9 ms·

SpaceX's Starship SN4 prototype fires rocket engine for first time

150 points by spking 6y ago

gameswithgo 6y ago
Does anyone with real expertise in aerospace have thoughts about Musk's choice to use steel instead of carbon fiber for star ship? Does his arguments make sense or is it likely just a cost saving measure? Would future Falcon rockets also switch to steel?
- deleted 6y ago
  [deleted]
- CarVac 6y ago
  Steel needs less heat shielding than carbon fiber. Additionally the ease of manufacture is not just a manufacturing cost saver, it's a development cost and time saver. Falcon is a frozen design and won't change, beyond a proposed longer fairing.
- dsfyu404ed 6y ago
  It's like the open source software of materials, not only is it cheap but it's fast because all the info you need is out there in industry. Steel is just so much more workable every step of the way. You can order your special steel from close to anywhere, your fancy epoxy might have two sources. Any engineer can design for steel and be really good at it (they probably even took classes on it in college) so you can have more cheaper engineers working parallel. Your engineers that know their way around CF are gonna be much more rare and expensive. The tool and die side of things is well known. The little tricks that are tribal knowledge for CF have long been compiled and published into textbooks for steel. If you fat finger a relief radius the die maker is gonna ask you to clarify whereas with some modern material that doesn't have that body of documentation yet they'll just assume you know what you're doing. The material handling side of things is well known, you'll never have to trash a part of delay a deadline because someone somewhere didn't store one of your constituent products in the right environment. When you've finally built your rocket anyone can test it. The techniques for inspecting steel are well known and widely practiced. For exotic materials you either have to track down experts or build that tribal knowledge internally (expensive and slow). These little conveniences compound throughout your entire "technology stack" so to speak and a rocket company has a really tall stack. It's hard to overstate just how much easier and faster you can work in a known-known like steel vs something that's new, hot and sexy that everyone wants to treat like a trade secret (as is the case with CF). Source: Former defense sector employee, granted on the software side but you still learn a lot of things through proximity.
  - dnautics 6y ago
    love the description. not an expert, but I heard that spacex's steel alloy composition is a trade secret.
    - airstrike 6y ago
      My understanding is lots of steel grades are trade secrets. Though how to actually make it isn't necessarily a secret, others might not know which alloy is specifically employed for a particular purpose https://en.wikipedia.org/wiki/SAE_steel_grades https://en.wikipedia.org/wiki/SAE_steel_grades Same is true for aluminum https://en.wikipedia.org/wiki/Aluminium_alloy#Alloy_designations https://en.wikipedia.org/wiki/Aluminium_alloy#Alloy_designat...
    - dsfyu404ed 6y ago
      It's a trade secret in the way that a pizza franchise's sauce is a trade secret. The specific combination of component parts and why that specific combination was chosen is a secret but what the components do and how they interact and affect the final product is well known.
      - skdjsjkhfkdsjh 6y ago
        I'm not sure why this is down-voted. Do people not believe that people with expertise in food can tell you what the amount of salt or sugar does to a sauce or that people in the steel industry knows what the amount of chrome does to a steel?
  - lmilcin 6y ago
    Disclaimer: no real experience. I would also say that I suspect it is much easier to ensure and test quality of steel. Ensuring every square inch of compound material like carbon fiber meets all requirements is much more difficult. Steel can be made pretty uniform in large quantities, shapes and sizes. On the other hand carbon fiber can easily have local faults ingredient imbalances, etc. that will be difficult to detect but might significantly affect strength of the material. In case of a huge rocket it does not matter how small part of it fails, even a single substandard square inch of it might cause entire rocket to fail catastrophically. I also understand that steel fails in relatively predictable ways compared to compound material. Carbon fiber has different properties in different directions which depend on how it was layered and that is probably going to cause any calculations to have potentially very large margin of error. As building the rocket is very much about calculating how much can be shaved off, unpredictability in material performance might be a huge issue.
