Most efficient way to gain orbit of a planet

[Ultermarto]

So as anyone who's ever tried visiting another planet, or even anyone who's ever just wanted to get their kerbals from the Mun to a stable orbit, will know, re-orbiting and stabilizing the orbit around a planet takes a lot of delta-V. Say you're hurtling toward's Duna at 10,000 mps, for example, you need to burn most of that to achieve a stable orbit. Normally these kind of maneuvers take up a significant amount of my mission fuel.

Anyway I've got this ship, consisting of a large lander coupled with a LDFB (long distance fuel buddy, carries fuel, you know), currently on its way back from Mun. What I want is to get it into a stable 70,000 km orbit around Kerbin, so that I can reuse it again (assembling these things is a pain). I'm pretty sure I can do it, but what I want to know is what's the most efficient way of doing it? I know, for example, that with our good friend the Oberth effect, adding 10mps to your orbit at a low periapsis can make a much greater difference than otherwise (since your additional velocity is introduced at a time when velocity is most poten), meanwhile, it's obviously much easier to kill your orbit whilst orbiting at 10mps at a very high altitude, rather than at 2,000 mps at a low one. So I know how to make use of the Oberth effect whilst escaping from a planet, but what about returning and stabilizing?

For example, right now I can see two options;

1. I do one relatively small burn at Mun's altitude to lower my Kerbin periapsis to 70,000m, then do another, necessarily much more powerful burn at the periapsis in order to lower my apoapsis.

2. I make several burns at varying periapses and apoapses, lowering my orbit each time, such that the route makes a sort of spiral shape. This way, I avoid making one huge burn whilst travelling at stupid-meters-per-second at 70,000m. But as far as I can see, the twi approaches seem to require the same amount of detla-V.

So what do I do?

[Khrissetti]

Aero-brake.

That is to say, dip your ship's pe just into the atmosphere (try 60km) and you'll see your ap come down as the atmosphere drags on it. Do several passes until your ap is where you want it to be, then do a little burn at ap to raise your pe. problem solved.

[GoDores]

Aerobrake.

[Pursuedtank]

Defiantly the best way is aerobreaking, which involves dipping your craft into the atmosphere to reduce your speed, and orbit. For a return from the Mun burn so that your periapsis is around 35 km, (At this point I should mention that this is a rough estimate and I am not responsible for any craft that you loose as a result of this. This website might help however, Don't forget to quicksave). Then your apoapsis should lower down to an acceptable hight, at which you would warp to apoapsis, burn to raise your periapsis out of the atmosphere and make any final adjustments.

Of course this can be used to transfer to any planet with an atmosphere. It reduces a lot of Delta V costs, but you have to get the correct height.

[RogueMason]

Argh, beaten to the suggestion of aerobraking. Hmm, maybe something a little more extreme then...

Lithobraking? That will slow you right down. Granted, you may experience rapid unplanned disassembly in the process, but you will practically instantly lower your orbit

This method is only if you want to plough into the surface at a high velocity though, so be warned

[Pursuedtank]

Argh, beaten to the suggestion of aerobraking. Hmm, maybe something a little more extreme then...

Lithobraking? That will slow you right down. Granted, you may experience rapid unplanned disassembly in the process, but you will practically instantly lower your orbit

This method is only if you want to plough into the surface at a high velocity though, so be warned

I'm not sure you would be able to establish a 70km by 70km orbit by doing that So I think that aerobreaking would be a slightly better option.

[Mr Shifty]

Without aerobraking, you have to escape the Mun's SOI and drop your periapsis to Kerbin. If you burn directly from the Mun's surface and escape retrograde to the Mun's orbit, this will take about 850 m/s. Then it's another 850 m/s or so to circularize at LKO. With aerobraking, you can reduce that second 850 m/s to a couple 10's of m/s.

[arq]

As a note, if Kerbin did *not* have an atmosphere, it would be most efficient to, from Mun, burn retro to Mun's orbit until your Kerbin periapsis is at the desired altitude, wait until you reach peri, then burn retro again to reduce your apoapsis. This is called a Hohmann transfer, and is most efficient for most manuevers (excepting a few where a bielliptic transfer is slightly more efficient).

But as others have suggested, aerobraking is, when possible, by-far the most efficient technique for lowering an orbit or for capture in a body's SOI.

