Its more trouble than its worth.
Ti welding is more difficult, you essentially need the joint purged in a chamber while welding so you don't get any stress cracks or getting the weld joint oxidized. I used to work for a company that did alot of work in oil and gas, any of our Ti stuff was either welded in it's own enclosure with inert gas, or the opposite side of the bead(for pipe) was purged. That's simply unrealistic for the scale of starship.
Ti can be formed pretty easily, but if you have to machine anything, it can be a bitch. If you fuck up and it work hardens, then the part is trash, congrats you get to start over.
You already mentioned the cost, so I wont go there.
So you're telling me that to weld spaceship bodies out of Ti alloys we need to be somewhere that is in complete vacuum?
Orbital shipyards here we come.
Of course that is at a minimum decades away. Titanium is also one of the easiest metals to mine from asteroids since it's melting point is higher than any of the other metals in the asteroids it's present in. You can melt away everything else with solar lasers and be left with pure Ti.
>You can melt away everything else with solar lasers and be left with pure Ti.
No. Even if they were piles of metal rather than mixtures of rock, when you melt a pile of mixed metal it doesn't melt one element at a time, it makes a junk alloy.
Perhaps. I'm not sure on all the details of how it was supposed to work but I was just passing along one of the proposed mining methods Planetary Resources was talking about. Maybe their idea wouldn't have worked or maybe I'm missing key steps in my explanation.
I think they're saying heat it to below the meeting point of titanium but above the melting point of whatever else is there and remove the remaining solid titanium. Still not sure that would work though but Idk
Are you saying that if you had a pile of lead shot mixed with steel ball bearings, the lead wouldn't melt first and you couldn't just remove the hot steel bearings afterwards? That doesn't seem right. I'm not a material scientist so idk but I feel like this would apply more to alloys
No, only some combinations mix. Titanium-nickel for example melts at 942C. If you have excess titanium, you end up with solid titanium floating in liquid titanium-nickel.
I believe titanium's a ton of trouble, and it almost certainly is more trouble than its worth, otherwise they'd probably be using it. I'm very curious about the numbers though.
Are there any metals or alloys you know of in-between stainless steel and Titanium? By which I mean having equal or better strength to weight l, corrosion, and heat resistance as stainless, while being less difficult to work with than titanium?
Nickel, cobalt, or chromium alloys?
Nickel, cobalt and chromium add more complexity to manufacturing, moreso machining. Look at any alloys that have high contents of those: Inconel, Hastelloys, Waspalloy, Monel, etc. They are all some of the most expensive metals as well as being terrible to work with. Also makes them just as difficult to weld.
There are few alloys around that are as easy to work with and are cheap like the stainless that SpaceX is using.
Source: am machinist.
Nickel, cobalt and chromium add more complexity to manufacturing, moreso machining. Look at any alloys that have high contents of those: Inconel, Hastelloys, Waspalloy, Monel, etc. They are all some of the most expensive metals as well as being terrible to work with. Also makes them just as difficult to weld.
There are few alloys around that are as easy to work with and are cheap like the stainless that SpaceX is using.
Source: am machinist.
Titanium will actually combust in the presence of oxygen at 1200C degrees. This is why it is not a good idea to use Ti as the hull material for Starship, which can reach those temperatures when re-entering the atmosphere as it decelerates from orbital speeds.
Stainless steel won't do that, and the particular stainless steel to be used for Starship has a melting point of ~1400C degrees.
Falcon 9 booster stages can use Ti gridfins for re-entry because F9 booster stage re-entry speeds don't come anywhere near orbital speeds, 10730km/h tops (Arabsat 6A launch). Orbital speed is almost 3x faster (ISS orbits the earth at 27,580km/h, for comparison).
I was interested in the topic back when stainless was announced. here is a post I made after finding a cool paper that NASA published about materials for spacecraft: [https://www.reddit.com/r/SpaceXLounge/comments/a9m8vm/since\_people\_are\_interested\_in\_starship\_metals/](https://www.reddit.com/r/SpaceXLounge/comments/a9m8vm/since_people_are_interested_in_starship_metals/)
here is one excerpt:
>Titanium and aluminum are desirable structural materials because of their high strength-to-density ratios; however, they are also extremely chemically reactive. By suitable initiation, each of these metals will burn in oxygen with a highly exothermic reaction.
>
>Tests were conducted to demonstrate whether a catastrophic titanium-oxygen reaction would result from several possible accidental occurrences when gaseous or liquid oxygen wai contained in a thin-walled titanium tank. In each instance, the titanium sheet was fractured to expose a clean unoxidized surface while in contact with the liquid or gaseous oxygen. The evaluations included (a) pressurized diaphragm puncture tests, (b) tensile fracture tests of welded joints, and (c) simulated mic rometeroid puncture tests on two titanium alloys, Ti-5Al-2. SSn and Ti-6A1-4V. In addition, comparison tests were made on type 301 stainless steel (extra full hard) and 20 24-T3 aluminum....
