Thread by @BellikOzan

Gonna read and comment 🧵

https://twitter.com/torybruno/status/1636117427829211142

- Figure 1 is highly misleading. Burns, longest coast, and time to sep do not materially impact whether a trajectory is low or high energy.
Also, GSO direct inject is not for USG only. There's a Viasat launch coming up in a month.

1/

Ooh and note that the way that 0-1x is styled in such a way to make it seem like just label space, so visually "high energy" looks a lot more intense than "low energy".
Moreover, the relative difficulty of the various categories are proportionately represented in the graph - 2/

quite the opposite -- about as misleading as you could make it. 1.5x LEO delta v means ~4.5km/s extra, which generally means 4+ times the rocket in practice for a given payload.

Whereas LEO typically calls for a minimum of 1 upper stage burn but typically 2 (as well as 3/

one or more lower stage burns (often involving more engines), and GEO can be achieved with as few as 1 additional burn.
Moreover, 6 burns isn't dramatically harder than 2 or 5. It's a relatively small design tweak in the engine, not the 4x rocket multiplier for delta v.

4/

Now look at how much more visual importance is given to burn count relative to delta v.

And even more than that, look at longest coast and time to sep, which measure almost the same thing as each other and practically dominate the chart.

Both are basically a matter of 5/

a) having enough battery power (or some other power source) to last the coast (which is on the order of 5-6 hours for direct GEO, and *easily* achieved
b) thermal management of both payload and stage, which isn't as easy as battery power but about as easy as burn count even 6/

for cryogenic propellants.
c) RAD shielding of electronics through the VA belts, for which there are off the shelf solutions, and homebrewing one w/ redundancy isn't all that hard either.

7/

Comments around staging high to optimize for high energy and this making it harder to propulsively recover the 1st stage are on point (for a 2 stage rocket).

8/

Note that flying back is not the only way to do propulsive recovery. Most Falcon 9 recoveries are downrange, and the only practical limit for how high you can stage and still do propulsive downrange recovery is how much heat your stage can take.
9/

Which is why component recovery is not necessarily a more appropriate choice, but it can be if you fly infrequently enough, as ULA so far has done.

More importantly, the missions that ULA labels "high energy" are both rare and high priced. Optimizing for "low energy" and 10/

flying expendable for high energy is more optimal (even for ULA's manifest), since you can expend pre-flown boosters at relatively low cost.

So neither the choice to stage high nor the choice to recover the engines only follows naturally from the desire to support 11/

"high energy" missions.

We have not only SpaceX's example of flying increasing numbers of "high energy" missions (they've had 4 since ULA's last one), but we have a better explanation for why ULA has chosen not to go this route. 12/

Simply put, Vulcan shares a lot with Atlas V (a fact ULA has used to tout Vulcan's expected reliability out of the gate) -- doing it any other way would have meant riskier (and likelier costlier and slower) development for ULA. They went the conservative low risk route, not 13/

the route that optimizes their rocket for the missions they'll fly.

14/

Furthermore, if you really want long coast and many restarts, it's hard to beat hypergolics. Hydrolox just makes those problems harder (though many restarts is a solved problem for RL10 engines).

And don't get me started on the performance misconceptions around hydrolox...

15/

"All of these, and more, are the unique and specialized technologies required for High Energy missions... Nor are they yet needed in the commercial space marketplace. These are unique government mission needs."

Absolutely and categorically false.

16/

Following that there's a decent beginner's intro to staging and an indefensible plug for SSTOs and VentureStar.

17/

Note in figure 3 how the 150t to LEO "future megaconstellation optimized lifter" has performance that drops to 0 between LEO and MTO, whereas the Starship user's guide advertised 21t to GTO (more than the most capable Vulcan).

18/

And I'm not sure whom they're referring to with a "typical LEO optimized [three core] reusable rocket" (see both figure and preceding paragraph), but the only one I know of is Falcon Heavy, which even w/ three core recovery will outperform "high energy" red rocket through GTO 19/

and well past GEO w/ two core recovery.
Looks like they've subbed in F9R for Falcon Heavy.

20/

"Given that this could be as many as seven launches “for the price of one”, the economics of this architecture will be difficult to close for many missions."

Not with full reuse w/ minimal refurb. The point is to bring the marginal cost down.

Furthermore you're getting

21/

way more capacity to high energy trajectories than you would w/ a medium/heavy launcher.

And for mere GEO runs w/ modest payloads, you don't need anywhere near that many refuels.

22/

"it is possible that this can be made to work, but likely for only very specific missions"

Likely for almost every mission under the sun.

23/

"Turning “one launch into seven”, on a frequent basis, would worsen an already increasingly challenged situation on ranges that are becoming crowded."

A problem that the USSF is happy to have and looking forward to solve, by all appearances.

24/

"let’s say 100–200 launches per year, that would constitute a massive increase in the total fossil fuel consumption of space launch."

LV in questions uses ~ 1kiloton of ch4/launch.

100-200 kilotons of ch4 a year would be ~0.003-0.007% of global natural gas consumption.

25/

"On the other hand, if the propellant is sourced from space, then the availability and cost of refueling in orbit would be substantially more enticing. "

Not in the foreseeable future. The investment required to extract materials, produce propellant, and ship it to LEO would 26/

be huge and have lower aggregate use (for the foreseeable future) over which to spread costs.

At the point where you have a well reusable LV, adding extra flights for propellant is cheap.

27/

"The in-space source will be the moon, where massive quantities of water reside, just waiting to be converted into propellant"

The known quantities are orders of magnitude less than known fossil fuel reserves on Earth, let alone comparable propellant feedstock (the oceans).

28/

Furthermore, extracting it in large quantities would have dramatic and permanent effects on the Moon. (and specifically on some of the most scientifically interesting locations).

So much for "sustainability"

29/

An excellent section on "tiny rockets".

30/

" Unlike conventional architectures, Vulcan employs a “dial-a-rocket architecture.”"

That... is a conventional architecture. How much more conventional does it get than doing it the way Delta II and Atlas V and Delta IV and Ariane 1-6 did / are doing it?

It's not the 60s.

31/

"One Centaur V version is optimized for High Energy and a second version is optimized, within the overall Vulcan architecture, for Low Energy LEO missions."

Can't wait to get more details on the LEO optimized Centaur.

"being judged as the most efficient, cost effective, and best suited in an open competition with participants from across the industry,"

That's a stretch for reasons that would take an essay to explain.

And I'm curious to see how things go in NSSL phase 3.

32/

"Sometimes, it’s OK the break the rules."

Break what rules? Vulcan is following the same rules set by its forefathers.

33/

"Your reward is that you are now privy to some of the subtleties of rocket architectural design that few aerospace professionals and even fewer laymen have understood."

Wow.

34/34

(similarly, MTO/MEO no longer USG only)

*aren't proportionately represented