Author Topic: F9 Second Stage Reusability  (Read 212355 times)

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #280 on: 04/10/2017 12:15 PM »
This line of reasoning is flawed; you are assuming that EM didn't decide to bring back the second stage until that event 1-2 weeks ago.  Us not knowing about his plan (and it is likely much more mature than he is letting on) doesn't have any bearing on him having a plan. 

His time constraints as you've outlined them don't exist... FH has been on drawing boards without a paying customer for years.  IIRC, five years ago, he asked -- if you could launch anything into space, what would it be -- he was referring to the FH demo launch.  The 'silly' payload and the hardware to return the second stage was probably ready last year when AMOS disrupted all plans.

I agree with all that.

It's not like Musk was telling us each week "This week we continued to do no work on upper stage recovery" until last week.

All we had was one data point that said that at a particular time some time ago their current thinking was that they were de-emphasizing upper-stage reusability. 
"de-emphasizing upper-stage reusability " is PR speak.

Musk was quite clear when he said (MIT 25th of September 2014) that
a) Upper stage use was "uneconomic" and
b) Full reusability will only come with the next generation after F9 or F9 derived (IE FH) hardware.

That suggests SX found something in their data that was not in their models and not in the textbooks that ruled out US reuse. 

The technical term for such a change in the knowledgebase is "science."

Quote from: ChrisWilson68 
We really don't know whether that meant nobody working on it or a significant team working on it but considering it risky so not the most likely plan.  And we don't know if a week after they spoke they changed their minds and decided to go full speed ahead on upper stage reusability again.
That's the thing about science. New discoveries invalidate old theories. Looking over those old proposals for stage recovery aerospace companies pitched to the USG in the 60's and 70's none of them show control surfaces on the top end of the stage. In fact SX didn't show them either in their 2011 video.

Yet that's what it takes to have adequate authority to get the job done.

It took actual flight tests of a high aspect ratio structure to find that out. It's quite conceivable that it was not the only new science that SX have discovered.

The trouble is science (except in funding proposals) does not operate on a timetable.

Quote from: ChrisWilson68 
They also might have purposely been sandbagging to avoid bad publicity.  Imaging they never really stopped working on upper stage reusability at all, but they wanted the press off their back, and no stories about how they had promised upper stage reusability but failed to deliver. 
Just to be clear there was a very clear implication that this was what they were going to do so such stories would be correct.

So far.
Quote from: ChrisWilson68 
They might just say they weren't planning for it, which is technically correct because they have a plan to succeed even without upper stage reusability, but, really, it was mainly just to lower expectations.
What would typically happen in a publicly quoted company which had created then not delivered on such an expectation would be the stock price would have fallen and the senior executives started spinning PR while the engineers responsible for non-delivery would be suitably punished for such termidity.

But SX is not subject (yet) to the whims of stock market expectations. It looks liked they did the smart thing and kept taking more data.

Somewhere between there (Sept 2014) and here something has shown up in their analyses that their previous assessment was harsh and it might yet be viable using LOX/RP1. IOW the science has changed again, as it tends to do.

However from S1 reuse I think it's clear this is a process and not an event. Even getting it back to close proximity to its planned landing area (IE not disintegrating in the upper atmosphere) will be a huge achievement. By then there will have also presumably have been several more PLF recovery attempts, perhaps to a state that some of them are reusable.

2017 will be quite an exciting year for space. and SpaceX.
« Last Edit: 04/10/2017 12:17 PM by john smith 19 »
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Offline Jim

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Re: F9 Second Stage Reusability
« Reply #281 on: 04/10/2017 01:36 PM »

That's the thing about science. New discoveries invalidate old theories. Looking over those old proposals for stage recovery aerospace companies pitched to the USG in the 60's and 70's none of them show control surfaces on the top end of the stage. In fact SX didn't show them either in their 2011 video.

Yet that's what it takes to have adequate authority to get the job done.

It took actual flight tests of a high aspect ratio structure to find that out. It's quite conceivable that it was not the only new science that SX have discovered.

The trouble is science (except in funding proposals) does not operate on a timetable.


Wrong takeaway and summary.  It isn't science, it is an engineering.  It was just a standard engineering trade within established ground rules.  Nothing new was discovered.  The control surfaces were required because Spacex uses low impulse GN2 thrusters (a ground rule).  Using higher performance thrusters (hyper or RP-1/GOX) would negate the need for control surfaces.   It was a complexity trade.
« Last Edit: 04/10/2017 01:38 PM by Jim »

Offline Robotbeat

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Re: F9 Second Stage Reusability
« Reply #282 on: 04/10/2017 01:44 PM »
SpaceX has done their fair share of innovation, but not much of what you might call science.

