Is a Mun/other orbit reversal practical?

[Dave Kerbin]

After testing a rover intended for Duna on the Mun my test pilots Jeb and Bob where sent down a lander from my Mun station to bring them back up. To get them back to Kerbin without using up the station's escape capsule, which the rest of the station crew very much wanted to keep, I sent over a spare crew module from my Kerbin station (Bill had already damaged one of its solar panels during an EVA so I was looking for an excuse to get rid of it).

However I screwed up the Mun approach and ended up being in an orbit opposite to the station. I looked into flipping the orbit by progressively changing the inclination until it turned over on itself but half way through it seemed like it would use up too much of my delta V so I changed it to a crash course with the Mun and started from scratch, sending up a brand new crew module, fueling it at Kerbin station and flying it to Mun station and back to a Kerbin landing with Jeb and Bob.

In hindsight I wonder, based on how Mun landings go, if I couldn't have just literally burned about 600m/s to kill my orbital velocity then kept burning with some altitude adjustment to reset it to the other direction. Essentially land and take off in the correct direction, but skip most of the landing part.

I also wonder if this kind of orbital correction is practical (or if there is a better way) on bigger planets with an atmosphere like Duna. When my ion probe first arrived at Duna it was also orbiting the wrong way. Fortunately that probe had tons of delta V and also a planned Ike observation period, so I pulled into orbit around Ike and then when I exited back to Duna I just exited backwards so that I got into the correct Duna orbit.

[Rage097]

Orbit reversal is really only practical in Minmus or Gilly Orbit.

[LeadMagnet]

Well I'm no expert, but the landing "without landing" to change direction seems a waste. If you have all that DV, I'd burn retro-grade until it becomes pro-grade, adjusting for a docking encounter in the process. Which I've had to do several times when I'm not paying attention tot he nav ball leaving a planet!

Alternatively, put you craft into a seriously elliptical orbit. At the AP, burn to change direction. Does save some fuel.

[Scarecrow88]

If you absolutely have to do it, keep your fingers crossed that your original orbit still has a really high apoapsis, as it cost less deltaV to change inclination the further out you are.

[Kasuha]

Apparently the most efficient way to do it is using three maneuvers:

link

[Sun]

Orbit reversal is really only practical in Minmus or Gilly Orbit.

I did an orbit reversal in Duna orbit. Still had fuel left. Only about 10-25 units.

[Depth]

What is the best method for turning around the orbit?

1. Burn retrograde until it becomes prograde

2. Increase apoapsis, do the previous method at higher altitude then circularize

3. Burn normal/antinormal at several nodes

I'd be inclined to guess 2. but it's probably going to be some long burns

EDIT: Ah thank you Kasuha

[M5000]

Of course it's practical, just make sure you do it as high up as possible! (That includes mid-transfer too)

I come in the wrong way almost every time, but I change it high up so it usually only takes 200-400m/s DV to change my orbit completely around, in a single retrograde-then-prograde burn.

[Kurtvw]

Given the proximity of bodies in the Kerbal Solar System, I've reversed an orbit at Duna by making a small prograde burn to get to its moon, and used that encounter to sling me back to Duna going to correct direction. The total Delta V for that was very low. It would probably not work at the Mun. But there are lots of places where it does work.

[Kasuha]

It's always a good idea to stop the time warp when you cross the SOI of your target. It happened several times to me that I was "fixing" my orbit from retrograde to prograde at that point. It is not cheapest but you don't waste mission time that way and it's still reasonably cheap.

[Geschosskopf]

What is the best method for turning around the orbit?

1. Burn retrograde until it becomes prograde

2. Increase apoapsis, do the previous method at higher altitude then circularize

3. Burn normal/antinormal at several nodes

There's a 4th method that works great and costs very little fuel, PROVIDED you do it when you 1st enter the SOI and are still on a hyperbolic escape trajectory. Or if you're in a very wide elliptical orbit, because the trick relies on you having a clear line of sight from your current position to your periapsis without the planet in the way.

What you do is simple burn anti-radial, lowering your periapsis right through the planet and out the other side. Voila, orbit direction changed. The closer you are to the planet, the more fuel it costs because you're having to move the periapsis across a wider angle, but this is still usually cheaper on delta-V than rotating the whole orbit around the poles after capturing into a long elliptical orbit.

For instance, one time I had a ship arriving at Duna with a retrograde orbit. I used the above method but Ike was in the way so I had to wait until I was inside Ike to do the burn. It still only cost about 60m/s.