Author Topic: F9 Second Stage Reusability  (Read 99363 times)

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #80 on: 04/01/2017 08:31 PM »
If i'm visualising this correctly, it puts too much surface area ahead of the centre of gravity, and the stage would be extemely unstable and want to fly backwards.

For sure if they come in engine first it can not survive reentry. It would need to be sideways somewhat like ITS and IXV reentry, with flaps doing the steering and protecting the engine. It needs a heatshield on the side of the stage.
The problem is that this is a stage, not a vehicle. It's very strong in exactly one axis. In the same way you can stack 10 loaded soda cans vertically. Now stack nine of those vertically so the base of the stack is pressing on the side of the bottom can, making sure to catch the spray when it ruptures.

Making something return intact from orbital velocity  and reusable (or at least refurbishable) is a solved problem if you start from a clean slate.

It's the fact that you start from something so far away from a clean slate that makes it hard.  :(

The question is what has changed from 2014 for Musk to consider upper stage recovery might be viable?

He's said the engines on the FH demo will have about 10% more thrust but he's also said that it's Isp that's the problem.

Now a bigger nozzle could increase Isp a few seconds, but is that a big enough change to consider giving this a go? the ongoing talk about a Methane upper stage would increase that by a fair bit more but is that enough?

A possibly relevant side item from the presser was that SX will be switching to forged Titanium alloy grid fins in future, from TPS coated Aluminum.

It's possible this would increase the maximum usage temperature enough to make putting a set of them on the US worthwhile.

Which leaves the landing legs to be installed.

Another obvious question is how close to a complete, stage landing on ship, first attempt they would be looking for?  Would ditching within a Km of the ship (with no provision for actual landing) be viewed as a good start, or a full actual landing?



« Last Edit: 04/01/2017 08:53 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
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Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #81 on: 04/01/2017 09:32 PM »
This a a modification of a Flyback Falcon I made up 6 years back using an X-37 like mold line for S2 before F9R. The current S2 would slide in the external airframe, once around and land back on a runway... (not to scale)
https://forum.nasaspaceflight.com/index.php?topic=27477.20
« Last Edit: 04/02/2017 11:01 PM by Rocket Science »
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Offline GWH

Re: F9 Second Stage Reusability
« Reply #82 on: 04/01/2017 10:05 PM »
Or an aft mounted toroidal inflatable skirt using similar technology to HIAD, and a forward mounted Pica-X heatshield.

Could they go even simpler where they just unfurl a consumable tail  "streamer" out the aft to provide stability?  Same flexible heat resistant materials as HIAD.

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #83 on: 04/01/2017 10:11 PM »
This a a modification of a Flyback Falcon I made up 6 years back using an X-37 like mold line for S2 before F9R. The current S2 would slide in the external airframe and land on a runway
https://forum.nasaspaceflight.com/index.php?topic=27477.20
The joker in any winged design is the shift in Cg and Cp as the design operates Mach 23.

Think of it as a vertically launched HOTOL.   :(

Logically the strongest area of the stage after the engine area would be the common bulkhead.

Again it's how much mass you'll have to add to give the strength to resist side loads.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Online Lars-J

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Re: F9 Second Stage Reusability
« Reply #84 on: 04/01/2017 10:24 PM »
Long term we already know what SpaceX's design will be for a reusable upper stage. We have already seen it - the ITS spacecraft. Sideways reentry using body fins and movable tail flaps (much like ESA's IXV), and then vertical landing.

I would not rule out them flying some subscale version of this as an FH upper stage if they decide they need to try it at a smaller scale. But I don't consider it likely.

Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #85 on: 04/01/2017 11:40 PM »
I haven't given up yet on propulsive landing as SpaceX has relatively all the components in house for such or capability to produce them. The trades are mass of prop vs the small wings on a lifting entry such as the proven X-37 plan form. It would also remove the pitch-up maneuver needed for a tail first landing. Other trades would be landing legs vs landing gear so it may be a wash there... The KISS rule is always how I view things... I have always known in my gut that Elon had not given up on an S2 reusabilty, it was just a matter of priorities... He could still go with the initial blunt body with TPS that he has showed in his videos in some variant, perhaps with Super Dracos on the sides....
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Online meekGee

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Re: F9 Second Stage Reusability
« Reply #86 on: 04/01/2017 11:41 PM »
Clearly SpaceX already has a second stage prototype ready to go. You just don't slap things on to an existing stage. This brings up an important point. Is SpaceX conducting super secret testing such as a black ops program for future designs away from the public eye.

I seriously doubt that. He wouldn't have called it "hail mary" then. Spacex doesn't have the time or resources to seriously devote to a one off hail mary attempt right now. I think it's more likely Elon is considering giving a couple of interns access to a used dragon and a healthy budget of zero, telling them to make something happen. Thinking it might be worth to fly that in lieu of a couple of extra tons of cheese (cheese is expensive you know).

