Elon Will Use X-Plane Hot Structures to Improve Re-entry

Elon Musk could use metal hot structures for rocket re-entry. This is a decades old concept. I do not think it has been used in flight since the early X-plane program days. There has been more lab and ground experiments on the concepts.

This could be another bold technology choice for SpaceX to once again raid the NASA warehouses of promising but underdeveloped technology. The X-planes did not reach orbit and did not re-enter from orbit. Elon Musk and SpaceX plan to have the Super Heavy Starship re-enter Earth and Mars at far higher speeds than have been tested before. These demands will put more stress and heat on the rocket.

Elon has tweeted that the redesigned Super Heavy Starship (aka BFR) would use a lot of metal in the design. He said it would be a radical counter-intuitive design. He mentioned that the tanks, airframe and heatshield were redesigned but the shape or counters would be roughly the same. In September when Elon was announcing the Japanese billionaire, he showed simulations showing the BFS re-entering unpowered like a human parachutists before the parachute opens. SpaceX Starship needs to come in fast, unpowered and survive for the planned thousands of re-uses with ideally no maintenance.

I am going to make the guesses on the material. I thnk Titanium alloy or nickel alloy for the hot metal structure will be used in the Super Heavy Starship. We will probably get confirmation in January 2019 when pictures and information could be released.

Previously Elon talked about changing the airframe, tanks and heatshield.

Metal Hot Structure for Re-entry

During re-entry a blunt body about 90% of friction heat is carried away by the bow shock wave and only 10% of the energy would reach the spacecraft.

All the reusable heat shields have had insulation behind the heat shield. The airframe of the rockets have been light-weight aluminum. The thinking was to protect the aluminum from heat but carry the weight of the insulation.

What was considered in the when the Space Shuttle was being designed was to make the airframe of the rocket with high-temperature alloys. There would be far less insulation to protect the crew. The main structure would reach about 1,000 degrees Celsius. There would be more mass to re-radiate away the heat.

X-15 was the fastest manned plane ever built

Some of the advantages, disadvantages and history were discussed at the Reddit SpaceX forum and at the Nasa flight forum. Gary Hudson (Designer of Phoenix SSTO) mentioned recently on the NASA forum.

Paul Werbos has been a proponent of the Boeing hot structures system designs. Ray Chase of ANSER did a lot of materials testing for hot structures.

It has been discussed on the Power Satellite Forums and on the Lifeboat Foundation mailing lists.

SpaceX Used Pica Materials for Their Heat Shield Already

Elon Musk and SpaceX did rapidly develop their heat shields using Pica materials. The Pica materials was virtually unused in flight before SpaceX began relying heavily upon them.

The Phenolic-Impregnated Carbon Ablator (PICA) heat shield, a lightweight material designed to withstand high temperatures, was first used by NASA. SpaceX later worked with PICA’s inventors at Ames Research Center to outfit its Dragon capsule, which is now delivering cargo to and from the International Space Station.

Elon Musk and SpaceX could again take concepts that have been floating around NASA for decades and then use them heavily and perfect them.

Elon Musk Will Leverage His Thermal Protection SpaceX Skunk Works and the 51% Rule of Testing

Skunk Works at SpaceX for Thermal Protection

SpaceX built an entire lab for thermal protection system research for re-entry vehicles. It became the best lab in the world in nine months starting from an empty room. They use rapid development cycles based on processes used for rapid fighter pilot reaction.

The OODA loop uses
observe
orient
decide
act

The faster a fighter pilot could through this loop of iterations, then the more likely they were to win a dogfight.

SpaceX engineers working 80-hour weeks don’t have to iterate between themselves and another engineer to get effective use of their time. Very fast engineering reaction also means avoiding meetings with managers or for review unless absolutely needed.

The Skunk Works was the small team at Lockheed that famously made the huge advances to make the SR-71 mach 3+ spyplane.

51% Experimentation Rule

SpaceX will test once they have a 51% chance of success. They will take the least amount of material that will get them valid results. NASA would wait until they had 80-90% chance of success and there would be lot more meetings about the work or process.

This more rapid testing leads to more rapid development.

Hot Metal Re-Entry Background Research

This has been considered with ceramics and other materials over the years.

88 thoughts on “Elon Will Use X-Plane Hot Structures to Improve Re-entry”

  1. On my posting issues; your points are well taken.

    My patience was stretched over a couple of days of watching my posts disappear, though you may have received all notifications at once. Very frustrating.

    Now that Brian has white-listed my comments, I should have fewer issues.

    The shield could begin as individual parts, as long as they are all one on use.

