 Why couldn't Dr. Mansard and his wife leave Jupiter?
50 THE JUPITER WEAPON By CHARLES L. FONTENAY Trella feared she was in for trouble even before Motwick's head dropped forward on his arms in a drunken stupor. It was a squalid saloon in the rougher section of Jupiter's View, the terrestrial dome-colony on Ganymede. A woman could not possibly make her way through these streets alone to the better section of town, especially one clad in a silvery evening dress. Perhaps she could call one of Motwick's friends; she had no one on Ganymede she could call a real friend herself. It smashed on Kregg's head, splashing the floor with liquor, and Kregg sank stunned to his knees. The dark man, who had grabbed Trella's arm, released her and ran for the door. The gravity of Ganymede was hardly more than that of Earth's moon, but the way the man picked up the limp Motwick with one hand and tossed him over a shoulder was startling: as though he lifted a feather pillow. He followed Trella out the door of the Golden Satellite and fell in step beside her. The transparent dome of Jupiter's View was faintly visible in the reflected night lights of the colonial city, but the lights were overwhelmed by the giant, vari-colored disc of Jupiter itself, riding high in the sky. “No one has ever landed on Jupiter. “My parents landed on Jupiter, and I blasted off from it,” he said soberly. But his ship was drawn into Jupiter and lost.”
 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.