'Best' Orbits

[Tux]

What are various orbit's 'best' for. For example is it more efficient to get into a low orbit of Kerman to then blast to another planet or is it better to get into a high orbit before going to another planet etc.

100km - ??

200km - ??

300km - ??

>300km = ??

[Taki117]

200km is good for space stations because at >160km the ground stops being partially loaded. 100km is a good parking orbit for interplanetary (Oberth and all that) Beyond that, it really doesn't matter.

[Pursuedtank]

Generally it is best to be in as low an orbit as possible, to take advantage of something called the Oberth effect (An explanation can be found here). This means that around Kerbin you want to be in a roughly 80km (or lower) orbit, in order to get maximum savings in terms of delta v.

[Vallius]

I don't usually think of a 'best' orbit in terms of altitude for transfers (so long as you don't reenter the atmosphere), since your delta V needs depends a lot more on your orbital transfer methods. Your orbital direction (normal or retrograde) and inclination matter far more in terms of saving fuel. That being said, the higher your orbit is, the cheaper it will be to change eccentricity and inclination (most important for docking and/or precision landings).

Personally, I like to use 100 km for a minimum 'safe' orbit, and between 200 and 300 km for space stations and other multi-launch constructions.

Edited June 2, 2014 by Vallius

[Tux]

they all seem like good answers. we can consider this string answered

[Pecan]

More agreement - I try to apply 'traffic separation' rules:

75km - Low-rendezvous/de-orbit orbit. Everything that launches should be able to make it higher than this so it's just for things preparing to re-enter and the occassional runtresearch ship that struggles to get to orbit at all - in which case a tug will be on its way to take it somewhere better.

100km - Interplanetary holding orbit (Oberth and all that, even if I STILL don't actually understand it ^^).

150km - Rendezvous-phasing orbit - high enough to phase against 75km below or 200/250km above, without getting in the way of station traffic.

200km - Station traffic orbit.

250km - High-rendezvous/parking orbit. The waiting room.

[michaelhester07]

The best orbit is one that Jeb didn't plan (you know the ones that end in a really large expensive fireball crashing into the mountains ).

For me the best orbit is wherever the ship ends up after I burn out the launch stage... unless there's 1300 dv left and my periapsis is 100km or more, then I cut the engines and save the orbit insertion stage for something else.

[Kasuha]

For example is it more efficient to get into a low orbit of Kerman to then blast to another planet or is it better to get into a high orbit before going to another planet etc.

If you're transferring from surface, then the most efficient starting orbit has periapsis at about -100 km. Meaning your ejection trajectory (the part behind you) will never raise above Kerbin's surface.

If you want to circularize and then eject towards outer space, then the lower the better.

If you plan a refueling station, stop there and only count dv from that station, disregarding any fuel transport between Kerbin and the station, then slightly above 600 km is a good place. Kerbin is small and serene and its map does not eat too much GPU from there. And most planets are cheaper to reach from there than from LKO. You lose somewhat on Oberth effect but you don't need to climb so much of Kerbin's gravity well.

[cantab]

My thoughts.

Lower orbits:

Are easier to launch into. This can matter especially for marginal launchers. Even for typical cases, a launcher capable of getting a payload in a 100 km orbit might not loft the same payload to 300 km.

Are easier to deorbit from, especially on bodies with atmosphere. Again, deorbiting from a few hundred km over Kerbin can require a non-negligible amount of fuel, especially if you plan on doing it with your RCS.

Are more efficient, ground to target, as parking orbits before making interplanetary travel.

May be easier to aerobrake into, since you won't have to raise periapsis so much.

Higher orbits:

Are easier to dock in. This is because things have less curved trajectories.

Are in darkness for a smaller percentage of the time. Since docking in the dark is no fun, this can be a factor if you haven't got lights.

Are easier to escape from, and for some interplanetary transfers require less fuel from that orbit. If you're using a fuel depot, reducing the fuel needed after visiting the depot may be more important than reducing the usage ground-to-target.

Are easier to change inclination in, though the difference is small until you start talking about several thousand km.

Can be quicker and less wasteful to rendezvous with, since you have the option of establishing a phasing orbit either below or above the target orbit.

Inclined orbits:

Are essential for surveying. In the stock game, this is mainly getting biome-specific science.

Are easier to land on non-equatorial locations from, with patience to wait for the landing site to rotate under the orbit. If you're in an equatorial orbit and want to land significantly north or south, you'll need a major normal component to your deorbit burn.

When coming into a planet or moon's SOI, are just as easy to reach as equatorial ones, you simply need a small mid-course correction on the way to line things up.

Eccentric orbits:

Are needed for rendezvousing.

May be useful for science by getting both low and high altitude results.

Are generally the easiest to get captured into on arrival at a body.

[Eric S]

Higher orbits:

Are in darkness for a smaller percentage of the time. Since docking in the dark is no fun, this can be a factor if you haven't got lights.

Correct, though you're in the dark for a longer period of time. Not much of an issue for docking, but if you're setting up an RT2 communications constellation, that might be an issue.

[James_Eh]

Lower orbits:

Are easier to launch into. This can matter especially for marginal launchers. Even for typical cases, a launcher capable of getting a payload in a 100 km orbit might not loft the same payload to 300 km.

Absolutely true, unless your upper stage (and the timing of your lower stages) has major TWR issues and you simply can't circularize a 100 km orbit once you clear the atmosphere. (I have one mess of a ship that can't do 100 km but easily does 140.)