Mars Rover Checkup
The first in-flight checkouts of the science instruments and engineering cameras on NASA’s twin Spirit and Opportunity spacecraft on their way to Mars have provided an assessment of the instruments’ condition after the stressful vibrations of launch.
|Rocket-camera, July 7th Delta launch rocket for MER mission, as imaged during Monday’s successful take-off. Opportunity could have launched as late as July 15th, with a 24 hour turnaround to troubleshoot any problems with its Delta rocket. But after the fifteenth, a stand-down of four years would have been needed for the same mission profile to reach Mars as efficiently. In a nail-biting series of finishing fixes, five launch delays pushed the take-off to late Monday night, when its spectacular take-off finally illuminated the Florida Space Coast.
The instrument tests run by the Mars Exploration Rover flight team at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., finished with performance data received Tuesday from two of the spectrometers on Opportunity.
Each rover’s suite of science instruments includes a stereo panoramic camera pair, a microscope camera and three spectrometers. The tests also evaluated performance of each spacecraft’s engineering cameras, which are a stereo navigation camera pair, stereo hazard-avoidance camera pairs on the front and back of the rover, and a downward-pointing descent camera on the lander to aid a system for reducing horizontal motion just before impact.
All 10 cameras on each spacecraft – three science cameras and seven engineering cameras on each – performed well. One of the three spectrometers on Spirit returned data that did not fit the expected pattern. The other two spectrometers on Spirit and all three on Opportunity worked properly. Teams have been busy since the tests began nearly three weeks ago analyzing about 200 megabits of instrument data generated from each spacecraft.
"All the engineering cameras are healthy," said JPL imaging scientist Dr. Justin Maki. "We took two pictures with each engineering camera — 14 pictures from each spacecraft. Even when the cameras are in the dark, the images give characteristic signatures that let us know whether the electronics are working correctly."
The science cameras on each rover – the Pancam color panoramic cameras and the Microscopic Imagers – all performed flawlessly. A spectrometer on each rover for identifying minerals from a distance, called the miniature thermal emission spectrometer, or mini-TES, also worked perfectly on each rover.
|Artist conception of dramatic airbag landing Credit: NASA.|
Two other spectrometers – an alpha particle X-ray spectrometer and a Mössbauer spectrometer – are mounted on an extendable arm for close-up examination of the composition of rocks and soil. Both instruments on Opportunity, as well as Spirit’s alpha particle X-ray spectrometer worked properly. The Mössbauer spectrometer on Spirit is the one whose test data did not fit the pattern expected from normal operation.
"The Mössbauer results we just received from Opportunity are helping us interpret the data that we’ve been analyzing from Spirit," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the suite of science tools on each rover. "Some of the theories we had developed for what might be causing the anomalous behavior of the Mössbauer instrument on Spirit have been eliminated by looking at the data from the one on Opportunity."
The remaining theories focus on an apparent problem in movement of a mechanism within the instrument that rapidly vibrates a gamma-ray source back and forth.
|A simulated image of the new Mars rover carrying the Athena science instruments.
"The Mössbauer spectrometer on Spirit is working, and even if we don’t come up with a way to improve its performance, we’ll be able to get scientific information out of the data it sends us from Mars," Squyres said. "But it’s a very flexible instrument, with lots of parameters we can change. We have high hopes that over the coming months we’ll be able to understand exactly what’s happened to it and make adjustments that will improve its performance. And if the Mössbauer spectrometer on Opportunity behaves on Mars the way it did today, we’ll get beautiful data from that instrument."
The two types of spectrometers on the rovers’ extendable arms complement each other. The alpha particle X-ray spectrometers provide information about what elements are in a rock. The Mössbauer spectrometers give information about the arrangement of iron atoms in the crystalline mineral structure within a rock.
Orbital projections of where the Mars Exploration Rovers are right now, can be continuously monitored over their half-year journeys. As of 6 a.m. Pacific Daylight Time August 7, Spirit will have traveled 157.1 million kilometers (97.6 million miles) since its June 10 launch, and Opportunity will have traveled 82.7 million kilometers (51.4 million miles) since its July 7 launch.
After arrival, the rovers will examine their landing areas for geological evidence about the history of water on Mars. To complete their scientific deployment, the rovers and landers must go through 17 carefully-orchestrated steps — from rolling out exit ramps for the rovers, to unfolding the solar arrays and popping the camera masts up — just so the rover can venture out and explore the red soil.
The panoramic camera at human-eye height, and a miniature thermal emission spectrometer, with infrared vision, help scientists identify the most interesting rocks. "The clues are in the rocks, but you can’t go to every rock, so you split the job into two pieces," said Squyres.
The rovers can watch for hazards and maneuver around them. Each six-wheeled robot has a deck of solar panels, about the size of a kitchen table, for power. The rover drives to the selected rock and extends an arm with tools on the end. Then, a microscopic imager, like a geologist’s hand lens, gives a close-up view of the rock’s texture. Then two spectrometers identify the composition of the rock, after exposing the fresh interior by scraping away the weathered surface layer.
JPL, a division of the California Institute of Technology, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Banner image credit: Artist rendering of Hesperia Planum on Mars, used by permission, space4case.com, © Kees Veenenbos.