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SalehRam

Retrograde orbit (from east to west) is it a thing?

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I never done this before, and never tried it, every time I go to orbit, I just make my gravity turn to east, so my orbit become the normal one west -> east...

But how about the other way around? any practical uses for it? any things related to planetary travel or stuff like that? other than some contracts which require a reversed orbit...

Edited by SalehRam

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You mean retrograde orbits? Apparently impractical since I heard that it costs more to go up that way, but will always guarantee you an encounter on your destination planet or moon.

Done it before, when orbital nodes and encounter indicators aren't a thing yet.

Edited by Flixxbeatz

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One possible use is when you are going for the outer planets with an ion powered craft - starting from a retrograde orbit puts your departure node on the side of Kerbin that's facing the sun.

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Only practical use I know for retrograde orbits (inclination around 180°), unless launching from a body revolving westward (unlike Earth and Kerbin) is to make rendezvous with objects in a retrograde orbit as well, or accomplish those contracts that specifically require so.

The penalty for a retrograde launch (the horizontal speed eastward due to a body rotation is not added, but subtracted) is generally enough to exclude such inclinations for practical reasons.

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If your purpose is just to orbit, not really. But if you want to transfer to another place, sometimes retrograde orbit is preferred , depending on how you want to approach your target.

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Launching into a retrograde orbit at Kerbin requires about 350 m/s additional delta-v, compared to launching into a prograde orbit.

When orbiting other bodies with an intention to land, once again it costs additional delta-v to match velocity with the surface if you are orbiting retrograde.

All bodies in the game rotate in the same direction.

Happy landings!

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But if you want to transfer to another place, sometimes retrograde orbit is preferred , depending on how you want to approach your target.

I do not understand this. How/why does it matter which orbit (prograde/retrograde) you have at Kerbin if you are intending to transfer to another body?

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The reason it takes more dV to get into a retrograde orbit is that you need to overcome the velocity that Kerbin's Eastward rotation gives you. Otherwise there's no trick or importance to it and there isn't that much extra work required (from the engines, there's no more extra difficultly for you at all).

Deutherius and diomedea said the important stuff though: the only practical reason to go into a retrograde orbit is if you need to do an ion burn in the sun or meet a vehicle/contract in retrograde orbit as well.

For transfer to the moons or other planets there's no benefit whatsoever.

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Retrograde orbits are fun. try to put a space station in orbit like that and you may have two. One will be missing a module.

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I haven't checked the math yet, but it may be cheaper (than going immediately retrograde) to launch straight up, raise apoapse very high, then establish a retrograde direction with periapse at desired altitude once you reach peak height. Fighting momentum will be easier while higher up in the gravity well. Even if this does save any dV, in order to maintain that advantage when going for a lower retrograde orbit you'd need to use aerobraking to bleed off velocity until apoapse comes back down to desired height. Will investigate and post any interesting results.

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Launching retrograde requires just 350 m/s more than launching prograde. With 350 m/s you don't even launch into a keosyncronous transfer orbit (it takes about 600 m/s). The orbit you should aim for to have a requirement of less than 350 m/s to change inclination of 180 deg extends higher than the Mun: an usual Mun return trajectory, with Pe inside Kerbin atmosphere and Ap about the radius of Mun orbit, has an apoapsis speed of 160 m/s circa.

So no, it' s better to aim to retrograde from the beginning.

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impyre just got it mixed up a bit, his maneuver is useful to turn orbit from prograde to retrograde or vice versa.

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I personally have used retrograde orbits for the thrill factor. If your equatorial LKO is getting crowded with satellites, consider adding a few retrograde sats so you can have the thrill of watching objects race by at closing speeds of nearly 5000 m/s. It conveys a palpable sense of just how fast orbital velocity really is.

I've challenged myself to put a satellite into the same (but retrograde) orbit as another satellite to try to get them to collide. In fact, once in a late game after I'd run out of other things to do, I once launched a fleet of 60 "Kessler" sats into retrograde LKO to see if I could generate high-speed collisions with my other sats. Turns out actual collisions are really difficult to achieve, but even the near misses can be thrilling to watch.

