Task: Question Generation
Input (English):  While seeking water for his cattle Travis Fox enters a little known canyon in the Arizona desert and gets captured by three men, one of whom he recognizes as Dr. Gordon Ashe, an archaeologist. After discovering that Fox studied archaeology and had done some digging in the very canyon they now occupy, the men have him cleared through security and offer to make him part of their team. Then Ashe tells him that he will be joining an expedition 10,000 years into the past to look for a spaceship.
Disguised as Folsom hunters, Fox, Ashe, and Ross Murdock travel into the past to scout out the area around the wreckage of an alien starship, a sphere perhaps 120 feet in diameter. They find the wreck near a lake and then, across a ridge, they find a smaller spaceship intact, its crew of Baldies dead. After receiving the scouts  report via transtemporal telegraph, Major Kelgarries, the project s director, and several technicians come into the past and examine the small ship, determining that they can shift it directly into the present.
Fox, Ashe, and Murdock serve as roving sentries in the area around the smaller globeship as technicians build a time transfer cage around it. The ash from a volcanic explosion and a stampede of mammoths drive the three men into the ship with Case Renfry, an electronics technician, on the day the transfer is to be made. An earthquake triggers the transfer, bringing the ship into the present, and then the ship s preset autopilot, jolted into action, takes the ship into space.
After carrying the men through hyperspace, the ship lands on a planet where faltering robots refuel the ship. Another leap through hyperspace brings the ship to the second planet of an alien solar system. The ship lands in a desert, sits for a couple of days, and then blasts off on a course that takes it to the system s Earth-like third planet. Upon landing the ship indicates that the voyage has ended by ejecting a small discus from its autopilot.
Renfry attempts to understand the autopilot and to rewind the course  tape  while the three time agents explore the jungle-draped ruins of a once-great city, in which they ve landed. After several weeks Renfry believes that he has succeeded and he attempts to launch the ship. The ship runs its course in reverse, pausing on the desert planet and the refueling station, and brings the four men back to Earth, landing on the very spot from which they had blasted off.
Output (English): While the technicians work on the time transfer cage, what causes the 3 sentries to enter the ship?