Geostationary Orbit

[DreadedEntity]

Since starting my career in astronomics and celestial physics, - just kidding I play KSP. Joking aside, I'm wondering if there's any special way to get into geostationary orbit in KSP. Googling that plus Earth have shown a very specific height you must reach to get to geostationary orbit(GSO) and you will automatically be in a GSO. My main question is why can't you have a GSO at any height, provided you've increased your speed accordingly? AND How can I reach a GSO in KSP?

Bonus: What is the best way to modify an existing orbit to get it into a GSO? (I imagine you would need to pull the purple markers in your maneuver to "twist" the axis to be completely in line with the planets axis of rotation, then adjust speed to match the planets rotational speed at your current height (assuming you had a completely circular orbit))

Double Bonus: Best way to reach a circular orbit (I have a satellite orbiting with a wild orbit that I cannot seem to fix).

[bang_coi]

You have to learn some orbital mechanics...

[stupid_chris]

You can't have GSO at at any height because each orbital altitude has a different energy and speed. When you go up, your orbital speed decreases, and at some point it'S slow enough to match the surface's. However, you can't just decide to have a given speed on the orbit of your choice. Your orbital speed is directly dependent of your orbital altitude. So if you were to burn until you were to negate your relative speed to the surface at a non GSO orbital height, your apoapsis would raise you would loose that orbit. The only way you could have a GSO at lower or higher altitudes would be to continuously burn towards or away from the planet to simulate a higher or lower gravitational force.

For the second point, it depends. If you want a circular GSO, you are indeed going to want to zero your inclination before going to GSO altitude. Else, a GSO can be considered for any orbit that has the same period as the rotation of the parent body. So there's a lot of possibilities for that. That being said, you can simply burn prograde until your apoapsis reaches GSO altitude then circularize.

Lastly, to obtain a circular orbit, you're going to have to take things slowly. Getting a near perfect circular orbit by hand can be a bit long. All you want to do is basically not overshoot your inserttion burn after liftoff, but you don't want to undershoot it too much neither. Then, if your periapsis is higher than the orbit you want, you will want to very gently burn retrograde at your apoapsis. If it moves, warp to your apoapsis and repeat. If it's lower, you will want to burn prograde. It works exactly the same way if you want to adjust your apoapsis, but you will want to burn at your periapsis then.

You might want to download MechJeb. I had troubles with orbital mechanics too when I started playing, and I downloaded MechJeb. By seeing how he does it, I basically learned how to do it myself. It can be a very good instructor!

Anyway, good luck!

[jheriko]

So, to explain a bit more about why distance and velocity in the orbit are related consider the simplified model where gravity is just acting in one direction, and you have an arrangement like in this diagram. v is the velocity, d is the distance - now you need v to be exactly right so that as the object falls it winds up being offset d away from the centre of mass along the horizontal direction. Of course the gravity direction varies as you go around - but all this does is make the calculation for v different - the principle remains the same. If v was greater the orbit would not be circular - it might even escape the gravity well altogether, if it was less then the same is true the orbit becomes elliptical, and if its small enough we hit the planet.

Note my diagram is not great the red x should be vertically above the black one... just pretend it is.

[Kialar]

Maybe this thread helps:

http://forum.kerbalspaceprogram.com/showthread.php/16653-Geostationary-Orbit

Can't reach the wiki, but the Kerbin-Document there holds information about the geostationary orbit.

[purpletarget]

The others have touched on most of the salient points. You need to be at the specific altitude where the orbital period of the s/c is equal to the planet below, pretty much circular, and you need to be equatorial if you want it to be properly geo-stationary, and not just geo-syncronous.

If you would a quick primer of why orbits work the way they do, I touch on it here.

[Fyrem]

also, (you may know this, but perhaps you don't). a geostationary orbit is MORE a function of Orbital Period, NOT height.

ok, the above line, while true, can be VERY confusing. But here is the better way to say it:

you can obtain a geostationary orbit two ways

1) your sat needs to be at "Exactly" 2,868.75 km for both AP and PE. this is NOT easy to achive.

or

2) your sat needs to be "Roughly" 2,868.75 km AND (using Mechjeb, or Kerbal Engineer, or other means of displaying orbital data) get your Orbital Period to be 6 Hours. this allows your AP and PE to be a little bit off, but still you will be in a geostationary orbit. Launch to 2868, perform a basic circulization, then using a SMALL thruster (EG: Ion) burn prograde/retrograde to fine tune your Orbital Period to 6h, 0m, 0s. or as close as you care to.