- avernon 6y ago
  One of the old Atlas rockets was stainless steel. The point is optimizing the entire rocket instead of a small section. Starship will spend most of its time being in high heating conditions (like reentry) or very cold because the rocket fuel is loaded into the rocket at very low temperatures. It turns out that while the strength to weight ratio of carbon fiber is better than this alloy of steel at room temperature, it is impacted negatively by both hot and cold. In contrast, the steel alloy they are using actually has higher strength at low temperature and performs much better than carbon fiber at higher temperatures. So the whole rocket can be lighter and simpler. Carbon fiber rockets that are going to reenter require a lot of heat shielding that this ship won't need. And rockets and their engines are designed together. So it would be very difficult to make a design change like moving from aluminum to steel on Falcon without essentially designing a new rocket. Instead they will focus all their energy on Starship and eventually replace the Falcon series. SpaceX has said it is possible that the build cost of a Starship/Superheavy stack could be lower than a Falcon 9. The variable costs of a launch would also be cheaper while delivering more payload. This is the rocket that could make a lot of science fiction come true. That is what the excitement is about and we should all hope they get it to work.
  - iso1631 6y ago
    > This is the rocket that could make a lot of science fiction come true The irony is that those 1930s scifi stories with silver rockets landing vertically on distant planets, which looked so ridiculous in the 80s with the Shuttle being the future, look like that's exactly what the future will be. Seeing the 2 boosters landing side by side after the first Heavy launch was something out of a scifi film.
    - mips_avatar 6y ago
      I can clearly remember the day of the Falcon Heavy launch. I almost cried when the fairing came off and starman in his tesla was in open space, it was so incredible. I think a lot of people clearly remember that day, probably more so than the 2018 superbowl which was played 2 days earlier.
- balfirevic 6y ago
  > Does his arguments make sense or is it likely just a cost saving measure? How is that a dichotomy?
  - happytoexplain 6y ago
    The implication of the sentence is to ask if there is a practical advantage or only a cost advantage (or both). I think you could give the writer more credit.
    - icegreentea2 6y ago
      In engineering, practical and cost advantages are generally one and the same.
      - ggm 6y ago
        Only if weight is the least concern. Most engineering is gravity bound and can replace thin expensive things with thick heavy ones for less cost. If weight or volume become sufficiently important then practicality moves away from cost: you could make a rocket out of bricks and bricks are cheap but it's not the best solution.
- calaphos 6y ago
  I don't know about steel but carbon fiber has so far never succeeded as a material for cryogenic rockets or fuel tanks. The proposed space shuttle successor was designed around carbon fiber fuel tanks / hull and engineering problems with them eventually killed the project. The material struggles with low temperatures of cryogenic fuels (brittle), high temperatures of re-entry (just burns), oxidation in oxygen tanks. Also they apparently tend to sponatiously combust with rocket fuels. Some reference: https://www.compositesworld.com/articles/an-update-on-composite-tanks-for-cryogens https://www.compositesworld.com/articles/an-update-on-compos...
  - NortySpock 6y ago
    That project that was killed, for those interested, was the Lockheed Martin X-33 / VentureStar https://en.wikipedia.org/wiki/Lockheed_Martin_X-33 https://en.wikipedia.org/wiki/Lockheed_Martin_X-33
  - greglindahl 6y ago
    RocketLab's rocket has carbon fiber tanks.
    - elteto 6y ago
      But the scale is much, much smaller than Starship. If I understand correctly after you pass a certain tank radius you basically step into “nobody’s ever done this with CF before”, which is not a good place to be for SpaceX. Starship was on that spectrum.
  - deleted 6y ago
    [deleted]
- Diederich 6y ago
  Rather indirect reply incoming. Elon Musk cares about one over-arching thing: making humanity an interplanetary species. I believe that everything he does is in service to that goal. In order to make humanity interplanetary, lift costs must be greatly and sustainably reduced. In order for lift costs to be greatly and sustainably reduced, everything in the lift vehicle except the propellant must be fully reusable. Also, the vehicle needs to be inexpensive, quick to manufacture and reasonably performant. In order for the orbital stage of a lift vehicle to be re-used, it must re-enter the earth's atmosphere and effectively shed a large fraction of the chemical energy that was used to accelerate it to 7.8km/s. In short, the 2nd stage must be able to repeatably handle intense re-entry heat. For performance (and other) reasons, it must also be able to handle the very low temperatures of liquid propellants. Given all of these constraints, specific types of steel are literally the only choice. 1. Low material cost 2. Low manufacture cost 3. Excellent high temperature performance 4. Excellent low temperature performance 5. Sufficient normal temperature performance In fact, Musk has said that his initial focus on carbon fiber was a big error. Re: Falcon: as others have stated, Falcon 9 is effectively a fixed design. It's now a 'cash cow', and there's no reason to substantially change it. In fact, changing it would risk a lot of profitable contracts that are effectively funding Starship/Superheavy development.