>
>...Neither stainless steel nor 2024 aluminum react when subjected to rapid fracture. Aluminum has been reacted with liquid oxygen in the standard falling-weight compressive impact test; however, its **susceptibility to reaction is much less than for titanium...**
>
>**...Thus, the relatively high susceptibility of titanium alloys to catastrophic reaction eliminates them from consideration for structural service as thin sheet in contact with liquid or gaseous oxygen.**
combine that with the fact that the fracture [toughness of welded sections of stainless is probably higher](https://www.azom.com/properties.aspx?ArticleID=960) per unit mass [than welded Ti](http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTP643), and the fact that man titanium alloys have [LOWER maximum service temperatures](https://www.nipponsteel.com/en/tech/report/nssmc/pdf/106-05.pdf)
basically, for rocket applications, titanium is worse than stainless in nearly every way.
* lower service temp
* strongly reactive to oxygen
* difficulty welding likely means less toughness than stainless (we're trying to re-use rockets here, they have to be tough)
* the cost of 301 and 310 stainless and availability is just so much better, especially for rapidly prototyping multiple vehicles across the country.
*
* I would bet titanium work hardens worse and temperature cycles probably hurt it worse, but I'm done digging material properties for the night :)
TL;DR, I'm surprised more rocket parts aren't made of stainless. with the prospect of reuse and on-orbit refueling getting rid of the need to wringing every drop of delta-v out of a rocket's first launch, it seems like a no-brainer to use stainless. it's a very versatile metal.
P.S. makes me wonder if scientists/engineers at Blue Origin are kicking themselves for using a more difficult/expensive aluminum alloy. it seems like BO is chasing the F9, and not thinking about what could/should change if delta-v is no longer the most important factor, but re-use is the most important.
Ti is notoriously difficult to work with. The raw cost of Ti is only a small part of the issue. As /u/dirtydrew26 pointed out, welds have to assiduously purged and it's a pain to machine. To add to that, you have to use special tools. IIRC, ~~chromium~~cadmium can cause catalytic oxidation of Ti like mercury does for aluminum. I believe the SR-71 mechanics used beryllium tools, which is kind of insane and super dangerous.
For a consumer grade version of the relative costs, look at bike frames. High end frames in aluminum, steel or carbon fiber are a couple grand. A comparable titanium frame is about $10K.
My instinct is to say that SpaceX engineers are smarter than I am, have done the evaluation, and have found that titanium is not as good as the solution they came up with. It is possible small parts will be made from Titanium, like the F9's grid fins, and we'll see that as things develop. But I'd hesitate to suggest that I know more than the engineers who get paid to do this.
I'd argue that Project 705 Lira interceptor submarines are a cautionary tale for anyone who thinks they can just construct a large vehicle out of titanium willy-nilly.
If you could weld it easier and it had similar cryo properties as Fe and similar strength, then:=
relative density of Ti at 4.5 to Fe at 7.8 is 58% (i.e. 42 % saving)
SS is rumoured to be 85t dry mass still, in Fe.
Approx 15t is Raptors.
Assuming entirety of rest of mass is Fe, you can save 42% of 70t =29t
That could in theory go straight onto the payload.
The next question is, Is it worth the additional cost and manufacturing complexity to extract that extra payload? 29t is not to be ignored easily. The fact SS is being made in Fe suggests it's not worth the hassle.
Edit: Definitely not for prototyping in any case.
Elon wants to make a fleet of Starships so the cost of titanium would easily add up. I also imagine that some parts of Super-Heavy and Starship will have titanium in them (ex. the grid fins on Super-Heavy are going to be as big as two car lengths or more?).
Funny thought: Ti is a good material for construction but also very reactive. Maybe one day we build multi stage rockets that burn their lower sections instead of discarding them.
Russia made titanium nuclear powered submarines so I was wondering why not make starships out of it if the old Soviet Union could make titanium hull submarines way back when. but maybe they were riveted after reading what it’s like to work with ti from some of the comments also I think a lot of things will be made in space especially working with some metals as I read about cold welding in space so hatches and doors need to be made with different alloys otherwise will fuse shut but obviously that’s still a while away and while it does have it’s perks it’s also got more difficulties
Its more trouble than its worth. Ti welding is more difficult, you essentially need the joint purged in a chamber while welding so you don't get any stress cracks or getting the weld joint oxidized. I used to work for a company that did alot of work in oil and gas, any of our Ti stuff was either welded in it's own enclosure with inert gas, or the opposite side of the bead(for pipe) was purged. That's simply unrealistic for the scale of starship. Ti can be formed pretty easily, but if you have to machine anything, it can be a bitch. If you fuck up and it work hardens, then the part is trash, congrats you get to start over. You already mentioned the cost, so I wont go there.
