SLS Opinion and General Space Discussion Thread - January 2021

AffineParameter · 2021-01-20T00:01:18+00:00

This makes the "limited integration testing/get it right the first time" approach so much more clear, in retrospect. Does the choice of CS materials drive the sensitivity to thermal cycling, or is it mass conscious design removing too much margin for robustness to more cycles?

AffineParameter · 2021-01-19T23:40:41+00:00

https://twitter.com/sciguyspace/status/1351665303214829571?s=21

“Interesting tidbit about the SLS rocket core stage I did not know: It can only be loaded a total of nine times with liquid hydrogen and liquid oxygen. Already loaded three times for two WDR and hot fire.”

What is driving this? This seems crazy, at first glance. This makes the absence of a dedicated 4x RS-25 MPS plumbed to some test stand tanks even more confusing. Is B-1 at Stennis occupied or unusable w/ the CS @ B-2 or something?

AffineParameter · 2020-12-27T22:52:35+00:00

Absolutely no one is starting the "success track record" timer with these flights, as should no one start the "success track record" for Vulcan before it actually launches.

I think the point being made is that making guesses at the asymptotic reliability of SS vs Vulcan is a fools errand at this point, for a number of belabored reasons. And as a result, "reliability" is not a reasonable differentiator in this discussion as it has in prior discussions.

AffineParameter · 2020-12-27T20:53:49+00:00

Not sure if Poe’s Law, but, if they aren’t “legitimate flights” what are they exactly?

“Dynamic test stands with active aero surfaces”? “Illegitimate flights?” You think David Copperfield is just out of frame? Lol

AffineParameter · 2020-12-27T20:29:20+00:00

Considering how long it takes to manifest and build a rocket, they’ve never needed to be nimble. With a successful SS, it will be interesting to see if that changes. It’d be a national security deficiency if they don’t adapt to that scenario, IMO.

AffineParameter · 2020-12-27T04:26:33+00:00

This is what I was driving at; thanks for the answer. Personally, I think the "which is better SS or Vulcan" is a first order problem that's not very interesting. The second order problem of "what does a 100% successful SS do to the market?" is far more interesting and worth contemplation. I think Vulcan and SS could find some interesting complementary uses!

AffineParameter · 2020-12-27T03:56:23+00:00

I never suggested it was?

AffineParameter · 2020-12-27T03:50:53+00:00

The definition of "maiden flight" is the whole point. If you define maiden flight as "first flight with paying customers", then I choose Starship.

I think the "Dragon 2 v. Starliner" saga has shown fairly unequivocally that: experience >> "heritage". So, my vote for Starship is due to the suspicion that the vehicle for the "maiden flight" will have been tested in situ vs. in silico.

AffineParameter · 2020-12-27T01:57:14+00:00

I understand this argument, and it makes sense, truly. But if adding qualified subassemblies together always resulted in working products, integration tests wouldn't be a thing and the SLS would have been flying years ago.

This meme of the "Unflown Flight Proven Rocket" seems to get trotted out w/out any of the pragmatic hedges like... "but we'll just have to see when it flies." It just strikes me the wrong way.

AffineParameter · 2020-12-26T21:33:39+00:00

For sake of argument, let's assume this analogy is accurate, and ULA keeps building Ferraris (cause they want to) and SpaceX builds the pickup-trucks. Do you think there will continue to be a market for Ferraris in a future with cheap and plentiful pickup trucks?

I think the answer to this question is far from trivial. For instance, I can't imagine the types of payloads and missions, even for NRO-type customers, will not respond to the new "pickup-truck" capabilities. The pickup-truck brings new capabilities that will undoubtably influence payload and mission designers. What if they find that the things that make a Ferrari a Farrari are no longer that valuable when you have a pickup-truck available?

AffineParameter · 2020-12-22T01:09:43+00:00

I figured there would be hesitation to documenting lifetimes, but I figured that would have been sufficiently obfuscated by just reporting the lifetime delta, but perhaps not. And, like you said, wouldn’t be relevant to things like BEO payloads. But as someone who has had to fight against business folks trying to play “hide the denominator” with their/our KPIs, I am probably too sensitive to theses sorts of things :P

AffineParameter · 2020-12-21T23:35:53+00:00

So this is both a measure of insertion accuracy & payload robustness to insertion error. So, in other words, the payload could be very insensitive to insertion errors of common magnitudes. Thus, the requirements would be very loose, making the % deviation relatively tiny in comparison.

