Author Topic: Using Carbon Composite tanks for F9/FH Impacts on payload capability  (Read 17561 times)

Offline wannamoonbase

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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.

Birdstrike would be a minor splat.
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Offline john smith 19

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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.

Birdstrike would be a minor splat.
Not so minor.

The NAO report on crewed Dragon stated this is an issue with why certification is taking so long.  :(

That would be a serious delay as NASA looked at the LV for Dragon 2 all over again, unless SX ran 2 separate mfg lines for "A" F9 and "C" F9. We know SX don't like to retain inventory or capability unnecessarily IE F1.  :(
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Offline Owlon

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The thread title says "impacts on payload capacity." We can consider the question as a theoretical exercise and ignore the practical certification issues.

Assuming 25000 kg 1st stage, 5000 kg 2nd stage, half of the mass of each stage is tank, 30% tank weight savings, and 1/7 ratio of first stage mass reduction to payload gain (a number I have seen thrown around often): 25000*.5*.3/7 + 5000*.5*.3 =  1285.71 kg. I suspect some of my assumptions lead to an optimistic number.

Anyone have a rough idea of how much of the mass in each stage is actually tankage?

Offline Robotbeat

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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.

Birdstrike would be a minor splat.
Not so minor.

The NAO report on crewed Dragon stated this is an issue with why certification is taking so long.  :(

That would be a serious delay as NASA looked at the LV for Dragon 2 all over again, unless SX ran 2 separate mfg lines for "A" F9 and "C" F9. We know SX don't like to retain inventory or capability unnecessarily IE F1.  :(
"The NAO report on crewed Dragon stated this is an issue with why certification is taking so long."
and
"Birdstrike would be a minor splat"

...are not incompatible with one another.
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Offline Req

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Isn't it intuitively obvious that a bird strike on the second stage is far less serious than a bird strike on Dragon due to the possible angles involved?

Offline Jim

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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.

Birdstrike would be a minor splat.
Not so minor.

The NAO report on crewed Dragon stated this is an issue with why certification is taking so long.  :(

That would be a serious delay as NASA looked at the LV for Dragon 2 all over again, unless SX ran 2 separate mfg lines for "A" F9 and "C" F9. We know SX don't like to retain inventory or capability unnecessarily IE F1.  :(

What is NAO?

Offline jpo234

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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.

Birdstrike would be a minor splat.
Not so minor.

The NAO report on crewed Dragon stated this is an issue with why certification is taking so long.  :(

That would be a serious delay as NASA looked at the LV for Dragon 2 all over again, unless SX ran 2 separate mfg lines for "A" F9 and "C" F9. We know SX don't like to retain inventory or capability unnecessarily IE F1.  :(

What is NAO?

That one: https://www.nao.org.uk/report/the-red-dragon-project/ ??????

Or did you get your Government watchdogs mixed up and meant that one: http://www.gao.gov/products/GAO-17-137 ?
« Last Edit: 08/10/2017 07:48 AM by jpo234 »
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Offline envy887

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The thread title says "impacts on payload capacity." We can consider the question as a theoretical exercise and ignore the practical certification issues.

Assuming 25000 kg 1st stage, 5000 kg 2nd stage, half of the mass of each stage is tank, 30% tank weight savings, and 1/7 ratio of first stage mass reduction to payload gain (a number I have seen thrown around often): 25000*.5*.3/7 + 5000*.5*.3 =  1285.71 kg. I suspect some of my assumptions lead to an optimistic number.

Anyone have a rough idea of how much of the mass in each stage is actually tankage?

Based on size (37 x 3.7 meter near-cylinder) and thickness (4.75 mm) the booster tanks walls are around 5800 kg. But the tank has internal stringers that also will contribute some mass.

The Merlins only mass 4230 kg including TVC, so the octaweb must mass quite a bit - and it could also be replaced with composites.

The interstage, legs, and COPVs are already composites, and the grid fins, RCS, TPS, avionics, and plumbing either can't use composites or don't mass much anyway.

Offline oldAtlas_Eguy

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For the booster there are secondary gains due to lighter stage, meaning less return prop needed (Boost back and reentry burns), lower landing prop needed (lower mass means a lower terminal velocity needing less prop to perform landing). This means more prop available for larger payloads (higher delta V from stage for given GLOW). So the payload gains for the booster are not just for its way up but also the impacts on its way back.

Offline speedevil

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Isn't it intuitively obvious that a bird strike on the second stage is far less serious than a bird strike on Dragon due to the possible angles involved?

To clarify, I meant on a returning second stage, with a CF tank, one of the variants that has been suggested to have significant sideways velocity in the low atmosphere.