  - bdamm 6y ago
    Then why wasn't Falcon 9 steel to start out with? Just more familiarity of aluminum (which I assume is its main structural element) within the rocket biz? Or does Falcon 9 just not deal with that re-entry requirement (it's only first stage, not the much faster second stage) and therefore aluminum is the right answer because it is cheaper/lighter?
    - elteto 6y ago
      Merlins are much, much less powerful than Raptors. Your payload capacity would be severely diminished which translates directly to lost revenue. With Starship there is no urge to make money with it yet, they can afford to be somewhat inefficient.
- wongarsu 6y ago
  According to Elon Musk it's not about saving costs but about speeding up development. Welding steel needs basically no tooling or setup time. It's hard to imagine their current methodology of rapid prototyping with carbon fiber. Other advantages are just a bonus.
- caconym_ 6y ago
  The arguments for it make a lot of sense. One of them is that it's a cost saving measure. All other things being equal, that's a good thing, not a bad one. The Falcon family is wildly successful, but it's small potatoes next to SpaceX's vision for the economics of space launch in the near future, so it seems unlikely that they'd go back to fix what isn't broken.
- elteto 6y ago
  Elon is all about tight, quick iterations on design and testing: “if it takes long is wrong” is an actual quote from him regarding Starship. With carbon fiber you get a lot of theoretical nice-to-haves, but you can’t iterate quickly with it. You need specialized tooling for manufacturing plus there is a lot of actual R&D that still needs to be done to manufacture with CF at Starship scale. SpaceX sees all this effort as a diversion from the goal of actually building a new rocket. Compare with steel where you can just hire a bunch of welders and build the damn thing out in the open. Falcon will never switch to steel. It makes no sense from a performance POV (Merlins are much less powerful than Raptors so your payload capacity hit is too high) and Falcon is a “dead” platform: only minor incremental updates from now on. Any change to it will trigger recertification with NASA, the USAF and a bunch of clients, which is a no-go. Falcon is SpaceX’s workhorse and money making machine, and it will continue on that role until Starship retires it.
  - henrikeh 6y ago
    > Compare with steel where you can just hire a bunch of welders and build the damn thing out in the open. I don't really know anything about welding nor about the forces acting on a rocket, but I remember reading that the effort in welding the Saturn V rocket was a feat in itself. It took a long time to train the workforce to perform the welds and extensive inspection was needed. Does anyone know if this applies to this rocket too? Has welding progressed (or simply kept the skill alive)? Edit: To anyone interested. The excellent book, Stages to Saturn, covered this (and everything else) in quite some detail.
    - NikolaeVarius 6y ago
      Welding has advanced since the Saturn 5. I've read that both TIG and MIG are being used. Inspection is much easier to do with modern equipment
      - CarVac 6y ago
        They are also using robotic welding, such as when assembling the domes.
- 101404 6y ago
  What do you mean "just" a cost saving measure? It's 3% the cost. So they can build 30 rockets for the price of one. Pretty important detail, when your goal is to reduce launch cost be two orders of magnitude. And no, F9 won't change.
- rst 6y ago
  Elon's long term plan for Falcon is to switch customers to Starship as soon as it's available, and they're comfortable switching. (Which might be a while for the Air Force and NASA.) In the meantime, any major changes to Falcon would be a serious distraction, which he'd probably forgo for that reason alone, regardless of the technical merits.
- greglindahl 6y ago
  A recent example of a steel rocket is Astra. I don't know why you think that cost saving measures are different from measures that "make sense".