Ironically, "maybe a few interns working on it" is how some folks characterized the Raptor project a couple of years ago.
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Online MichaelBlackbourn

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Re: F9 Second Stage Reusability
« Reply #87 on: 04/02/2017 04:23 AM »
Can an entire S2 with a stub nozzle, experimental TPS over the nose+side, nearly empty tanks, and Grid fins fit inside the fairing as the payload?

That way you get a nominal testing standard S2, and you get an experimental S2 with modifications up there at the same time. Best of both worlds.


Online MichaelBlackbourn

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Re: F9 Second Stage Reusability
« Reply #88 on: 04/02/2017 04:39 AM »
Hell, you can probably mate the 'nose' of the experimental S2 to interface used to mount the payload. So it would ride uphill backwards.

This really seems like the best 'weight simulator' they could do, and fill with as much propellant in it as they need to get the weight up for a proper test.

Offline Long EZ

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Re: F9 Second Stage Reusability
« Reply #89 on: 04/02/2017 04:55 AM »
My idea for getting the second stage through re-entry is as follows. Fly the payload fairing to orbit. Open the fairing to a 90 degree angle but do not release them. Release the payload. Rotate each fairing 180 degrees about the radial axis. Then close them encapsulating the second stage within. This would put the second stage engine and nozzle inside the fairing pointing at its tip. Then re-enter the atmosphere fairing tip first. This obviously would require heat shield material on the front of the payload fairing. Not sure if the second stage would fit, or if the cg and the geometry of the pointy end of the fairing would result in a stable re-entry.

Super sonic flight is solved by two ways, first is the blunt body with the shock wave standing off of the vehicle. The second is with pointy noses like all super sonic aircraft. So this idea is essentially inverting the payload fairing around the second stage then re-enter pointy end first. Hope this sparks some interesting discussion.

This seems to follow the idea described in the previous few posts.


« Last Edit: 04/02/2017 05:14 AM by Long EZ »

Offline GWH

Re: F9 Second Stage Reusability
« Reply #90 on: 04/02/2017 06:17 AM »
That has been propsed many times. Couple problems:
-the fairing is actually quite heavy, would mean a big hit to payload
-they have invested time and money to recover fairings as is

Offline gin455res

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Re: F9 Second Stage Reusability
« Reply #91 on: 04/02/2017 06:56 AM »
How hard would it be to re-engineer stage 2 to have an oxygen drop tank?


Would the remaining heat-shield, fuel tank, engine, nozzle have shifted the centre of gravity far enough backwards to be passively stable on re-entry?


It would definitely look more like a shuttlecock.


Could the nozzle act like grid fins?

Offline Kaputnik

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Re: F9 Second Stage Reusability
« Reply #92 on: 04/02/2017 07:58 AM »
How hard would it be to re-engineer stage 2 to have an oxygen drop tank?


Would the remaining heat-shield, fuel tank, engine, nozzle have shifted the centre of gravity far enough backwards to be passively stable on re-entry?


It would definitely look more like a shuttlecock.


Could the nozzle act like grid fins?

Pretty hard given it is a common bulkhead.
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Offline gin455res

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Re: F9 Second Stage Reusability
« Reply #93 on: 04/02/2017 09:46 AM »
thought as much. so might be simpler to drop both and have the heat shield between the tanks and engine. How would they plumb that?

shame to lose the  tanks, but still a lot of value in the remainder.

(maybe dock the detachable tanks with the engine bell to sort out the c-of-g.)

Offline MikeAtkinson

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Re: F9 Second Stage Reusability
« Reply #94 on: 04/02/2017 01:00 PM »
Anything that changes the basic design of the stage, such as adding heat shields, let alone adding thrusters or dropping the tanks, just takes too long. There are lots of things to do, specification, basic and detailed design, simulation, manufacture, testing, installation, changes to software and procedures. It would amaze me if these could be done in less than a couple of years, let alone the 6 months before the FH first flight.

For the FH demo flight the second stage must be fairly close to what will be flown on subsequent flights, so no major changes will be allowed. Even minor changes will be discouraged if they could possibly affect the success of the demonstration.

The only way that I can think of, which does not involve major changes to S2 (not going to happen for FH demo flight) and which will take under 2 years from decision to start to flight, is to use a ballute.

Potentially, deploying a ballute in LEO, then using it to bleed off much of the velocity high in the atmosphere, then capturing the descending stage by helicopter could work.


Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #95 on: 04/02/2017 02:20 PM »
When people are thinking about this they might like to consider how SX approached their first PLF recovery attempt.

No attachment to the PAF, no keeping the two halves together. Let each run operationally exactly as normal but add some hardware to them to. That works in this context.

At this late stage in the preparations for the FH test your options will be quite limited. It's way too late to design, model, mfg and install any complex hardware that's not already sitting on the shelf, but perhaps not deployed for whatever reason.

Musk mentioned that the heating energy involved rises as the cube of the velocity you have to bleed off. That suggests every m/s you can avoid adding to the US is better.

