lightening the SM's fuel load. The spacecraft and engine passed every test, sometimes proving more robust than expected. The performance of the CSM in remaining stable while the engine was being gimbaled would in 1972 help cause McDivitt, by then manager of the Apollo Spacecraft Program, to approve the continuation of Apollo 16 when its CSM was experiencing an unstable gimbal after separation from its LM in lunar orbit. The flight plan for the third day in space was to have the commander and lunar module pilot enter the LM to check out its systems and use its descent engine to move the entire spacecraft. The descent engine was the backup to the SPS; the ability to use it in this manner would prove critical on Apollo 13. The flight plan was thrown into question when Schweickart, suffering from space adaptation sickness, vomited, while McDivitt felt queasy as well. They had been avoiding sudden physical motions, but the contortion-like maneuvers to don their space suits for the LM checkout caused them to feel ill. The experience would teach the doctors enough about the sickness to have the astronauts avoid it on the lunar landings, but at the time Schweickart feared his vomiting might endanger Kennedy's goal. They were well enough to continue with the day's plan, and entered the LM, thus transferring between vehicles for the first time in the US space program, and making the first ever transfer without needing to spacewalk, as Soviet cosmonauts had. The hatches were then closed, though the modules remained docked, showing that Spider communications and life support systems would work in isolation from those of Gumdrop. On command, the landing legs sprang into the position they would assume for landing on the Moon. In the LM, Schweickart vomited again, causing McDivitt to request a private channel to the doctors in Houston. The first episode had not been reported to the ground because of its brief nature, and when the media learned what had happened to Schweickart, there were "repercussions and a spate of unfriendly stories". They finished the LM checkout, including the successful firing of the descent engine, and returned to Scott in Gumdrop. The burn lasted 367 seconds and simulated the throttle pattern to be used during the landing on the Moon. After they returned, a fifth firing of the SPS was made, designed to circularize Apollo9's orbit in preparation for the