There might be things you could fairly characterize as science in combustion modeling or metallurgy, but that's a very small part of what SpaceX does.
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Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #283 on: 04/10/2017 01:50 PM »
Seems like we have several 2nd stage reusability threads that are becoming redundant now. I suggested an inflatable heat shield a couple of years back...Post#42
https://forum.nasaspaceflight.com/index.php?topic=37069.40
« Last Edit: 04/10/2017 02:01 PM by Rocket Science »
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Offline Okie_Steve

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Re: F9 Second Stage Reusability
« Reply #284 on: 04/10/2017 04:16 PM »
It isn't science, it is engineering.
Maybe a bit of both. SpaceX may well know more about high velocity retro-propulsion than anybody, which is why NASA was so interested in data from the early reentry attempts - remember the aircraft they scheduled to observe them? So, if somebody analyzing the engineering telemetry data said "That's funny*" some science may have crept in too.

* http://quoteinvestigator.com/2015/03/02/eureka-funny/

Offline rakaydos

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Re: F9 Second Stage Reusability
« Reply #285 on: 04/10/2017 04:52 PM »
Would SpaceX's pad failure count as science? They (presumably) created novel states of matter outside a lab, after all.

Offline Jim

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Re: F9 Second Stage Reusability
« Reply #286 on: 04/10/2017 04:52 PM »
It isn't science, it is engineering.
Maybe a bit of both.

No, engineering.  The discussion was about control and not entry

Offline CraigLieb

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Re: F9 Second Stage Reusability
« Reply #287 on: 04/10/2017 04:58 PM »
One reason for this announcement may be to tighten the screws on the competition. 
     SpaceX 100% planned reuse
              vs.
     Getting most of the propulsion sub-system back in pieces.

Companies that make buggy whips no longer have the same level of business they used to have...
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Offline Space Ghost 1962

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Re: F9 Second Stage Reusability
« Reply #288 on: 04/10/2017 06:03 PM »
Suggest that what's on the table is F9US recovery like fairing recovery was. Actual reuse may depend on the what one finds afterward.

Don't get the cart too far ahead of the horse.

And ... as to motivations ... suggest for F9/FH it is simply aggressive ROI to justify launch provider costs, over life of vehicle operations.

Offline orulz

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Re: F9 Second Stage Reusability
« Reply #289 on: 04/10/2017 09:17 PM »
If spacex is seriously considering their satellite constellation, which it certainly seems they are, it will involve a rather large number of launches to LEO. Throwing away an US for every launch probably is not desirable. If they could only carry half as many satellites per launch, but recover and reuse the upper stage every time, then the economics of the constellation start to look pretty good. Whatever customizations to the US are needed can be included in the budget for the satellite constellation, along with things like a dedicated payload adapter and satellite dispenser.

For a lack of a better way of saying it, when customers are paying them to launch something, they can just bundle an expendable US up into the cost of the launch. Nobody can really touch them on price anyway. But when they are launching their own satellites, the full cost of every launch comes straight out of their bottom line, so there is more incentive to get the savings that US reuse would provide.
« Last Edit: 04/10/2017 09:22 PM by orulz »

Offline Kaputnik

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Re: F9 Second Stage Reusability
« Reply #290 on: 04/10/2017 09:32 PM »
Back to the heat shield for a moment... How about just having the heat shield come up to the end of the thrust chamber and jettisoning the nozzle extension. 2nd stage would return engine first.

CG  (I assume) would much closer to the heat shield than it would be if it were on the nose of the 2nd stage.  Aerodynamic center of pressure (I assume) would be way behind the CG. Jettisoning the huge bell would hopefully reduce the likelihood of it's area causing the 2nd stage to swap ends at hypersonic speeds.

Curious what you guys think.

You'd better be damn sure that nozzle separates on the way down, not the way up :)
There may also be issues with radiative heat if the engine is enclosed behind a heatshield- although the s1 engines face a similar environment.
And then there is the hole left in the heatshield... little GNC door style hatch, maybe?
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Offline orulz

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Re: F9 Second Stage Reusability
« Reply #291 on: 04/10/2017 10:07 PM »
Could a new nozzle extension be attached to the engine after recovery or are the nozzles manufactured as a unit? If you can't put on a new extension, then recovering the US without the nozzle extension would be pretty pointless.

