# object motion in space when at maximum speed.

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can't figure how to describe it better than that. what I am trying to figure out is ... when a space craft is being pushed forwards by its engine at the maximum capability of that engine (top speed) hwat happens if it rotates itself 90 degrees and starts thrusting that way... the motion "forward" would continue vector (100,0,0) example but if I add the new vector of thrust to it vector (0,.1,0) example it will build up to (100,100,0) eventually but the speed of that vector exceedes the maximum thrust of the engine. I know that it will change direction if it thrusts sideways, but what does the speed do in a situation like that? [Edited by - Ebola0001 on November 16, 2006 11:19:32 AM]

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Well, the thrust is a Force, which directly affects acceleration, not velocity. So in open space, assuming no external forces, there is no maximum velocity (except the speed of light). The max thrust of your engine only impacts your ship's maximum acceleration, not maximum velocity. So yes, you can reach whatever speed you'd like.

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so the top speed discussed when they speak about stuff they launch in space is solely based on acceleration from the fuel, and how much fuel they carry?

I thought there was a limit on how fast a particular type of propulsion could propel you in space...

eventually you will outrun the explosion of a chemical rocket, and the like

[Edited by - Ebola0001 on November 16, 2006 11:59:40 AM]

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There is no maximum speed in space for any onboard fuel, as far as I know.

So you can handle it in whatever way you see fit; the maximum speed is fake to start with so there's no one 'correct' way of doing it. Many space games allow you aeroplane style controls as that's what is intuitive for people – never mind the realism. In which case you'd turn the ship, not thrust it sideways.

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so what your saying is that given unlimited fuel, a chemical rocket could propel you to just short of the speeed of light???!!!

[Edited by - Ebola0001 on November 16, 2006 11:32:22 AM]

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You would asymptotically approach the speed of light, yes.

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you can't outrun the "explosion" as it is attached to you. That's like trying to outrun a "kick me" sign tatooed into your back.

Yes you can get to 0.99999999999c with a chemical engine. And a crap load of fuel. And an engine big enough to push that fuel...

The only real propulsion method limitation short of the speed of light would be a solar sail. It can only be so efficient, and as you get further away from the star pushing you, power drops away. But thats ok since you're already moving at an appreciable fraction of the speed of light.

If you want to try a real spaceflight sim that is free, go to:
http://www.orbitersim.com

You can try it yourself even. hope that clear enough.

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I don't think the stuff about reaching the speed of light is right, but anyway I'm not going to argue cause you probably know more than me. But for your original question, are you saying that now that the ship's going at (100,100,0) it is breaking it's maximum engine speed because it's actually going at sqrt(100^2+100^2)? Well it's not.

The ship is moving at sqrt(100^2+100^2), but it's engines are only propelling it at (0, 100, 0) thereby not exceeding your maximum engine speed.

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The typical prescription to correctly limit the speed in the way you want is to normalise the velocity vector once per frame.

I.e. multiply each component (x, y, z) of the velocity vector by the desired masimum speed, over the current velocity vector length.

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yeah I have the functionality to limit the speed of travel, but i was thinking that in reality there were such limits on speed, but since there are only artificial limits based on the game rules set.

I think I will use something like iMalc suggested) in that once your at your maximum speed you will only change direction when thrusting 90deg to movement. but with the overall length of the vector being capped at the engines maximum movement speed.

:)

[Edited by - Ebola0001 on November 16, 2006 11:48:59 AM]

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