Comment by SV_BubbleTime
3 days ago
Hilarious the the intellectual forum downvoted you for being absolutely right.
Artemis II never escaped Earth’s pull.
That video that NASA put out where the craft did a sling shop around the moon is extremely deceptive. The pull of the moon had very little effect.
If they had missed, they would have eventually crashed back to earth in the worst case, and best case just re-adjusted and returned a little bummed.
> The pull of the moon had very little effect.
No, it had a very significant effect: it's what made possible the free return trajectory while observing the far side of the moon.
Ok, but no not really. This is incorrect, the “free return” would have happened if they launched entirely in the wrong direction.
Like I said, the gif you saw makes it look that way.
Here is a link that explains it very well. https://youtu.be/MF8IbYbVIA0?t=269
I’ll agree, it seems crazy that it left earth, made it to the moon, and never really left earth orbit at all. That the furthest we’ve been away is still destined to return on its own.
> the gif you saw makes it look that way.
Makes it look what way?
Watch the NASA video carefully. It's clear that, even before the "loop" begins, Artemis is slowed down and is soon going to reverse direction relative to Earth. Which of course it would anyway, as you say--because, as the video you linked to points out, it doesn't have Earth escape velocity. The TLI burn gave it just enough velocity to reach the Moon's orbit with a little extra speed left over to get it about 4000 miles further.
But what would not happen without the Moon there is the "backwards" part of the loop--the part that took Artemis around the far side of the Moon. The Moon's gravity is what did that. In the Moon-centered frame in the video, yes, it looks like just a slight deflection--because that frame is moving with the Moon, whereas Artemis was moving backwards--in the opposite direction from the Moon in the Earth-centered frame.
Without the Moon there, Artemis would never have moved backwards, relative to the Moon's orbit, at all. Its trajectory in the Earth centered frame would have been a simple ellipse, with a maximum altitude from Earth a little higher than what it actually achieved (since the Moon's gravity did pull it back a little bit).
> This is incorrect
No, it's not. You aren't responding to what I actually said. See below.
> the “free return” would have happened if they launched entirely in the wrong direction.
But it would not have been a free return that let them see the far side of the moon, which is what I said. The Moon's gravity is what made that possible. And that was very significant.
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"Artemis II never escaped Earth’s pull."
Hmm. Maximum speed attained by Artemis II when they left their initial orbit was about 11.1 km/s IIRC. While this is somewhat less than true escape velocity from Earth (11.2 km/s) and you are technically correct, it is also enough of a speed that if you fly away in any random direction (and not a carefully calculated one), perturbances from the Sun and other massive objects will probably prevent you from reaching any sort of stable orbit around the Earth, and you will start bouncing around the inner Solar System in an erratic way.
I certainly wouldn't like to model that trajectory for months or years.
The sun’s pull on the ship at the outside limit at the moon, is obviously negligible compared to the pull of the Earth. This should be obvious, because otherwise the moon would have left long ago.
Why is this so difficult to understand? Honestly I think that misleading NASA graphic did a lot of damage.
You throw in acceleration, which I never mentioned and doesn’t matter. The Artemis II never left Earth’s gravitional pull, the original issue was effectively what if it missed - and the answer is no big deal.
I wonder if you are replying to a different comment. I never mentioned acceleration in mine.
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