- nickik 6y ago
  I'm just a hobbiest but I have tried to look into this. We really need to talk about the first and second stage differently. Of course Elon is a great one for communiality in the way he build things, common fuel, common engines and so on. He does this agian with Starship/Super Heavy, Metholox, Raptor Engine, Steel tanks. Lets talk about the most difficult part, the second stage, ie Starship. The big problem you have to solve, is to build a vehicle that can go from incredibly cold structure to a very hot one. Because you start very cold, and when coming back, it gets really hot. SpaceX loves deep cryo, meaning not just going to the point of making that fuel/oxidiser liquid, but really pushing it down as far as possible. This has a number of advantages but also many disadvantages. SpaceX took a long time to perfect the deep cryo technology with Falcon 9 (that was of course Kerolox). Because the fuel heating up it forced their operations to be very tight, and in the beginning cause many launch delays. It also cause the famous AMOS 6 failure, as a pretty interesting mostly unknown effect was taking place dring these temparatures. The upside is that you increase desnisty and thus vehicle performance, and it helps keep your turbo pumps cool as well. SpaceX very much wanted to continue this for Starship architecture, as they think its a huge win you are leaving on the table if you don't do it. What this means is that Starship is incredibly cold on the pad, really as cold as they can get it. Any structural material, needs to be able to handle this. This by itself is very challanging with carbon fiber even with the best carbon fiber technology perfomrance degrades the deeper you go. It forces you to really build a carbon fiber structure like we have never seen before. While some steels are terrible brittle under that condition, 301 stainless (and of course the new alloy SpaceX is developing) are the opposite. Their strengh actually increases, and basically the colder the better. So with incredibly cheap steel that you can make pots out of, you can basically match the performance of super expensive carbon fiber. On the hot side, you have the reentry. Starship is design not just to come in from LEO like the Shuttle, but actually come from interplantary and then use the air to break. So this is a much hotter profile then Shuttle. And as most people know, Shuttle heat shield caused endless problems. With both carbon fiber and aluminum you really don't want to let them get them to hot (500C is pushing the issue). Any such design basically requires packaging most of the Starship in a very thick Heatshield. Steel however is very tolerant of heat, meaning that even under fairly high tempratures (800C ish), once it cools down, your structure is still as good as before. When designing and insulating heat shield (rather then an non-reusable ablative one) the question is really how thick, and thus how heavy does it have to be. The amount of heat that can be handled by the structure behind the heat shield, directly impacts how thick the shield needs to be. So the combination of being almost as good as peak carbon fiber in deep cryo, and being clearly a much superior choice for reentery makes it a good choice. Once you combine that with the operational apspects, meaning both the per-unit material cost and much cheaper manufacturing its a no-brainer at that point. This is why I believe Musk called it 'The best desision in the whole design', it just made everything easier. Another bonus is that you have access to a far larger group of engineers with experinace, plus an even larger gorup of workers that can work with steel reliably compared with carbon fiber. Now for the First Stage, there is a good argument to be made that steal probebly can't quite reach the peak performance level of a carbon fiber design. Maybe not of an aluminum design. In this case I think its really more about material and manufacturing price and of communality with the Starship.
- redis_mlc 6y ago
  This is a very naive question. Metals can be used in supersonic and cryogenic aerospace applications. Composites and carbon-fiber cannot, regardless of cost.
lifeAsNerd 6y ago
I'd like the title better if it mentioned SpaceX was a defense contractor. A reminder SpaceX lives off taxes to enrich the lives of Billionaires. Congrats on the working design. Sounds expensive.
- TomMarius 6y ago
  It is the cheapest AND most advanced rocket design ever conceived. You can thank Musk for saving taxpayers' money; if he didn't come, you would have to remain dumping massive tons of money (IIRC 10x more per year than the whole Starship program has cost SpaceX - SpaceX, not taxpayers, they contributed only a very minor part of that budget) to Boeing and other very expensive parties. BTW I am sure you know that SpaceX was funded with private money at the beginning and does a lot of private flights. BTW 2, I am sure that you know that advancing spaceflight has widespread positive effects on humanity as a whole; the people using Starlink won't be billionaires, but ordinary dudes.
  - jandrese 6y ago
    In a lot of ways the Space Shuttle was more advanced. But more advanced is not always better. Sometimes the simple solution is the best. Complaining that a rocket company gets government funding is dumb. All of the major players get government funding to one degree or another. SpaceX gets less than most.
