Cepheus Posted January 22, 2012 Share Posted January 22, 2012 It is well known that the traditional approach to construct a transfer trajectory to the Mun, from Kerbin, is through a Hohmann transfer. This transfer uses 2-body dynamics (and rendered by patched conics, I believe.) The recent GRAIL mission used a slightly different approach, utilizing a three to four month low-energy trans-lunar cruise (via the Sun-Earth Lagrange point L1) to reduce fuel requirements (In 1991, the Japanese 'Hiten' mission used a similar low energy transfer.) Now, I know that 3-body systems are pretty much impossible in KSP, but is the general premise of a 'low energy transfer' without using a Hohmann or Bi-Elliptical transfer possible?This idea was somewhat inspired by meteorite 101 from over in requests. He requested GRAIL, and I wondered of the mission was even possible. Link to comment Share on other sites More sharing options...
Hypocee Posted January 22, 2012 Share Posted January 22, 2012 To the best of my knowledge no; those missions are what I mean when I reference 'one or two missions ever in history' not using conics. Link to comment Share on other sites More sharing options...
PD Posted January 22, 2012 Share Posted January 22, 2012 I do not believe they are possible as they require more than 1 active gravitational well (they make use of Lagrange points) and at present we do not model more than 1 celestial body at any given time.Shame though that is. Also, they require MASSIVELY accurate piloting (the launch window is about 1 second in length). To achieve that in KSP (even I the great believer) fear we don\'t have the instruments!PD Link to comment Share on other sites More sharing options...
lars Posted January 24, 2012 Share Posted January 24, 2012 You could consider a bi-elliptic transfer, but once you get that far away from the earth you may accidentally find yourself in sun orbit.(!)And Anyway, if you are just trying to land on the moon the hohman transfer is not necessary, and if you do that you are not taking advantage of the oberth effect. I just keep an ellipse with the major axis 11,400 km and wit until the moon gets close for orbit insertion/ direct landing.I don\'t know how much of this is already obvious to people. Link to comment Share on other sites More sharing options...
Kosmo-not Posted January 24, 2012 Share Posted January 24, 2012 You could consider a bi-elliptic transfer, but once you get that far away from the earth you may accidentally find yourself in sun orbit.(!)And Anyway, if you are just trying to land on the moon the hohman transfer is not necessary, and if you do that you are not taking advantage of the oberth effect. I just keep an ellipse with the major axis 11,400 km and wit until the moon gets close for orbit insertion/ direct landing.I don\'t know how much of this is already obvious to people.It is my understanding that people do half of a hohman transfer to get to the Mun. I haven\'t heard of anyone doing a complete one. Is your method the same, or something else?Oh, and how is a hohman transfer, at least the first part, not taking advantage of the Oberth effect when trying to get to the Mun? Link to comment Share on other sites More sharing options...
PD Posted January 24, 2012 Share Posted January 24, 2012 I used to go for that method, but now I set up for a Free Return, insert myself into a nice little orbit around the Mun, and select a landing site. Then I try to actually touch down there. I find it slightly more fulfilling than just being happy with getting grey dust from any part of the mun on my boots, and then engaging boosters to get home in 1 (or more) bits.I\'m trying to add a little realism to my Mun missions now, and I try to do things efficiently. I\'ve certainly found that using a very eliptical orbit, to transfer to the Mun saves on fuel, but that quite an obvious one?PD - This thread can potentially be locked as the OP\'s question was answered a while ago and we\'re all just wandering around off topic! Link to comment Share on other sites More sharing options...
Cepheus Posted January 24, 2012 Author Share Posted January 24, 2012 Actually, since I\'ve posted this topic, I noticed an interesting phenomenon.On a recent visit to the moon with the Gemini capsule (along with the new Saturn V) I found that I was a little low on fuel - enough to transfer to earth orbit, but not enough to land. So, my thoughts going the way they do, I tried to use the moon to slingshot into a Very High Kerbin Orbit (which I will refer to as VHKO). There\'s a funny little thing that happens with high apoapsides - the higher they are, the less ? - v they take to make the same change in the altitude of the periapsis. While in Munar orbit, I burned to about 4.5 million meters. About 2 million meters out, I left the Mun\'s SOI, and was in a VHKO; right on the border between orbiting Kerbol and Kerbin (both the map view and the camera were spazzing out) It may be a bug, but that\'s a lagrangian point right there. Even with a tiny burn (.1 m/s of ? - v) it stopped. I don\'t remember what the Apoapside was but with only 30 m/s of ? - v, my periapsis had gone from 1.2 million meters to 0.So while there may be no active langrangian points in the game, there are still bugs like this, which can be exploited. Link to comment Share on other sites More sharing options...
Kosmo-not Posted January 24, 2012 Share Posted January 24, 2012 Actually, it\'s not a langrangian point. Out at 84 million meters, which is the extent of Kerbin\'s SOI, gravity there is .0005 m/s2. It would take about 33 minutes to change your velocity by 1m/s. Link to comment Share on other sites More sharing options...
Cepheus Posted January 24, 2012 Author Share Posted January 24, 2012 Not exactly, I actually cranked up the time compression to 10000x, and sat, and watched it. It kept switching, and orbited with Kerbin. Link to comment Share on other sites More sharing options...
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