Author Topic: Testing upper stage propulsive entry survivability  (Read 11443 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?
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Online 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.
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Offline 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?

Offline 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.

Online 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.
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Offline uhuznaa

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Re: Testing upper stage propulsive entry survivability
« Reply #29 on: 03/31/2017 02:26 PM »
Recovering the second stage with retropropulsion isn't going to work, too much fuel is needed. Just stick a heat shield (perhaps expandable) on the nose.

A heat shield on the nose won't help at all. The CoG is very far back (engine, thrust structure), with nothing but empty tankage on the top. So the stage WILL fly with the nozzle forward as soon as it hits the atmosphere. Also the big vacuum nozzle won't keep together with that kind of aerodynamic loads. The only way to do this would be to have a heat shield at the bottom that covers the base of the nozzle, then jettison most of the nozzle (although everything needed to do this would interfere with radiation cooling of the nozzle during ascend), do a long throttled reentry burn with lots of fuel kept for this and hope for the best.

And even then the engine would be much too powerful to land on it. Well, maybe with a really brutal suicide burn. But probably you'd need dedicated landing engines. And legs of course. And steerable fins for controlling the descent. And enough power for the time you have to wait until you again arrive over the landing site in orbit. And now you will have ended up with almost no payload.

The F9 second stage is just too small to be made reusable and still serve roughly the same payload market. You need a bigger craft to do that (even if not as big as ITS).


Online guckyfan

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Re: Testing upper stage propulsive entry survivability
« Reply #30 on: 03/31/2017 02:54 PM »
A heat shield on the nose won't help at all. The CoG is very far back (engine, thrust structure), with nothing but empty tankage on the top. So the stage WILL fly with the nozzle forward as soon as it hits the atmosphere. Also the big vacuum nozzle won't keep together with that kind of aerodynamic loads. The only way to do this would be to have a heat shield at the bottom that covers the base of the nozzle, then jettison most of the nozzle (although everything needed to do this would interfere with radiation cooling of the nozzle during ascend), do a long throttled reentry burn with lots of fuel kept for this and hope for the best.

And even then the engine would be much too powerful to land on it. Well, maybe with a really brutal suicide burn. But probably you'd need dedicated landing engines. And legs of course. And steerable fins for controlling the descent. And enough power for the time you have to wait until you again arrive over the landing site in orbit. And now you will have ended up with almost no payload.

The F9 second stage is just too small to be made reusable and still serve roughly the same payload market. You need a bigger craft to do that (even if not as big as ITS).

You believe Elon Musk has not thougt of these things?

Offline Kaputnik

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Re: Testing upper stage propulsive entry survivability
« Reply #31 on: 03/31/2017 02:59 PM »
My premise in starting this thread was that on low performance missions, SpaceX will end up with a second stage with considerable residual propellant. So much in the same way as their initial tests with first stages, this paid-for opportunity could be exploited to research how well a rocket stage can survive entry when using a long, low engine burn to cushion the entry. There are quite large holes in our knowledge of how this would work, and it is of great interest to NASA as well as SpaceX, as it could be directly applicable to Mars entry. I wasn't really suggesting that this would allow recovery of the existing design of second stage, but I thought for the relatively low cost it would be valuable.

if we were to consider major hardware changes.... well then a front mounted heatshield and a toroidal aft inflatable skirt to change the CoP would be one way of doing things... perhaps that skirt would itself act as enough of a drogue to allow mid air recovery of the falling stage lower in the atmosphere? But there are other threads for that.
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Offline TrevorMonty

Re: Testing upper stage propulsive entry survivability
« Reply #32 on: 03/31/2017 07:29 PM »
The shape and flight profile of reusable 2nd stage likely be same as for ITS.

Offline Lar

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Re: Testing upper stage propulsive entry survivability
« Reply #33 on: 03/31/2017 07:38 PM »
Good bump on this older thread, based on Elon's "hail Mary" comment, perhaps they are going to try some of the experiments Kaputnik outlined on a mission that has low mass so there is spare propellant.  Would this also require adding some lifetime to the S2 to allow multiple orbits before starting down? I guess if you're just experimenting, you start burning whererever convenient, as long as your entry point is the South Pacific somewhere?

See also  http://forum.nasaspaceflight.com/index.php?topic=42637 which is similar but different focus.
« Last Edit: 03/31/2017 07:56 PM by Lar »
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
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Offline TrevorMonty

Re: Testing upper stage propulsive entry survivability
« Reply #34 on: 03/31/2017 07:44 PM »
Elon Musk (@elonmusk) tweeted at 7:44 AM on Sat, Apr 01, 2017:
Considering trying to bring upper stage back on Falcon Heavy demo flight for full reusability. Odds of success low, but maybe worth a shot.

Elon comment 2nd reuse wasn't after thought, looks like they have been working on it.

Economics of F9, FH  reusable 2nd stage maybe marginal but its lot cheaper than using ITS to iron out bugs. For ITS it has to work 1st time, every time.


