News
SpaceX CEO Elon Musk explains Starship’s ‘transpiring’ steel heat shield in Q&A
Speaking in a late-December 2018 interview with Popular Mechanics’ editor-in-chief, SpaceX CEO Elon Musk shared considerable insight into the thought processes that ultimately led him to – in his own words – “convince” his team that the company’s BFR rocket (now Starship and Super Heavy) should pivot from an advanced composite structure to a relatively common form of stainless steel.
Aside from steel’s relative ease of manipulation and affordability, Musk delved into the technical solution he arrived at for an advanced, ultra-reusable heat shield for Starship – build it out of steel and use water (or liquid methane) to wick reentry heat away.
When going to ~1750 Kelvin, specific heat is more important than latent heat of vaporization, which is why cryogenic fuel is a slightly better choice than water
— Elon Musk (@elonmusk) January 22, 2019
Although there has been some successful experimental research done on “transpirational” heat shields (relying on the heat capacity of vaporizing liquids or gases to soak up thermal energy during orbital rocket reentries), Musk is by no means wrong when he says that a stainless steel sandwich-hulled spaceship regeneratively cooled by microscopic holes and liquid water or propellant “has never been proposed before”. While the basic concept probably arose somewhere over the last 50-100 years, it does not appear that any serious theoretical or experimental research has been conducted to explore transpiration-cooled metallic heat shields, where metallic thermal protection systems (TPS) are already fairly exotic and unproven in the realm of modern aerospace.
“Very easy to work with steel. Oh, and I forgot to mention: [SpaceX’s high-quality] carbon fiber is $135 a kilogram, 35 percent scrap, so you’re starting to approach almost $200 a kilogram. [301] steel is $3 a kilogram.” – Elon Musk
While Musk’s solution could dramatically simplify what is needed for Starship’s high-performance heat shield, a stainless steel sandwich on half of Starship offers another huge benefit: the spacecraft can still gain many of the mass ratio benefits of stainless steel balloon tanks (metal tanks so thin that they collapse without positive pressure) while retaining structural rigidity even when depressurized. At the end of the day, Musk very well might be correct when he states that a stainless steel Starship can ultimately be more mass-efficient (“lighter”) than a Starship built out of advanced carbon composites, a characteristic he rightly describes as “counterintuitive”.
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- Starhopper and SpaceX’s spartan assembly facilities are pictured here, showing the inside of the aft section and a completed tank dome. (Austin Barnard)
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- Starship has been shown with actuating fins and canard wings since SpaceX’s September 2018 update. (SpaceX)
What does Science™ have to say?
Based on research done in the 2010s by German space agency (DLR), a porous thermal protection material called Procelit 170 (P170) – 91% aluminum oxide and 9% silicon oxide – was cooled from a peak heat of ~1750 C (3200 F) to ~25 C (75 F) during wind tunnel testing, demonstrating that an average of 0.065 kg (~2.3 oz) of water per second would be needed to cool a square meter of P170 to the same degree, assuming a heating rate of around 200 kW/m^2. Given that 300-series stainless steels have a comparatively huge capacity for radiating heat at high temperatures, will be dramatically thinner than Procelit in any given Starship use-case, and will not need to be cooled all the way to 25C/75F during hot operations, the DLR-derived number is barely relevant without another round of wind tunnel tests focused on metallic thermal protection systems. Still, it allows for the creation of a sort of worst-case scenario for BFS/Starship’s water-cooled shield.
Assuming that the windward side of Starship’s regeneratively cooled heat shield has roughly the same surface area as half of a cylinder, 800 m^2 (8600 ft^2) will have to be actively cooled with water, translating to a water consumption rate of approximately 52 kg/s (115 lb/s) if the entire surface is being subjected to temperatures around ~1750 C. That is, of course, a grossly inaccurate generalization, as aerodynamic surfaces dramatically shape, dissipate, and concentrate airflows (and thus heat from friction) in complex and highly specific ways. Much like NASA’s Space Shuttle or DLR’s theoretical SpaceLiner, the reality of reentry heating is that that heat typically ends up being focused at leading edges and control surfaces, which thus require uniquely capable versions of thermal protection (TPS). Shuttle used fragile reinforced carbon-carbon tiles at those hotspots, while DLR was exploring water cooling as a viable and safer alternative for SpaceLiner.