- NikolaeVarius 6y ago
  You are currently on the internet. Which was funded by defense contracts. You also probably use a hundred objects every day directly funded by taxpayer money given to private corporations.
dwaltrip 6y ago
Nice milestone. I think the first test hop to 150m will be in a few weeks. Very exciting!
louislaccanore 6y ago
amazing :OO

150 points by spking 6y ago

Does anyone with real expertise in aerospace have thoughts about Musk's choice to use steel instead of carbon fiber for star ship? Does his arguments make sense or is it likely just a cost saving measure? Would future Falcon rockets also switch to steel?

deleted 6y ago
[deleted]
CarVac 6y ago
Steel needs less heat shielding than carbon fiber. Additionally the ease of manufacture is not just a manufacturing cost saver, it's a development cost and time saver. Falcon is a frozen design and won't change, beyond a proposed longer fairing.
dsfyu404ed 6y ago
It's like the open source software of materials, not only is it cheap but it's fast because all the info you need is out there in industry. Steel is just so much more workable every step of the way. You can order your special steel from close to anywhere, your fancy epoxy might have two sources. Any engineer can design for steel and be really good at it (they probably even took classes on it in college) so you can have more cheaper engineers working parallel. Your engineers that know their way around CF are gonna be much more rare and expensive. The tool and die side of things is well known. The little tricks that are tribal knowledge for CF have long been compiled and published into textbooks for steel. If you fat finger a relief radius the die maker is gonna ask you to clarify whereas with some modern material that doesn't have that body of documentation yet they'll just assume you know what you're doing. The material handling side of things is well known, you'll never have to trash a part of delay a deadline because someone somewhere didn't store one of your constituent products in the right environment. When you've finally built your rocket anyone can test it. The techniques for inspecting steel are well known and widely practiced. For exotic materials you either have to track down experts or build that tribal knowledge internally (expensive and slow). These little conveniences compound throughout your entire "technology stack" so to speak and a rocket company has a really tall stack. It's hard to overstate just how much easier and faster you can work in a known-known like steel vs something that's new, hot and sexy that everyone wants to treat like a trade secret (as is the case with CF). Source: Former defense sector employee, granted on the software side but you still learn a lot of things through proximity.
- dnautics 6y ago
  love the description. not an expert, but I heard that spacex's steel alloy composition is a trade secret.
  - airstrike 6y ago
    My understanding is lots of steel grades are trade secrets. Though how to actually make it isn't necessarily a secret, others might not know which alloy is specifically employed for a particular purpose https://en.wikipedia.org/wiki/SAE_steel_grades https://en.wikipedia.org/wiki/SAE_steel_grades Same is true for aluminum https://en.wikipedia.org/wiki/Aluminium_alloy#Alloy_designations https://en.wikipedia.org/wiki/Aluminium_alloy#Alloy_designat...
  - dsfyu404ed 6y ago
    It's a trade secret in the way that a pizza franchise's sauce is a trade secret. The specific combination of component parts and why that specific combination was chosen is a secret but what the components do and how they interact and affect the final product is well known.
    - skdjsjkhfkdsjh 6y ago
      I'm not sure why this is down-voted. Do people not believe that people with expertise in food can tell you what the amount of salt or sugar does to a sauce or that people in the steel industry knows what the amount of chrome does to a steel?
- lmilcin 6y ago
  Disclaimer: no real experience. I would also say that I suspect it is much easier to ensure and test quality of steel. Ensuring every square inch of compound material like carbon fiber meets all requirements is much more difficult. Steel can be made pretty uniform in large quantities, shapes and sizes. On the other hand carbon fiber can easily have local faults ingredient imbalances, etc. that will be difficult to detect but might significantly affect strength of the material. In case of a huge rocket it does not matter how small part of it fails, even a single substandard square inch of it might cause entire rocket to fail catastrophically. I also understand that steel fails in relatively predictable ways compared to compound material. Carbon fiber has different properties in different directions which depend on how it was layered and that is probably going to cause any calculations to have potentially very large margin of error. As building the rocket is very much about calculating how much can be shaved off, unpredictability in material performance might be a huge issue.