BTW might be interesting to put a large asteroid into retrograde equatorial LKO. It might be big enough to get some actual collisions. Has anyone done this?

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I think someone needs to audit your mission planning department, Yakky.

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I think someone needs to audit your mission planning department, Yakky.

Yes, the guy who designed that mission was fired. Literally. Under a rocket engine.

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I personally have used retrograde orbits for the thrill factor. If your equatorial LKO is getting crowded with satellites, consider adding a few retrograde sats so you can have the thrill of watching objects race by at closing speeds of nearly 5000 m/s. It conveys a palpable sense of just how fast orbital velocity really is.

I've challenged myself to put a satellite into the same (but retrograde) orbit as another satellite to try to get them to collide. In fact, once in a late game after I'd run out of other things to do, I once launched a fleet of 60 "Kessler" sats into retrograde LKO to see if I could generate high-speed collisions with my other sats. Turns out actual collisions are really difficult to achieve, but even the near misses can be thrilling to watch.

BTW might be interesting to put a large asteroid into retrograde equatorial LKO. It might be big enough to get some actual collisions. Has anyone done this?

Good luck with that, I don't think the game is even capable of recording an impact at those velocities. Even if the two crafts hit each other dead on, the physics engine won't have enough time to notice and they'll just pass through each other (just like time warping straight through a planet).

Your best bet is probably to work with really long vessels and right positioning (to maximize the volume they will share when passing through each other) and to set your delta physics time to something huge. But small satellites or asteroids are most likely not going to cut it

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Good luck with that, I don't think the game is even capable of recording an impact at those velocities. Even if the two crafts hit each other dead on, the physics engine won't have enough time to notice and they'll just pass through each other (just like time warping straight through a planet).

I suspect you're right. But maybe with a big asteroid so that there's an increased chance of collision detection while the two objects are overlapping? Not sure, just curious.

Shrinking the delta physics time is one potential solution. But then the game will crawl...

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Launching retrograde requires just 350 m/s more than launching prograde. With 350 m/s you don't even launch into a keosyncronous transfer orbit (it takes about 600 m/s). The orbit you should aim for to have a requirement of less than 350 m/s to change inclination of 180 deg extends higher than the Mun: an usual Mun return trajectory, with Pe inside Kerbin atmosphere and Ap about the radius of Mun orbit, has an apoapsis speed of 160 m/s circa.

So no, it' s better to aim to retrograde from the beginning.

Yep. I wasn't sure how high you'd have to go to make the inclination change maneuver become cheaper than the extra cost associated with retrograde launch. In my test I went to apo of about 250km and still suffered heavy losses from launch inefficiency (and still didn't save hardly anything on the direction change)... so I'd definitely agree. Besides, using a retrograde gravity turn is just simpler anyhow.

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impyre just got it mixed up a bit, his maneuver is useful to turn orbit from prograde to retrograde or vice versa.

I wasn't really mixed up, I was just wondering aloud whether the savings of executing inclination change at higher altitudes would be worth it in the context of this discussion.... which they aren't lol.

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How about cost of changing to retrograde if already in prograde orbit ? At some point I had couple satellite contracts which I tried to fulfil with single satellite. There were 2 Kerbin orbits to achieve (one retro and one prograde) and one orbit around the Mun. After reaching prograde orbit around Kerbin I tried to go retrograde but it showed that I lacked dV, so I went for the Mun instead. After reaching Mun orbit it turned out I could still go for Kerbin retrograde orbit. I just used Mun to turn around. Is this way really more effective one or just my attempt to switch from prograde Kerbin orbit to retrograde without going around Mun was wrongly calculated ?

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Changing to a retrograde orbit can be massively cheaper out by the mun than in low kerbin orbit. In LKO you are moving at over 2500m/s to turn around and head the other way you are going to need >5000m/s. Out by the mun you are going at only a few hundred m/s and using the mun's gravity you can slingshot for even less.

Wikipedia says that a few Israeli satelites are launched retrograde, possible mostly because they only have a west facing coastline and they don't want to launch over their neigbours. Sun synchronous satelites are slightly retrograde too.

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