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- Starship’s first full-scale prototype is being rapidly assembled in South Texas. (NASASpaceflight – bocachicagal)
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- Starship’s first full-scale prototype is being rapidly assembled in South Texas. (NASASpaceflight – bocachicagal)
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- Meanwhile, giant 9m-diameter tank domes are being assembled and welded together a few hundred feet away from Starhopper. (NSF – bocachicagal)
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- SpaceX’s Starhopper seen in a January render and a January photo. (SpaceX/Elon Musk)
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- BFS seen standing vertically on the pads of its tripod fins. (SpaceX)
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- A NASA team—via a US Navy aircraft—captured high-resolution, calibrated infrared imagery of Space Shuttle Discovery’s lower surface in addition to discrete instrumentation on the wing, downstream, and on the Boundary Layer Transition Flight Experiment protuberance. In the image, the red regions represent higher surface temperatures. (NASA)
Aside from heat flux, it’s also unclear when or how long the cooling system will need to be supplied with water during potential Starship reentries. At worst, the spacecraft would need to supply a constant 50+ kg/s throughout a 5+ minute (600+ second) regime of high-velocity, high-drag reentry conditions. Assuming that Starship will need to rely heavily on aerobraking to maintain efficient interplanetary operations, it might have to perform 2+ active-cooling cycles per reentry, potentially requiring a minimum of 15 tons of water per reentry. Given that SpaceX intends (at least as of September 2018) for Starship to be able to land more than 100 tons on the surface of Mars, 15t of water would cut drastically into payload margins and is thus likely an unfeasibly large mass reserve or any given interplanetary mission.
“You just need, essentially, [a stainless-steel sandwich]. You flow either fuel or water in between the sandwich layer, and then you have [very tiny] perforations on the outside and you essentially bleed water [or fuel] through them … to cool the windward side of the rocket.” – SpaceX CEO Elon Musk (Popular Mechanics, December 2018)
The assumptions needed for the above calculations do mean that 30T is an absolute worst-case scenario for a regeneratively-cooled Starship reentry, given that SpaceX may only have to vigorously cool a small fraction of its windward surface and will likely be able to cut more than half of the water needed by allowing Starship’s steel skin to heat quite a lot while still staying well below its melting point (likely around 800C/1500F or higher). This also fails to account for the fact that a regeneratively-cooled stainless steel heat shield would effectively let SpaceX do away with what would otherwise be a massive and heavy ablative heat shield and mounting mechanism. Perhaps the benefits of stainless steel might ultimately mean that carrying around 10-30T of coolant is actually performance-neutral or a minimal burden when all costs and benefits are properly accounted for.
Probability at 60% & rising rapidly due to new architecture
— Elon Musk (@elonmusk) December 27, 2018
Musk clearly believes with almost zero doubt that a stainless steel Starship and booster (Super Heavy) is the way forward for the company’s BFR program, and he has now twice indicated that the switch away from advanced carbon composites will actually “accelerate” the rocket’s development schedule. For now, all we can do is watch as the first Starship prototype – meant to perform short hop tests ASAP – gradually comes into being in South Texas.
Elon Musk said in late November that he’s “tried to warn” legacy automakers and “even offered to license Tesla Full Self-Driving, but they don’t want it,” expressing frustration with companies that refuse to adopt the company’s suite, which will eventually be autonomous.
Tesla has long established itself as the leader in self-driving technology, especially in the United States. Although there are formidable competitors, Tesla’s FSD suite is the most robust and is not limited to certain areas or roadways. It operates anywhere and everywhere.
The company’s current position as the leader in self-driving tech is being ignored by legacy automakers, a parallel to what Tesla’s position was with EV development over a decade ago, which was also ignored by competitors.