Most people actually find that achieving option 2 is a HECK of a lot easier.

[Jod]

Your speed in orbit creates centrifugal force that counteracts gravity, more speed = more centrifugal force that pushes you into higher orbit. Hence no increasing velocity and staying at the same height.

That is the simple explanation that does not involve vectors. If anyone is interested how it really works in vector form then there is only one force - gravity, that constantly changes the velocity vector even in circular orbit because rotation is in fact a change in x/y/z components of the velocity vector. By increasing your velocity using thrust, the same change from gravity force accounts for a lesser angle change because your velocity vector is now larger, hence you get a more elliptic orbit because it takes more time for gravity to rotate your velocity vector.

The only other way to keep your position stationary besides GSO is constantly burning fuel, basically hovering above the point you want. Orbits are freefall, you can't just throw a ball and expect it to obey your will mid-flight, physics don't work that way.

Edited June 10, 2013 by Jod

[Tex_NL]

Does ANYBODY ever bother to read the wiki before asking questions like this? The wiki link is at the top of the screen for crying out loud!

[inigma]

Answer:

Geostationary orbit over Kerbin:

Orbital Altitude: 2868.75km (I've got it memorized by now as I just put up 5 sats there over the past week while trying to develop the Age of Satellites Campaign)

Inclination: 0 degrees relative to the Mun plane since the Mun's orbit is at 0 degree relative to KSC and KSC is at Kerbin equator.

HOWTO: Set the Mun as your target and make your orbital planes match. Then get your AP and PE to average right at the 2868.75km mark. To cancel out your drift over time, you should set a goal to have a difference between the two points of 1000m or better with the target alt as close to the middle of that as possible, but 2000m is acceptable for the Campaign. I've managed to get it the difference down to 168m with great practice and actually hit the target once on the dot. As long as your average is near that altitude, you will stay in GSO predictably for years.

Edited June 12, 2013 by inigma

[GROOV3ST3R]

Answer:

Geosynchronous aka Geostationary orbit over Kerbin:

Orbital Altitude: 2868.75km (I've got it memorized by now as I just put up 5 sats there over the past week while trying to develop the Age of Satellites Campaign)

Inclination: 0 degrees relative to the Mun plane since the Mun's orbit is at 0 degree relative to KSC and KSC is at Kerbin equator.

HOWTO: Set the Mun as your target and make your orbital planes match. Then get your AP and PE to average right at the 2868.75km mark. To cancel out your drift over time, you should set a goal to have a difference between the two points of 1000m or better with the target alt as close to the middle of that as possible, but 2000m is acceptable for the Campaign. I've managed to get it the difference down to 168m with great practice and actually hit the target once on the dot. As long as your average is near that altitude, you will stay in GSO predictably for years.

I REALLY wonder why nobody has pointed that out before.

[Tank Buddy]

This is simple, a Keostionary orbit (around Kerbin) is at an altitude of 2 868.75 km and a speed of 1 009.019 m/s. To get to this orbit, simply raise your apoapsis by burning at periapsis to roughly 2868 Km, then burn again to raise the periapsis to 2868 km, fine tuning is necessary, and it may take several orbits to get it perfect. Here's the wiki: http://wiki.kerbalspaceprogram.com/wiki/Main_Page

You can direct yourself to see any information about any planet, so knock yourself out. You seem to be knew to the KPS scene, so congrats on joining the party boat (or rather space ship). Youtube is a great resource for tutorials. Channels like HOC Gaming, Try Dying To Live, Werner Von Kerman, and others are excellent resources. Just watching them play is a good way to learn, but for a very beginner, Read up on the Wiki and watch plenty of tutorials. Good Luck!

[DreadedEntity]

Does ANYBODY ever bother to read the wiki before asking questions like this? The wiki link is at the top of the screen for crying out loud!

Wiki's tend to be written by very experienced players for less experienced players; As such, they tend to make complex ideas seem elementary while being incredibly impersonal. This way average people can miss important information and leave more confused than before. By going to the forums you can put a question out there and get many answers, which you can parse into something you understand.