avernon 6y ago
One of the old Atlas rockets was stainless steel. The point is optimizing the entire rocket instead of a small section. Starship will spend most of its time being in high heating conditions (like reentry) or very cold because the rocket fuel is loaded into the rocket at very low temperatures. It turns out that while the strength to weight ratio of carbon fiber is better than this alloy of steel at room temperature, it is impacted negatively by both hot and cold. In contrast, the steel alloy they are using actually has higher strength at low temperature and performs much better than carbon fiber at higher temperatures. So the whole rocket can be lighter and simpler. Carbon fiber rockets that are going to reenter require a lot of heat shielding that this ship won't need. And rockets and their engines are designed together. So it would be very difficult to make a design change like moving from aluminum to steel on Falcon without essentially designing a new rocket. Instead they will focus all their energy on Starship and eventually replace the Falcon series. SpaceX has said it is possible that the build cost of a Starship/Superheavy stack could be lower than a Falcon 9. The variable costs of a launch would also be cheaper while delivering more payload. This is the rocket that could make a lot of science fiction come true. That is what the excitement is about and we should all hope they get it to work.
- iso1631 6y ago
  > This is the rocket that could make a lot of science fiction come true The irony is that those 1930s scifi stories with silver rockets landing vertically on distant planets, which looked so ridiculous in the 80s with the Shuttle being the future, look like that's exactly what the future will be. Seeing the 2 boosters landing side by side after the first Heavy launch was something out of a scifi film.
  - mips_avatar 6y ago
    I can clearly remember the day of the Falcon Heavy launch. I almost cried when the fairing came off and starman in his tesla was in open space, it was so incredible. I think a lot of people clearly remember that day, probably more so than the 2018 superbowl which was played 2 days earlier.
balfirevic 6y ago
> Does his arguments make sense or is it likely just a cost saving measure? How is that a dichotomy?
- happytoexplain 6y ago
  The implication of the sentence is to ask if there is a practical advantage or only a cost advantage (or both). I think you could give the writer more credit.
  - icegreentea2 6y ago
    In engineering, practical and cost advantages are generally one and the same.
    - ggm 6y ago
      Only if weight is the least concern. Most engineering is gravity bound and can replace thin expensive things with thick heavy ones for less cost. If weight or volume become sufficiently important then practicality moves away from cost: you could make a rocket out of bricks and bricks are cheap but it's not the best solution.
calaphos 6y ago
I don't know about steel but carbon fiber has so far never succeeded as a material for cryogenic rockets or fuel tanks. The proposed space shuttle successor was designed around carbon fiber fuel tanks / hull and engineering problems with them eventually killed the project. The material struggles with low temperatures of cryogenic fuels (brittle), high temperatures of re-entry (just burns), oxidation in oxygen tanks. Also they apparently tend to sponatiously combust with rocket fuels. Some reference: https://www.compositesworld.com/articles/an-update-on-composite-tanks-for-cryogens https://www.compositesworld.com/articles/an-update-on-compos...
- NortySpock 6y ago
  That project that was killed, for those interested, was the Lockheed Martin X-33 / VentureStar https://en.wikipedia.org/wiki/Lockheed_Martin_X-33 https://en.wikipedia.org/wiki/Lockheed_Martin_X-33
- greglindahl 6y ago
  RocketLab's rocket has carbon fiber tanks.
  - elteto 6y ago
    But the scale is much, much smaller than Starship. If I understand correctly after you pass a certain tank radius you basically step into “nobody’s ever done this with CF before”, which is not a good place to be for SpaceX. Starship was on that spectrum.
- deleted 6y ago
  [deleted]
Diederich 6y ago
Rather indirect reply incoming. Elon Musk cares about one over-arching thing: making humanity an interplanetary species. I believe that everything he does is in service to that goal. In order to make humanity interplanetary, lift costs must be greatly and sustainably reduced. In order for lift costs to be greatly and sustainably reduced, everything in the lift vehicle except the propellant must be fully reusable. Also, the vehicle needs to be inexpensive, quick to manufacture and reasonably performant. In order for the orbital stage of a lift vehicle to be re-used, it must re-enter the earth's atmosphere and effectively shed a large fraction of the chemical energy that was used to accelerate it to 7.8km/s. In short, the 2nd stage must be able to repeatably handle intense re-entry heat. For performance (and other) reasons, it must also be able to handle the very low temperatures of liquid propellants. Given all of these constraints, specific types of steel are literally the only choice. 1. Low material cost 2. Low manufacture cost 3. Excellent high temperature performance 4. Excellent low temperature performance 5. Sufficient normal temperature performance In fact, Musk has said that his initial focus on carbon fiber was a big error. Re: Falcon: as others have stated, Falcon 9 is effectively a fixed design. It's now a 'cash cow', and there's no reason to substantially change it. In fact, changing it would risk a lot of profitable contracts that are effectively funding Starship/Superheavy development.