    Material and manufacturing choices are many. I have a fondness for Aluminium Oxide foams.

    Aluminium Oxide powder, with a foaming agent, injected into a break-down mould heated to activate the foaming agent on contact.

    Or, assemble a huge polymeric sponge framework, each piece coated in a dried alumina slurry, fire-off the framework as a whole, then sinter the dried foam structure.

    This would be perfect for eventual on-orbit fabrication. No slumping of larger wet “sponge”, and copious amounts of thermal energy to bake the cake.

    Reply
  2. It seems like you’re having a lot more trouble posting than anyone else.. I would suggest checking your browser for any extensions etc that might be causing problems. Also, avoid posting pictures directly, since that flags the comment for moderation. Post a link instead, with a short description of what it’s about.

    If that still gets shunted to moderation, add spaces like we had to do with Vuukle: example com /path/to/image jpg . Don’t bother reposting the same 10 times, since it’ll all get moderated the same, and then show up as multi-posts a few days later. I got 3 email notifications for essentially the same reply now.

    Anyway, that kind of structure is extremely difficult and expensive to do monolithically. Hence additive manufacturing to the rescue. But I’m not sure if current AM can produce the necessary part quality, strength, and other requirements, especially at the size that these parts need to be.

    Hmm, on 2nd thought, maybe a cast or some sort of dye stamping could work for the bottom part, but then you don’t get channels – just a panel with fins. So you’d still need a 2nd part to close the channels. And the metallurgical properties probably won’t be optimal this way, if they’re even good enough at all.

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  3. Below is a photo of a heat transfer plate built-up from separate pieces; foamed nickel mats, cross-shaped pillars and plates.

    For use as the leading surface of the craft, this would be a monolithic construct. The cold side would have fins or posts to dump heat into some “fluid”.

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  4. “REPOST FATIGUE: The progressive degradation of informational value of a comment through a cycle of failed posting, re-writing and reposting of comment over a prolonged period of time until little of the originals impact remains.”

    I’m giving up on having my reply to a post below successfully posting…. after two days of trying.

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  5. Michael K

    I have been trying to respond to your comment elsewhere in this section for a couple of days, with no success. So, I’ll put it here. I’m not thrilled with the obstacles spot puts between users who are trying to engage in discussions.

    *Reposting again… but not to the same level of detail. Comment now suffers from “Repost Fatigue”.

    “REPOST FATIGUE – i.e. the progressive degradation of informational value of a comment through a cycle of failed posting, re-writing and reposting of comment over a prolonged period of time until little of the originals impact remains.”

    Below is a photo of a heat transfer plate built-up from separate pieces; foamed nickel mats, cross-shaped pillars and plates. For use as the leading surface of the craft, this would be a monolithic construct. The cold side would have fins or posts to dump heat into some “fluid”.

    Reply
  6. *I’ve tried posting this reply for a couple of days. Here I go again… but not to the same level of detail. It suffers from “Repost Fatigue”.

    “REPOST FATIGUE – i.e. the progressive degradation of informational value of a comment through a cycle of failed posting, re-writing and reposting of comment over a prolonged period of time until little of the originals impact remains.”

    Below is a photo of a heat transfer plate built-up from separate pieces; foamed nickel mats, cross-shaped pillars and plates.

    For use as the leading surface of the craft, this would be a monolithic construct. The cold side would have fins or posts to dump heat into some “fluid”.

    Reply
  7. Yeah i’d wager on Inconel.

    Just wish the two “bottom” fins weren’t pointing downward. It is like Mr musk wants to channel the hot gasses to the area where the fuselage meets the fins.

    I’m still a fan of attaching the bottom fins at the bottom and angling them up but having them end short of the center of mass. Just seems more stable that way.

    Reply
  8. Take a look at the photo below. It’s a cutaway view of a heat plate. It’s not exactly what I’m talking about, but points in the same direction.

    Used as a heat shunting leading surface, the construct would be monolithic, not an assembly of foamed mesh, sheets and pillars.

    The cold side would have fins or fingers, like a rubber bar mat, to efficiently shed heat into a “fluid”.

    Reply
  9. It would basically be liquid cooling. The integrated pipes you’re suggesting sound similar to the cooling channels in turbine blades. These are difficult to manufacture. Additive manufacturing may be up to the task eventually. Not sure if it is today – remember these leading edges must bear very high thermal and mechanical loads. Also, these parts are much larger than typical AM parts.

    For the cooling fluid, you ideally want something that would phase change somewhere between the two temperature points. That’s a more effective way to transfer heat than just changing the fluid’s temperature.

