From: jfindley@cinci.nospam.rr.com
In article ,
jfmezei.spamnot@vaxination.ca says...
>
> On 2020-09-09 17:17, Jeff Findley wrote:
>
> > Why not? They're both HLVs. NASA even has a contract with SpaceX to
> > design a lunar landing Starship, which would be part of the Artemis
> > program (SLS is obviously part of Artemis).
>
> Because SLS is opaque. Once it will be ready, it will be 100% ready,
> until then, it is 0% ready.
Actually, there are a decent amount of press releases from the SLS
program. And they did live-stream the last five segment SRB test. NASA
is opening up a bit more than they have in the past. I think that this
is surely because they see how being open has made SpaceX hugely
popular.
> Starship is slowly and visibly increaing its readiness percentage,
> although we can't know what the actual percentage is.
Slowly? LOL. SLS started in what, 2011? And that was based off all
the previous development work done for Ares! And I think it's not
likely to fly until 2021 at the earliest. So, more than 10 years of
development with nothing flying. And it's not using any new large
liquid fueled rocket engines (which take on the order of 5-10 years to
develop). So, SLS ought to have been cheap and quick to develop.
Raptor started development in 2009 and is the most advanced liquid
fueled rocket engine in the US utilizing full flow staged combustion.
It's literally the first full flow staged combustion rocket engine that
has flown (Russia developed one, but it never flew).
Development of Starship began around 2012, after SLS started. And
prototypes are already flying. And that's on top of the fact that
Starship is intended to be fully reusable while SLS is completely
expendable. Developing Starship ought to be many times harder than SLS,
by NASA's thinking.
> And we also don't know whether Hawthorne designs are far ahead of what
> BocaChica builds, or whether Hawthorne waits for results from basic
> designs in BocaChica before advancing designs.
It's iterative. All of the test data from Boca Chica feeds right back
into the development work at Hawthorne.
> For instance, does Hawthorne already have final designs for engine
> mounts, and also designed a temporary simpler one for SN tests, or is it
> waiting for various metrics and construction difficulty feedback of the
> simpler sdesigns before moving to design the final one?
This isn't an either/or. They're using an aft dome and plumbing for up
to three sea level Raptors on the Starships prototypes built so far.
Surely they have a design for adding the three vacuum Raptors. But
could that design be impacted by the testing of the prototypes? Of
course it could.
> > Only because they chose not to invest in cheaper production which would
> > have enabled more testing (both ground testing and flight testing).
>
> It is somewhat ironic because for SLS, they already had so much of the
> tech to draw from and experience with those materials/designs. You'd
> think they would have had an advantage of building fast and at lower cost.
Not when they're farming the work out to contractors on a cost plus
basis. Coming in cheaper or earlier than planned actually hurts long
term profits in that case. This is because using cost plus, the
contractors generally get a certain percentage of profit out of what
they're paid. So if they're paid more, they make more overall profit.
SpaceX isn't a contractor working on a cost plus contract. Both
commercial cargo and commercial crew are fixed cost. So are all of
their DOD launch contracts. So are all of their commercial launch
contracts. SpaceX is also its own customer (i.e. Starlink). So
lowering launch costs is quite important to SpaceX.
> had SpaceX stuck to its original plans, I have to wonder if the
> iterative design would have been so "agressive" since making the tooling
> to make carbon fibre parts is the time consuming part so one would
> assume they would have designed once instead of iterative design.
Not really. You can wind any thickness of tank you want on the same
cylindrical mandrel (the big piece of tooling SpaceX destroyed when it
switched away from carbon fiber). The tooling only changes if you
change the inner diameter of the tank (which they would not have done).
> The move to steel certainly has allowed SpaceX to afford to learn how
> to handle steel, make mistake and rapidly build very simple beer kegs.
> The downside of seeing so many failures is that one never really knows
> how "solved" the welding problem is and whether newer beer kegs are now
> far from breaking up, or still very close to breaking up with
> spectacular fireworks.
One of the next test articles is a tank using their new alloy of
stainless steel, which is a better fit for what they're doing with it.
> > SLS ignored this approach entirely. As Henry Spencer used to say,
they
> > were using the "performance uber alles" design philosophy.
>
> In fairness, they were told to use complex designs (SRBs, ET, SSMEs).
> SpaceX had the luxury of not only having clean sheet design, but also
> being able to change it radically midway by going to steel.
True. Again, they're not a cost plus government contractor and are
therefore not as subject to the whims of Congress. It's Congress that
came up with SLS and told NASA, by law, that they had to use those
suppliers to build SLS. There were no new contracts bid when switching
from Ares to SLS. That was all Congress's doing.
Jeff
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