The reluctance mirrors how legacy automakers initially dismissed EVs, only to scramble in catch-up mode years later–a pattern that highlights their historical underestimation of disruptive innovations from Tesla.
Elon Musk’s Self-Driving Licensing Attempts
Musk and Tesla have tried to push Full Self-Driving to other car companies, with no true suitors, despite ongoing conversations for years. Tesla’s FSD is aiming to become more robust through comprehensive data collection and a larger fleet, something the company has tried to establish through a subscription program, free trials, and other strategies.
Tesla CEO Elon Musk sends rivals dire warning about Full Self-Driving
However, competing companies have not wanted to license FSD for a handful of speculative reasons: competitive pride, regulatory concerns, high costs, or preference for in-house development.
Déjà vu All Over Again
Tesla tried to portray the importance of EVs long ago, as in the 2010s, executives from companies like Ford and GM downplayed the importance of sustainable powertrains as niche or unprofitable.
Musk once said in a 2014 interview that rivals woke up to electric powertrains when the Model S started to disrupt things and gained some market share. Things got really serious upon the launch of the Model 3 in 2017, as a mass-market vehicle was what Tesla was missing from its lineup.
This caused legacy companies to truly wake up; they were losing market share to Tesla’s new and exciting tech that offered less maintenance, a fresh take on passenger auto, and other advantages. They were late to the party, and although they have all launched vehicles of their own, they still lag in two major areas: sales and infrastructure, leaning on Tesla for the latter.
I’ve tried to warn them and even offered to license Tesla FSD, but they don’t want it! Crazy …
When legacy auto does occasionally reach out, they tepidly discuss implementing FSD for a tiny program in 5 years with unworkable requirements for Tesla, so pointless. 🤷♂️
🦕 🦕
— Elon Musk (@elonmusk) November 24, 2025
Musk’s past warnings have been plentiful. In 2017, he responded to critics who stated Tesla was chasing subsidies. He responded, “Few people know that we started Tesla when GM forcibly recalled all electric cars from customers in 2003 and then crushed them in a junkyard,” adding that “they would be doing nothing” on EVs without Tesla’s efforts.
Companies laughed off Tesla’s prowess with EVs, only to realize they had made a grave mistake later on.
It looks to be happening once again.
A Pattern of Underestimation
Both EVs and self-driving tech represent major paradigm shifts that legacy players view as threats to their established business models; it’s hard to change. However, these early push-aways from new tech only result in reactive strategies later on, usually resulting in what pains they are facing now.
Ford is scaling back its EV efforts, and GM’s projects are hurting. Although they both have in-house self-driving projects, they are falling well behind the progress of Tesla and even other competitors.
It is getting to a point where short-term risk will become a long-term setback, and they may have to rely on a company to pull them out of a tough situation later on, just as it did with Tesla and EV charging infrastructure.
Tesla has continued to innovate, while legacy automakers have lagged behind, and it has cost them dearly.
Implications and Future Outlook
Moving forward, Tesla’s progress will continue to accelerate, while a dismissive attitude by other companies will continue to penalize them, especially as time goes on. Falling further behind in self-driving could eventually lead to market share erosion, as autonomy could be a crucial part of vehicle marketing within the next few years.
Eventually, companies could be forced into joint partnerships as economic pressures mount. Some companies did this with EVs, but it has not resulted in very much.
Self-driving efforts are not only a strength for companies themselves, but they also contribute to other things, like affordability and safety.
Tesla has exhibited data that specifically shows its self-driving tech is safer than human drivers, most recently by a considerable margin. This would help with eliminating accidents and making roads safer.
Tesla’s new Safety Report shows Autopilot is nine times safer than humans
Additionally, competition in the market is a good thing, as it drives costs down and helps innovation continue on an upward trend.
Conclusion
The parallels are unmistakable: a decade ago, legacy automakers laughed off electric vehicles as toys for tree-huggers, crushed their own EV programs, and bet everything on the internal-combustion status quo–only to watch Tesla redefine the industry while they scrambled for billions in catch-up capital.