Offline DatUser14

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Re: F9 Second Stage Reusability
« Reply #292 on: 04/10/2017 10:15 PM »
MVac's are static tested w/o the nozzle, so maybe. Probably not, rockets aren't LEGO elements.


Edit/Lar: fixed pet peeve.
« Last Edit: 04/12/2017 01:16 AM by Lar »
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Offline CharlieWildman

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Re: F9 Second Stage Reusability
« Reply #293 on: 04/10/2017 10:29 PM »
And then there is the hole left in the heatshield... little GNC door style hatch, maybe?

Yup, something like that should do the trick!

Question for the experts:  If the CG is maybe 10 feet behind the heatshield, does the heatshield still need to wrap around under the second stage as it does in the SpaceX video?   
Seems like having a farther aft CG almost requires that the second stage act like a lifting body.

Edit: Typo
« Last Edit: 04/10/2017 10:35 PM by CharlieWildman »
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Online meekGee

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Re: F9 Second Stage Reusability
« Reply #294 on: 04/10/2017 10:50 PM »
This line of reasoning is flawed; you are assuming that EM didn't decide to bring back the second stage until that event 1-2 weeks ago.  Us not knowing about his plan (and it is likely much more mature than he is letting on) doesn't have any bearing on him having a plan. 

His time constraints as you've outlined them don't exist... FH has been on drawing boards without a paying customer for years.  IIRC, five years ago, he asked -- if you could launch anything into space, what would it be -- he was referring to the FH demo launch.  The 'silly' payload and the hardware to return the second stage was probably ready last year when AMOS disrupted all plans.

I agree with all that.

It's not like Musk was telling us each week "This week we continued to do no work on upper stage recovery" until last week.

All we had was one data point that said that at a particular time some time ago their current thinking was that they were de-emphasizing upper-stage reusability. 
"de-emphasizing upper-stage reusability " is PR speak.


Seems like it might not have been.

Sounds more like they wanted to just hush it down, a bit like GS was downplaying commX, prompting some folks to declare it all-but-dead.
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Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #295 on: 04/11/2017 05:47 AM »
SpaceX has done their fair share of innovation, but not much of what you might call science.
That would be a fair statement if it was started "AFAIK"
Quote from: Robotbeat
There might be things you could fairly characterize as science in combustion modeling or metallurgy, but that's a very small part of what SpaceX does.
No company want to do science unless that's it's core function. It is not SpaceX's.

Science is unpredictable and difficult to cost. It might work, it might not work or it might work too late to matter.


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Online AncientU

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Re: F9 Second Stage Reusability
« Reply #296 on: 04/11/2017 10:26 AM »
What SpaceX does could be better characterized as R&D.  I build astronomical instruments to do science.  The distinction is that tons of research goes into how to implement various 'features' of the instrument -- each of these research projects is jokingly called a 'science project' -- but really they are engineering or technical evaluations, thus R&D.  Once the instrument is built, tested, and integrated at an observatory, science begins.
« Last Edit: 04/11/2017 10:28 AM by AncientU »
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Offline JamesH65

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Re: F9 Second Stage Reusability
« Reply #297 on: 04/11/2017 11:04 AM »
What SpaceX does could be better characterized as R&D.  I build astronomical instruments to do science.  The distinction is that tons of research goes into how to implement various 'features' of the instrument -- each of these research projects is jokingly called a 'science project' -- but really they are engineering or technical evaluations, thus R&D.  Once the instrument is built, tested, and integrated at an observatory, science begins.

Cooper vs Walowitz....

Offline Robotbeat

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Re: F9 Second Stage Reusability
« Reply #298 on: 04/11/2017 12:09 PM »
SpaceX has done their fair share of innovation, but not much of what you might call science.
That would be a fair statement if it was started "AFAIK"
Quote from: Robotbeat
There might be things you could fairly characterize as science in combustion modeling or metallurgy, but that's a very small part of what SpaceX does.
No company want to do science unless that's it's core function. It is not SpaceX's.

Science is unpredictable and difficult to cost. It might work, it might not work or it might work too late to matter.
My post was not supposed to be critical of SpaceX. They're not in business to do science.
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Offline Radical_Ignorant

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Re: F9 Second Stage Reusability
« Reply #299 on: 04/11/2017 06:00 PM »
One thought. This comes close after successful experiment with bringing back fairing. And fairing probably doesn't have any complicated solutions for reusability.

And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.

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