11.   Engineers believe the older gyros failed as hair-thin electrical wires corroded and broke.

12.   Engineers believe an air bubble trapped in the water line of its cooling system is causing a circulation pump to run too fast, tripping an automatic shutdown mechanism.

13.   Engineers believe the damage occurred as Columbia ascended from a newly refurbished launch pad at Kennedy.

14.   Engineers believe they have fixed the problem and made other improvements in the vehcile since the explosion.

15.   Engineers believe they have solved the twisting problem and expect to conduct two additional flights in December.

16.   Engineers believe hair-thin internal copper and silver electrical wires have crumbled from corrosion.

17.   Engineers believe several flushes will free the ice, as it has when similar problems arose on past missions.

18.   Engineers believe the sensor reacted improperly to a pressure change in the engine compartment as it was ventilated during the final seconds of the countdown.

19.   Engineers believe they have a general understanding of why the World Trade Center towers fell.

20.   It was a sleek delta-winged craft that many aviation engineers still believe was a generation ahead of the competition in the United States and the Soviet Union.