- bdamm 6y ago
  Then why wasn't Falcon 9 steel to start out with? Just more familiarity of aluminum (which I assume is its main structural element) within the rocket biz? Or does Falcon 9 just not deal with that re-entry requirement (it's only first stage, not the much faster second stage) and therefore aluminum is the right answer because it is cheaper/lighter?
  - elteto 6y ago
    Merlins are much, much less powerful than Raptors. Your payload capacity would be severely diminished which translates directly to lost revenue. With Starship there is no urge to make money with it yet, they can afford to be somewhat inefficient.
wongarsu 6y ago
According to Elon Musk it's not about saving costs but about speeding up development. Welding steel needs basically no tooling or setup time. It's hard to imagine their current methodology of rapid prototyping with carbon fiber. Other advantages are just a bonus.
caconym_ 6y ago
The arguments for it make a lot of sense. One of them is that it's a cost saving measure. All other things being equal, that's a good thing, not a bad one. The Falcon family is wildly successful, but it's small potatoes next to SpaceX's vision for the economics of space launch in the near future, so it seems unlikely that they'd go back to fix what isn't broken.
elteto 6y ago
Elon is all about tight, quick iterations on design and testing: “if it takes long is wrong” is an actual quote from him regarding Starship. With carbon fiber you get a lot of theoretical nice-to-haves, but you can’t iterate quickly with it. You need specialized tooling for manufacturing plus there is a lot of actual R&D that still needs to be done to manufacture with CF at Starship scale. SpaceX sees all this effort as a diversion from the goal of actually building a new rocket. Compare with steel where you can just hire a bunch of welders and build the damn thing out in the open. Falcon will never switch to steel. It makes no sense from a performance POV (Merlins are much less powerful than Raptors so your payload capacity hit is too high) and Falcon is a “dead” platform: only minor incremental updates from now on. Any change to it will trigger recertification with NASA, the USAF and a bunch of clients, which is a no-go. Falcon is SpaceX’s workhorse and money making machine, and it will continue on that role until Starship retires it.
- henrikeh 6y ago
  > Compare with steel where you can just hire a bunch of welders and build the damn thing out in the open. I don't really know anything about welding nor about the forces acting on a rocket, but I remember reading that the effort in welding the Saturn V rocket was a feat in itself. It took a long time to train the workforce to perform the welds and extensive inspection was needed. Does anyone know if this applies to this rocket too? Has welding progressed (or simply kept the skill alive)? Edit: To anyone interested. The excellent book, Stages to Saturn, covered this (and everything else) in quite some detail.
  - NikolaeVarius 6y ago
    Welding has advanced since the Saturn 5. I've read that both TIG and MIG are being used. Inspection is much easier to do with modern equipment
    - CarVac 6y ago
      They are also using robotic welding, such as when assembling the domes.
101404 6y ago
What do you mean "just" a cost saving measure? It's 3% the cost. So they can build 30 rockets for the price of one. Pretty important detail, when your goal is to reduce launch cost be two orders of magnitude. And no, F9 won't change.
rst 6y ago
Elon's long term plan for Falcon is to switch customers to Starship as soon as it's available, and they're comfortable switching. (Which might be a while for the Air Force and NASA.) In the meantime, any major changes to Falcon would be a serious distraction, which he'd probably forgo for that reason alone, regardless of the technical merits.
greglindahl 6y ago
A recent example of a steel rocket is Astra. I don't know why you think that cost saving measures are different from measures that "make sense".
