Request: H-1/Centaur Jr. fuel tank, avionics and fairing

[JacobB094]

Probably the last omission from the Centaur family in BDB. Centaur Jr. was a single engine, 96 inch (so 1.5m) upper stage proposed for Atlas:
https://web.archive.org/web/20220406014718/http://www.spacelaunchreport.com/atlas-eff-centaur.jpg
It would have likely had a shroud of similar diameter. Coincidentally, this is similar to the H-1 upper stage:
https://web.archive.org/web/20220406014752/http://www.spacelaunchreport.com/N1-N2-H1.jpg
The H-1 used a Delta 8 foot shroud and a 98 inch diameter stage, which also works out to 1.5m (I'm not opposed to it being slightly fatter). They're both common bulkhead stages, it's possible that Centaur Jr. would have had Centaur-style insulation panels, but I haven't found much info on that, so a H-1 style stage would probably cover both of them (for the actual H-1, LE-5 and the UM-129A kick stage would also be needed, but I don't know if that's desirable for BDB).

The existing hydrolox stage for Delta is clearly based on Delta K proposal, being considerably longer than either of those, and with a tapered avionics section meant to terminate in an Agena shroud. It would not be a bad idea to add the new variant (if not going with jettisonable insulation) as a mesh switch for that tank. Engine mount could be shared without issue.

[CobaltWolf]

I believe the HOSS stage (the 1.5m hydrolox stage for Delta) is already configured as a balloon tank, balance-wise. When it was added there was a brief discussion where we decided it was sufficient for Centaur Jr. And I actually wound up using photos of an H-1 upper stage as reference. So the 1.5m cryogenic stage in BDB is kind of already a mish-mash of all 3 of these designs.

[JacobB094]

What irks me is that it doesn't look like one, what with its prominent intertank (worth noting, the original Delta K HOSS had a common bulkhead). It's also quite a bit longer than the H-1 second stage. I agree, it's not a big omission, and my current Centaur Jr. build works with that, however I'd very much like to see a shorter variant for that tank, preferably sans intertank. I don't know if it's possible with how it is UVed, but would that be possible to just "cut out" the intertank (perhaps with some length around it) and join the sections together?

Another matter is that of the fairing base and avionics. The current avionics section doesn't look like something that goes inside a fairing. In fact, BDB doesn't really have one that does, nor does it have a fairing base that would go around it. A Centaur-style top assembly for 1.5m would be handy for many other purposes, right now 1.5m upper stage options are centered around sub-diameter Delta style stages.