[espm400]

Just one thing to keep in mind when aerobraking; eventually, re-entry heat is going to be permanently added to the game. Although you'll still be able to aerobrake to a limited degree after that, dipping yourself way into a planets atmosphere may cause some minor issues, like blowing up.

Personally, as I'm using the Deadly Re-entry mod, I generally only use light aerobraking to bring a highly elliptical orbit down to a more circular one in a series of passes. I just decided not to get too used to it, as you won't be able to do it forever.

[Ultermarto]

As a note, if Kerbin did *not* have an atmosphere, it would be most efficient to, from Mun, burn retro to Mun's orbit until your Kerbin periapsis is at the desired altitude, wait until you reach peri, then burn retro again to reduce your apoapsis. This is called a Hohmann transfer, and is most efficient for most manuevers (excepting a few where a bielliptic transfer is slightly more efficient).

But as others have suggested, aerobraking is, when possible, by-far the most efficient technique for lowering an orbit or for capture in a body's SOI.

Thanks for answering my question. But yeah, I guess aerobreaking it is.

[Cashen]

Use this calculator: http://alterbaron.github.io/ksp_aerocalc/

Once inside the sphere of influence of the desired planet, enter your current orbital altitude and velocity, and it will compute what orbit you're on. Enter the desired apoapsis of your final orbit after aero-capture, and it will spit our what periapsis you need to aerobrake through to get that. Be careful not to be too aggressive with a low apoapsis, the calculator may instruct you to fly through a periapsis low enough that you'll re-enter and crash. Better to do several aero-breaking passes, gradually shrinking your orbit, and then boosting periapsis out of the atmoshphere and circularizing with your engines.

[Superfluous J]

Just one thing to keep in mind when aerobraking; eventually, re-entry heat is going to be permanently added to the game. Although you'll still be able to aerobrake to a limited degree after that, dipping yourself way into a planets atmosphere may cause some minor issues, like blowing up.

But I don't wanna explode!

Personally, as I'm using the Deadly Re-entry mod, I generally only use light aerobraking to bring a highly elliptical orbit down to a more circular one in a series of passes. I just decided not to get too used to it, as you won't be able to do it forever.

That is a great idea, actually. I haven't installed any mods yet because I don't want to hurt my ability to play the game vanilla, but you gave a very good reason for a vanilla player to install Deadly Re-Entry.

[SRV Ron]

When aerobraking, you want to aim for a window that doesn't slow you down too rapidly (and subject your Kerbals to excessive G forces.) Neither do you want to skip back out of the atmosphere unless the goal is to orbit at a lower overall altitude or enter a planetary system when short on fuel.

[espm400]

~snip~

That is a great idea, actually. I haven't installed any mods yet because I don't want to hurt my ability to play the game vanilla, but you gave a very good reason for a vanilla player to install Deadly Re-Entry.

I don't think I could go back to vanilla. All at once I installed FAR, DRE, IonCross Crew Support, and RemoteTech, and although it took some serious getting used to, I wouldn't go back to a stock build. I can't wait for the features that these mods bring to the table to be implemented in the actual game (if they are...).

[TheHengeProphet]

Another way of gaining planetary orbit, if you can path in right, is gravity capture, or gravity assist, using the gravity of a body's moon to turn you in and slow you down. This is more difficult, but less dangerous than aerobraking, but if the window is wrong, you might waste more fuel trying to achieve it.

On a moonless body, or on one where the window is wrong to gain gravity capture, the best place to slow down is nearest to the body as possible, so it is advisable to nudge that in before you get there. All you need to do is get the apoapsis inside the sphere of influence, and after that point, manoevering is fairly simple.

[KerbMav]

Just one thing to keep in mind when aerobraking; eventually, re-entry heat is going to be permanently added to the game. Although you'll still be able to aerobrake to a limited degree after that, dipping yourself way into a planets atmosphere may cause some minor issues, like blowing up.

Personally, as I'm using the Deadly Re-entry mod, I generally only use light aerobraking to bring a highly elliptical orbit down to a more circular one in a series of passes. I just decided not to get too used to it, as you won't be able to do it forever.

But it was so cool to aerobreak just 30km above Laythe while coming in real fast! ;p

Well, maybe I should give DRE mod shot finally, just to make sure I am prepared for whats to come.

[lammatt]

aerobrake is your friend...

(that's why moho is harder to orbit since it has no atmosphere and your approach speed is pretty high)