Author Topic: F9 Second Stage Reusability  (Read 217207 times)

Offline aero

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Re: F9 Second Stage Reusability
« Reply #800 on: 06/17/2018 04:28 PM »
If SpaceX does build up an inventory of 30 or more Falcon 9 first stages, where will they keep them? That is a lot of floor space. I suppose some will be at Vandenberg and some in Florida but what will the split be and where will the hangers be? Surely they won't store them outside in the weather and using tents in Florida doesn't sound like a good idea long term.

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« Last Edit: 06/17/2018 04:30 PM by aero »
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Offline RonM

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Re: F9 Second Stage Reusability
« Reply #801 on: 06/17/2018 04:33 PM »
If SpaceX does build up an inventory of 30 or more Falcon 9 first stages, where will they keep them? That is a lot of floor space. I suppose some will be at Vandenberg and some in Florida but what will the split be and where will the hangers be? Surely they won't store them outside in the weather and using tents in Florida doesn't sound like a good idea long term.

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Offline aero

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Re: F9 Second Stage Reusability
« Reply #802 on: 06/17/2018 04:49 PM »
If SpaceX does build up an inventory of 30 or more Falcon 9 first stages, where will they keep them? That is a lot of floor space. I suppose some will be at Vandenberg and some in Florida but what will the split be and where will the hangers be? Surely they won't store them outside in the weather and using tents in Florida doesn't sound like a good idea long term.

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Hangars are cheap.

I suppose. And I guess 30 first stages would only need a little more than a 50 x 150-meter footprint. 7500 square meters or 80,800 square feet. Should be able to find that much space for storage.
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Offline mme

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Re: F9 Second Stage Reusability
« Reply #803 on: 06/17/2018 05:18 PM »
...I imagine the R&D is currently being done "on the cheap."  The beauty of US reuse is it means that you can shut down the production lines sooner.  Assuming that the attrition rate is low enough to keep flying well past any BFR delays this is the difference between making 75 more upper stages versus 300 more. [1]
...

Hey, if they can get it to work I'm all in.  However, can one do recovery of orbital equipment on the cheap?

Pick some numbers, if a US costs $10 million and it costs a few hundred million to develop recovery, if it works at all, is it worth it?  Even if it can be recovered what will it cost to reuse for each mission, what's the net benefit to recover the cost?

Like I said I'm all for it, but I can see the business case not working out.
Using 10 million per US, building 225 fewer upper stages saves 2.25 billion dollars (minus whatever recovery of those stages cost.) And it shuts down two production lines (vacuum Merlin and US) sooner freeing up people to work on Raptors, BFS and BFR.
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Online hkultala

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Re: F9 Second Stage Reusability
« Reply #804 on: 06/17/2018 05:30 PM »
...I imagine the R&D is currently being done "on the cheap."  The beauty of US reuse is it means that you can shut down the production lines sooner.  Assuming that the attrition rate is low enough to keep flying well past any BFR delays this is the difference between making 75 more upper stages versus 300 more. [1]
...

Hey, if they can get it to work I'm all in.  However, can one do recovery of orbital equipment on the cheap?

Pick some numbers, if a US costs $10 million and it costs a few hundred million to develop recovery, if it works at all, is it worth it?  Even if it can be recovered what will it cost to reuse for each mission, what's the net benefit to recover the cost?

Like I said I'm all for it, but I can see the business case not working out.
Using 10 million per US, building 225 fewer upper stages saves 2.25 billion dollars (minus whatever recovery of those stages cost.) And it shuts down two production lines (vacuum Merlin and US) sooner freeing up people to work on Raptors, BFS and BFR.

Realistically they can only recover upper stages of LEO stages, OR for most GTO missions they will have to switch from F9 to FH to allow upper stage recovery,.

And for the heaviest satellites to GTO with full reusability of FH is simply impossible, not enough capacity in fully reusable mode.

This means costs related to upper stage reuse are considerably greater for many of their missions, and they cannot recover it for all mission.

Offline mme

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Re: F9 Second Stage Reusability
« Reply #805 on: 06/17/2018 05:44 PM »
...I imagine the R&D is currently being done "on the cheap."  The beauty of US reuse is it means that you can shut down the production lines sooner.  Assuming that the attrition rate is low enough to keep flying well past any BFR delays this is the difference between making 75 more upper stages versus 300 more. [1]
...

