Author Topic: Using Carbon Composite tanks for F9/FH Impacts on payload capability  (Read 26978 times)

Offline oldAtlas_Eguy

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Here is a thought.

SpaceX is investigating use of carbon composite tanks for ITSy. But what if they changed over to its use on F9/FH prior to the ITSy being operational.

What would that up to 30% weight savings on tank weight do to the F9/FH payload capability?

What would that do to the capability of doing RTLS for a size of payload?

Impacts for life (number of reuse flights)?

Just using a reduction of 1mt of tank weight for example in US that translates directly to a increase of 1mt of payload weight to any orbit. Instead of just 6mt for an EXPD F9 it would be 7mt for a EXPD F9. For FH those TLI and Mars payloads would increase by that same 1mt for example.

By reducing the booster weight the boosters would have more prop and more DV due to the available prop to be able to do RTLS in situations of much larger payloads where now the F9 would have to be ASDS recovered.

Then there is the final item about this is that SpaceX would gain the needed extensive flight data on the reuse of carbon composite tanks. This without the need to do an extensive test program of the ITSy to get this same data set.


Offline yokem55

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Here is a thought.

SpaceX is investigating use of carbon composite tanks for ITSy. But what if they changed over to its use on F9/FH prior to the ITSy being operational.

What would that up to 30% weight savings on tank weight do to the F9/FH payload capability?

What would that do to the capability of doing RTLS for a size of payload?

Impacts for life (number of reuse flights)?

Just using a reduction of 1mt of tank weight for example in US that translates directly to a increase of 1mt of payload weight to any orbit. Instead of just 6mt for an EXPD F9 it would be 7mt for a EXPD F9. For FH those TLI and Mars payloads would increase by that same 1mt for example.

By reducing the booster weight the boosters would have more prop and more DV due to the available prop to be able to do RTLS in situations of much larger payloads where now the F9 would have to be ASDS recovered.

Then there is the final item about this is that SpaceX would gain the needed extensive flight data on the reuse of carbon composite tanks. This without the need to do an extensive test program of the ITSy to get this same data set.
Part of their challenge with carbon fiber tankage is the effects of hot oxygen from autogenous pressurization on the lox tank. If they go linerless, how do they keep the fibers from combusting. If they go with a liner, how do they keep the liner from separating in cryogenic temps.

With Falcon based design, they won't be able to test that aspect out.

Offline ulm_atms

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I've never understood how they were going to keep the LOX in the tank using carbon-composite without a liner.  The COPVs apparently allowed some LOX to go through them at standard LOX tank operating pressures or AMOS-6 would not of happened...and from my understanding, a COPV without the Al liner is basically what they are testing(test tank that had...um...issues)...and are wanting to build just in a much bigger size.  Does anyone know ways to keep the LOX from seeping through the tank without a liner of some sort?  Does RocketLab use a liner?  They are the only ones I know using a carbon composite tank currently.

Now to the original question, it would do everything you say.  I just think that the shear size of ITSy compared to the Falcon series would not be a good gauge for them.  The Falcon series is super skinny and would have a completely different loading profile then ITSy.  Plus, they have so many things going on currently that it's better they just go straight to what they want size wise and learn, then learn at the Falcon size and then find out their time/money would of been better spent elsewhere.  My 2 cents anyways.


Offline john smith 19

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Part of their challenge with carbon fiber tankage is the effects of hot oxygen from autogenous pressurization on the lox tank. If they go linerless, how do they keep the fibers from combusting. If they go with a liner, how do they keep the liner from separating in cryogenic temps.

With Falcon based design, they won't be able to test that aspect out.
This has been discussed by HMX in another thread. (I think specifically to do with the ITS tank)

He said the trick is to start with an inner layer of polymer before moving onto the CF.

How big an issue this warm (or hot) GO2 is depends on the chemistry of the inner tank that it's exposed to. Polymer stability has been creeping up over the decades, to the point you can now buy plastic baking trays good to at least 220c. There are reports of polymers based around benzene rigns good to 400c+

However I'm  not sure how compatible these polymers are with CF construction.

