Thread by @SpaceHaxx

Starstack 2 Orion Special *revA*: "Princess' Special Needs"

It's about solar panels, and how Orion was designed for a
- pre-SpaceX
- RL-10-centric
- low-thrust
...solar system.

Real complexity -> real pain -> real brains. 🧵 Let's go...

1/11 #SpaceXStarstack (@elonmusk)

First, meet "Universal Stage Adapter", the piece of the EUS Exploration Upper Stage that Orion rides on, and then separates from.

@KenKirtland17 sensibly advised that it only makes sense to use it here too.

4.4 tonnes(!), but it turns out we need the weight anyway 🤓...

2/11

Next, meet Orion's solar panels. They unfold and deploy as soon as Orion reaches LEO. They need the solar power ASAP so they can relax a little as they get ready for their TLI burn toward the Moon (or abort back to Florida).

OK fine, but there's a "problem"...

3/11

The "problem" is these panels can only take 1G of acceleration (or so), or they'll break.

And this was JUST FINE back then, when "everyone knew" that the Orion would be pushed off to TLI by low-thrust high-efficiency engines.

But if you're working with Raptors, oh boy...

4/11

"Orion Special" is a Starship derivative w/ Raptor engines. Fine. But:

Even if (the earlier version) finished it's TLI burn on just ONE of the center-3 (gimbaled) Raptor-SL's, throttled-down to 50%, the acceleration was still TOO HIGH to NOT break the panels.

What now?

5/11

Our buddy @BellikOzan had to work the knobs & levers a bit to find something that really works.
- more tankage & fuel (1600 tonnes)
- more engines (3SL+6Vac)
- added payload/ballast (like that stage adapter)

...going way PAST what would be "optimal" for raw payload only.

6/11

This new "revA" machine, after jumping off an RTLS'ing SuperHeavy booster, gets ~35 tonnes off to TLI, which is more than enough for
- the Orion capsule
- the Universal Stage Adapter
- (+ cube sats?)

...assuming 50% throttle for the last phase of the TLI burn, all at <1G.

7/11

This TLI burn does need careful planning.

All 9x Raptors are on after separating from the SuperHeavy...

...but it switches to Raptor-Vac's-only soon, first all 6xVac, and then just 3xVac, etc., until it finishes the job on 1x of the Raptor-SL's at 50% throttle. Phew!

8/11

You'll recall that the Raptor-SL's are in that center ring of three, so when the machine is running on just one, it has to "crab-walk" a little.

We've seen the early Boca Chica SN's do this just fine, though, and there's no air drag in space anyway.

9/11

That said, we CAN talk about an engine arrangement of the same circle of 6x Raptor-Vac's, but just 1x Raptor-SL right in the middle, so no crab-walking.

(I don't like it myself, though, because no Raptor-SL redundancy and it needs new plumbing, new thrust structure, etc.)

10/11

And there we have it, a believable way to send the Orion capsule off to the Lunar Gateway, without breaking it, for only
- (SuperHeavy working)
- 9x Raptors
- some stainless steel
- some LCH4 & LOX

Incredible.

'Got more "what-ifs" and "what-abouts"? Sock 'em to us!

11/11