Jon Goff has a proposal for doing lunar missions with a bi-elliptic transfer. It makes a lot of sense, actually, for Low Lunar Orbit, or deep space, though I’m not sure there’s any benefit for a Lagrange point, because the plane change out at that distance doesn’t cost much anyway (one of the many reasons that I find Lagrange points preferable to LLO).
The basic idea is to do the plane change at a very high altitude. In fact, this is a technique that can make sense even for LEO plane changes, if they’re big enough. I forget where the crossover is, but there is a certain amount of plane change where it is actually cheaper to go out to GEO (or higher) and back than to do it with a single burn in LEO. We looked at it a lot back in the eighties when we were doing tug studies.
Rand,
Actually, the trip from LEO to L1/L2 faces at least some of the same restrictions as from LEO to LLO. Even for L1/L2, you really want your departure plane to be lined up with the Moon. So, you’d need to use something like this at least for the TLI departure if you want frequent opportunities. The benefit L1/L2 has in this case over LLO is that you don’t have to do anything tricky on the lunar side of things. But you’d still likely need to do stuff on the TLI and EOI side (assuming you want to return from L1/L2 to your LEO station)…
That enough acronyms for one comment?
And as to your other comment (about doing an LEO plane change by going to GTO, doing the plane change there, and then returning to LEO), I found a paper a while back that went into the math. I was going to blog about it at the time, but got swamped at work. I’ll see if I can dig it up.
~Jon
Now that I think about it, you’re correct. I was thinking about the planar difference between the inclinations, but you’re talking about eliminating the need to line up the nodes. But it’s still easier than LLO.
Yeah, I agree that L1/L2 has a lot going for it. I do think though that LLO also has some benefits in some situations. Let’s do both. 🙂
~Jon
Hey Rand,
I was looking over my idea some more, and it looks like it probably won’t actually do what I think it would do. It might expand the launch windows a bit at low cost, but it doesn’t look like it’ll be able to give daily windows like I thought it would.
Maybe I should stick with blogging about something I actually understand…
~Jon
Jon-
If you didn’t blog about this particular topic, it would have remained an unexplored option in your head, or just on paper. Getting it out of your brain and to the internet gives you and others an opportunity to comment on it and flesh it out.
Great ideas come from refining and culling huge groups of mediocre ideas. If everyone left everything bottled up in their heads, we’d never get anything good done.
John,
Good point. I guess I was more thinking that I should’ve made it clearer that this was an idea that I wasn’t sure would work but thought might be interesting if it did. I’m just worried that I may have misled a lot of people who know just as little about orbital mechanics as I do.
~Jon