Talk:1356: Orbital Mechanics

Explain xkcd: It's 'cause you're dumb.
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I just put in a first attempt at the explanation. Could do with links to pages regarding KSP, etc, etc. (Or rewrite entirely how it ought to be done, of course.) Also, if anyone knows for sure that "aim nose at destination, fire retros", as seen in the film Gravity, would or would not give the desired effect, that'd be useful to clarify or dismiss. From my own experience with the Kerbals, it wouldn't (never mind all the other broad assumptions made in that otherwise spectacular film ), but KSP also rather fudges away the N-body problem, artificially. 05:38, 16 April 2014 (UTC)

You are correct that "aim nose, fire retros" doesn't work in reality. KSP fudges the n-body problem by putting the planets and moons on tracks, and then changing you into a different 2-body problem when you cross into a smaller hill sphere than the one you were in. The maneuver node system does a little bit of n-body work when you get a maneuver close to another body, but you'll notice that when the ship actually crosses into the other hill sphere the trajectory for the maneuver goes weird. It's a rather clever optimization for a simulator like KSP. lcarsos_a (talk) 06:21, 16 April 2014 (UTC)

I really wish there was a downwards curve for "I saw Armageddon". 06:26, 16 April 2014 (UTC)

There will be a huge upwards curve on "how much I think i know about orbital mechanics" - See Dunning-Krueger effect for more info. -- 14:40, 16 April 2014 (UTC)
Future mission failure due to discrepancies in Kerbal Space Program

I note some differences in KSP (from wikipedia):

The game simulates trajectories and orbits using patched conic approximation instead of a full n-body simulation, and thus does not support Lagrange points and halo orbits.
The celestial bodies in the Kerbal solar system are about 1/10 the radius of their real-universe equivalents yet have comparable surface gravity, implying that they have unrealistically high densities. This change to scale makes many tasks considerably easier. For example, a surface to low-Kerbin-orbit launch requires a delta-v of about 4.5 km/s, compared to 9.5 km/s for a low-Earth-orbit launch. In particular, because of the game also having unrealistically efficient and flexible (in terms of speed and altitude) turbojet engines, this means it is much easier to make a single-stage-to-orbit vehicle using jet engines to accelerate a vehicle to orbital speed on only a small fraction of its mass in jet fuel, then give a tiny boost with rockets to reach orbit, whereas in real life, a highly efficient but powerful and lightweight scramjet would be necessary to do the same with several times the amount of fuel.

So I predict some probability that, after reading this comic, some NASA person will make the mistake of designing real missions using notions or designs from it, which will fail in real life (or at least be ridiculed at mission design review time). And then Randall will have to write a really challenging comic about it..... Nealmcb (talk) 13:12, 17 April 2014 (UTC)

Once at that lower orbit, your velocity is faster ... really? I though that on lower orbit, your velocity is slower BUT your ANGULAR velocity is faster, which is the reason you start to overtake your target ... but I never played Kerbal, so I may be wrong. -- Hkmaly (talk) 23:37, 24 April 2014 (UTC)