Apollo 9 to land on the Moon; when the crews for Apollo 8 and 9 were swapped, their backup crews were also swapped. Since the rule of thumb was for backup crews to fly as prime crew three missions later, this put Neil Armstrong's crew (Borman's backup) in position for the first landing mission Apollo 11 instead of Pete Conrad's crew, who made the second landing on Apollo 12. Apollo 9 was the first space test of the complete Apollo spacecraft, including the third critical piece of Apollo hardware besides the command and service module and the Saturn V launch vehicle—the lunar
Return of Apollo 15 to Earth which was launched using a spring-loaded mechanism, a pin in a curved groove to impart a spin in the satellite. The spinning helped to stabilise the craft. After having the information needed to burn the SPS to send them home radioed from Mission Control, "Apollo 15" disappeared behind the Moon for the last time. Igniting on time, the SPS burned for 2 minutes, 21 seconds, adding 3,050 ft/s (930 m/s) to their speed. Little was left for the crew to do on their tenth day in space. They continued to photograph the lunar surface as it receded from them, using