Hey, if they can get it to work I'm all in.  However, can one do recovery of orbital equipment on the cheap?

Pick some numbers, if a US costs $10 million and it costs a few hundred million to develop recovery, if it works at all, is it worth it?  Even if it can be recovered what will it cost to reuse for each mission, what's the net benefit to recover the cost?

Like I said I'm all for it, but I can see the business case not working out.
Using 10 million per US, building 225 fewer upper stages saves 2.25 billion dollars (minus whatever recovery of those stages cost.) And it shuts down two production lines (vacuum Merlin and US) sooner freeing up people to work on Raptors, BFS and BFR.

Realistically they can only recover upper stages of LEO stages, OR for most GTO missions they will have to switch from F9 to FH to allow upper stage recovery,.

And for the heaviest satellites to GTO with full reusability of FH is simply impossible, not enough capacity in fully reusable mode.

This means costs related to upper stage reuse are considerably greater for many of their missions, and they cannot recover it for all mission.
Once they start deploying their constellation the vast majority of their missions will be LEO. That, I believe, is the forcing function for SpaceX to revisit US reuse.  I don't see how having to expend GTO upper stages is an argument against reusing LEO stages.

As I said originally, SpaceX can't let BFR delay the constellation. Reducing the cost of LEO missions makes deploying that constellation less expensive.
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Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #806 on: 06/17/2018 06:07 PM »
Going by Elon's statements on twitter  - there are no mentions of 2nd stage wings. Only a party balloon and landing on a bouncy house (which so far have been taken to mean a ballute). It would be fair to presume that they didn't consider the ballute until recently.
Yes, I know he's floated that balloon.  :)
Quote from: noogie
He's also mentioned that they want to keep the mass down on any 2nd stage recovery system. It looks doubtful that they would proceed with it if it did take a massive payload hit or need a major redesign
Given the mass trade on the 2nd stage is 1:1, rather than something like 7-13:1 on boosters, that's pretty much a given.

US recovery is a step change in difficulty compared to booster recovery.  :( It's not surprising it's been on again/off again for so long.
Using 10 million per US, building 225 fewer upper stages saves 2.25 billion dollars (minus whatever recovery of those stages cost.) And it shuts down two production lines (vacuum Merlin and US) sooner freeing up people to work on Raptors, BFS and BFR.
I'd forgotten how different the Vac Merlins are.
Good point.
SpaceX stated they are planning to shutdown F9 booster production to concentrate on BFR. That means in the future they will have a vehicle inventory for all future flights.
Which I think will make them extremely cautious about accepting any launches that they cannot get as many boosters as possible recovered from.
Quote from: RonM
Wings on an F9 US? C'mon, you've been posting in this thread and replying to discussions about HIAD and other methods. Stop making stuff up.
I'm just going by what SX did when they had no constraints on a new design.
First out of the gate BFS is a big upper stage.
2nd go around it's a big wing/body structure.

These are not armchair rocket engineers.
This is what is arguably the finest design team in the industry, with access to SoA computing resources for CFD and FAE simulations, came up with, with full access to the flight data from more than 50 F9 flights to anchor their simulations.

That's with (in principle) a CFRP structure which should be much lighter and stronger than Aluminum and a higher Isp, higher T/W ratio engine to play with.

I certainly want to see SX succeed in demonstrating US recovery.
It's certainly a sensible idea to pursue, if you believe that the cut over from F9 to BFR may take longer than Musk hopes for.

But grafting US recovery hardware onto an existing stage (even one that's been designed with recovery and reuse in mind) has made booster recovery and reuse look easy by comparison.
Because, by comparison, it was.
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Online envy887

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Re: F9 Second Stage Reusability
« Reply #807 on: 06/18/2018 02:04 AM »
As long as F9 is flying, there will be some FH cores available. They can refuse flights that would expend the FH core.
AIUI SX doesn't really do "inventory." They make to order. If it can be recovered and reflown, great. The only FH flown had a new build core. That's still available (I guess) but how many more did they build?
Quote from: RonM
SpaceX should look into F9 US reuse. While I'm confident in BFS flying, it's schedule is pretty optimistic. Good chance F9 and FH will be in use longer than the current plan.
SX have been looking at US recovery and reuse. During 2011-2014 they thought they could.  Then musk announced it was off the table for any F9 based architecture.