The obvious tactic in that case is to have the US burn to near orbital velocity, then separate the payload.
This means the payload has to add some delta V of its own. While not directly applicable I'll note that REL looked at this wrt to Skylon and found it could double payload to orbit, if the payload could supply the last 100m/s. Payload separation while still (nominally) in the atmosphere is in principal easier for a VTO rocket. 

The stage then essentially falls back to Earth by falling around the Earth in a not quite complete full orbit.

This cuts on orbit time from a day to come back over the landing area (plane changes eat a lot of propellant) to less than 90 mins. It also allows time for any kind of decellerator to work and bleed off more of that speed through the very high atmosphere. Perhaps early deployment of the grid fins spread wide in drag brake mode?

The fact the stage is not in orbit means it needs no retro burn to bring it out of orbit, which should be quite a substantial saving. Every m/s shaved in it's near 90min orbital coast can be directly calculated as a thinner TPS layer on the relevant parts, since that delta V does not have to be bled off passing through the much denser lower atmosphere.

The higher thrust engines should also mean they can thrust for a shorter time to kill the residual velocity in the hoverslam landing. It's not clear if that would put them closer to the stages -ve g limit or if they are already there now.

And yet none of this seems quite enough of an improvement.

OK the engine thrust's going to be quite a bit higher than it was in 2014 (Musk said 10% above what it is now, which is quite a lot higher than its 2014 level), when Musk said US reuse was "uneconomic" but that just does not seem enough to put reuse back on the agenda. Wasn't most of this predictable in 2014?
 
Eliminating the retro burn (since technically the stage is not in orbit) eliminates an engine restart and potentially a large chunk of propellant, which didn't have to be carried up the hill in the first place.

Having seen how many attempts it took SX to land their first first stage intact on the barge bringing the US to within 1Km of the barge would be a significant achievement from orbit.  The ultimate of course would be to land the US on the barge without hitting the already secured first stage, which is still attached to the deck.  Ironic to think you could get the US back from NEO only to be destroyed by hitting the successfully landed first stage.

The downside of this plan is that any payload that wants to use it will have to do some of the heavy lifting of getting to LEO in the first place. This would also apply if the payload was to GTO to allow the US to fall back to Earth.
 
I'm excited that Musk has not given up on reuse for the F9 US, even if it will take an FH stack to make it happen.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Offline robert_d

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Re: F9 Second Stage Reusability
« Reply #96 on: 04/02/2017 03:00 PM »
This is why I think my idea of developing a Falcon Medium (a two core Falcon that has the two cores stay together and land as a unit) has merit. It gives enough margin for a substantially heavier 2nd stage, while eliminating all expendable 1st stage launches. Reusable 2nd stage could have an elliptical cross section with extra fuel tanks for both a wider TPS surface and larger deceleration burn. 

The 1st stages can likely be equivalent to the Falcon heavy booster stages (and not the upgraded heavy core) because they would not be concentrating all of the compression force onto either booster and there would never be a single core pushing the much heavier payload (and heavier 2nd stage?) by itself. 

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #97 on: 04/02/2017 05:15 PM »
thought as much. so might be simpler to drop both and have the heat shield between the tanks and engine. How would they plumb that?

shame to lose the  tanks, but still a lot of value in the remainder.

(maybe dock the detachable tanks with the engine bell to sort out the c-of-g.)
So essentially apply the ULA Vulcan plan to the US.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.
So you're going to Mars to seek a better life. What does that mean to you? Always spot a fanbois by how they react to their idols failures.

Offline Kaputnik

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Re: F9 Second Stage Reusability
« Reply #98 on: 04/02/2017 06:45 PM »
@JohnSmith19
The difference between now and 2014 isn't simply that the MVac thrust has changed. IMHO it's much simpler than that. They were unsure whether the first FH was going to have a payload until quite recently and having determined that it's not going to have one, Musk says they might have a go at bringing back the US. Basically it's a free opportunity to do something interesting.

I think everyone is reading way too much into this and assuming it implies some sort of future US recovery program, of which this will be a demo.
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Offline gin455res

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Re: F9 Second Stage Reusability
« Reply #99 on: 04/02/2017 07:09 PM »
thought as much. so might be simpler to drop both and have the heat shield between the tanks and engine. How would they plumb that?

shame to lose the  tanks, but still a lot of value in the remainder.

(maybe dock the detachable tanks with the engine bell to sort out the c-of-g.)
So essentially apply the ULA Vulcan plan to the US.


yes.
The Vulcan video says 25% the weight, but 65% the cost. I don't know if it would be similar for the Falcon-9 S2.  If it were, the loading of the heat shield would become much lower than for full recovery.


It might be great in a world of 12,000-satellite constellations, if the tanks could become payload. Perhaps, cannibalized for structural components; or sent to an 'exterrestrial scrap yard' for use sometime in the future.

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