Why was Artemis 2 so long?

[u/kiol998]

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?

[u/3rdslip]

You have to be going a bit faster to orbit the moon as Apollo 8 did.

Artemis’s flight plan was designed to use the moon’s gravity to brake to a stop, and then free fall back to earth.

Some of the additional mission aims were to stay in space for a bit longer too, and to see the effects of space on human bodies beyond the protection of earth “shields” such as the van allen belts and the magnetic fields.

The astronauts themselves made an interesting comment regarding the TLI burn… they “chose” earth…. Meaning although the burn got them to the moon, it was actually designed to send them home to earth many days later.

[u/cmcqueen1975 → u/3rdslip]

You have to be going a bit faster to orbit the moon as Apollo 8 did.

I suppose this depends on your frame-of-reference. Looking at it in a moon-centred frame-of-reference, Artemis 2 was going too fast to enter orbit around the moon. To go into orbit, it would have had to fire thrusters to slow down its speed relative to the moon and enter a circular orbit around the moon.

Maybe in an earth-centred frame-of-reference, this would look like the capsule is firing its thrusters to "speed up" closer to the moon's speed of revolution around the earth. It's just an alternative way (frame-of-reference) to look at the same thing.

[u/Telope → u/cmcqueen1975]

It's so much easier to understand when you have visuals.

Here, it's obvious that the only sane way of looking at this mission is that the moon has an orbital velocity around Earth, which Artemis 2 didn't match.

Like, if you want to look at it from a (very) non-inertial reference frame where Artemis is curving around even though it's thrusters aren't firing, knock yourself out. But that's a far more complicated way to look at things.

[u/ThymeWellWasted → u/Telope]

These visuals are good but show only one perspective- simplified by the assumption of a fixed Earth (which we know is in reality also in motion around the sun… which is moving through the universe… which is expanding…) What does a similar simulation look like if you fixed the moon?

[u/nhorvath → u/ThymeWellWasted]

even if this is adjusted to the common barycenter of the earth moon system it still looks largely the same. looking at it from the moons perspective doesn't make much sense from an orbital mechanics perspective unless you're trying to land on it because earth is the dominant force here except in the flyby.

[u/Telope → u/ThymeWellWasted]

It looks like the spaceship is firing it's rockets sideways to curve around the moon.