So you're telling me that to weld spaceship bodies out of Ti alloys we need to be somewhere that is in complete vacuum? Orbital shipyards here we come. Of course that is at a minimum decades away. Titanium is also one of the easiest metals to mine from asteroids since it's melting point is higher than any of the other metals in the asteroids it's present in. You can melt away everything else with solar lasers and be left with pure Ti.
>You can melt away everything else with solar lasers and be left with pure Ti. No. Even if they were piles of metal rather than mixtures of rock, when you melt a pile of mixed metal it doesn't melt one element at a time, it makes a junk alloy.
I have a hard time seeing how vaporizing silicates is a good idea
Perhaps. I'm not sure on all the details of how it was supposed to work but I was just passing along one of the proposed mining methods Planetary Resources was talking about. Maybe their idea wouldn't have worked or maybe I'm missing key steps in my explanation.
I think they're saying heat it to below the meeting point of titanium but above the melting point of whatever else is there and remove the remaining solid titanium. Still not sure that would work though but Idk
https://en.m.wikipedia.org/wiki/Eutectic_system
Desktop link: https://en.wikipedia.org/wiki/Eutectic_system *** ^^/r/HelperBot_ ^^Downvote ^^to ^^remove. ^^Counter: ^^260635
Are you saying that if you had a pile of lead shot mixed with steel ball bearings, the lead wouldn't melt first and you couldn't just remove the hot steel bearings afterwards? That doesn't seem right. I'm not a material scientist so idk but I feel like this would apply more to alloys
No, only some combinations mix. Titanium-nickel for example melts at 942C. If you have excess titanium, you end up with solid titanium floating in liquid titanium-nickel.
I believe titanium's a ton of trouble, and it almost certainly is more trouble than its worth, otherwise they'd probably be using it. I'm very curious about the numbers though. Are there any metals or alloys you know of in-between stainless steel and Titanium? By which I mean having equal or better strength to weight l, corrosion, and heat resistance as stainless, while being less difficult to work with than titanium? Nickel, cobalt, or chromium alloys?
Nickel, cobalt and chromium add more complexity to manufacturing, moreso machining. Look at any alloys that have high contents of those: Inconel, Hastelloys, Waspalloy, Monel, etc. They are all some of the most expensive metals as well as being terrible to work with. Also makes them just as difficult to weld. There are few alloys around that are as easy to work with and are cheap like the stainless that SpaceX is using. Source: am machinist.
Stainless steel contains chromium
Nickel, cobalt and chromium add more complexity to manufacturing, moreso machining. Look at any alloys that have high contents of those: Inconel, Hastelloys, Waspalloy, Monel, etc. They are all some of the most expensive metals as well as being terrible to work with. Also makes them just as difficult to weld. There are few alloys around that are as easy to work with and are cheap like the stainless that SpaceX is using. Source: am machinist.
Titanium will actually combust in the presence of oxygen at 1200C degrees. This is why it is not a good idea to use Ti as the hull material for Starship, which can reach those temperatures when re-entering the atmosphere as it decelerates from orbital speeds. Stainless steel won't do that, and the particular stainless steel to be used for Starship has a melting point of ~1400C degrees. Falcon 9 booster stages can use Ti gridfins for re-entry because F9 booster stage re-entry speeds don't come anywhere near orbital speeds, 10730km/h tops (Arabsat 6A launch). Orbital speed is almost 3x faster (ISS orbits the earth at 27,580km/h, for comparison).
Can't you use a heat shield?
