Several instruments have failed, including a star tracker that was an important navigation and orientation device.

The picture was taken by the star tracker and shows a point of light, believed to be the asteroid, moving across the starfield.

The problem, it seems, was that its star trackers were overly sensitive to light.

The main problem was that the system's star trackers, which help determine the pointing direction, were oversensitive to light.

The main sensor of the line of sight in both spacecraft is the star tracker.

There were four other working star trackers, and in any case spacecraft attitude control was not important during this phase of the mission.

Another failure was the loss of the star tracker.

Ironically, the star tracker was an off-the-shelf component, expected to be highly reliable.

Without a working star tracker, ion thrusting was temporarily suspended.

But those plans were dashed when the pointing system's star trackers had problems shortly after the shuttle was launched early Sunday.