A detailed survey of Eros has been completed and will help researchers obtain the best possible photographs during the first landing of a spacecraft on an asteroid.
The Near Earth Asteroid Rendezvous (NEAR) spacecraft is scheduled to touch down on Eros鈥� surface in February 2001. The plan is to move NEAR gradually inwards from its present orbit 35 kilometres out until it hits the space rock.
快猫短视频s expect the craft to be fatally damaged on impact because it was never designed to land safely. But they hope to get the on-board camera to photograph the asteroid鈥檚 surface as the craft crunches into it.
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To achieve this, scientists at Caltech in Pasadena, California, and the National Space Studies Centre in Toulouse, France, have been taking careful measurements of the asteroid鈥檚 rotation.
An asteroid鈥檚 rotation and shape can be highly irregular, so a spacecraft that orbits it experiences a very complicated gravitational field. Unless scientists get the calculations just right, the craft may bump into the surface at the wrong angle as the asteroid rotates. This would ruin the chance of a good picture.
So the Caltech team tracked NEAR鈥檚 velocity and position by bouncing radio signals off the craft. Then they measured Eros鈥檚 rotation by looking at the movement of landmarks on pictures beamed back from the craft鈥檚 on-board camera. 鈥淲e had to try and keep NEAR orbiting within sight of Earth,鈥� says Donald Yeomans of Caltech, 鈥渢hough we did mistakenly lose contact several times.鈥�
The actual landing will be painfully slow and deliberate, taking days. This is because the gravitational field is so low. Eros has a mass less than a billionth that of the Earth, and NEAR takes 28 days to complete just one orbit.
The team have plotted the contours of Eros, which is about 30 by 13 by 13km, to an accuracy of 1 kilometre. That doesn鈥檛 sound good enough for the purposes of landing, but Yeomans hopes to pinpoint the craft鈥檚 position relative to the ground by using the on-board laser altimeter.
Yeomans hopes that future spacecraft will be able to land on asteroids without breaking. 鈥淲e learned from the Mars missions that we need to keep close track of what鈥檚 happening to landers, so hopefully this will be good practice in getting as close as possible.鈥�
Source: Science (vol 289, p 2085)