Aborting before LOI

If the mission had Lo be aborted before the LOI burn. Retro’s response would attempt to achieve two things. It would ensure that the spacecraft was set on an accurate path, not only to Earth but also to a landing site, usually in the mid-Pacific Ocean, where a recovery fleet would be on station. In addition his solution would strive to increase the speed of the spacecraft slightly, so that it would return home 24 hours (one Earth axial rotation) earlier than would occur without intervention. On Apollo 8, Retro had planned to use two separate burns to achieve these goals: & flyby manoeuvre that would have been carried out just before the spacecraft disappeared around the far side of the Moon; and a pericynthion plus 2 manoeuvre, or ‘PC — 2′ for short, to he made Lw’o hours after their closest approach to the Moon. On later missions, both of these functions were combined into a single planned abort contingency.

The PC —2 abort burn was actually used on one oeeasion as part of the effort to get the ailing Apollo 13 back to Earth. On this mission. Retro had to calculate the burn using the descent engine of the lunar module, the SPS engine being unusable owing to the loss of power in the CSM.