 Why couldn't Dr. Mansard and his wife leave Jupiter?
“If Dr. Mansard succeeded in landing on Jupiter, why didn't anyone ever hear from him again?” she demanded. For some reason she decided against telling him that the assignment on which she had come to the Jupiter system was to gather his own father's notebooks and take them back to Earth. The ship that they boarded on Moon Nine was one of the newer ships that could attain a hundred-mile-per-second velocity and take a hyperbolic path to Earth, but it would still require fifty-four days to make the trip. Dr. Mansard and his wife had disappeared into the turbulent atmosphere of Jupiter just after his invention of the surgiscope, and it had been developed by Dom Blessing.
 A human would not survive the force of acceleration that would be needed to break free of Jupiter's gravity.
 A human would not survive the force of acceleration that would be needed to break free of Jupiter's gravity.  Dr. Mansard and his wife ran out of oxygen before they could complete the repairs to their ship.  Dr. Mansard and his wife were torn apart by gravitational forces when they tried to leave Jupiter.  Dr. Mansard and his wife were unable to repair their ship after crash landing on Jupiter.