Since the Direct baseline architecture is 2 J-246's, with two JUS's, one fully fueled, one fueled just enough for LEO of CEV/LSAM.
Could both JUS's be partially fueled, and have a rendevous in LE1 or LLO? You have to expend two anyway, couldn't the docking procedures be simplified that way?
Also, in that vein, if a Centaur or D4US (are they the same? Don't know much about them, if they are two terms for the same upper stage or not) can take Orion around the moon for an Apollo 8 type flyby, could one be used to take the LSAM there too, again for a LE1 or LLO rendevous?
I know fueled LSAM is heavier than Orion, so I don't know.
But now I'm curious.
You've just stumbled upon what, in my view, is the biggest weakness of the EOR-LOR mission profile. Try as you might, you can't distribute the total payload evenly among multiple identical launch vehicles without on-orbit propellant transfer.
If the DIRECT ethos can be distilled to "one kind of vehicle launched multiple times", then EOR-LOR is a questionable mission profile, a holdover from the 1.5-launch approach that doesn't make as much sense in a 2-launch architecture.
The DIRECT 3.0 architecture calls for one launch of about 100 mT and another of about 70 mT. It's not really a 2-launch architecture, hence the heavily-offloaded J-24x CLV and the barely-viable J-130 CLV alternative.
With LOR-LOR, L1R-L1R, or (especially) L2R-L2R, the CEV and LSAM each have their own upper stage for TLI and insert themselves into rendezvous orbit separately.
The key thing to understand is that the LSAM actually masses less than the CEV when it separates for lunar descent. The LSAM is only heavier than the CEV at liftoff because it does the LOI burn for itself and the attached CEV.
Remember, the Apollo CSM was much more massive than the LM, mostly because the CSM did the LOI burn for the combined mass. Whichever spacecraft does LOI becomes much bigger than the other.
But if both spacecraft do LOI and their rendezvous masses are similar, then their TLI masses are similar, and therefore their LEO requirements are similar, and they can be lofted on identical launch vehicles.
With LOR-LOR, the rendezvous mass of the CEV is notably higher than the LSAM, because now it has to do its own LOI instead of relying on LSAM. So the CEV drives launch vehicle requirements.
But with L1R-L1R or (especially) L2R-L2R, the CEV takes a cheaper round trip to the rim of the moon's gravity well. This increases LSAM mass, but it decreases CEV mass by a much greater amount, and the combined effect helps even out the rendezvous masses.
With L2R-L2R, CEV liftoff mass is roughly the same as with EOR-LOR (depending on trajectory), even though it does its own LOI, and LSAM liftoff mass is dramatically reduced to about 20 mT, not much less than the CEV.
Either J-130 or Not Shuttle-C could lift a 25 mT spacecraft with a 45 mT EDS to put it through TLI. With a 2-launch L2R-L2R profile, this is enough for the baseline lunar mission.
Additionally, this same 5m Centaur-derived EDS could double as the new upper stage for EELV, and it would only make sense for ULA to lead the development, rather than NASA/MSFC.
This mission profile allows for the development of a significantly smaller upper stage that's much more versatile and would see higher flight rates. It also allows for the development of a significantly smaller LSAM descent stage with a lower center of gravity for landing stability.
The number of SSMEs expended per mission is reduced to six, global access to the lunar surface without expensive plane-change maneuvers, and global communications relay to earth via CEV at EML2.
If you try to replicate a 1.5-launch EOR-LOR architecture with one kind of launch vehicle, the closest you can get is DIRECT. But for a true 2-launch architecture, L2R-L2R makes more sense.
Ok, you now make me ask a lot more questions than the first time.
To help me understand what you just described better, maybe you can explain a few of your comments.
Briefly, what are the advantages/disadvantages to renevous at EML1, EML2, and lunar orbit. Apollo went to orbit, correct?
I can understand EML1, as you are between the Earth and Moon. For L2R, you'd need to be on the far side of the moon? Wouldn't that burn extra fuel to get there than L1R?
In either L1R or L2R, the CSM would stay there, and the LSAM would decend to LLO, with the descent stage performing LOI, and then firing more to degrade that orbit slowly until you're over your landing zone, correct?
And the advantage with this is the CSM doesn't need to escape lunar gravity, so it doesn't need that fuel? It just nudges itself out of the lagrange point and falls back to Earth? How would that work at the L2 point? It'd fall to the moon would it not? Would it do a swing by to the L1 point, then fall to Earth? Seems like it'd need some fuel for that, that the L1 points wouldn't require.
Why did Apollo take the CSM and LEM to LOI?
How do you come to a stable position at a lagrange point? Does it require an insertion burn like orbit, or do you escape with just enough velocity so you coast to a stop right at the lagrange point and require no braking burn?
Just not sure how that works, so when you are whipping out terms about masses to rendevous, etc. I was a bit lost.
So when I understand that better, that will help be understand your ideas better.
So, are you saying that if the CSM and LSAM were each launched separately, with an L2 rendevous, they could each utilize a 5m Centaur? And the LSAM mass could be reduced from 45mt to 20mt because it doesn't need to perform LOI for itself and the CSM? Would it still be as capable? Would lit only be 25mt lighter of propellent? That seems like a lot.
So what you are saying is that by launching the LSAM and CSM separately, and having them rendevous at the L2 point, you could use the already developed Centaur, Orion and Altair with as much hardware and as capable as the current Ares baseline, and launch them on a Pair of J-130's?
So why isn't that the baseline???
Is the rendevous and docking at L1 or L2 complex and dangerous or something?
Otherise, why worry about a new 8.4m upper stage? And the somewhat tricky docking in LEO of the LSAM and CSM with the 8.4m EDS?
Man, now you really have me curious!