« Last Edit: 03/31/2017 07:50 PM by TrevorMonty »

Offline uhuznaa

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Re: Testing upper stage propulsive entry survivability
« Reply #35 on: 04/02/2017 05:05 PM »
A heat shield on the nose won't help at all. The CoG is very far back (engine, thrust structure), with nothing but empty tankage on the top. So the stage WILL fly with the nozzle forward as soon as it hits the atmosphere. Also the big vacuum nozzle won't keep together with that kind of aerodynamic loads. The only way to do this would be to have a heat shield at the bottom that covers the base of the nozzle, then jettison most of the nozzle (although everything needed to do this would interfere with radiation cooling of the nozzle during ascend), do a long throttled reentry burn with lots of fuel kept for this and hope for the best.

And even then the engine would be much too powerful to land on it. Well, maybe with a really brutal suicide burn. But probably you'd need dedicated landing engines. And legs of course. And steerable fins for controlling the descent. And enough power for the time you have to wait until you again arrive over the landing site in orbit. And now you will have ended up with almost no payload.

The F9 second stage is just too small to be made reusable and still serve roughly the same payload market. You need a bigger craft to do that (even if not as big as ITS).

You believe Elon Musk has not thougt of these things?

Of course he thought of these things, that's the reason he didn't try to return the F9 second stage. It probably would eat half of the payload.

Now, with the Falcon Heavy things look different, it has plenty of payload to spare. The easiest way to return the second stage would be to add some ballast on top of the second stage, with a heat shield, more batteries, propellant tanks, some SuperDracos and legs, and some flaps on the bottom of the stage. This would move the CoG of the S2 with empty tanks forward so it could do a head-first reentry, maybe with a reentry burn with deeply throttled SuperDracos to move the shock wave away. Later control the trajectory with the flaps, for landing deploy the legs and land on the SuperDracos. This would add some tons to the second stage and take this out of the payload, but the Heavy has more than enough of that.

For FH missions that don't need all of the payload you could return the second stage this way, this wouldn't actually be much different from Dragon 2 with powered landings, the dry mass and diameter of both is pretty similar. You'd basically add the bottom part of a Dragon 2 to the top of the second stage and return and land it on its head.

For an experiment on the FH demo flight you could just try to add some ballast and a heat shield to the top of the second stage and try to make it survive reentry.

Offline watermod

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Re: Testing upper stage propulsive entry survivability
« Reply #36 on: 04/02/2017 11:59 PM »
Another way of looking at it would be a much cheaper disposable S2.
Could a very cheap disposable S2 be made with a small 3D printed Raptor and alternate materials to aluminium?

Offline SweetWater

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Re: Testing upper stage propulsive entry survivability
« Reply #37 on: 04/03/2017 12:33 AM »
Another way of looking at it would be a much cheaper disposable S2.
Could a very cheap disposable S2 be made with a small 3D printed Raptor and alternate materials to aluminium?

I don't think a Raptor-powered upper stage for Falcon 9 is going to make anything cheaper - or smaller, for that matter. Vacuum-optimized Raptor has been estimated to have a ~4 meter nozzle (source: https://www.nasaspaceflight.com/2016/10/its-propulsion-evolution-raptor-engine/ ); as it is, Falcon 9 has a 3.7 meter diameter.

Moving to a Raptor-powered upper stage would mean developing a new, wider-diameter upper stage. That would require a new, wider fairing to fit on the wider upper stage, a new interstage between S1 and S2, and modifying the strongbacks for the wider interstage/S2/fairing combination. That's in addition to all the pad modifications needed to support the methane fuel for a Raptor S2.

I don't think a Raptor-powered upper stage is out of the question for Falcon 9 at some point in the future, but it won't be for a while, and it will be neither small nor cheap.

Offline Rocket Surgeon

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Re: Testing upper stage propulsive entry survivability
« Reply #38 on: 04/03/2017 01:13 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.

A few questions about this:
Has there been any word on this Raptor Upper Stage for the Falcon 9?
Wasn't congress trying to kill this or something?
Does the contract say that SpaceX actually has to build and fly it or is it just paper work and component testing?

Offline meekGee

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Re: Testing upper stage propulsive entry survivability
« Reply #39 on: 04/03/2017 01:27 AM »
Recovering the second stage with retropropulsion isn't going to work, too much fuel is needed. Just stick a heat shield (perhaps expandable) on the nose.

A heat shield on the nose won't help at all. The CoG is very far back (engine, thrust structure), with nothing but empty tankage on the top. So the stage WILL fly with the nozzle forward as soon as it hits the atmosphere. Also the big vacuum nozzle won't keep together with that kind of aerodynamic loads. The only way to do this would be to have a heat shield at the bottom that covers the base of the nozzle, then jettison most of the nozzle (although everything needed to do this would interfere with radiation cooling of the nozzle during ascend), do a long throttled reentry burn with lots of fuel kept for this and hope for the best.

And even then the engine would be much too powerful to land on it. Well, maybe with a really brutal suicide burn. But probably you'd need dedicated landing engines. And legs of course. And steerable fins for controlling the descent. And enough power for the time you have to wait until you again arrive over the landing site in orbit. And now you will have ended up with almost no payload.

The F9 second stage is just too small to be made reusable and still serve roughly the same payload market. You need a bigger craft to do that (even if not as big as ITS).
There's a leap in logic between where you finish counting the difficulties (and your solutions), and where you conclude that no reasonable payload capacity is left.

You have 20 tons of payload to start with.

How much do you figure are:
The heat shield
The parachute
The propellant reserve?

Assume air capture for a moment.
ABCD - Always Be Counting Down

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