    If the cooling fluid doesn’t cool fast enough to loop it back, then you may as well dump it along with the heat it absorbs, rather than wait for it to cool. In that case, it can just be some extra fuel. A denser fluid with more optimized thermal properties may work better, but if it is fuel, you can fire it from retro-thrusters to slow down more quickly. Same rocket equation considerations apply as always.

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  10. Incorporating the heat pipe system into the framing and even surfaces themselves would reduce the added weight of stand alone add-ons.

    Solid outer surface with honeycomb backing. Integrated heat pipes dumping into pumped fluid which circulates to leeward surface to radiate.

    High gees during re-entry might be a catch, so, sintered wick?

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  11. Your mention of corrugation reminded me of the Air Forces Dyno-Soar project.

    If I remember correctly, that craft was to use corrugated moly plating to take the heat.

    Could’a been these taking folk up and down, but everyone went with capsules instead. Disappointing.

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  12. You might use heat pipes behind the very highest heat loading areas, but they’re probably a bit too heavy to use as a general strategy.

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  13. PICA isn’t indefinitely reusable, it is an ablator. With the BFR, maybe SpaceX is looking to dozens or scores of reuses between refurbishments & TUFROC seemed like a better long-term solution.

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  14. Hmm…

    I do not think that titanium would be a good metal: we perhaps have collectively forgotten the video images of Challenger’s fateful atmospheric reentry, with the brilliant white streamers of breaking up titanium-dominant aircraft structures flying thru the atmosphere at Mach 20, but that’s what titanium does. Brilliant white exothermic catching fire.

    I also don’t think that any metal that oxidizes substantially can be used for the same reason. Molybdenum is pretty non-oxidizing in general, but isn’t inert.

    My thought — which really isn’t very tricksy — is that nested structure metamaterials will hold the key to a working solution. A tough metallic-ceramic underlayer, probably corrugated on the microscopic level (i.e. vitreous but also quite porous for excellent heat-insulation properties), overcoated with a non-ceramic very, very low oxidative layer, again micro corrugated … topped in turn with mossy platinum, the ultimate non-reactive metal offering both outstanding high-temperature tolerance and nearly-complete non-oxidative thermochemical properties. Its high density wouldn’t matter. It’d only be a few microns thick.

    And “no” to tungsten. It oxidizes rapidly above 2,000 C. No to most every non-platinum group metal for the same reason.

    GoatGuy

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  15. Food for thought: too much cadence can backfire too. Obviously, it can hurt the quality. But more than that, readers have limited time.

    Speaking for myself, there’s another interesting blog which I want to follow, but I’ve been avoiding lately because their cadence is too high. They’ve even upped it further recently, which only made me avoid them more. I don’t have the time to sift through all those articles trying to find the ones that are actually interesting to me.

    So consider quality over quantity.

    (At this opportunity, I’d like to repeat my request to consider adding the option to subscribe to a comment thread. This would save me a lot of time, and allow me to focus on newer articles. I’m probably not the only one.)

    Reply
  16. What about designing the structures/frameworks behind the leading surfaces to incorporate heat pipe tech to remove heat to the cooler leeward surfaces?

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  17. I agree. It is valid. I am thankful to you for the help you are providing in pointing this out and the valuable comments and insight you provide.

    I am taking as something that needs to be improved for my own sites success. An inferior title and writing on this article alone cost me three times the traffic. I can clearly see the opportunity cost. I do have to balance with the importance of article cadence.

    I also have a lot of what I think is really valuable information to convey. I have no shortage of content.

    There are first person interviews.

    There are insights and analysis that I have which would be useful.

    Reply
  18. Strongly concur. He’s put together a fun and in depth video library that touches on nearly all the same tech goodies talked about here.

    I’ve thought he’d be a good choice as a guest writer for NBF.

    Reply
  19. Hafnium Carbide is fine for heat resistance, but I wouldn’t even think of using it in an application that requires tensile strength, it’s a brittle ceramic.

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  20. I like the way he writes. Brian is a real person plowing through all the stuff he has to plow through at top speed. Slow him down just to make it sound slicker and you’ll get junk.

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  21. Mat… Sometimes when redesigns after redesigns happen it makes one wonder if its safe. I can understand if new materials go to market that would be better to use. Think it all through for a while. Then after all is considered show us the final model. Ideally not model after model after model. I only want to see model after model on trashy runways. Good luck make a good one. I know you will.

    Reply
  22. I had no trouble understanding. My Taiwanese chemistry TA used to have me translate between broken Chinese accent English, and good old boy Confederate American accent when he and the other students could not understand each other.
    Some of the other students in the lab section asked me why I was mocking the TA. I told them I was speaking so it was easiest for him to understand. The way I spoke sounded like his English teachers did.

