Stable Orbit

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Krasny
Posts: 6
Joined: Tue Oct 15, 2013 5:34 pm

Stable Orbit

Post by Krasny »

For a few hours I have been trying to get into a stable orbit around Earth, with comic failure.

The two methods have have used are thrust upwards until I'm at 100 km, then thrust to the edge of the Earth until my left velocity is 11.2 km/s.

The second is to take off at a slight angle to the horizon and thrust until my direction indicator is the same as my direction of thrust indicator.

Could someone post a method of getting into a stable orbit?

Yes I know there is an autopilot, but Machete don't use autopilot!
nozmajner
Posts: 1079
Joined: Mon Jul 01, 2013 3:25 pm
Location: Budapest HU

Re: Stable Orbit

Post by nozmajner »

The Community forum is be a better place to ask this kind of questions (this forum isn't supposed to be a support forum really). Here's the kitchen version of how to orbit (from somebody who learned this from KSP, so it's sure inaccurate and not properly worded), and please open a thread for this in the community forum if you need more elaboration.

The first method you are using will make a quite long ballistic path, because you are not burning prograde (velocity vector direction), so you are rotating your course while you are making it longer and more eccentric at the same time. Also 10km/s is a bit more then you need for an orbit, even for a LEO, it's almost escape velocity (~11km/s), you want about 7.2 km/s for a stable LEO.

For a stable orbit, first accelerate vertically for a while, you can even start to turn slowly to the direction you want to achieve your orbit. Like until your pressure indicator (bottom left gauge, P: #.## atm) is closing to zero, then you can cut your engines. Then you can do two things:
1. Wait for apogee, the highest point of your orbit (vertical speed is 0, or when the prograde marker is at the crosshair if you are horizontal relative to the ground.). At apogee, start burning towards your prograde marker until you reach the speed needed for orbit. ~7 km/s is a good bet, and if you press F2 while you are holding the thruster key, then it will keep firing while you can check your orbit in the system view of the map, and when you switch back to cockpit, it will cut your engines.
2. You can do something like the autopilot does: After you left the atmosphere, and you are level, fire your main thrusters and top thrusters simultaneously so you are making your orbit more elongated, but you are rotating it at the same time, sou you end up with a more circular orbit at the end. Or similarly you pitch your ship's nose a bit under the horizon (not much though) and fire only the main thrusters for the same effect. This method is usually a bit faster, but wastes fuel and it's more difficult to be precise this way, and you have to be more careful to avoid hitting the ground.

The thing with orbits is that if you do a maneuver, the effect never manifests itself on the spot you are performing it. Thrusting prograde or retrograde (where you are heading or the opposite) changes the height of the other side, Thrusting inwards or outwards (to the ground or away from it) rotates the orbit around the craft, and thrusting normal-antinormal changes the inclination (planechange, the most expensive maneuver). And thrusting in any direction will do a combination of these, and most maneuvers affect the eccentricity too (the difference between the height of apoapsis and periapsis).
Krasny
Posts: 6
Joined: Tue Oct 15, 2013 5:34 pm

Re: Stable Orbit

Post by Krasny »

Thanks for the great reply!

I was not aware there was a community forum.

I looked up the escape velocity of Earth and it said 11.2 km/s, but maybe escape velocity lowers with distance from the planet.
nozmajner
Posts: 1079
Joined: Mon Jul 01, 2013 3:25 pm
Location: Budapest HU

Re: Stable Orbit

Post by nozmajner »

You're welcome! :)
Escape velocity is the speed needed for leaving orbit. This isn't really affected by your speed as far as I know, if you hit it in any direction away from the planet, you are out and bon voyage!
You are right about that orbital speed changes with distance. The closer you are to the planet, the faster you need to travel, to miss the planet and fall indefinitely.

Anyway it's good you asked. We need a proper section about orbiting on our wiki. And that needs some proper illustrations to be useful and interesting.
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