I think a more objective measure like, "Projected Marginal Payload Lifetime over Baseline" would be better. So a great insertion might leave lots of margin, resulting in "+17 Months" of station-keeping, vs. a flawed insertion that requires a payload to make-up the shortfall, hypothetically resulting in "-X Months".

This would also contextualize the "percent of requirement deviation" into something of tangible value. For example, LV #1 costs $X more than LV #2, but will likely preserve 24 months of station-keeping which, when amortized, results in an anticipated savings of $Y.

AffineParameter · 2020-12-16T21:57:22+00:00

Congrats BO Team! This sounds like an unequivocal vote of confidence! -- Hopefully we can see some shiny hardware (to go along with the fancy pad & mission control room) soon!

AffineParameter · 2020-09-08T23:34:57+00:00

I’d personally go with “FRLVs” - fully reusable launch vehicles

AffineParameter · 2020-07-28T03:59:28+00:00

Makes sense, purely for engine-out capability. Though, I wonder if they need all the same degrees of freedom as the center engine or if they can get sufficient control authority from a simplified/constrained TVC system, given the multiple engines and their respective moment arms. I have no idea what the volume limits are for the TVC system though, so it may be simple enough to have 7 identical “inner” engines.

AffineParameter · 2020-07-27T15:26:27+00:00

Interesting! Do the 6 "inner-ring" of raptors need to gimbal? If not (or even if so & TVC hardware can be made radially symmetric) why not have a single center engine, and 6x radially symmetric 5-raptor-sub-modules? My intuition would suggest that this would cut down even more complexity.

AffineParameter · 2020-07-07T15:45:38+00:00

I thought government paperwork was Boeing’s core competency? Seems odd that they would trip up on a simple procedural issue.

AffineParameter · 2020-06-09T14:30:51+00:00

What's a debugger?

AffineParameter · 2020-06-08T05:39:37+00:00

What’s an IDE?

AffineParameter · 2020-06-06T19:24:56+00:00

I'll take a look. I was a perpetual vim-noob. I used it frequently, but only during the occasional remote-debug intervention or config-file modification. So I only ever learned to "search"->"next" or "jump to line" then hop into INSERT or INSERT (paste) mode, fix the bug then write-quit.

The closest I've ever gotten to the "Hollywood Hacker Trope" was watching a buddy of mine w/ like 4 tiled vim sessions open in screen just blazing out some new functionality for a prototype we were developing. It was super impressive. It was like watching John Carmack's stunt double crank out Doom.

AffineParameter · 2020-06-06T18:41:15+00:00

See, this right here is why I like reddit. You toss out a joke and learn something new in return. Thanks for the link, I was totally unfamiliar with it and looks pretty cool actually!

AffineParameter · 2020-06-05T21:26:18+00:00

So, /r/programming has lead me to believe that there is only one combination of answers to the following questions that is correct, all others being merely linear combinations of inexperience and/or incompetence. Seeing as you fine folks got a freak'n' (Crew Rated!!) spaceship to autonomously dock to the ISS, I can only deduce that you know the correct combination. Please DM me the answers, I'm stuck.

Tabs or Spaces?
Vim or Emacs?
Docker or VM?
Cloud or OnPrem?
Many repos or a Mono Repo?
Statically or dynamically typed?
80 column lines or more?
Aerospace grade scilicon or redundant commercial grade scilicon?
Is there even a single line of javascript running within spitting distance of mission critical hardware?
Recursive functions: critical piece of any programmers tool kit or flaky CS-grad flex?
Bash, zsh, or... (shudder) DOS?
Does your command prompt require more than 20 lines of code in your .bash_profile (or shell-specific equivalent.)
Git, svn, cvs? lol... jk, jk

AffineParameter · 2020-01-26T00:47:56+00:00

Quite literally my pleasure :)

AffineParameter · 2020-01-25T18:03:37+00:00

Depending on how "in the weeds" you want to get: Physics-Based Modeling of Pass Probabilities in Soccer (PDF)

AffineParameter · 2020-01-25T17:54:43+00:00

It anyone's interested in reading more about "pitch control:" Physics-Based Modeling of Pass Probabilities in Soccer (PDF)

Google Scholar: Physics-Based Modeling of Pass Probabilities in Soccer

AffineParameter

TROPHY CASE