Author Topic: Titanium Falcon  (Read 10048 times)

Offline sevenperforce

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Titanium Falcon
« on: 08/24/2016 07:34 PM »
Obviously, when the Falcon 1, Falcon 5, and Falcon 9 were being designed, they chose aluminum for a lot of reasons. It was strong and lightweight and cheap, which is good when you're building rockets that will be expended for a while until you manage to nail down reuse.

Now that returning the stages seems to be a pretty regular thing and reuse appears to be just around the corner...what kind of margins would you get from replacing the aluminum-lithium alloy in the body of the Falcon 9 with titanium instead? Cost would be far higher, of course, but the specific strength of titanium is roughly 40% higher, meaning you could afford to reduce the weight of the stage body by more than 20% and still have a 10% higher safety margin.

Granted, the stage body is not all the dry mass of the stage. With 4.2 tonnes of engine on the bottom of the first stage, you're looking at less than 80% of the stage weight being aluminum-lithium body. So mass savings are not terrific...but it is still a reduction in dry weight of 10-15%, permitting pretty substantial increases in orbital throw weight.

Of course, they'd never do this now; everything they have is designed around their aluminum-lithium alloy.

But what about BFR? Since BFR will be designed for reuse from the very start, is it possible that SpaceX would go for a more expensive, higher-performing body material?

Offline spacenut

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Re: Titanium Falcon
« Reply #1 on: 08/24/2016 08:22 PM »
I think they are going to composites which are lighter than aluminum and also stronger pound for pound.  Titanium is heavier than aluminum and does have a higher melting point, but not necessary on the tanks which is 90% of the body of the booster. 

Offline sevenperforce

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Re: Titanium Falcon
« Reply #2 on: 08/24/2016 08:59 PM »
I think they are going to composites which are lighter than aluminum and also stronger pound for pound.  Titanium is heavier than aluminum and does have a higher melting point, but not necessary on the tanks which is 90% of the body of the booster.
Ah, I see.

How do composites compare to titanium? Titanium is 40% stronger than aluminium alloy, pound for pound, so you could use almost 30% less of it by weight and still have the same tank strength.

Offline acsawdey

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Re: Titanium Falcon
« Reply #3 on: 08/24/2016 09:43 PM »
I think they are going to composites which are lighter than aluminum and also stronger pound for pound.  Titanium is heavier than aluminum and does have a higher melting point, but not necessary on the tanks which is 90% of the body of the booster.
Ah, I see.

How do composites compare to titanium? Titanium is 40% stronger than aluminium alloy, pound for pound, so you could use almost 30% less of it by weight and still have the same tank strength.

How well understood are the properties of titanium alloys at cryogenic temperatures? Is it compatible with direct LOX contact?

Offline sevenperforce

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Re: Titanium Falcon
« Reply #4 on: 08/24/2016 10:28 PM »
How do composites compare to titanium? Titanium is 40% stronger than aluminium alloy, pound for pound, so you could use almost 30% less of it by weight and still have the same tank strength.

How well understood are the properties of titanium alloys at cryogenic temperatures? Is it compatible with direct LOX contact?
If I recall correctly, titanium alloys have comparable or superior cryogenic performance against aluminum alloy. I imagine the oxidization chemistry is also similar.

How about composites? Does carbon-fiber composite lose tensile strength at subcooled LOX temperatures?

All other things being equal, it is better to go with denser materials if equal or better specific strength can be attained, because a denser tank metal will have a larger internal volume for the same strength and external volume. Probably a negligible difference between aluminum and titanium despite the significant volume-specific strength difference, thanks to our old friend square-cube.

Online Herb Schaltegger

Re: Titanium Falcon
« Reply #5 on: 08/24/2016 10:33 PM »
This reminds me of the all the post-STS 107 chit chat on Usenet. "What if Columbia's wing spar had been titanium instead of aluminum?!?!"

Titanium is not a miracle metal; it's generally more difficult to work for large structural members and actually, I doubt SpaceX could afford the material cost hit even if they could work through the manufacturing and assembly process changes. This isn't a Cold War project like the B-70 (which was ultimately too expensive to produce more than the 3 airframes anyway).
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Offline acsawdey

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Re: Titanium Falcon
« Reply #6 on: 08/24/2016 10:39 PM »
This is the link I was looking for:

http://www.dtic.mil/dtic/tr/fulltext/u2/273489.pdf

"Unalloyed titanium (Ti-75A) and Ti-6Al-4V alloy were consumed by violent reactions when ruptured in gaseous oxygen under suitable pressure from -190F to room temperature."


Online CameronD

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Re: Titanium Falcon
« Reply #7 on: 08/25/2016 12:02 AM »
Titanium is not a miracle metal; it's generally more difficult to work for large structural members and actually, I doubt SpaceX could afford the material cost hit even if they could work through the manufacturing and assembly process changes. This isn't a Cold War project like the B-70 (which was ultimately too expensive to produce more than the 3 airframes anyway).

Titanium's strength also requires using extremely dangerous chemicals (like HF/Nitric Acid mix using in the etching process) it which is at least part of the reason for the high cost of large structural components.

I remember the line manager of one component processing facility here telling me a rookie OH&S guy asked him why there was no ladder on the inside of the open HF/Nitric bath so if someone fell in they could climb out.  His response was "if anyone falls in there, they won't even hit the bottom!".  The fume scrubber hiccupped one day and a smallish cloud of vapour wafted across the car-park, but before it could dissipate it neatly stripped the paint off the top of five cars and turned the windows opaque.  Fortunately no-one was in the car-park at the time..

Although aerospace-grade aluminium etching still uses nasty chemicals (including some weak HF/Nitric for desmutting) it's not quite in the same league safety-wise.
 
