.msss.com/msss_images/latest_weather.html.

Free Spirit

Meanwhile, in JPL’s In-Situ Instrument Laboratory, the rover team is continuing testing of strategies for getting Spirit out of a patch of soft soil where it is embedded on Mars. On Sol 2005 (Aug. 23, 2009) Spirit used its panoramic camera to examine the nature of how soil at the site has stuck to the rover’s middle wheels. The team has also used Spirit’s rock abrasion tool as a penetrometer to measure physical properties of the soil around Spirit by pressing into the soil with three different levels of force. The team is aiming to start sending drive commands to Spirit in September. With careful planning, Spirit may continue its search for signs of past environments on Mars that may have been habitable for life.

This full-circle view from the panoramic camera (Pancam) on NASA’s Mars Exploration Rover Spirit shows the terrain surrounding the location called "Troy," where Spirit became embedded in soft soil during the spring of 2009.
Credit: NASA/JPL-Caltech/Cornell University

A second, lighter-weight test rover has entered the testing setup at JPL where rover team members are assessing strategy for getting Spirit out of the soft soil. This test rover does not carry a science payload or robotic arm, as do Spirit and Opportunity on Mars, and the primary engineering test rover at JPL. While the primary test rover’s weight on Earth is greater than Spirit’s weight on Mars, the second rover is even lighter on Earth and closer to the weight of Spirit on Mars.

Making comparisons between motions of the two test rovers in duplicated drives will aid the rover team in interpreting effects of differing gravity on rover mobility. The testing team plans to run such comparisons both in the soft, fluffy material being used to simulate the soil at Spirit’s current location and also on coarser, crushed rock that offers better traction.

Testing at NASA’s Jet Propulsion Laboratory in August 2009 is assessing possible maneuvers that the Mars rover Spirit might use for escaping from a patch of soft soil where it is embedded at a Martian site called "Troy."
Credit: NASA/JPL-Caltech/Cornell University

"There is no perfect Earth analog for Spirit’s current situation," said JPL’s John Callas, project manager for the twin Mars Exploration Rovers. "There’s less gravity on Mars, little atmosphere, and no moisture in the soil where Spirit is. It is not anything like being stuck in sand or snow or mud on Earth. Plus, since the rover moves only about as fast as a tortoise, you cannot use momentum to help. No rocking back and forth as you might do on Earth."

The comparison experiments with the two test-rover siblings to Spirit and Opportunity precede a planned "dress rehearsal" long-duration test of driving as far in the test setup as the distance that Spirit would need to achieve on Mars to escape its predicament at the site called "Troy."

The team has also made further assessments of the position of a rock underneath Spirit relative to the rover’s center of gravity. Part of the strategy for getting Spirit free will be to avoid getting in a position with the center of gravity directly over a rock touching the rover.