1.   A navigational component called an inertial measurement unit, one of three used by the spacecraft, faltered earlier this week.

2.   He had no details of the problem, except that it involved one of the three inertial measurement units aboard Discovery.

3.   One of three inertial measurement units aboard Endeavour malfunctioned early Thursday, setting off an alarm in the cockpit after the astronauts had gone to bed.

4.   One of three inertial measurement units on the shuttle started having problems early Thursday, setting off an alarm in the cockpit after the astronauts had gone to bed.

5.   The problem with the navigation unit, called an inertial measurement unit, developed on Wednesday afternoon.