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Offline dorkmo

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Re: Titanium Falcon
« Reply #8 on: 08/25/2016 03:11 AM »
heres a discussion that talks a bit about the pros and cons of ti

http://forum.nasaspaceflight.com/index.php?topic=39295.0

Offline octavo

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Re: Titanium Falcon
« Reply #9 on: 08/25/2016 10:10 AM »
With regard to use on BFS, higher-density (afaik) actually hurts you as the secondary radiation from gamma rays striking the titanium would be far worse than if they strike a less dense material

Offline sevenperforce

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Re: Titanium Falcon
« Reply #10 on: 08/25/2016 07:21 PM »
With regard to use on BFS, higher-density (afaik) actually hurts you as the secondary radiation from gamma rays striking the titanium would be far worse than if they strike a less dense material
Wouldn't be an issue for the first-stage booster.

Offline Jim

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Re: Titanium Falcon
« Reply #11 on: 08/25/2016 07:25 PM »
With regard to use on BFS, higher-density (afaik) actually hurts you as the secondary radiation from gamma rays striking the titanium would be far worse than if they strike a less dense material
Wouldn't be an issue for the first-stage booster.

But having booster and upper stage made of different materials eliminates any production synergism.  it would require separate tank production lines.

Offline sevenperforce

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Re: Titanium Falcon
« Reply #12 on: 08/25/2016 07:37 PM »
With regard to use on BFS, higher-density (afaik) actually hurts you as the secondary radiation from gamma rays striking the titanium would be far worse than if they strike a less dense material
Wouldn't be an issue for the first-stage booster.

But having booster and upper stage made of different materials eliminates any production synergism.  it would require separate tank production lines.
Well, the MCT is (purportedly) more than just a second stage, so comparing BFR to MCT is less like comparing Falcon 9's stage 1 to stage 2 and more like comparing Falcon 9's stage 1 to the Dragon 2.

Offline Jim

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Re: Titanium Falcon
« Reply #13 on: 08/25/2016 07:48 PM »

Well, the MCT is (purportedly) more than just a second stage, so comparing BFR to MCT is less like comparing Falcon 9's stage 1 to stage 2 and more like comparing Falcon 9's stage 1 to the Dragon 2.

No, it is still the same comparison.  The MCT will have a propulsion system with elements common to the booster.

Offline sevenperforce

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Re: Titanium Falcon
« Reply #14 on: 08/25/2016 07:57 PM »

Well, the MCT is (purportedly) more than just a second stage, so comparing BFR to MCT is less like comparing Falcon 9's stage 1 to stage 2 and more like comparing Falcon 9's stage 1 to the Dragon 2.

No, it is still the same comparison.  The MCT will have a propulsion system with elements common to the booster.
But it will also have a pressure vessel designed for human occupancy, so....

Offline Lee Jay

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Re: Titanium Falcon
« Reply #15 on: 08/25/2016 08:09 PM »
This isn't a Cold War project like the B-70 (which was ultimately too expensive to produce more than the 3 airframes anyway).

Only two XB-70s were built (the second crashed, the first is in the USAF museum in Dayton, OH), and they were almost entirely made of stainless steel, with titanium just in the most critical parts.

The SR-71, on the other hand...

Offline Jim

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Re: Titanium Falcon
« Reply #16 on: 08/25/2016 08:16 PM »

But it will also have a pressure vessel designed for human occupancy, so....

So that is the same as the Dragon on top of the second stage

Offline mvpel

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Re: Titanium Falcon
« Reply #17 on: 08/25/2016 08:17 PM »
Cryogenic composite fuel tanks have been the subject of very aggressive R&D work over the past few years.

NASA/Boeing composite launch vehicle fuel tank scores firsts - January 2016
Quote
For more than 50 years, heavy metal cryogenic tanks have carried the liquid hydrogen (LH2) and oxygen necessary to launch vehicles into space. But in a joint effort, NASA and The Boeing Co. (Chicago, IL, US) have designed, fabricated and tested a composite cryotank that, if scaled up to current space launch system dimensions, would weigh 30% less and cost 25% less than the best aluminum-lithium cryotanks used today, and could warrant transport of as much as 1,400 kg of additional payload to low-Earth orbit and beyond.

The US$25 million Composite Cryotank Technologies and Demonstration (CCTD)  project, part of the NASA Space Technology Mission Directorate’s Game Changing Development (GCD) program, involved a team of Boeing and NASA engineers.

“This is the first effort to successfully build and test a tank of this scale,” says Douglas McCarville, Technical Fellow at Boeing Research & Technology (BR&T) in Seattle, WA, US. “The tank would work for liquid oxygen or liquid hydrogen on a variety of next-generation launch systems.”
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Offline Robotbeat

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Re: Titanium Falcon
« Reply #18 on: 08/26/2016 07:37 PM »
Might make sense to make /portions/ of Falcon out of Titanium. Like the grid fins or maybe parts of the thrust structure. To enhance durability and reduce the amount of TPS you need.

But I don't think they'll make the tanks (etc) out of it. Hard to work, not generally as good structure/mass (the lower density of aluminum helps for compressive structures in ways beyond pure strength/weight ratio because of reduced buckling).
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Offline Robotbeat

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Re: Titanium Falcon
« Reply #19 on: 08/18/2017 04:09 AM »
Might make sense to make /portions/ of Falcon out of Titanium. Like the grid fins or maybe parts of the thrust structure. To enhance durability and reduce the amount of TPS you need.

But I don't think they'll make the tanks (etc) out of it. Hard to work, not generally as good structure/mass (the lower density of aluminum helps for compressive structures in ways beyond pure strength/weight ratio because of reduced buckling).
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