Historically Graphite (in nuclear reactors) has been stable to 450c in air, with fully dense graphite even more stable (but was impossible to make at the time the tests were done).

If high temperature stable polymer linings are not possible there are some mitigation approaches.

The obvious ones are to position the GO2 injector heads along the centreline of the tank and exhaust into the LO2, however this may lower the average density of the mixture to the turbopumps.

Option b would be to dilute high temp GO2 (more likely supercritical O2) with some LO2 from the turbopump inlet to deliver a lower temperature mix.

Tank pressure is one of those easily changed parameters that tempts engineers in a bind to change it. Engine turbo pumps cavitating? Increase inlet pressure.
LV not quite stiff enough? Increase tank pressure a bit more.

But every psi you increase it means more mass that's carried to orbit, although you should relax that pressure after Max Q on the structure.

If you're really concerned about payload to orbit, or you're dealing with SSTO concepts it's something that should be managed very carefully.

Time will tell how serious the issue with warm O2 pressurant really is.  Ideally they run with a stable polymer inner layer and full GO2 temp, allowing minimal mass pressurization of the stage.
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Offline AncientU

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Here is a thought.

SpaceX is investigating use of carbon composite tanks for ITSy. But what if they changed over to its use on F9/FH prior to the ITSy being operational.

What would that up to 30% weight savings on tank weight do to the F9/FH payload capability?

What would that do to the capability of doing RTLS for a size of payload?

Impacts for life (number of reuse flights)?

Just using a reduction of 1mt of tank weight for example in US that translates directly to a increase of 1mt of payload weight to any orbit. Instead of just 6mt for an EXPD F9 it would be 7mt for a EXPD F9. For FH those TLI and Mars payloads would increase by that same 1mt for example.

By reducing the booster weight the boosters would have more prop and more DV due to the available prop to be able to do RTLS in situations of much larger payloads where now the F9 would have to be ASDS recovered.

Then there is the final item about this is that SpaceX would gain the needed extensive flight data on the reuse of carbon composite tanks. This without the need to do an extensive test program of the ITSy to get this same data set.

Their revenue source is the rising launch rate of F9, especially after Block 5 starts flying. Doubt that GS would support R&D on their breadwinner.  ConnX isn't going anywhere without F9 high flight rate, ITSy discussions and possibilities notwithstanding.

If they want to test carbon composite tankage, they can do it many other ways on 'Test Articles' -- when one fails, testing and operational flights are uninterrupted.
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Offline Robotbeat

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They explicitly said that they'd stop major revisions of Falcon family after Block 5. So no. Lock thread?
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Offline Jimmy Murdok

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They explicitly said that they'd stop major revisions of Falcon family after Block 5. So no. Lock thread?

I guess it worth to keep it open until question from title (Impact on payload capability) and from 1st post are reasonably estimated and answered. I find it interesting.

- What would that up to 30% weight savings on tank weight do to the F9/FH payload capability?
- What would that do to the capability of doing RTLS for a size of payload?
- Impacts for life (number of reuse flights)?

Offline john smith 19

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Their revenue source is the rising launch rate of F9, especially after Block 5 starts flying. Doubt that GS would support R&D on their breadwinner.  ConnX isn't going anywhere without F9 high flight rate, ITSy discussions and possibilities notwithstanding.

If they want to test carbon composite tankage, they can do it many other ways on 'Test Articles' -- when one fails, testing and operational flights are uninterrupted.
If we're specifically talking about applying composites to F9 tank construction then it's a non starter due to all the knock on effects.
F9 is affected
F9/Dragon is affected
FH is affected

Which is essentially all of SX's current, and potential revenue earning business.  :(

Carbon fiber <> Aluminum. It would invalidate a huge amount of test data. We know that SX has carried out a continuing programme of upgrades, tests and mods to its LV's practically since F1 but something this fundamental would really be for a completely new LV, which ITS (or mini-ITS or ITS-Lite, whatever flies) will be.

