A single, large rocket engine of the command and service module (CSM) used for the Apollo space missions that began in the 1960s. It took the form of a cone projecting from the rear of the service module. The SPS was burned for 6 minutes to slow the spacecraft as it neared the Moon, and for 2.5 minutes to power the CSM out of lunar orbit for the return journey. There was no back-up, so any malfunction of the SPS would have stranded the astronauts in permanent lunar orbit.
Subjects: Astronomy and Astrophysics.