Author Topic: Testing upper stage propulsive entry survivability  (Read 5748 times)

Offline mvpel

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Re: Testing upper stage propulsive entry survivability
« Reply #20 on: 03/09/2017 12:18 PM »
I can certainly see why they've tabled this for the time being - they're already recovering 90% of the engines and 70% of the cost of the launch vehicle, and bringing down that last engine and its tankage is clearly a very tricky proposition.
1 MVac costs more than all 9 of the SL Merlins put together.

Per the public statements of Elon Musk:

Quote from: Elon Musk via Motley Fool
As Elon Musk explains, "The boost stage [of a Falcon 9 rocket] is about 70% of the cost of the rocket ... it's sort of on the order of $30 to $35 million dollars."

It seems far-fetched to me that the Mvac would cost in excess of 9x more than the SL Merlin when those 9 Merlins plus legs, fins, and some longer tanks rolled out with the same equipment as the upper stage tanks is 70% of the $43 - $50 million cost of the rocket.
"Ugly programs are like ugly suspension bridges: they're much more liable to collapse than pretty ones, because the way humans (especially engineer-humans) perceive beauty is intimately related to our ability to process and understand complexity. A language that makes it hard to write elegant code makes it hard to write good code." - Eric S. Raymond

Offline Kaputnik

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Re: Testing upper stage propulsive entry survivability
« Reply #21 on: 03/09/2017 08:51 PM »
I can certainly see why they've tabled this for the time being - they're already recovering 90% of the engines and 70% of the cost of the launch vehicle, and bringing down that last engine and its tankage is clearly a very tricky proposition.
1 MVac costs more than all 9 of the SL Merlins put together. 

Niobium must be really expensive stuff.

Source?
Waiting for joy and raptor

Offline HMXHMX

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Re: Testing upper stage propulsive entry survivability
« Reply #22 on: 03/09/2017 10:42 PM »
I vaguely remember a Gary Hudson concept where the upper stage would return engine first, with the engine firing during re-entry. Apparently, this would be sufficient for the stage to survive the re-entry heating.


My approach was a bit more subtle than stated here; my idea dates from the early 1980s when I was looking at recovery of a lifting-ballistic VTOL, base-first, and proposed firing a small centrally-located thruster or gas generator to push off the main re-entry shock.  That dramatically lowers the conductive, radiative and convective heating of the base.  Applied to the F9 S2, it might be possible to operate the engine's GG only, perhaps with additional H2O injected to increase mass flow and to lower temperatures, and then to exhaust the flow out of the main bell.  But the large bell would almost certainly need to be jettisoned first.  This concept is informed by some of the wind tunnel work done by NASA Langley on supersonic retropropulsion, which can be seen on youtube videos.

Offline deruch

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Re: Testing upper stage propulsive entry survivability
« Reply #23 on: 03/11/2017 12:27 AM »
I can certainly see why they've tabled this for the time being - they're already recovering 90% of the engines and 70% of the cost of the launch vehicle, and bringing down that last engine and its tankage is clearly a very tricky proposition.
1 MVac costs more than all 9 of the SL Merlins put together.

Perhaps your reputation alone can attest to this, but I would like to see this claim substantiated with some evidence.
Was based on a series of comments from a former SpaceX employee who worked on the MVac.  @gongora put them all together in a comment in the Merlin 1D thread (quoted pertinent bits below).  Most specifically that at the time he worked there, it took 1-2 days to produce an M1D vs. 18-21 days for an MVac. due to its complexity.  My understanding of the disparate costs wasn't based on materials cost but man-hours.

The Reddit comments section is here: https://www.reddit.com/r/spacex/comments/5h94xv/picture_of_a_mvac_engine_sitting_inside_its/

Some interesting notes from a former employee who used to work on the MVac engines.  He left in the Fall of 2015 so some things may be a little out of date.
Comment by Foximus05 on whether employees floated between different tasks:
Quote
Not when I was there. You might float if someone was behind and needed help, but there was a set tam that only did MVAC, only did M1D's, only did octaweb, etc. the M1D guys might move around from lowers to uppers, or chambers, but not Mvac, because it required so much more attention to detail.
Comment by Foximus05 on assembly times for the engines:
Quote
When I left it was a day or two for an M1D (dependant on parts) Vs 18-21 days for an MVAC. Mvac is a lot more complex, has more systems and has a bunch of made on assembly parts
Comment by Foximus05 on M1D vs. MVac
Quote
Very. MVAC contains more systems that M1D's have inside the octaweb, along with some control valves for the second stage. The chamber and a few other parts are the only similarities. Its in the same class, but its like comparing a Small Block Chevy V8 to a Ferrari engine.
Comment by Foximus05 on M1D vs. MVac:
Quote
MVAC was around ~400 pounds heavier than M1D, sans vacuum nozzle. But that was before they went to FT and I left.
In theory, there is no difference between theory and practice.  But, in practice, there is.  --Jan van de Snepscheut

Online stcks

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Re: Testing upper stage propulsive entry survivability
« Reply #24 on: 03/11/2017 12:54 AM »
Comment by Foximus05 on M1D vs. MVac
Quote
Very. MVAC contains more systems that M1D's have inside the octaweb, along with some control valves for the second stage. The chamber and a few other parts are the only similarities. Its in the same class, but its like comparing a Small Block Chevy V8 to a Ferrari engine.