Recently it seems it's back on the table, maybe.

Given that SX couldn't manage to do it with BFS without adding wings despite increasing its size about 7x (and new, high Isp engine with better fuel) that suggests the only viable way to do F9 recovery is likewise to put wings on it.

And that's going to be a massive payload hit and effectively a complete stage redesign.

Come on. Bigger stages are HARDER to recover, they have more mass per surface area due to cube-square scaling. The exception might be hydrolox stages, but methalox stages aren't appreciably fluffier than kerolox.

And the wings are for returning PAYLOAD, not for simply recovering the stage. F9US would never have a widely varying mass or CG location like BFS will. And it doesn't have to every at high and low speeds and on both Earth and Mars.

Online meekGee

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Re: F9 Second Stage Reusability
« Reply #808 on: 06/18/2018 06:40 AM »
That "1:1 mass penalty" meme is very misleading when applied to LEO launches.

First of all, LEO launches are often volume limited, and then there's no penalty at all since the extra mass would have been wasted anyway.

Second, LEO launches can put some 20 tons in orbit, and the second stage has a dry mass of 5 tons. Instead of counting tons, count fractions.  If the stage takes a 50% mass penalty (bringing it to 7.5 tons), the payload goes from 20 to 17.5 tons.  That's not exactly the end of the world.

My money is on a towed balloon, maybe with some active system to prevent gyrations, and said system being used mostly for LEO (constellation) launches.
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Offline rsdavis9

Re: F9 Second Stage Reusability
« Reply #809 on: 06/18/2018 11:47 AM »
That "1:1 mass penalty" meme is very misleading when applied to LEO launches.

First of all, LEO launches are often volume limited, and then there's no penalty at all since the extra mass would have been wasted anyway.

Second, LEO launches can put some 20 tons in orbit, and the second stage has a dry mass of 5 tons. Instead of counting tons, count fractions.  If the stage takes a 50% mass penalty (bringing it to 7.5 tons), the payload goes from 20 to 17.5 tons.  That's not exactly the end of the world.

My money is on a towed balloon, maybe with some active system to prevent gyrations, and said system being used mostly for LEO (constellation) launches.

I like the towed balloon also. KISS.
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Offline edzieba

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Re: F9 Second Stage Reusability
« Reply #810 on: 06/18/2018 12:21 PM »
Remember that BFS is designed for maximum-payload EDL for Mars, not Earth. Two very different regimes, design changes to optimise BFS for Mars entry from interplanetary velocities may not be optimal (or even counterproductive) for Earth EDL from orbital velocities.

Offline UKobserver

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Re: F9 Second Stage Reusability
« Reply #811 on: 06/18/2018 12:29 PM »
That "1:1 mass penalty" meme is very misleading when applied to LEO launches.

First of all, LEO launches are often volume limited, and then there's no penalty at all since the extra mass would have been wasted anyway.

Second, LEO launches can put some 20 tons in orbit, and the second stage has a dry mass of 5 tons. Instead of counting tons, count fractions.  If the stage takes a 50% mass penalty (bringing it to 7.5 tons), the payload goes from 20 to 17.5 tons.  That's not exactly the end of the world.

My money is on a towed balloon, maybe with some active system to prevent gyrations, and said system being used mostly for LEO (constellation) launches.

I also think they are going for a towed balloon. It's a really simple and elegant solution, and potentially extremely effective. Consider;

1) If you tow it from the payload attach fairing end then you avoid all sorts of complicated stowage/deployment/interaction that you would encounter trying to deploy some sort of HIAD at the vacuum nozzle end. Deploying from the payload end means you can keep the nozzle pointing forward into the airflow on re-entry, as S1 already does, and for me that's a positive, not a negative, because you now don't need to add a completely separate head shield, only beef up what you already have protecting the base of the stage from the heat of the nozzle. Many commentators have said how fragile they think the MerlinVac nozzle is, but consider the forces it copes with at startup (often well off-nominal in rockets) and then during it's very long burn. It is capable of withstanding extreme heat and extreme forces and to gimble while doing so. So flying backwards on re-entry isn't necessarily a problem, as long as it's not required to do all the work of deceleration on it's own, and take all of the massive heat load that that would entail. That's where the balloon comes in;

