Author Topic: F9 Second Stage Reusability  (Read 99464 times)

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #180 on: 04/05/2017 09:31 PM »
They don't support the stage, they all slide back in unison as "a ring of control surfaces" prior to entry...
Let me see if I have this straight. You are talking about a ring of petals on the side of the upper stage that after stage separation will move backwards to act as control surfaces and protect the engine during re-entry?
Meanwhile there is a package of super dracos, landing gear, prop tanks and TPS mounted around, under or inside the payload attach fitting for the main payload. Is that right?
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Offline mme

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Re: F9 Second Stage Reusability
« Reply #181 on: 04/05/2017 09:36 PM »
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?

Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!
What I like about this is that:

1. Same S2 for expendable and recoverable missions (just connect the recovery module to the PAF).
2. GTO, mass and volume limited missions expend the S2.
3. First test does not need functioning legs, SDs, etc.  Just the heat shield and enough mass to shift the CG forward.  Being in one piece and hitting the water at terminal velocity is a good first step.

No idea how the (module's) PA through the heat shield works but it seems solvable.
« Last Edit: 04/05/2017 09:37 PM by mme »
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Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #182 on: 04/05/2017 09:53 PM »
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?

Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!
Nice! :) How are you going to descend, chute?
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Offline punder

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Re: F9 Second Stage Reusability
« Reply #183 on: 04/05/2017 10:03 PM »
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?

Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!
Nice! :) How are you going to descend, chute?

I was thinking propulsive landing just like (eventually) Dragon, using the SDs. The MVac does the deorbit burn, the SDs do the landing. But I must leave the dV calculations showing that to be impossible, to you guys.   ;)

Perhaps a drogue would save some propellant, I don't know.

In answer to the PA question... maybe little T.Rex arms that retract into the shell after payload sep?

Offline Lars-J

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Re: F9 Second Stage Reusability
« Reply #184 on: 04/05/2017 10:55 PM »
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?

Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!
Nice! :) How are you going to descend, chute?

I was thinking propulsive landing just like (eventually) Dragon, using the SDs. The MVac does the deorbit burn, the SDs do the landing. But I must leave the dV calculations showing that to be impossible, to you guys.   ;)

Perhaps a drogue would save some propellant, I don't know.

In answer to the PA question... maybe little T.Rex arms that retract into the shell after payload sep?

Load bearing can be done through the heat shield... Dragon already does it. (See picture below - there are 6 connecting points through the heat shield) This type of attachment has been in use since Apollo. (probably even Mercury and Gemini as well)

But that is a simple mechanical interface. For fluids and power you'll likely need a similar "claw arm" (like Dragon to its trunk) to the disposable payload adapter.
« Last Edit: 04/05/2017 10:56 PM by Lars-J »

Offline punder

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Re: F9 Second Stage Reusability
« Reply #185 on: 04/05/2017 11:07 PM »
Like this one on the Apollo CSM? But yes, it would somehow have to retract behind the heat shield on the "mme-punder-you-land" module.   ;D

Offline shooter6947

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Re: F9 Second Stage Reusability
« Reply #186 on: 04/05/2017 11:13 PM »
Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!

Still need a way to make sure that the center of drag is behind the center of mass so that the entry is stable.  Maybe an inflatable module at the engine end, or extendable ablative airbrakes back there?

Offline punder

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Re: F9 Second Stage Reusability
« Reply #187 on: 04/05/2017 11:22 PM »
Here is my quick-n-dirty cad model of the landed stage. So, yeah, sort of!

Still need a way to make sure that the center of drag is behind the center of mass so that the entry is stable.  Maybe an inflatable module at the engine end, or extendable ablative airbrakes back there?

The module has to be pretty massive, what with the TPS, legs, a number of SuperDracos, and prop tanks--but I don't know how it stacks up against the engine on the other end. There are also the COPVs inside... someone else would have to do the math.

Offline rakaydos

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Re: F9 Second Stage Reusability
« Reply #188 on: 04/05/2017 11:54 PM »
I see a lot of discussion of how to make stage 2 go nose first. But the interstage has plenty of volume around the base of the MVac, that I wonder if could be used for superdracos, fuel and legs, and to reentry-rate the Mvac bell.

Offline punder

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Re: F9 Second Stage Reusability
« Reply #189 on: 04/06/2017 02:03 AM »
I see a lot of discussion of how to make stage 2 go nose first. But the interstage has plenty of volume around the base of the MVac, that I wonder if could be used for superdracos, fuel and legs, and to reentry-rate the Mvac bell.

