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SpaceX just did a full duration test firing of a recovered 1st stage



 
 
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  #21  
Old August 2nd 16, 03:13 AM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default SpaceX just did a full duration test firing of a recovered 1st stage

In article , says...

On 8/1/2016 7:06 PM, Rick Jones wrote:
But will they really learn that much more from N (greater than one or
two as you implied from "life leader") iterations of "fill, fire and
inspect" on the ground from a stage which has been launched only once
than from one that wasn't launched?


I get your point but... Given that they have several recovered boosters
now, why would they use a new one? And if they DID use a new one,
everyone would ask "why not a recovered one? What are they trying to hide?"

Also, I am sure that SpaceX has tested enough Merlin engines on their
test stands to have a very educated idea about their MTBF without even
bothering to test a recovered booster. IMO, Part of the point of this
present testing of a recovered booster surely is to convince customers
and underwriters that pre-used boosters can be a safe bet.

In other words, it's not just science and engineering that's happening
here, it's also a public relations and sales campaign. Which is why I
wonder why it took them so long to start it.


My guess is it only made sense to spend the money on this sort of
testing *after* it had been proven that they could recover a good
percentage of flown stages. We seem to be beyond that point, with even
the most risky of landings (the three engine hover slams on the barge)
proving to be somewhat successful.

Jeff
--
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  #22  
Old August 2nd 16, 06:23 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default SpaceX just did a full duration test firing of a recovered 1st stage

JF Mezei wrote:

When burning fossil fuels such as Kerosene, how much does that affect
resusability because of carbon/soot residue ?


It depends.

..
Would any such residue cause any abrasion or does combustion happen at a
point where it no longer matters much?


The issue isn't 'abrasion'. The issue is more 'gunk'.


Also, while there was discussion of tank reusability, what about all the
metal structures through which LOX flows (pipes etc) ? Apart from
temperature variations that could weaken the metal, would oxydation
become a problem with time ? (LOX tends to oxydize stuff, right ? )


Thermal cycling is a concern. Oxidation not so much. And it's reuse
of the whole stage being talked about, not just tanks.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #23  
Old August 2nd 16, 06:25 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default SpaceX just did a full duration test firing of a recovered 1st stage

JF Mezei wrote:

On 2016-08-01 13:19, Rick Jones wrote:

I suppose even one "actual" launch of the stage is not too far from
crossing the Rubicon, but why wait for a successfully returned stage
to do this testing?


I think there is more to it than igniting engines a few times.
Structural issues from impact of landing, exposure to cold of space and
then land back in warm humid ocean, and I assume there is some warming
of skmin due to friction during launch and re-entry.

Consider this theoretical scenario:

First one is fine, but they see damage to the one that landed hard and
had 1 leg compress. They will want to draw some line below which damage
is not expected and above which special inspections are needed. Drawing
that line will require multiple landed stages to get an idea of what
sort of landing G force is OK. Test firings don't help.


Jesus, are you back on this again?

If the compression core doesn't compress, there is no structural
damage.

If there's no visible fire damage, there is no thermal damage.

Lines drawn. Now STFU, you ignorant yammerhead.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #24  
Old August 2nd 16, 05:10 PM posted to sci.space.policy
Rick Jones[_6_]
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Posts: 106
Default SpaceX just did a full duration test firing of a recovered 1st stage

Vaughn Simon wrote:
On 8/1/2016 7:06 PM, Rick Jones wrote:
But will they really learn that much more from N (greater than one or
two as you implied from "life leader") iterations of "fill, fire and
inspect" on the ground from a stage which has been launched only once
than from one that wasn't launched?


I get your point but... Given that they have several recovered
boosters now, why would they use a new one? And if they DID use a
new one, everyone would ask "why not a recovered one? What are they
trying to hide?"


Indeed. My point I suppose is similar to your question at the end -
why did they take so long to start when they could have started with a
non-recovered stage? The only thing that comes to mind, and I suppose
it is a non-trivial consideration, is that the recovered stage is
comparatively inexpensive compared to a never-flown one. Some
customer has already paid for its construction.

Also, I am sure that SpaceX has tested enough Merlin engines on
their test stands to have a very educated idea about their MTBF
without even bothering to test a recovered booster. IMO, Part of
the point of this present testing of a recovered booster surely is
to convince customers and underwriters that pre-used boosters can be
a safe bet.


In other words, it's not just science and engineering that's
happening here, it's also a public relations and sales campaign.
Which is why I wonder why it took them so long to start it.


I'd like to think that I'm at least as much "peanut gallery" as the
potential customers for "Elon's Lightly-Used Rocket Stages." As such,
would they actually accept ground-based static fires? I'd think they
would want to see actual launches of the stage.

rick jones
--
denial, anger, bargaining, depression, acceptance, rebirth...
where do you want to be today?
these opinions are mine, all mine; HPE might not want them anyway...
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  #25  
Old August 2nd 16, 10:57 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default SpaceX just did a full duration test firing of a recovered 1st stage

Rick Jones wrote:


Indeed. My point I suppose is similar to your question at the end -
why did they take so long to start when they could have started with a
non-recovered stage? The only thing that comes to mind, and I suppose
it is a non-trivial consideration, is that the recovered stage is
comparatively inexpensive compared to a never-flown one. Some
customer has already paid for its construction.


I thought someone had already offered a pretty reasonable explanation
for that. Until you've shown you can recover a high enough percentage
of boosters to make reuse worthwhile, why spend the money on the test
firing program? That's not exactly cheap, either.