nickik 6y ago
I'm just a hobbiest but I have tried to look into this. We really need to talk about the first and second stage differently. Of course Elon is a great one for communiality in the way he build things, common fuel, common engines and so on. He does this agian with Starship/Super Heavy, Metholox, Raptor Engine, Steel tanks. Lets talk about the most difficult part, the second stage, ie Starship. The big problem you have to solve, is to build a vehicle that can go from incredibly cold structure to a very hot one. Because you start very cold, and when coming back, it gets really hot. SpaceX loves deep cryo, meaning not just going to the point of making that fuel/oxidiser liquid, but really pushing it down as far as possible. This has a number of advantages but also many disadvantages. SpaceX took a long time to perfect the deep cryo technology with Falcon 9 (that was of course Kerolox). Because the fuel heating up it forced their operations to be very tight, and in the beginning cause many launch delays. It also cause the famous AMOS 6 failure, as a pretty interesting mostly unknown effect was taking place dring these temparatures. The upside is that you increase desnisty and thus vehicle performance, and it helps keep your turbo pumps cool as well. SpaceX very much wanted to continue this for Starship architecture, as they think its a huge win you are leaving on the table if you don't do it. What this means is that Starship is incredibly cold on the pad, really as cold as they can get it. Any structural material, needs to be able to handle this. This by itself is very challanging with carbon fiber even with the best carbon fiber technology perfomrance degrades the deeper you go. It forces you to really build a carbon fiber structure like we have never seen before. While some steels are terrible brittle under that condition, 301 stainless (and of course the new alloy SpaceX is developing) are the opposite. Their strengh actually increases, and basically the colder the better. So with incredibly cheap steel that you can make pots out of, you can basically match the performance of super expensive carbon fiber. On the hot side, you have the reentry. Starship is design not just to come in from LEO like the Shuttle, but actually come from interplantary and then use the air to break. So this is a much hotter profile then Shuttle. And as most people know, Shuttle heat shield caused endless problems. With both carbon fiber and aluminum you really don't want to let them get them to hot (500C is pushing the issue). Any such design basically requires packaging most of the Starship in a very thick Heatshield. Steel however is very tolerant of heat, meaning that even under fairly high tempratures (800C ish), once it cools down, your structure is still as good as before. When designing and insulating heat shield (rather then an non-reusable ablative one) the question is really how thick, and thus how heavy does it have to be. The amount of heat that can be handled by the structure behind the heat shield, directly impacts how thick the shield needs to be. So the combination of being almost as good as peak carbon fiber in deep cryo, and being clearly a much superior choice for reentery makes it a good choice. Once you combine that with the operational apspects, meaning both the per-unit material cost and much cheaper manufacturing its a no-brainer at that point. This is why I believe Musk called it 'The best desision in the whole design', it just made everything easier. Another bonus is that you have access to a far larger group of engineers with experinace, plus an even larger gorup of workers that can work with steel reliably compared with carbon fiber. Now for the First Stage, there is a good argument to be made that steal probebly can't quite reach the peak performance level of a carbon fiber design. Maybe not of an aluminum design. In this case I think its really more about material and manufacturing price and of communality with the Starship.
redis_mlc 6y ago
This is a very naive question. Metals can be used in supersonic and cryogenic aerospace applications. Composites and carbon-fiber cannot, regardless of cost.

lifeAsNerd 6y ago

I'd like the title better if it mentioned SpaceX was a defense contractor. A reminder SpaceX lives off taxes to enrich the lives of Billionaires. Congrats on the working design. Sounds expensive.

TomMarius 6y ago
It is the cheapest AND most advanced rocket design ever conceived. You can thank Musk for saving taxpayers' money; if he didn't come, you would have to remain dumping massive tons of money (IIRC 10x more per year than the whole Starship program has cost SpaceX - SpaceX, not taxpayers, they contributed only a very minor part of that budget) to Boeing and other very expensive parties. BTW I am sure you know that SpaceX was funded with private money at the beginning and does a lot of private flights. BTW 2, I am sure that you know that advancing spaceflight has widespread positive effects on humanity as a whole; the people using Starlink won't be billionaires, but ordinary dudes.
- jandrese 6y ago
  In a lot of ways the Space Shuttle was more advanced. But more advanced is not always better. Sometimes the simple solution is the best. Complaining that a rocket company gets government funding is dumb. All of the major players get government funding to one degree or another. SpaceX gets less than most.
NikolaeVarius 6y ago
You are currently on the internet. Which was funded by defense contracts. You also probably use a hundred objects every day directly funded by taxpayer money given to private corporations.

dwaltrip 6y ago

Nice milestone. I think the first test hop to 150m will be in a few weeks. Very exciting!

louislaccanore 6y ago

amazing :OO