Looking for an old scifi book from either the 1980s or 1990s.
It starts out with some confusion, but the gist is that an entire class of students on an aircraft are abducted by aliens. I believe that the wings of the aircraft are also cut off, and the cabin is placed in storage. The students believe they are being attacked by robots, so they defend themselves and cut off the wires controlling them.
It is eventually revealed that the aliens arranged for their flight and to be abducted, and that the robots are used for maintenance and were to help with communication.
The shuttle is deposited on a stalk attached to an artificial planet. The planet has dinosaurs. The aliens look like starfish, but they uploaded their minds into computers a real long time ago. And now, due to problems of maintenance and software glitches, they are dying out. So they want the human students to take care of their starship, teach them all they know, before they cease to exist.
The artificial planet's surface is mostly dirt. But underneath it's a shell of diamond. In the center of the planet is a black hole, which the aliens use to provide earth-normal gravity and power. Robots can be controlled remotely.
The students divide into groups. One is a bully. The others don't trust the aliens no matter what. The rest make due to best they can to learn as much as possible and to operate the robots.
I never finished the book. Can anybody help me?