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw
  #26  
Old August 2nd 16, 11:19 PM posted to sci.space.policy
William Mook[_2_]
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Posts: 3,840
Default SpaceX just did a full duration test firing of a recovered 1st stage

On Tuesday, August 2, 2016 at 5:25:38 PM UTC+12, Fred J. McCall wrote:
JF Mezei wrote:

On 2016-08-01 13:19, Rick Jones wrote:

I suppose even one "actual" launch of the stage is not too far from
crossing the Rubicon, but why wait for a successfully returned stage
to do this testing?


I think there is more to it than igniting engines a few times.
Structural issues from impact of landing, exposure to cold of space and
then land back in warm humid ocean, and I assume there is some warming
of skmin due to friction during launch and re-entry.

Consider this theoretical scenario:

First one is fine, but they see damage to the one that landed hard and
had 1 leg compress. They will want to draw some line below which damage
is not expected and above which special inspections are needed. Drawing
that line will require multiple landed stages to get an idea of what
sort of landing G force is OK. Test firings don't help.


Jesus, are you back on this again?

If the compression core doesn't compress, there is no structural
damage.

If there's no visible fire damage, there is no thermal damage.

Lines drawn. Now STFU, you ignorant yammerhead.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn


Commercial space launch providers must obtain insurance or self-insure. I am absolutely certain the insurers have some input to this process.
  #28  
Old August 3rd 16, 07:27 PM posted to sci.space.policy
Rick Jones[_6_]
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Posts: 106
Default SpaceX just did a full duration test firing of a recovered 1st stage

Jeff Findley wrote:
In article ,
says...
Rick Jones wrote:
Indeed. My point I suppose is similar to your question at the
end - why did they take so long to start when they could have
started with a non-recovered stage? The only thing that comes to
mind, and I suppose it is a non-trivial consideration, is that
the recovered stage is comparatively inexpensive compared to a
never-flown one. Some customer has already paid for its
construction.


I thought someone had already offered a pretty reasonable
explanation for that. Until you've shown you can recover a high
enough percentage of boosters to make reuse worthwhile, why spend
the money on the test firing program? That's not exactly cheap,
either.


I believe that was me. First things first. Gantt charts and
whatnot (which my managers usually take care of, since I'm a
technical guy).


I guess I'm still on a chicken-and-egg circle or perhaps thinking too
much about wasting anything but time. Indeed, it isn't worth trying
to figure-out how many times you can successfully launch a booster
before you know you can reliably land one. At the same time though,
there isn't much point to making it possible to land a stage if you
cannot reliably launch it a reasonable number of times.

Presumably, SpaceX needs (or at least "high wants") both. Starting
with sticking the landings seems like a reasonable place to break the
circle, but I think we are still left with the conclusion that more
than a small handful of static fires of a one-launch stage is
basically for show because if there was indeed value to the 4th
through Nth static fire of a stage, that value would have been there
with a non-flown stage and it would seem that only a question of money
would have precluded doing N repeated full static fires on a non-flown
stage in parallel with the landing experiments.

--
Don't anthropomorphize computers. They hate that. - Anonymous
these opinions are mine, all mine; HPE might not want them anyway...
feel free to post, OR email to rick.jones2 in hpe.com but NOT BOTH...
  #29  
Old August 4th 16, 06:08 AM posted to sci.space.policy
Fred J. McCall[_3_]
external usenet poster
 
Posts: 10,018
Default SpaceX just did a full duration test firing of a recovered 1st stage

Rick Jones wrote:


I guess I'm still on a chicken-and-egg circle or perhaps thinking too
much about wasting anything but time. Indeed, it isn't worth trying
to figure-out how many times you can successfully launch a booster
before you know you can reliably land one. At the same time though,
there isn't much point to making it possible to land a stage if you
cannot reliably launch it a reasonable number of times.


Both true and false. If you intend to refly them you have to design
them for some minimum number of reflights. You can't add that in
later. So you know they're good for at least that many flights.
Figuring out how far beyond that you can go can be left until later.


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw
  #30  
Old August 4th 16, 07:02 AM posted to sci.space.policy
snidely
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Posts: 1,303
Default SpaceX just did a full duration test firing of a recovered 1st stage

Jeff Findley asserted that:
In article , says...

On 8/1/2016 7:06 PM, Rick Jones wrote:
But will they really learn that much more from N (greater than one or
two as you implied from "life leader") iterations of "fill, fire and
inspect" on the ground from a stage which has been launched only once
than from one that wasn't launched?


I get your point but... Given that they have several recovered boosters
now, why would they use a new one? And if they DID use a new one,
everyone would ask "why not a recovered one? What are they trying to hide?"

Also, I am sure that SpaceX has tested enough Merlin engines on their
test stands to have a very educated idea about their MTBF without even
bothering to test a recovered booster. IMO, Part of the point of this
present testing of a recovered booster surely is to convince customers
and underwriters that pre-used boosters can be a safe bet.

In other words, it's not just science and engineering that's happening
here, it's also a public relations and sales campaign. Which is why I
wonder why it took them so long to start it.


My guess is it only made sense to spend the money on this sort of
testing *after* it had been proven that they could recover a good
percentage of flown stages. We seem to be beyond that point, with even
the most risky of landings (the three engine hover slams on the barge)
proving to be somewhat successful.


Didn't they do a fair amount of Merlin cycling testing with
Grasshopper? If you're interested in what the engines can take, that
seems like a good source of data.

/dps

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a Tcl extension that has escaped into the wild.
http://www.sqlite.org/lang_expr.html
 




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