Offline Robotbeat

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Not a concern. If they lose one out of every 100,000 to a bird strike (unlikely), then who cares?
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline deruch

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IIRC, the length of the upper stage was limited by the vehicle's bending moment.  i.e. In the change to F9v1.2, SpaceX would have liked to lengthen the upper stage even more than they did, based on thrust/power, but were limited by shear/bending.  Could a switch to carbon composite tanks allow them to go back and stretch the vehicle even more?  Given all the thrust increases they've eked out of the Merlin, such a move is probably even more attractive today than it was during the last update.  That's really the only situation where I could see them making the swap.  Otherwise, IMO, the potential gains aren't worth all the work.
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Offline john smith 19

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Not a concern. If they lose one out of every 100,000 to a bird strike (unlikely), then who cares?
If only that were true. :(

It was cited as one of the reasons neither contractor can make the NASA goal (LOC in 1 in 270 flights IIRC).

TBH I'd never thought bird strike was even applicable to VTO rocket systems at all. I can only presume it would have to be something like the bird hitting one of the windows and crashing through it.  :(
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Offline John Santos

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Not a concern. If they lose one out of every 100,000 to a bird strike (unlikely), then who cares?
If only that were true. :(

It was cited as one of the reasons neither contractor can make the NASA goal (LOC in 1 in 270 flights IIRC).

TBH I'd never thought bird strike was even applicable to VTO rocket systems at all. I can only presume it would have to be something like the bird hitting one of the windows and crashing through it.  :(
I thought the topic was carbon composite tanks for the Falcon 9, not the Dragon, and the particular topic you are replying to is the vulnerability of a carbon composite 2nd stage to bird strikes during re-entry and landing.  I don't see how LOC possibly enters into it.  Worst case, you lose a 2nd stage that you otherwise might have recovered.

A bird strike on the 2nd stage during launch would have to be from the side, which would either be low-velocity (while the rocket was still moving slowly and the bird could fly into it) or extremely unlikely due to the geometry, when the rocket has accelerated significantly.  A bird in the path of the rocket would be far more likely to hit the nose cone (or Dragon) than the 2nd stage.


As far as I know, the Dragon is made out of aluminum honeycomb, not carbon composite.

Offline livingjw

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Not honeycomb. Solid aluminum isogrid type structure.

John

Offline Nomadd

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 I've heard more like a 10% payload benefit for 1st stage weight reduction. In any case, they're not going to build a whole different rocket for a few hundred kilos extra payload. The 2nd stage might be different, but still no chance it's in the cards.
« Last Edit: 08/14/2017 07:21 PM by Nomadd »

Offline tdperk

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Not a concern. If they lose one out of every 100,000 to a bird strike (unlikely), then who cares?
If only that were true. :(

It was cited as one of the reasons neither contractor can make the NASA goal (LOC in 1 in 270 flights IIRC).

TBH I'd never thought bird strike was even applicable to VTO rocket systems at all. I can only presume it would have to be something like the bird hitting one of the windows and crashing through it.  :(

My gut tells me that as a grotesque over-reaction to the foam strike on an RCC leading edge loss of a Shuttle, that NASA has baked into their requirements some quite unrealistic assumptions.  Are the engineering justifications for that requirement as written available?

Are there any recorded birdstrikes in launch vehicle history?

How many launches have there been?
« Last Edit: 08/15/2017 06:18 PM by tdperk »

Offline Norm38

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Regarding high temp auto-pressurization: 
How thick does a layer of epoxy have to be to prevent reaction to LOx?  Is a linerless tank simply lined with extra epoxy from the molding process?

Offline Robotbeat

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Epoxy burns in LOx, too.
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Online Eric Hedman

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Not a concern. If they lose one out of every 100,000 to a bird strike (unlikely), then who cares?
If only that were true. :(

It was cited as one of the reasons neither contractor can make the NASA goal (LOC in 1 in 270 flights IIRC).

TBH I'd never thought bird strike was even applicable to VTO rocket systems at all. I can only presume it would have to be something like the bird hitting one of the windows and crashing through it.  :(
Which begs the question of how big a bird and at what altitude are they typically distributed at.  A couple of weeks ago I was listening to a Q&A by the Blue Angels pilots.  They said their F-18s can handle strikes of small birds up to around 700 mph including on their canopies.  Bigger birds have been known to punch holes in their aircraft.  The solutions are making the top surfaces including windows tougher, chasing the birds away, or detecting if the birds are flying above the launch pad and only launching if there is a clear path.  One of the three has to be possible.  I could see drones chasing birds away as one solution.

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