    Reply
  23. Comparing the X-15 to BFR scale lands us the fundamental square to cubic error. The X-15 had a very high area to mass ratio, allowing the airframe to re-radiate much of its thermal energy from drag quickly, slow it down quickly keeping the high-temperature time to a minimum.

    The BFR’s slow-down is going to be protracted affair. Consider a cork fired from a shot-gun, and then a metal ball.

    Reply
  24. The switch from composite to metal didnt make any sense to me until this theory. I had figured carbon failed structurally didnt think about renetry temps as a failure. Still going to be a massive weight penalty going to metal but at least it wont burn up in the atmosphere. Maybe PICA on composite didnt survive burn tests. This still will end up shrinking the total lbs to leo by half or more.

    Reply
  25. On the space shuttel the highest temperatures reached was about 1600C. The X-15 or SR71 aircraft never came close to this temperature. Any metal at that temperature is going to either melt or loose most of its strength. tungsten will melt at 3400C. but at that temperature it has lost a lot of its strength. Titanium and nickel melt at this temperature.

    So like Nasa’s space shuttle, Space X will have to use different materials in different places to withstand reentry temperatures. Space X plans to use PICA X heat shield material to protect the hottest surfaces. For areas that don’t get as hot they might be able to some metals is little or no structural strength. but any places that need structural strength will need to be protected by PICA X. That is about 1/2 the surface

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  26. When you type that many articles, it happens. I find the best way is to either double check your stuff or have someone you can do it for you.

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  27. I think this line of commenting is interesting.

    Determining what the best materials are for hot structures and correctly anticipating the details of the SpaceX solution.

    Thanks for initiating these areas.

    Reply
  28. It is not just something that I do.

    There are many space and technology websites and forum which devote a lot of effort to analyzing and expanding Elon Musks tweets.

    It is a service which is valued by the general public.

    CBS 60 minutes has had at least three episodes devoted to interviewing and understanding Elon Musk.

    I think my value add is that I am trying to put together obscure and relatively unknown science, technology and engineering sources. I think I am getting to the truth or closer to the truth.

    It is not random text. I am trying to digest many papers and filter down to the useful papers. I am trying to pull out the important highlights.

    This is not easy to do when I am going from tweet to article in one to two hours. I will now slow up and spend another hour on the proof-reading.

    Reply
  29. Thanks for cutting me some slack. I do want to fix the articles and make them high quality. This article in particular is one I wanted to get right. I could sense that it was going to be very popular. It is my most popular article today. I think it could have done twice the traffic, if I had cleaned it up last night.

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  30. I have started using Grammarly. I am trying to make a habit of re-reading the articles all the time and proof read all the way through. It is on my list of tasks to hire a proof reader. I will also take more care when blogging late at night.

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  31. They’re promising. The key thing about HEA’s isn’t the use of heavier metals. It’s the departure from the previous alloy model where your alloy is predominantly one element, with just a bit of other elements to modify the properties.

    In HEA’s, you have approximately equal amounts of 4 or 5 or more elements, so the metal can’t be analyzed as a single metal that’s just alloyed. This is a part of the alloy design space that’s poorly explored, there are bound to be some seriously useful discoveries in it.

    Reply
  32. Perhaps Molybdenum would be a good shell material. Much better melting point than Titanium and Nickel and good corrosive properties too. Very low thermal expansion and also high tensile strength.
    It’s heavier though.

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  33. Like your 51% slides. The whole all-in leading edge (no pun intended) aero-braking approach described is quite a challenge. The Dragon and F9 experience reuse experience will probably have little applicability except getting the team tuned up for the ultimate re-entry challenge ever attempted. I expect a lot of cargo runs before human trials start. We should all start thinking up some great low cost payloads for the test flights.

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  34. It’s not lame to prefer to read sentences that make sense the first time and aren’t ambiguous.

    That said, we shouldn’t beat up Brian too much about this, he does do a lot of work getting articles for this website and maintaining things.

    Reply
  35. I concur. This is my goto futurism blog that isn’t yet infested with gloomy catastrophism and nihilism like almost all the others on the net.

    Reddit /r/futurology passes all the time talking why AI and robots will leave us jobless, homeless and finally kill us, or why UBI rulz, oh, and the umpteen iteration of The Sky is Falling AGW hysteria.

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  36. Yeah, I thought my brain was melting at first and I re-read that paragraph multiple times…

    It’s such a shame as it’s a fascinating article, it just needs some serious unscrambling and more coherent sentence structuring.