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Offline john smith 19

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I guess it worth to keep it open until question from title (Impact on payload capability) and from 1st post are reasonably estimated and answered. I find it interesting.
- Impacts for life (number of reuse flights)?
That's an interesting one.  Impact tests on composite tanks have show a 30% reduction in maximum load before failure but without visual signs of impact damage.

Note that the interstage and fairings are both large or largish composite structures but the interstage is a single use object and the fairings are planned to be recovered without slamming them into the ground, or a pitching deck.  Obviously the landing legs should absorb quite a lock of the initial shock loading but it's unclear if that would be enough to prevent tank damage if the tanks were composite.

So you could get a situation where what  you gained on the tank mass you lost on the leg weight and/or the stage life in terms of how many flights it could do. Heavier legs could substantially reduce any increases in payload due to the switch to composite tanks, but shortened life expectancy (compared to Aluminum tanks) would probably be an even worse issue.  :(
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Offline Nomadd

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 Since when is the interstage a single use object?
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Offline MP99

A composite F9 could conceivably use autogenous pressurization on its LOX, but at the expense of Merlin changes to generate hot GOX.

However, the RP1 would need to continue with GHe pressurization, with the COPVs embedded in the LOX. Would there be an issue with needing penetrations to the LOX tanks to support the COPV struts?

Cheers, Martin

Offline wannamoonbase

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Here is a thought.

SpaceX is investigating use of carbon composite tanks for ITSy. But what if they changed over to its use on F9/FH prior to the ITSy being operational.

What would that up to 30% weight savings on tank weight do to the F9/FH payload capability?

What would that do to the capability of doing RTLS for a size of payload?

Impacts for life (number of reuse flights)?

Just using a reduction of 1mt of tank weight for example in US that translates directly to a increase of 1mt of payload weight to any orbit....

If they were to pursue carbon composites on the F9/FH perhaps it makes sense on the US. 

The weight savings could produce enough weight savings to enable US reuse technology. 

Allowing the development and flight experience of both technologies.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline envy887

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Since when is the interstage a single use object?

It is most definitely not a single use object.

Offline john smith 19

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Since when is the interstage a single use object?

It is most definitely not a single use object.
It was my understanding it separated from the first stage to let the US go free.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Ictogan

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It was my understanding it separated from the first stage to let the US go free.
No, it stays attached to the first stage until landing.

Offline AncientU

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It was my understanding it separated from the first stage to let the US go free.
No, it stays attached to the first stage until landing.

The 'sport' interstage houses the grid fins and reaction control system... booster wouldn't make it back if it was separated.
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Offline Lars-J

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Since when is the interstage a single use object?

It is most definitely not a single use object.
It was my understanding it separated from the first stage to let the US go free.

I suspect you have watched too much Apollo footage. Take another look at stage separation for any F9 mission - or practically any modern rocket. No, for F9 the interstage is always attached to the first stage, it has the nitrogen thrusters and grid fins which are necessary for landing.
« Last Edit: 08/08/2017 07:21 pm by Lars-J »

Offline spacenut

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EM said they are working on second stage reusability.  So, carbon fiber on second stage may be used.  I thought Block 5 was only for the first stage upgrades. 

If carbon fiber tanks on the second stage helps 30%, then the heat shielding, landing legs, and either parachutes or landing thrusters could be enough to offset the weight savings and still keep the same payload capability. 

If they decide to use and expendable carbon fiber second stage on say a multiple used first stage to improve GTO performance, would it be worth going to carbon fiber?


Offline wannamoonbase

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If they decide to use and expendable carbon fiber second stage on say a multiple used first stage to improve GTO performance, would it be worth going to carbon fiber?

Potential FH market would get smaller yet again.  Not that there is anything wrong with that.
« Last Edit: 08/08/2017 10:18 pm by wannamoonbase »
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline speedevil

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That's an interesting one.  Impact tests on composite tanks have show a 30% reduction in maximum load before failure but without visual signs of impact damage.
I wonder on birdstrikes.

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