It's difficult (for me) to imagine how you'd leave the engine compartment open during engine operation, then cover it with a TPS for reentry. Which doesn't mean it can't be done, but it seems to require an elaborate mechanically articulated cover--which means more mass, complexity, and critical failure modes (i.e. failure to close the cover means loss of the stage.) But maybe I'm just not seeing what you mean.

Offline rakaydos

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Re: F9 Second Stage Reusability
« Reply #190 on: 04/06/2017 02:26 AM »
I see a lot of discussion of how to make stage 2 go nose first. But the interstage has plenty of volume around the base of the MVac, that I wonder if could be used for superdracos, fuel and legs, and to reentry-rate the Mvac bell.

It's difficult (for me) to imagine how you'd leave the engine compartment open during engine operation, then cover it with a TPS for reentry. Which doesn't mean it can't be done, but it seems to require an elaborate mechanically articulated cover--which means more mass, complexity, and critical failure modes (i.e. failure to close the cover means loss of the stage.) But maybe I'm just not seeing what you mean.
Does the whole engine compartment need to be open, or just the nozzle? If just the nozzle, then can the nozzle be reinforced to survive tail-first reentry loads?
(Not the engine gimbal surviving, just the nozzle- there might need to be some kind of mechanical brace that secures the nozzle from gimballing during a nozzle-first reentry)

Offline uhuznaa

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Re: F9 Second Stage Reusability
« Reply #191 on: 04/06/2017 10:29 AM »
I see a lot of discussion of how to make stage 2 go nose first. But the interstage has plenty of volume around the base of the MVac, that I wonder if could be used for superdracos, fuel and legs, and to reentry-rate the Mvac bell.

It's difficult (for me) to imagine how you'd leave the engine compartment open during engine operation, then cover it with a TPS for reentry. Which doesn't mean it can't be done, but it seems to require an elaborate mechanically articulated cover--which means more mass, complexity, and critical failure modes (i.e. failure to close the cover means loss of the stage.) But maybe I'm just not seeing what you mean.
Does the whole engine compartment need to be open, or just the nozzle? If just the nozzle, then can the nozzle be reinforced to survive tail-first reentry loads?
(Not the engine gimbal surviving, just the nozzle- there might need to be some kind of mechanical brace that secures the nozzle from gimballing during a nozzle-first reentry)


I think having something like the sharp circumference of the thin open nozzle  (as opposed to a flat or rounded heatshield) sticking into the supersonic stream is the worst you can do to something that you want to survive reentry.


« Last Edit: 04/06/2017 10:30 AM by uhuznaa »

Offline Ionmars

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Re: F9 Second Stage Reusability
« Reply #192 on: 04/06/2017 11:03 AM »
Elon has stated his intention to develop a reusable second stage. We are scrambling to figure out how the second stage with the M1D engine could be modified with add-ons. We might add on landing legs, a nose-end heatshield, and my own modified interstage heat shield.

Elon has a Air Force contract for a Raptor engine intended for a second stage F9 or FH.

But SpaceX especially wants to develop an ITS spaceship using multiple Raptors. Some people suggest that a small version of a Raptor-equipped vehicle would be a desirable testbed for the full-size version, which is also a second stage spacecraft to be recovered and reused. But Elon wouldn't roll three objectives into one project. That would mean we should start with the ITS spaceship design and work backward with legs and heatshields to see how a FH reusable second stage with legs and shields could be derived from the ITS design.

But Elon wouldn't roll three objectives into one project, would he?  :)
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Offline JamesH65

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Re: F9 Second Stage Reusability
« Reply #193 on: 04/06/2017 11:24 AM »
Elon has stated his intention to develop a reusable second stage.

No, he hasn't. He said they might try a Hail Mary attempt to bring back the 2nd stage, and see what happens.

Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #194 on: 04/06/2017 02:07 PM »
Elon has stated his intention to develop a reusable second stage.

No, he hasn't. He said they might try a Hail Mary attempt to bring back the 2nd stage, and see what happens.
He as also stated that "they don't trow away airliners after a single use, so why should they throw away rockets" (I'm paraphrasing of course) which to me means all of it... YMMV
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Offline rpapo

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Re: F9 Second Stage Reusability
« Reply #195 on: 04/06/2017 02:16 PM »
Elon has stated his intention to develop a reusable second stage.