    I was going to share this article and still will if / when the grammar gets resolved.

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  37. Is this a joke? Did the author even read what he wrote? This article is absolutely terrible. Even Word or Grammarly (which is an online freeware) would definitely scream in pain seeing this. I stopped reading in the middle as it just stopped making sense altogether.

    You had one job…

    Is this how you operate, dear author?
    Elon posts a tweet -> generate random text from English words -> publish

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  38. It is not a language problem. I sometimes write too many articles and need to reread what I wrote. I write a first pass and forget to go back and check. In this case the problem was writing at the same time that I was listening to the speaker in the video who was describing the technical situation.

    Reply
  39. I believe I fixed it. I had originally taken notes off of the video and was too focused on understanding the concepts. I obviously did not then read to see if meaning made it to what was in the article. Apologies. Let me know if it makes sense now.

    SpaceX built an entire lab for thermal protection system research for re-entry vehicles. It became the best lab in the world in nine months starting from an empty room. They use rapid development cycles based on processes used for rapid fighter pilot reaction. 

    The OODA loop uses 
    observe 
    orient 
    decide 
    act 

    The faster a fighter pilot could through this loop of iterations, then the more likely they were to win a dogfight. 
     
    SpaceX engineers working 80-hour weeks don’t have to iterate between themselves and another engineer to get effective use of their time. Very fast engineering reaction also means avoiding meetings with managers or for review unless absolutely needed.

    The Skunk Works was the small team at Lockheed that famously made the huge advances to make the SR-71 mach 3+ spyplane.

    Reply
  40. I understood it after a bit.

    I think he routinely using speech to text, but speech to text doesn’t work well for technical subjects, it’s “tuned” for ordinary conversation. He needs to at least use a grammar checker, and ideally a proof reader.

    Reply
  41. The OODA loop witches got me. 🙂 That just… wow.

    Okay, I get that English may not be Brian’s first language – but let’s just look at the sentence fragments here.

    SpaceX built an entire

    they built the best thermal protection system like for re-entry vehicles as of

    Wirth lab in the world in nine months

    Starting with an empty shell of a room

    in fighter pilot circles they

    a guy named John Boyd came up what was called the OODA loop witches (which is) observe orient decide act and the faster a fighter pilot could through this loop of iterations the more likely they were to win a competition and in the air between them and an opponent

    this has been applied to other circles well

    part of the other reason you have engineers working 80-hour weeks is they don’t have to iterate between themselves and another engineer to get that 80 hours

    it’s one guy doing everything in his own head so he has a very fast reaction loop he doesn’t have to go to a meeting.

    Dang. That stuff’s hard to unpack.

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  42. Over at NASA Spaceflight Forums, Mongo62 notes that Elon has previously liked a scientific article about something called High Entropy Alloys (HEAs) which use heavier metals and have properties which may explain his tweets.

    Reply
  43. People complaining about how the articles are written are acting lame… there are better ways to ask for a job. We are lucky that this distraction of a website even exists (distrac literally translates to fun).

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  44. I couldn’t read what might have been a top-notch article because of the spelling and plain bad writing.

    You had only one job…

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  45. “There would be more mass to re-radiate away the heat.”

    IIRC, part of the thinking was that, if the air frame was all very heat resistant, it would have enough thermal mass to absorb the heat without ever reaching a dangerous temperature. (Since the dangerous temperature was so high to begin with.)

    A serious downside of the insulating tiles over aluminum model used in the space shuttle was that the heat would eventually soak through and anneal the air frame. Before that could happen, you had to hook up a cooling system on the ground to pull that heat out.

    This requires infrastructure in place wherever you plan to land, an obvious problem for colonizing Mars, but generally an inconvenience even when landing on Earth.

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  46. No, seriously, Brian: You need a proof reader.

    “SpaceX built an entire they built the best thermal protection system like for re-entry vehicles as of Wirth lab in the world in nine months starting with an empty shell of a room in fighter pilot circles they a guy named John Boyd came up what was called the OODA loop witches observe orient decide act and the faster a fighter pilot could through this loop of iterations the more likely they were to win a competition and in the air between them and an opponent this has been applied to other circles well part of the other reason you have engineers working 80-hour weeks is they don’t have to iterate between themselves and another engineer to get that 80 hours it’s one guy doing everything in his own head so he has a very fast reaction loop he doesn’t have to go to a meeting.”

    Or at the least you need to invest in a good grammar checker, and pay attention to what it says. Paragraph length run on sentences make you look bad, even if somebody can puzzle out what you mean.

    Reply

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