Apollo 13 - Orbits And You

[SuperWeegee4000]

I have taken to wondering. Watching a documentary, I discovered that the Apollo 13 LEM used its engine to "speed up its orbit." This is something that has always bothered me about orbital mechanics - how was their trajectory changed to shave a full nine hours off their return time? Was the reentry steeper and hotter? How did the return trajectory match up with the other Apollo missions?

[deadshot462]

Keep your Periapsis roughly the same, but burn towards a direction that would throw you out of Earth's orbit if there was no atmosphere. Basically, Apollo 13 probably made their Apoapsis much higher than what it used to be.

[Kerbin Dallas Multipass]

Interesting question.

All I could find out is this:

They had to re-establish their free return trajectory by burning the LM engines

This trajectory gave them a moon periapsis of 100km higher than "normal" (not sure if higher than free return or just higher than mission plan)

The "speed up the orbit" burn is called a PC+2 burn, meaning its done 2 hours after lunar periapsis. Not sure what that means yet.

The reentry was a bit unusual but not sure how unusual

[goldenpeach]

The reentry was longer than expected.

This has nothing to do with the burn tough.

[tizalee]

Though the speed up its orbits still the return was slower than it was expected.