No, he hasn't. He said they might try a Hail Mary attempt to bring back the 2nd stage, and see what happens.
He as also stated that "they don't trow away airliners after a single use, so why should they throw away rockets" (I'm paraphrasing of course) which to me means all of it... YMMV
Yes, but these are the same people who step by step worked out many of the issues with recovering boosters by getting data from boosters they expected to lose anyway.  So it is perfectly possible they will simply be trying to get data from an attempt they don't seriously expect will succeed.  Remember the early GTO launches where the first stage was reorienting itself after MECO, even though they weren't attempting even a sea landing?

They've discarded 30+ second stages already (some are still orbiting).  What we don't know is whether they gathered any information from the ones that reentered on their way down.
An Apollo fanboy . . . fifty years ago.

Offline punder

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Re: F9 Second Stage Reusability
« Reply #196 on: 04/06/2017 02:23 PM »
Maybe I'm  fooling myself, but the nose-mounted recovery module just seems like a very doable, relatively inexpensive way to make the US reusable. Basically, it just replaces the Dragon 2 pressure vessel with an upside-down 2nd stage!

Would be nice if someone could run the numbers. I seem to remember the US dry weight is a lot less than that of the spacecraft.

Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #197 on: 04/06/2017 03:06 PM »
Elon has stated his intention to develop a reusable second stage.

No, he hasn't. He said they might try a Hail Mary attempt to bring back the 2nd stage, and see what happens.
He as also stated that "they don't trow away airliners after a single use, so why should they throw away rockets" (I'm paraphrasing of course) which to me means all of it... YMMV
Yes, but these are the same people who step by step worked out many of the issues with recovering boosters by getting data from boosters they expected to lose anyway.  So it is perfectly possible they will simply be trying to get data from an attempt they don't seriously expect will succeed.  Remember the early GTO launches where the first stage was reorienting itself after MECO, even though they weren't attempting even a sea landing?

They've discarded 30+ second stages already (some are still orbiting).  What we don't know is whether they gathered any information from the ones that reentered on their way down.
I'm not interpreting it as they plan to succeed on the next flight, only that the will continue trying...YMMV
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Offline Ionmars

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Re: F9 Second Stage Reusability
« Reply #198 on: 04/06/2017 03:57 PM »
Maybe I'm  fooling myself, but the nose-mounted recovery module just seems like a very doable, relatively inexpensive way to make the US reusable. Basically, it just replaces the Dragon 2 pressure vessel with an upside-down 2nd stage!

Would be nice if someone could run the numbers. I seem to remember the US dry weight is a lot less than that of the spacecraft.
IMHO the question is whether a heat shield on one end alone will provide the area required to protect the stage and also to reduce speed sufficiently. Usually it is a short capsule rather than a stage that employs a blunt ablative heat shield. Someone has a model to run that analysis. If it lacks area, you just need to take a tip from ITS and place PICA-x on one side of the stage. Then rerun the model. Even if the shield on one side is the primary shield for re-entry, you will still need your shield on the end.

Edit: If you still lack the needed area, you will have to broaden the side with heat shield until you have enough area to protect the stage. At some point you will approach the shape of the Space Shuttle. There are reasons for that shape that go beyond aesthetics.
« Last Edit: 04/06/2017 04:23 PM by Ionmars »
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Offline Kaputnik

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Re: F9 Second Stage Reusability
« Reply #199 on: 04/06/2017 05:13 PM »
Putting some numbers to this, a Soyuz descent module has a heatshield area of 3.8m2, and a mass of 2850kg, for a loading of 750kg/m2.
F9 US would have a frontal heatshield area of 10.5m2, but we don't know the mass. If we assume the same loading as Soyuz the mass could be up to 7875kg.

Estimates for the dry mass of the US are around 4500kg- so that gives a margin of 3375kg to add the recovery systems. Seems pretty healthy to me.

Another factor to consider is that Soyuz is manned; an unmanned re-entry vehicle could possibly endure higher deceleration, which is what would happen if the spacecraft was 'denser' and hit the lower atmosphere before slowing down as much. Further, Soyuz was designed for return from lunar velocities, not just LEO. So it is possible that the F9 US could be even heavier and still not need a larger frontal heatshield area.

However, a separate issue is sidewall heating. All re-entry capsule have some degree of taper from the widest point at the base, towards a narrower top. This keeps the sidewalls out of the worst of the plasma, but they still need some degree of TPS. The greater the sidewall protection (by angle and/or TPS), the higher an angle of attack can be flown, opening up the option of using a lifting entry. So it's not as simple as slapping a heatshield on the front of a cylindrical stage- there will need to be some sort of TPS on the sides as well.
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