Second test rover added to driving experiments
Sat Aug 22, 2009 at 12:43 UTC
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 soft soil where it is embedded on Mars.
The rover team has begun using a test rover that 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.
"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 second rover, called the Surface System Testbed Lite (far right) is lighter weight than the primary engineering test rover, called the Surface System Testbed (left foreground). The lighter version does not carry a science payload and robotic arm, as Spirit, Opportunity and the Surface System Testbed do.
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. An object that weighs 10 pounds on Earth weighs just 3.8 pounds on Mars, due to the smaller mass of Mars compared to Earth.
Credit: NASA/JPL-Caltech
Rover team members used Spirit's microscopic imager during the 1,990th Martian day, or sol, of the rover's mission on Mars (Aug. 8, 2009) to look beneath Spirit for only the second time since before it left Earth in 2003. They did so to get a better understanding of Spirit's predicament, with wheels embedded deeply enough in soft soil at a site called "Troy" for the rover to be at risk of getting hung up on the rock beneath the belly.
The microscopic imager is designed to focus on rock or soil targets 6 centimeters (2.4 inches) away. It rides on the end of the rover's robotic arm so that it can be placed close to targets for inspection. It cannot focus on objects as far away as the rover underbelly and rocks that are visible in this image despite being out of focus. However, its position on the maneuverable arm enables positioning it for a view that none of the other cameras on the rover could get. The rover team used this technique for an initial view underneath Spirit on Sol 1925 (June 2, 2009) after trying out the technique first with an Earthbound test rover and with Spirit's twin, Opportunity. The Sol 1990 imaging viewed the rock from slightly different camera positions for improved three-dimensional understanding of its location.
Credit: NASA/JPL-Caltech/USGS
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.
| Source: Jet Propulsion Laboratory | |
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