Guys, I am not a mathematician or a physicist (and according to my spell-check after writing those two words, particularly great at spelling). I am willing to learn, however, and most of you have given me explanations. All of which were excellent and I am pleased to say that I'm leaving smarter than when I came. So thanks everyone. But I am a little worried about the height of the GSO, I've been positioning most of my craft around 150-300km. 3000km is a bit much to me.

ALSO, I may have gone overboard with bold wording. I was a little drunk when I wrote that.

EDIT: I have gotten some very useful information here, if someone could tell me how to change this to answered that would be great. If it's not possible, a mod is certainly welcome to.

Edited June 11, 2013 by DreadedEntity

[Margaul]

Just to add to all the other great information, the reason that orbits are specific altitudes for specific speeds (in a very oversimplified explanation) is that orbits are really nothing more than controlled falling. Your spacecraft "falls" through space. It just happens to miss hitting the planet. You "fall" and the speed takes you to specific altitude on the other side of the planet, where you basically start to "fall" again, once again missing the planet, until you reach the other side. All of this falling is due to gravity. In the Kerbin system, when you fall so fast you leave the gravity of a planet, you immediately get grabbed by the gravity of the sun or another celestial body.

Now, once your falling speed is very similar to the rotational velocity of the planet, you are basically falling as fast as the planet. As explained above, this falling speed relates exactly to how far you will "fall" to the other side, and therefore, the size of the orbit.

A little weird to grasp at first, but that's how it works. Being "weightless" in orbit doesn't mean that you or your spacecraft is not affected by gravity. It's, strangely, freefall. The same weightless affect can be duplicated (and is by NASA and other space agencies) by diving a plane through the air creating a few seconds of free fall. This is part of astronaut training called "The Vomit Comet."

[inigma]

3000km does seem a bit much when you're used to LKO and MKO orbits (Low and Medium Kerbin Orbits), especially when you start seeing that circle reach out almost halfway to the Mun. But it's necessary, and realistic. And it looks great. ComSats are best at that altitude since just three of them positioned equidistant can "relay" communications to and from the KSC to any point in space. Nothing like looking down on your spacecraft/satellite on the KSC and spinning in timewarp as the ground never changes but the day/night cycle over the KSC is seen. To wil change this thread to answered, you will need to edit your original post in Advanced mode.

[Mr Shifty]

Launch to 2868, perform a basic circulization, then using a SMALL thruster (EG: Ion) burn prograde/retrograde to fine tune your Orbital Period to 6h, 0m, 0s. or as close as you care to.

It is easiest to use RCS for this because you have both forward and reverse thrusters that way. (You can adjust the orbital period up and down without having to turn the ship around.) Just point your vessel prograde, turn on RCS, then use H and N to adjust the period.

Your speed in orbit creates centrifugal force that counteracts gravity, more speed = more centrifugal force that pushes you into higher orbit. Hence no increasing velocity and staying at the same height.

Argh, no. More speed means you travel further before gravity pulls you back toward the planet. Centrifugal force is an artifact of considering the rotating reference frame as stationary. It does not actually exist. You have inertia, and gravity curves your path; that's it.

Set the Mun as your target and make your orbital planes match.

Or just push/pull your prograde marker until it's at the point where the horizon and 90 degrees cross on your Navball. This method is general and will work even when there is no moon with an equatorial orbit.

Geosynchronous aka Geostationary orbit over Kerbin

They are not the same. Geosynchronous is any orbit with a period of 6h0m0s. Geostationary is a circular equatorial geosynchronous orbit.

[Sephta]

simply try it - you'll see, the first couple of 100km raising the apoapsis eats up quite a lot of dV, but in the end it gets really fast. you need only 15m/s more to cover the last half of the distance to Mun... so yes, 3000km starts slow, but gets really fast in the end, so be carefull going full throtle...

[inigma]

Or just push/pull your prograde marker until it's at the point where the horizon and 90 degrees cross on your Navball. This method is general and will work even when there is no moon with an equatorial orbit.

It's not exact though. Useful though when you have no reference at all, but its inexact since the navball's marker dot is larger than .1 degree. But still, I didn't think to use the navball to eyeball one's inclination. Good info.