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tech / sci.space.policy / SN11 - One hop wonder

SubjectAuthor
* SN11 - One hop wonderDavid Spain
+- Re: SN11 - One hop wonderJF Mezei
`- Re: SN11 - One hop wonderDavid Spain

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SN11 - One hop wonder

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From: nos...@127.0.0.1 (David Spain)
Newsgroups: sci.space.policy
Subject: SN11 - One hop wonder
Date: Tue, 30 Mar 2021 10:06:08 -0400
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 by: David Spain - Tue, 30 Mar 2021 14:06 UTC

It goeth, it cometh, it go bloeyth.

Well put it this way, we saw a lot of mist, some fire behind this mist,
some short video feeds from SpaceX showing three, then two, then one
Raptor firing. Then none. Some belly flop video, Then perhaps a relight
but then video froze. Shortly thereafter NasaSpaceFlight ground
equipment picked up a tremendous boom and some evidence of debris
flying. Because of the foggy conditions this will likely be the hardest
test flight to piece together what happened from video alone. Will have
to wait for SpaceX analysis of the telemetry.

Next up BN1? The next Starship is SN-15. So far the trials have shown
some progress but I can't help but feel SN-11 was a set back, since it
didn't appear to get even as far as SN-10. What I'm more concerned about
is what SpaceX plans are post SN-15? They are going to have to build
more Starship prototypes obviously until they can routinely stick the
landing post belly flop maneuver. That is the goal here. I haven't seen
any evidence that SpaceX plans to deviate from the plan of a fully
reusable Starship. If this was their *first* rocket prototypes, ala
Falcon 1, it might be a different story. In order to generate revenue it
might have been a two-track plan. One for expendable and one for
recoverable as we saw with Falcon 9. But with F9 generating revenue, an
expendable Starship isn't necessary.

But seems to me they need to keep cranking out the Starship hardware
until they stick at least two or three landings, preferably in sequence.

Also I remain somewhat concerned about the plumbing of a methalox
rocket. The SpaceX video upon ascent shows what appear to be some
evidence of small methane leaks around the firing Raptors. New fuel, new
headaches. I'm not convinced they have all the kinks dealing with
methane propellant worked out yet. Which is to be expected given the
novel fuel.

Re: SN11 - One hop wonder

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Subject: Re: SN11 - One hop wonder
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 by: JF Mezei - Wed, 31 Mar 2021 00:15 UTC

On 2021-03-30 10:06, David Spain wrote:
> It goeth, it cometh, it go bloeyth.

Hey, no spoilers, I am just catching up !

The SPaceX video on Youtube is puzzling. Did they purposefully make the
public video unreliable (but privately have good video) or was video
really bad? Considering they had good video for all other tests, and
this was was no different, why would the video be _so_ useless this time?

Also, they chose a super foggy day and didn't wait for fog to lift. the
Video producer didn't even switch to ground view after video of engine
froze as if he had been told not to bother filming the bright orange
flash when it crashed.

If you know it will fail, and know it has unfixable design problems,
might has well fly it destructively and get some data during that test,
but choose a terrible day so people don't see it.

Also notable: the frozen frame in SpaceX feed included view of one
landing pod (not yet extended) attached to the skirt.

While some may point the SN09/10/11 as failures, I think they
overestimate "iterative design".

The landing gear hasn't been designed yet. There are placeholder pods
and the software is designed to send the command to deploy at right
time. But lack of landing gear means that landing hasn't yet been
developped and there may have been no expectations of any of the
previous SNs being abvlae to land. (and one wonders if those landing
pods attached to think skirt have the structural strength to widthstand
the landing of a very heavy steel silo.

Assuming this is true, these tests have proven quite succesful: all have
succesfully reached 10km. All have succesfully done the bellyflop with
the flaps keeping the ship in perfect control and bringing it over the X.

And the relighting of engines pror to landing, despite being
problematic, has shown in 2 attempts that it is capable of bringing ship
nearly verticla right over the X. So that is a huge accomplishement.

Not long ago, I commented on how the static test fires were unrealistic.
If you are not yet at a stage where you expect a landing, you don't test
for it and would explain the unrealistic static fires.

But deapite not having reached the stage in iterative design to work on
the landing, they have already collected much data for it and will helop
design what is missing to make landing possible.

I think that once SpaceX is ready to start testing landing, we'll see
proper static test fires with liftoff and landing sequences played on
ground and then debug engine problems. So I expect SN15 to remain on
ground with more realistic static fires for much longer than the
previous SNs.

I noticed there were still flames above engines during flight, but less
than before. Cleaner engine shut off, but not "clean" yet. Since this
is litterally rocket science, I have to wonder about quality assurance
to ensure engines are "perfect" and have no leaks and have clean shutdowns.

The other possibility is thet SN15 is another disposable one, that will
test the new steel and a few more things, and may have an interim
landing gear where they will test/measure landing more carefully. And
once would then eexpect flight tests to happen in clear weather since
they want video of a landing.

But with the iterative design, with SN15 built some time ago, I suspect
it doesn't yet implement all of what they learned. But the engines
fitted to it will be improved.

With regards to landing gear, remember that the original concept was a
super lights composite rocket. Then reality set in and instead of heat
shield, the made heavy steel silos with less heat shield. It may be
lighter than what composite+shield was, but still much heavier than
anything done before.

And until they know how much weight Starship will be with no only its
heavy steel, but also heat shield and cargo/passenger condo building
with pools, tennis courts and what not, you can't really design the
landing gear since you don't know what sort of strength is needed.

But the itenarive design is getting to the point now where landing will
become possible.

The hint I look for is whether SpaceX starts to show off the landing
gear for SN15, and whether static fires will replicate the 10km
flighT/landing or still be just a 1 secodn firing.

So while I have been critical and doubtful of these fancy steel flying
grain silos, I don't see SN11 as a failure or a setback.

Re: SN11 - One hop wonder

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From: nos...@127.0.0.1 (David Spain)
Newsgroups: sci.space.policy
Subject: Re: SN11 - One hop wonder
Date: Fri, 9 Apr 2021 13:25:20 -0400
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 by: David Spain - Fri, 9 Apr 2021 17:25 UTC

On 2021-03-30 10:06 AM, David Spain wrote:
> Also I remain somewhat concerned about the plumbing of a methalox
> rocket. The SpaceX video upon ascent shows what appear to be some
> evidence of small methane leaks around the firing Raptors. New fuel, new
> headaches. I'm not convinced they have all the kinks dealing with
> methane propellant worked out yet. Which is to be expected given the
> novel fuel.

I had also speculated elsewhere about the possibility of a hard start
during one of the engine relights:

Per an Elon tweet:

> https://twitter.com/elonmusk/status/1379022709737275393

Dave

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