Pro or Retrograde Capture

[Przemqo]

Hey, can someone clarify me this: if I am approaching other planet (other SOI, to be exact) and I want to perform burn to get captured, does it make a difference on which side of the planet periapsis will be? I know it is important for slingshots, but for that? I tried to find the answer but I am still confused. Thanks!

Edited September 8, 2015 by Przemqo

[Alshain]

It doesn't matter unless you want to be orbiting a specific direction. If you don't care, you can go in on either side.

If you do care, you need to make sure your direction of travel across the planet is the same or opposite the rotation of the planet, and then there are polar orbits.

Edited September 8, 2015 by Alshain

[Warzouz]

If you want to land, you'll need to expend more fuel if you come from a retrograde orbit than from a prograde one.

Fixing your orbit early in transfer is very cheap, and while you're there: put your PE on equatorial, so you'll get a very far AN or DN node to do some cheap inclination change.

[ghpstage]

Most of the results of a retrogradce orbit are felt after the orbit is achieved, the increased dV cost for landing on planets that has already been mentioned being one, but also as all moons in the stock system orbit their parent planets prograde it makes getting to those extremely costly!

[tbarcello]

Hey, can someone clarify me this: if I am approaching other planet (other SOI, to be exact) and I want to perform burn to get captured, does it make a difference on which side of the planet periapsis will be? I know it is important for slingshots, but for that? I tried to find the answer but I am still confused. Thanks!

For example, you want to make eccentric orbit 50 km on 500 km. I would set up my approach to 500km and make a burn to circulize or make 50k periapsis, only because I'm using nuclear engines that take longer to burn, so it is easier to time the burn on higher orbit.

[Geher]

For example, you want to make eccentric orbit 50 km on 500 km. I would set up my approach to 500km and make a burn to circulize or make 50k periapsis, only because I'm using nuclear engines that take longer to burn, so it is easier to time the burn on higher orbit.

But it costs more fuel, because you're not exploiting the oberth effect.

[mrclucks]

I don't believe it matters which way you end up orbiting to get captured. Coming in prograde will speed you up relative to solar orbit, but not the body you're orbiting and coming in retro is the reverse.

If you are in a retrograde orbit and you enter an atmosphere, you will expirence more drag and heat due to the atmosphere rotating against you at the speed of the planets rotation. On the flip side, when you enter an atmosphere on a prograde orbit, the atmosphere is rotating with you and your relative speed to the atmosphere is your orbital speed minus the planet rotation (its not 100% due to needing some sort of angle to enter an atmosphere)

[Gaarst]

As said above prograde or retrograde orbit do not change much. If you orbit a body prograde and want to land on it then you'll spare the dV corresponding to the body's rotation velocity.

Retrograde orbits allow you to have free return trajectories (used by Apollo) but it's not really useful for KSP...

[Przemqo]

Okay, now I understand, thank you all!

[KerikBalm]

Most bodies rotate so slowly that it won't matter much for landing - not more than 100 m/s.

When you've landed, look at the difference between yoursurface and orbital velocity... that is how much you save.

That's also how much you save if you launch into a prograde orbit afterwards.

It won't matter much (the heating will be different, that is all) if you will be landing in a body with an atmosphere

The biggest difference is if you plan on going to a moon orbiting the planet that you captured at, because they all orbit prograde

[GoSlash27]

I generally enter prograde because it saves me a little DV for landing, orbit, and escape.

But often for bodies that are tidally- locked I will enter polar so I can hit all of the biomes.

Best,

-Slashy

[Starhawk]

This ^.

Happy landings!

[jstnwht]

Why does a tidally locked planet deserve a polar orbit? Do not all bodies require some sort of inclination to get science in different biomes? I always attempt a prograde capture first, but for flybys (of the mun) I enter retrograde so it slings me back into a kerbin atmospheric capture. It depends on what you are trying to accomplish.

Edit: I know biomes are all along the equator, but polar orbits always guarantee all the biomes will be hit, as long as your orbit isn't synchronous or resonant with sidereal rotation.

Edited September 9, 2015 by jstnwht

[jiminator]

I reentered the kerbin soi with a reusable craft but found I was retrograde, thus all all encounters were going to be difficult. I was able to use mun though to flip my orbit around, so that works.