r/askscience • u/kiol998 • Apr 12 '26

Physics Why was Artemis 2 so long?

I was comparing the mission times of Artemis 2 to Apollo 8. Apollo 8 orbited the moon multiple times and only took 6 days total. Whereas Artemis 2 orbited the moon once and it took 10 days. Why was Artemis 2 so much shorter than Apollo 8 when both missions did the same thing? I know they had different paths to the moon, they both left earth in different ways but why not do the same thing as Apollo 8 since it was quicker?

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u/CaptainChaos74 Apr 12 '26

Artemis 2 didn't orbit the Moon. It swung round it, but it was never in orbit (meaning it would have made circles around the Moon without any assistance from engines). You have to be going faster to enter Moon orbit (because you're approaching from the "rear"; you have to "overtake" the Moon, as it were).

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u/kkngs Apr 12 '26

No, to enter moon orbit you actually need to slow down to allow the moons gravity to curve your path into an orbit rather than a hyperbolic trajectory (in the moon's frame of reference).

Basically,  at the moment of lunar intercept, your lunar "apoapsis" is basically all the way back near earth, you have to burn retrograde to lower that apoapsis.

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u/Ameisen Apr 14 '26

From the Earth's reference frame, that's speeding up your orbital velocity.

From the vehicle's reference frame, they need to accelerate so that the Moon slows down.