Apollo 8 was the first manned spacecraft to orbit the Moon. The crew’s mission was to test the ship, which was made up of a command module and a service module. In future missions, a lunar module would be added to land the first astronauts on the Moon. Anything might go wrong. So far, nothing had. But the crucial firing of the rocket that would return the men to Earth was still to come. If the rocket engine failed, the men would be trapped in lunar orbit with no hope of rescue.