2) Consider that by towing the balloon on a long line, as meekGee said, you can make it huge; say 10x the cross-sectional area of the stage itself, for instance. Making it huge means that it starts exerting a significant slowing effect on the stage at a much higher altitude, and while the atmosphere is much thinner, than would be the case if you were relying on just the drag of the stage itself. And that effect continues all the way down, such that, even though the vaccuum nozzle isn't shielded in any way, it is spared a large portion of the heat load because at any given altitude on descent the stage has already been decelerated to a slower speed than normal by the massive cross-section drag of the balloon, which is doing most of the work.

3) Finally consider deployment; although it is possible to simply eject the balloon package backwards from the payload end, the NASA paper suggests that there is a risk of it elastically bouncing back and wrapping itself around the stage in the absence of any atmospheric drag to keep it behind the spacecraft. One way to avoid that is to delay deployment until there is sufficient drag to keep it safely tensioned as it deploys, but that's not ideal as that means you have already wasted some of the height of the atmosphere that you could have used for deceleration. So I favour the other approach suggested in the NASA paper, which is to deploy the balloon by way of gradual extension of a rigid boom system, to keep it stretched out until atmospheric drag takes over that role. There could be a towing line running through that boom if need be, to ensure maximum strength in tension as the forces start to mount. Then when S2 reaches a low-enough altitude the balloon can simply be jettisoned (it's own massive drag ensuring that S2 drops away cleanly) prior to parachute deployment, or even used to pull out first the drogue and then the main parachutes in sequence, as is so commonly done already.

All of this fits neatly with the idea of bolting minimal recovery hardware onto the unchanging outer moldline of a B5 S2 and then gradually iterating to improve any aspects that struggle to cope with re-entry initially (probably the nozzle end heat-shielding).

Online envy887

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Re: F9 Second Stage Reusability
« Reply #812 on: 06/18/2018 12:42 PM »
The MVac nozzle only sees tensile loads during operation, while it would see alternating tensile and compressive load from buffeting during tailfirst entry. And the thermal protection around the base of the second stage is just plastic sheets, probably aluminized mylar. It's not like the booster.

Offline UKobserver

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Re: F9 Second Stage Reusability
« Reply #813 on: 06/18/2018 01:02 PM »
Good point, but that was also the case with all first stage rocket nozzles until SpaceX tried it with their S1. Admittedly the S2 vac nozzle is much longer and I would guess less good at withstanding those stresses flying backwards, but who knows until they try it..

Why is there such minimal heat-shielding on S2? Is radiative heating less of an issue than hot gas recirculation? What base heat shielding is there generally on the bottom of a rocket booster that isn't designed to return tail first?

Online envy887

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Re: F9 Second Stage Reusability
« Reply #814 on: 06/18/2018 01:34 PM »
Good point, but that was also the case with all first stage rocket nozzles until SpaceX tried it with their S1. Admittedly the S2 vac nozzle is much longer and I would guess less good at withstanding those stresses flying backwards, but who knows until they try it..

Why is there such minimal heat-shielding on S2? Is radiative heating less of an issue than hot gas recirculation? What base heat shielding is there generally on the bottom of a rocket booster that isn't designed to return tail first?

Boosters have atmospheric hot gas recirculation, and generally have much greater areal thrust density because they have more mass to lift atop the same cross-section area. Both of those get the base quite hot; if you look at pictures of the base of Atlas V, Delta IV, or the engine section of the Shuttle Orbiters, you can see the thermal protection systems required, including blankets around the gimbaling engine nozzles.

Compare those to pictures of the tail end of Centuar, Falcon upper stage, Delta upper stages, S-IVB, and S-II, and you will see a distinct difference in thermal protection.

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Re: F9 Second Stage Reusability
« Reply #815 on: 06/18/2018 01:52 PM »
Remember that BFS is designed for maximum-payload EDL for Mars, not Earth. Two very different regimes, design changes to optimise BFS for Mars entry from interplanetary velocities may not be optimal (or even counterproductive) for Earth EDL from orbital velocities.
It really wasn't.
Unless you choose to entirely ignore IAC2017 and P2P, which in concert with the later tweet about 'adding an engine for safe engine out landing' pretty much implies landing nearly maximum weight BFS on earth, repeatedly.