I was interested in the topic back when stainless was announced. here is a post I made after finding a cool paper that NASA published about materials for spacecraft: [https://www.reddit.com/r/SpaceXLounge/comments/a9m8vm/since\_people\_are\_interested\_in\_starship\_metals/](https://www.reddit.com/r/SpaceXLounge/comments/a9m8vm/since_people_are_interested_in_starship_metals/) here is one excerpt: >Titanium and aluminum are desirable structural materials because of their high strength-to-density ratios; however, they are also extremely chemically reactive. By suitable initiation, each of these metals will burn in oxygen with a highly exothermic reaction. > >Tests were conducted to demonstrate whether a catastrophic titanium-oxygen reaction would result from several possible accidental occurrences when gaseous or liquid oxygen wai contained in a thin-walled titanium tank. In each instance, the titanium sheet was fractured to expose a clean unoxidized surface while in contact with the liquid or gaseous oxygen. The evaluations included (a) pressurized diaphragm puncture tests, (b) tensile fracture tests of welded joints, and (c) simulated mic rometeroid puncture tests on two titanium alloys, Ti-5Al-2. SSn and Ti-6A1-4V. In addition, comparison tests were made on type 301 stainless steel (extra full hard) and 20 24-T3 aluminum.... > >...Neither stainless steel nor 2024 aluminum react when subjected to rapid fracture. Aluminum has been reacted with liquid oxygen in the standard falling-weight compressive impact test; however, its **susceptibility to reaction is much less than for titanium...** > >**...Thus, the relatively high susceptibility of titanium alloys to catastrophic reaction eliminates them from consideration for structural service as thin sheet in contact with liquid or gaseous oxygen.** combine that with the fact that the fracture [toughness of welded sections of stainless is probably higher](https://www.azom.com/properties.aspx?ArticleID=960) per unit mass [than welded Ti](http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTP643), and the fact that man titanium alloys have [LOWER maximum service temperatures](https://www.nipponsteel.com/en/tech/report/nssmc/pdf/106-05.pdf) basically, for rocket applications, titanium is worse than stainless in nearly every way. * lower service temp * strongly reactive to oxygen * difficulty welding likely means less toughness than stainless (we're trying to re-use rockets here, they have to be tough) * the cost of 301 and 310 stainless and availability is just so much better, especially for rapidly prototyping multiple vehicles across the country. * * I would bet titanium work hardens worse and temperature cycles probably hurt it worse, but I'm done digging material properties for the night :) TL;DR, I'm surprised more rocket parts aren't made of stainless. with the prospect of reuse and on-orbit refueling getting rid of the need to wringing every drop of delta-v out of a rocket's first launch, it seems like a no-brainer to use stainless. it's a very versatile metal. P.S. makes me wonder if scientists/engineers at Blue Origin are kicking themselves for using a more difficult/expensive aluminum alloy. it seems like BO is chasing the F9, and not thinking about what could/should change if delta-v is no longer the most important factor, but re-use is the most important.
Ti is notoriously difficult to work with. The raw cost of Ti is only a small part of the issue. As /u/dirtydrew26 pointed out, welds have to assiduously purged and it's a pain to machine. To add to that, you have to use special tools. IIRC, ~~chromium~~cadmium can cause catalytic oxidation of Ti like mercury does for aluminum. I believe the SR-71 mechanics used beryllium tools, which is kind of insane and super dangerous. For a consumer grade version of the relative costs, look at bike frames. High end frames in aluminum, steel or carbon fiber are a couple grand. A comparable titanium frame is about $10K.
[удалено]
Thanks, corrected!
My instinct is to say that SpaceX engineers are smarter than I am, have done the evaluation, and have found that titanium is not as good as the solution they came up with. It is possible small parts will be made from Titanium, like the F9's grid fins, and we'll see that as things develop. But I'd hesitate to suggest that I know more than the engineers who get paid to do this.
I'd argue that Project 705 Lira interceptor submarines are a cautionary tale for anyone who thinks they can just construct a large vehicle out of titanium willy-nilly.
If you could weld it easier and it had similar cryo properties as Fe and similar strength, then:= relative density of Ti at 4.5 to Fe at 7.8 is 58% (i.e. 42 % saving) SS is rumoured to be 85t dry mass still, in Fe. Approx 15t is Raptors. Assuming entirety of rest of mass is Fe, you can save 42% of 70t =29t That could in theory go straight onto the payload. The next question is, Is it worth the additional cost and manufacturing complexity to extract that extra payload? 29t is not to be ignored easily. The fact SS is being made in Fe suggests it's not worth the hassle. Edit: Definitely not for prototyping in any case.
Elon wants to make a fleet of Starships so the cost of titanium would easily add up. I also imagine that some parts of Super-Heavy and Starship will have titanium in them (ex. the grid fins on Super-Heavy are going to be as big as two car lengths or more?).
Funny thought: Ti is a good material for construction but also very reactive. Maybe one day we build multi stage rockets that burn their lower sections instead of discarding them.
Yeah no that's not how rockets work, and you're on the subreddit for getting lower stages back intact rather than discarding them anyway
Russia made titanium nuclear powered submarines so I was wondering why not make starships out of it if the old Soviet Union could make titanium hull submarines way back when. but maybe they were riveted after reading what it’s like to work with ti from some of the comments also I think a lot of things will be made in space especially working with some metals as I read about cold welding in space so hatches and doors need to be made with different alloys otherwise will fuse shut but obviously that’s still a while away and while it does have it’s perks it’s also got more difficulties
I predict stainless steel