September 28, 2004Tracking Spirit
On Sol 62, as the Mars rover Spirit clambered over jumbled ejecta around Bonneville Crater, the Mars Global Surveyor flew overhead. Using an innovative technique, the orbiter snapped an image that shows both the rover and its track across the martian surface.
"Over the past year and a half, the camera and spacecraft teams for Mars Global Surveyor have worked together to develop a technique that allows us to roll the entire spacecraft so that the camera can be scanned in a way that sees details at three times higher resolution than we normally get," said Ken Edgett, staff scientist at Malin Space Science Systems, San Diego, California, which built and operates the Mars Orbiter Camera.
Called cPROTO, for "compensated Pitch and Roll Targeted Observation," the technique pitches the spacecraft along its ground track and simultaneously rolls it to keep a specific target in view. Controllers time both maneuvers to compensate for the apparent motion of the camera's target.
"The image-motion compensation is tricky, and the spacecraft does not always hit its target. However, when it does, the results can be spectacular," Edgett said. Because the maneuvers are complex, and the amount of data that can be acquired is limited, the technique is not used for most images.
Mars Global Surveyor has been productive longer than any other spacecraft sent to Mars. It has returned 170,000 images — more than all previous Mars missions combined. A third mission extension for the long-lived spacecraft continues operations through September 2006. For a larger version of the Spirit image, as well as others taken with the Mars Orbiter Camera, visit Malin Space Systems
on the web. — Francis Reddy