It is also an interesting coincidence that reentry from GTO, and reentry from interplanetary transit from Mars are comparable, as are reentry from LEO and interplanetary entry to Mars.
(at least at near minimum energies).

Online envy887

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Re: F9 Second Stage Reusability
« Reply #816 on: 06/18/2018 02:08 PM »
Remember that BFS is designed for maximum-payload EDL for Mars, not Earth. Two very different regimes, design changes to optimise BFS for Mars entry from interplanetary velocities may not be optimal (or even counterproductive) for Earth EDL from orbital velocities.
It really wasn't.
Unless you choose to entirely ignore IAC2017 and P2P, which in concert with the later tweet about 'adding an engine for safe engine out landing' pretty much implies landing nearly maximum weight BFS on earth, repeatedly.

It is also an interesting coincidence that reentry from GTO, and reentry from interplanetary transit from Mars are comparable, as are reentry from LEO and interplanetary entry to Mars.
(at least at near minimum energies).

BFS isn't designed only for minimum velocity entries, as those transits are unreasonably slow for crew. A more realistic Mars entry (12-12.5 km/s) is 35-40% more energetic than a GTO entry (10.3 km/s).

But entry velocity probably in not the main reason for the wing. Rather, is is to balance the rear-heavy landing fuel and many engines, and the front heavy cargo which can vary from 150 tonnes (or more) to nothing at all.

F9S2 has only one (much lighter) engine, no landing fuel, probably ins't even tail heavy, and will never need to re-enter with cargo, so there's only one CG location.
« Last Edit: 06/18/2018 02:08 PM by envy887 »

Offline whvholst

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Re: F9 Second Stage Reusability
« Reply #817 on: 06/18/2018 02:26 PM »
Assuming a head-first re-entry, with an inflatable heatshield and a balute to move back the center of drag, what would be impractical about landing the whole thing on a bouncy castle somewhere on land using a parafoil? Would chasing it with a ship be really necessary? Alternatively, how disastrous would a dip in, say, one of the great lakes be?

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #818 on: 06/23/2018 10:22 AM »
That "1:1 mass penalty" meme is very misleading when applied to LEO launches.

Second, LEO launches can put some 20 tons in orbit, and the second stage has a dry mass of 5 tons. Instead of counting tons, count fractions.  If the stage takes a 50% mass penalty (bringing it to 7.5 tons), the payload goes from 20 to 17.5 tons.  That's not exactly the end of the world.

My money is on a towed balloon, maybe with some active system to prevent gyrations, and said system being used mostly for LEO (constellation) launches.
You make it sound like childs play if they have that much margin to play with.

And yet somehow they are still struggling 7 years after they thought they could do it.

Is it possible there are things about this problem you're missing that make it substantially more difficult?
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline ChrisWilson68

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Re: F9 Second Stage Reusability
« Reply #819 on: 06/23/2018 11:18 AM »
That "1:1 mass penalty" meme is very misleading when applied to LEO launches.

Second, LEO launches can put some 20 tons in orbit, and the second stage has a dry mass of 5 tons. Instead of counting tons, count fractions.  If the stage takes a 50% mass penalty (bringing it to 7.5 tons), the payload goes from 20 to 17.5 tons.  That's not exactly the end of the world.

My money is on a towed balloon, maybe with some active system to prevent gyrations, and said system being used mostly for LEO (constellation) launches.
You make it sound like childs play if they have that much margin to play with.

And yet somehow they are still struggling 7 years after they thought they could do it.

Is it possible there are things about this problem you're missing that make it substantially more difficult?

He never said it was child's play.  Just that mass penalty isn't necessarily a huge issue for LEO launches, and he backed that up with good numbers.

And they're no more "struggling" to do it than they were "struggling" to do first-stage reuse.  It just takes time and resources.  The term "struggling" implies that they're somehow not on a path that is likely to lead to success, and there's no evidence of that.

As to the seven years, we all know that they chose for business reasons not to work on it for many years.  Now they have chosen to work on it again, though we don't know how much they've decided to focus on it.

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