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Kerbal Space Program is an independent spaceflight simulation game, which has become quickly popular due to being (kind of) precise at simulating actual spaceflights.

But how precisely? How close is Kerbal Space Program to reality in the aspect of difficulty of flights?

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Kerbal Space Program is somewhat of a medium fidelity simulation. It manages a few things quite well, and a few things not as well. Let me try and give a list (which might be a bit out of date):

The Good:

  • The orbit simulation is quite accurate, including how to change inclination, raise/lower orbits, leave a planet, and approach a new planet.
  • The staging is somewhat accurate.
  • The use of fuel, acceleration, mass, etc. are pretty accurate.
  • Structural stability is pretty accurate, at least modeling the key components.
  • The new Aerodynamic's model is pretty good. It doesn't model everything perfectly, but is pretty good overall.

The Bad:

  • Only one body affects an orbiting object, the object of most influence. It might even do something like a Hill sphere. However, there are plenty of multi-object systems which aren't managed at all correctly; Lagrange points aren't taken into account, for instance.
  • The aerodynamics model doesn't model well things like breaking the sound barrier.
  • Reaction wheels aren't modeled properly (Can do with a mod, but...)
  • A number of effects aren't really modeled, but can be included with mods (Communication delay, rocket fuel settling, etc)
  • Re-entry heating is now modeled, although it isn't great.

The Ugly:

  • No life support requirements.

For more, see Wikipedia.

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    $\begingroup$ Just wanted to add the aerodynamics, life support and jet engine issues can actually be improved with some mods. Nothing for multi-body systems yet (as far as I know). $\endgroup$ – user3319 May 10 '14 at 16:18
  • $\begingroup$ People are working on that. $\endgroup$ – Zoltán Schmidt May 10 '14 at 16:20
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    $\begingroup$ Also, there are no random part failures (so redundancy is less important and you don't have to worry about complexity decreasing reliability), and rockets have full throttling capability and can be restarted infinitely many times. $\endgroup$ – cpast May 10 '14 at 19:30
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    $\begingroup$ and do remember that the game is still in beta, aerodynamics are on the list of things to improve. Multi body physics might be, but may well have been left out to improve performance. List support is I think deliberately left out to reduce complexity and increase playability. $\endgroup$ – jwenting May 13 '14 at 7:17
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    $\begingroup$ I must object on the re-entry heating being modeled well. I'm playing 1.2.2 as I write this, I've got an early Mun rocket coming home. It's now made two passes through the fire tail first, burning off half the heat shield. I decided to try going nose first and while things are getting hot nothing is in danger. Obviously on the pass where I actually come out of orbit I will have to be tail first but I can aerobrake this way without burning my heat shield. $\endgroup$ – Loren Pechtel Dec 20 '16 at 5:13
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One thing that is different is the lack of orbital decay. In kerbal, if you get above 68km, you will stay there forever. In real life, even extremely high orbits are subject to decay, since our atmosphere is much more complicated than KP can model.

Things like the ISS have to constantly make adjustments to stay in orbit. Things like solar flares have a tendency to spew atmospheric particles up into higher orbits and make orbiting objects slow down.

I think the game is definitely much easier with its simplified atmospheric model, and I for one am glad to not have to worry about my orbit changing once I achieve one.

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    $\begingroup$ When not time-warping orbits will decay due to the numerical integration which is used. However the opposite side of the orbit will actually increase while the near side decreases. So by switching time-warp on and off on the right time allows you to make and orbit more or less eccentric. $\endgroup$ – fibonatic May 10 '14 at 22:54

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