No-Orbit Free-Return

[SgìobairOg]

Is it possible to do a free return orbit, to Mün just to keep it simple, without first completing an orbit around Kerbin?

It looks like if you launch just slightly earlier and do your escape burn at your initial apoapsis it should work out. I feel like the hard part would be the timing. Unless I'm missing something it doesn't look like you gain any advantage when you circularize.

Edited January 28, 2014 by SgìobairOg

[blizzy78]

As you mentioned, going into a parking orbit first saves you from the hassles of perfect timing.

[Dave Kerbin]

Yes you can go to the Mun (free return or otherwise) without establishing an orbit, timing is important (and critical if you want free return) unless you want to waste a lot of fuel.

This was actually how I frequently got to the Mun in the demo - I hadn't really gotten the hang of making a good orbit (I wasn't even at the gravity turn stage) so I would frequently get on a suborbital trajectory and then instead of getting a Kerbin orbit I'd make a direct burn for the Mun somewhere on my suborbital path. Of course this technically meant that I had a Kerbin orbit for a period during the burn, it just wasn't a very round one or at any predetermined altitude.

[Taki117]

Is it possible to do a free return orbit, to Mün just to keep it simple, without first completing an orbit around Kerbin?

It looks like if you launch just slightly earlier and do your escape burn at your initial apoapsis it should work out. I feel like the hard part would be the timing. Unless I'm missing something it doesn't look like you gain any advantage when you circularize.

A free return orbit just means that in order to return to your starting point you don't have to use your engines again (This is what the first Apollo missions did when going to the Moon). However, (Also with Apollo) it is more beneficial to get into a parking orbit first as instead of a transfer window once a month (or so) you would have a transfer window every 30 minutes or so (Or rather once every orbit) So while you may not actually save any dV from circularizing first it does give you time to plan your transfer and perform any plane adjustments you need. Overall it's more beneficial to go into a parking orbit first.

[Tank Buddy]

You can, but it's just overly complicated. It does not require any more DV to get into a circular orbit first, so there really is no point.

[MajorThomas]

Just cause I always wanted to try it*, I took off from KSC when it was "pointed" 45 degrees ahead of the Mun. Went straight up, no turning. Up and up until Apoapsis was near the Mun. Sure enough, encountered the Mun as though I had departed from Kerbin orbit. But at no point during the flight from Kerbin did I have a Periapsis above ground.

*I call this "comic book spaceflight." Never mind orbiting.

[SgìobairOg]

Thanks, all. I tend to do FRT a lot for the moon and minmus just for the realism. If I were to screw something up (was more likely when I first started) I would be able to get back. I just tried a few without the parking orbit and I don't think I have the patience for it.

[Taki117]

Just cause I always wanted to try it*, I took off from KSC when it was "pointed" 45 degrees ahead of the Mun. Went straight up, no turning. Up and up until Apoapsis was near the Mun. Sure enough, encountered the Mun as though I had departed from Kerbin orbit. But at no point during the flight from Kerbin did I have a Periapsis above ground.

*I call this "comic book spaceflight." Never mind orbiting.

You should make note of the amount of dV you used doing this, and then compare that to the amount of dV used in your "standard" mun trip.

[MajorThomas]

You should make note of the amount of dV you used doing this, and then compare that to the amount of dV used in your "standard" mun trip.

Good idea. I sense the numbers will be close, but perhaps the most variation will come from the type of engines used. Powerful engines that get you up there quickly may perform better against gravity than the weaker, longer-burning engines.

[Taki117]

Thanks, all. I tend to do FRT a lot for the moon and minmus just for the realism. If I were to screw something up (was more likely when I first started) I would be able to get back. I just tried a few without the parking orbit and I don't think I have the patience for it.

If you want realism circularize first, also, after Apollo 12 they didn't do free returns anymore. (The only reason 13 did was because they had a problem, and they had to do a correction burn to do it.)

[Xavven]

A free return orbit just means that in order to return to your starting point you don't have to use your engines again (This is what the first Apollo missions did when going to the Moon). However, (Also with Apollo) it is more beneficial to get into a parking orbit first as instead of a transfer window once a month (or so) you would have a transfer window every 30 minutes or so (Or rather once every orbit) So while you may not actually save any dV from circularizing first it does give you time to plan your transfer and perform any plane adjustments you need. Overall it's more beneficial to go into a parking orbit first.

You should be able to get a "transfer window" slightly less than once per day (from the ground) due to Kerbin rotating.

[Champ]

Just cause I always wanted to try it*, I took off from KSC when it was "pointed" 45 degrees ahead of the Mun. Went straight up, no turning. Up and up until Apoapsis was near the Mun. Sure enough, encountered the Mun as though I had departed from Kerbin orbit. But at no point during the flight from Kerbin did I have a Periapsis above ground.

I always do that, because it is a good way to go to the mun without leaving any debris (they all fall on kerbin).

EDIT : same for minmus, except you have KSC "pointing" little less than 90 degrees (let's say, 85degrees ?) ahead of minmus. Oh, and of course make sure you won't intercept the mun before minmus ^^