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<ProjectThoth>
Anyone in here with a really good grasp of kinematics?
<taniwha>
I don't know about "really good", but...
<taniwha>
what's up?
<taniwha>
ProjectThoth: ^
<ProjectThoth>
taniwha: Okay, so I've got a rocket hanging out in freefall.
<ProjectThoth>
I'm interested in kicking myself back towards the launch site. I fire the engine to do so.
<ProjectThoth>
Is the net velocity thus a function of the acceleration and burn time of that rocket, or is it just the horizontal velocity minus the delta-v available?
<ProjectThoth>
I would assume that it it's the former.
<taniwha>
there's actually no difference
<taniwha>
though the latter will be more accurate
<taniwha>
(because the acceleration is non-linear, thus the ΔV equation having ln in it)
* ProjectThoth
checks the spreadsheet.
<taniwha>
er, sorry, not non-linear (though it is), but non-constant
<ProjectThoth>
Son of a gun, look at that.
<ProjectThoth>
That's not something I would have expected from just looking at the data.
<ProjectThoth>
taniwha: Seems to be most accurate (vs just using the difference in velocities) when considering peak acceleration, interestingly enough.
<taniwha>
any differences in actual velocity should be due to gravity
<taniwha>
so higher acceleration means less time for gravity to mess you up
<ProjectThoth>
I was considering a purely horizontal burn.
<taniwha>
you still have gravity adding to your velocity vector
<taniwha>
thus why NASA's first rendezvous attempt went badly :)
<taniwha>
(I can never remember which mission it was)
<ProjectThoth>
Oh, that just clicked.
<taniwha>
Yeah, there's a lot of that in true 3d physics
<taniwha>
(the stuff they teach in school is mostly 2d with flattened earth (for simplicity))
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<ProjectThoth>
taniwha: Explains my lack of understanding.
<taniwha>
e
<taniwha>
oops
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