Pardon the stupid question, but is this common for upper stage engines in general? Or is this just unique to MVac vs M1D? What are the reasons why MVac should be so much more complicated than M1D?

Online mattstep

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Re: Testing upper stage propulsive entry survivability
« Reply #25 on: 03/11/2017 01:23 AM »
I can certainly see why they've tabled this for the time being - they're already recovering 90% of the engines and 70% of the cost of the launch vehicle, and bringing down that last engine and its tankage is clearly a very tricky proposition.
1 MVac costs more than all 9 of the SL Merlins put together.

Perhaps your reputation alone can attest to this, but I would like to see this claim substantiated with some evidence.
Was based on a series of comments from a former SpaceX employee who worked on the MVac.  @gongora put them all together in a comment in the Merlin 1D thread (quoted pertinent bits below).  Most specifically that at the time he worked there, it took 1-2 days to produce an M1D vs. 18-21 days for an MVac. due to its complexity.  My understanding of the disparate costs wasn't based on materials cost but man-hours.

The Reddit comments section is here: https://www.reddit.com/r/spacex/comments/5h94xv/picture_of_a_mvac_engine_sitting_inside_its/

Some interesting notes from a former employee who used to work on the MVac engines.  He left in the Fall of 2015 so some things may be a little out of date.
Comment by Foximus05 on whether employees floated between different tasks:
Quote
Not when I was there. You might float if someone was behind and needed help, but there was a set tam that only did MVAC, only did M1D's, only did octaweb, etc. the M1D guys might move around from lowers to uppers, or chambers, but not Mvac, because it required so much more attention to detail.
Comment by Foximus05 on assembly times for the engines:
Quote
When I left it was a day or two for an M1D (dependant on parts) Vs 18-21 days for an MVAC. Mvac is a lot more complex, has more systems and has a bunch of made on assembly parts
Comment by Foximus05 on M1D vs. MVac
Quote
Very. MVAC contains more systems that M1D's have inside the octaweb, along with some control valves for the second stage. The chamber and a few other parts are the only similarities. Its in the same class, but its like comparing a Small Block Chevy V8 to a Ferrari engine.
Comment by Foximus05 on M1D vs. MVac:
Quote
MVAC was around ~400 pounds heavier than M1D, sans vacuum nozzle. But that was before they went to FT and I left.

I don't think we have enough information here to make a cost comparison. There is nothing in those quotes about numbers of people on each team to make a comparison on total labor hours to produce each engine.

Offline Adaptation

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Re: Testing upper stage propulsive entry survivability
« Reply #26 on: 03/11/2017 08:24 AM »
"Really tempting to redesign upper stage for return too (Falcon Heavy has enough power), but prob best to stay focused on the Mars rocket" -Elon

https://twitter.com/elonmusk/status/755167487017291776

SpaceX is also experimenting with an upper stage raptor for F9/FH.

https://www.defense.gov/News/Contracts/Contract-View/Article/642983

There is no real rush on this, core block 5 will be more or less finalized but new upper stages will be needed continually for the foreseeable future.  A reusable version could be developed years down the line.   It would likely be raptor based and still be expendable for F9 the reusable version would probably only fly on FH.

The current Merlin sized raptor was mostly 3d printed so perhaps machining and manufacture time wont be such a big deal.  Or maybe if the Vulcan reuse system of just returning the engines with an inflatable heat shield works well SpaceX could copy that for the upper stage.

Offline saliva_sweet

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Re: Testing upper stage propulsive entry survivability
« Reply #27 on: 03/11/2017 09:55 AM »
it took 1-2 days to produce an M1D vs. 18-21 days for an MVac. due to its complexity.  My understanding of the disparate costs wasn't based on materials cost but man-hours.

That's flawed because you assume the same number of people working on both. It would make sense for them to proprtion their workforce such that they can produce 9 M1Ds during the time it takes to make an MVac.

Offline Kaputnik

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Re: Testing upper stage propulsive entry survivability
« Reply #28 on: 03/11/2017 11:56 AM »
Of course an Mvac *must* function flawlessly every time, whereas there is some margin for failure on the other engines. Would enhanced QC play a part?

Instinctively, though, it seems likely that Mvac is simply produced in smaller numbers by a smaller team.
Waiting for joy and raptor

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