Rover set to roll off lander in pre-dawn hours Thursday

By David Brand

This mosaic image taken by the navigation camera on the Mars Exploration Rover Spirit represents an overhead view of the rover as it prepares to roll off the lander and onto the Martian surface. The yellow arrow illustrates the direction the rover may take to roll safely off the lander. The rover is now facing south (bottom of image). To change direction, the rover will back up a few inches, then make three short turns on it swivel wheels. Click on the image for a high-resolution version (1000 x 750 pixels, 464K)

PASADENA, Calif. -- The rover Spirit, which has been sitting on its lander platform in the Gusev crater on Mars since its bounce-down landing on Jan. 3, is set to roll onto the Martian surface in the early hours of Thursday morning following a complex 115-degree turn-in-place.

The back-and-forth debate among the mission team on when to set the rover free seemed to be settled at a press briefing today (Jan. 11) at the Jet Propulsion Laboratory (JPL), which is managing the twin-rover Mars mission for NASA. Arthur Amador, a mission manager, said that although the status of the rover "is pretty darned perfect," with the vehicle standing on all six of its wheels, preparation for its rolloff will be now be spread over two days, giving the rover an extra day on the lander. "As we get over these steps our uncertainty decreases," he said.

The science team for the Spirit and its twin rover, Opportunity, scheduled for a Martian landing on Jan. 24, is being led from Cornell by astronomy professor Steven Squyres. Cornell astronomer Jim Bell is heading the rovers' panoramic camera, or Pancam, team.

The delay in getting the rover off the lander has been caused by balky, deflated airbags, used for the bounce-down landing, that have failed to retract around the rover's south-facing forward ramp. Fearing that the rover's solar panels would brush against the airbag on the left side of the ramp during exit, mission engineers have decided to turn the rover around to the ramp facing north-northwest. On Saturday night engineers carried out the operation on a full-scale model in JPL's "sandbox" testbed and determined that the rover would first have to be backed up 25 centimeters (about 10 inches) on the lander, then gradually swiveled around on its six wheels to the rear petal.

On Sunday night the rover's robotic arm, which carries three scientific instruments for examining rocks and soil, will be released and locked into place for driving across the crater surface. On Monday night the rover's final lifeline to the lander, an umbilical cord for power and communications, will be cut, leaving the rover as a fully functioning vehicle. At the same time the rover will back up then make a 45-degree turn. Images of the vehicle's status will then be studied, and on Tuesday night one turn of 95 degrees will be made, then studied in images. If all goes well, the final turn to the exit ramp will be made on the same night.

A test at JPL's In-Situ Instruments Laboratory, where the procedure for turning the rover and rolling it off in a new direction was given a dry run on a full-scale model of the rover. Click on the image for a high-resolution version (1920 x 1080 pixels, 1.4MB)

Following the exit, said science manager John Callas at the news briefing, Spirit will use its robotic arm to make the first measurements of soil and rock around the landing area. Then the rover will probably stay in the same location for two or three days making soil and rock measurements that will be "key to the mission," he said.

Because the mission is costing $4 million a day, scientists will use "the extra day on the lander doing unplanned science," said Callas. This will include taking a new Pancam stereo color panorama of the area in front of the rover as it leaves the lander. He said this will provide a new perspective of the area because the lander is now the highest it will ever be above the surface -- about six feet above the crater floor.

The rover's Mini-TES (for miniature thermal emission spectrometer) instrument will also obtain data on three selected targets to be co-registered, or laid over, Pancam images. The overlay consists of dots, each one a spectrum converted into a temperature of the crater area, either fine-grain "soil" or a rock The Mini-TES views the scene around the rover in the infrared, determining the types and amounts of many different kinds of minerals, particularly those that are formed by the action of water.

NASA chose Spirit's landing site based on evidence from Mars orbiters that Gusev crater might have held a lake long ago. The crater is a basin the size of Connecticut created by an asteroid or comet impact. Spirit will spend the coming months exploring for clues in rocks and soils for evidence that Mars once had conditions suitable to sustain life.

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