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Wednesday, January 7, 2004

Mars Global Surveyor Spots Pathfinder, Vikings

Pathfinder as seen by MGS.
Pathfinder as seen by MGS.
You've heard it time and time again. The spacecraft orbiting Mars does not have the resolution in their cameras to pinpoint landers on the surface. After all, NASA's Mars Global Surveyor only has a resolution of 1.5 meters per pixel, right? Wrong. Driven by the desire to pinpoint Spirit's location exactly, scientists have developed a new imaging technique. Scientists have now been able to spot not only the large Viking landers of the 70's, but also the smaller Pathfinder lander of 1997, which is the exact same size as Spirit.

Before we get into the details, we have to answer a question. If we can increase the resolution to spot Pathfinder, why can't we look for the ESA's presumed-crashed Beagle 2 or NASA's ill-fated Polar Lander? The answer lies in the details. In obtaining the higher resolution images, the imaging field is reduced dramatically, meaning that we have to already know the position of the object on the ground to around a kilometer to find it. This is incredibly difficult, and the positions of most objects have not been determined to nearly that much detail.

How can we find the other spacecraft then? As the MGS spacecraft orbits the locations, it bounces radio signals off the surface of the planet. Then, using complicated calculations, a line is determined that could contain the lander. With three such measurements, scientists can then triangulate the exact position--to within a little more than a kilometer, anyway. Then they take panoramic views from the lander and superimpose them on images to determine lines of sight to obvious landmarks, like mountains.

Finally, the camera is used. Normally, to take a picture the spacecraft must be rotating to compensate for the high velocity of its orbit to eliminate blurring. If the spacecraft rotates a little more then normally necessary, even higher resolution pictures can be obtained, down to 50 square centimeters per pixel, or about 20 square inches. Even through the loss of size of the image to outside distortion from rotating, it's enough to find the lander.

The picture above is the Pathfinder landing site. On the left is the panoramic view superimposed on an orbital photograph to determine lines of sight to mountains nearby. On the right is the high resolution photograph. The larger image (obtained by clicking on the image) shows the white of the parachute and the rock named Yogi in the center. You will probably have to stop your browser from shrinking the image. In Internet Explorer 5+, hold your mouse over the image and click on the picture box that shows up on the bottom right corner. In Netscape 7.x, click on the image.

(More info: Malin Space Science Systems - Extremely high traffic at the moment)

- posted by Brian @ 19:44 EST