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Doubts Grow Over Mars 2003 Rover Duo
Pasadena - Aug 20, 2002 So again, less than 18 months before launch, in January 2002, the MER project decided to look into designing and adding a second "Descent Imager Motion Estimation Subsystem" warning sensor to the TIRS system. The DIMES system involves adding a lightweight camera to the lander that would take three successive photos of the surface in the 18 seconds before the braking rocket is ignited. The photos would then be immediately analyzed by the spacecraft's computer to locate surface features and calculate an estimate of the lander's sideways drift that would be added to the gyro package's tilt data to decide which TIRS rockets to fire up. The DIMES camera system seems to work well in tests - but the decision as to whether it's worthwhile to add it to the MER spacecraft to further reduce landing risks won't be made until November or December. And even with the whole TIRS system added, winds still remain a serious problem for the engineers building the MER landers to fully factor in. Already, new data on possible wind speeds in different places on Mars has forced two of the top six candidates for MER landing sites to be rejected at last March's MER landing site selection workshop - both of the very scientifically interesting sites within the great Marineris Valley, which unsurprisingly channels winds to higher speeds. Since then, another site - in the Athabasca Valley, which may be the site of recent volcanic eruptions and geothermal liquid-water outbursts less than 20 million years ago - has been rejected because Earth-based radar studies indicate that its ground may be unacceptably rough and rocky. And of the remaining three sites, studies are still going on to determine whether two of them have horizontal winds too strong for the landing risk to be acceptable.
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