Today, the same companies are turning down repeated offers to license Tesla’s Full Self-Driving technology, insisting they can build better autonomy in-house, even as their own programs stumble through recalls, layoffs, and missed milestones. History is not merely rhyming; it is repeating almost note-for-note.
Elon Musk has spent twenty years warning that the auto industry’s bureaucratic inertia and short-term thinking will leave it stranded on the wrong side of technological revolutions. The question is no longer whether Tesla is ahead–it is whether the giants of Detroit, Stuttgart, and Toyota will finally listen before the next wave leaves them watching another leader pull away in the rear-view mirror.
This time, the stakes are not just market share; they are the very definition of what a car will be in the decades ahead.
News
Waymo driverless taxi drives directly into active LAPD standoff
No injuries occurred, and the passengers inside the vehicle were safely transported to their destination, as per a Waymo representative.
A video posted on social media has shown an occupied Waymo driverless taxi driving directly into the middle of an active LAPD standoff in downtown Los Angeles.
As could be seen in the short video, which was initially posted on Instagram by user Alex Choi, a Waymo driverless taxi drove directly into the middle of an active LAPD standoff in downtown Los Angeles.
The driverless taxi made an unprotected left turn despite what appeared to be a red light, briefly entering a police perimeter. At the time, officers seemed to be giving commands to a prone suspect on the ground, who looked quite surprised at the sudden presence of the driverless vehicle.
People on the sidewalk, including the person who was filming the video, could be heard chuckling at the Waymo’s strange behavior.
The Waymo reportedly cleared the area within seconds. No injuries occurred, and the passengers inside the vehicle were safely transported to their destination, as per a Waymo representative. Still, the video spread across social media, with numerous netizens poking fun at the gaffe.
Others also pointed out that such a gaffe would have resulted in widespread controversy had the vehicle involved been a Tesla on FSD. Tesla is constantly under scrutiny, with TSLA shorts and similar groups actively trying to put down the company’s FSD program.
A Tesla on FSD or Robotaxi accidentally driving into an active police standoff would likely cause lawsuits, nonstop media coverage, and calls for a worldwide ban, at the least.
This was one of the reasons why even minor traffic infractions committed by the company’s Robotaxis during their initial rollout in Austin received nationwide media attention. This particular Waymo incident, however, will likely not receive as much coverage.
Tesla Model Y demand in China is through the roof, and new delivery dates show the company has already sold out its allocation of the all-electric crossover for 2025.
The Model Y has been the most popular vehicle in the world in both of the last two years, outpacing incredibly popular vehicles like the Toyota RAV 4. In China, the EV market is substantially more saturated, with more competitors than in any other market.
However, Tesla has been kind to the Chinese market, as it has launched trim levels for the Model Y in the country that are not available anywhere else. Demand has been strong for the Model Y in China; it ranks in the top 5 of all EVs in the country, trailing the BYD Seagull, Wuling Hongguang Mini EV, and the Geely Galaxy Xingyuan.
The other three models ahead of the Model Y are priced substantially lower.
Tesla is still dealing with strong demand for the Model Y, and the company is now pushing delivery dates to early 2026, meaning the vehicle is sold out for the year:
NEWS: New orders for all four Tesla Model Y trims in China are now officially sold out for 2025, as the factory’s remaining production capacity for the year has been fully allocated.
Estimated delivery dates for new orders now show January-February 2026. pic.twitter.com/Dfnu7yY58N
— Sawyer Merritt (@SawyerMerritt) December 1, 2025
Tesla experienced a 9.9 percent year-over-year rise in its China-made EV sales for November, meaning there is some serious potential for the automaker moving into next year despite increased competition.
There have been a lot of questions surrounding how Tesla would perform globally with more competition, but it seems to have a good grasp of various markets because of its vehicles, its charging infrastructure, and its Full Self-Driving (FSD) suite, which has been expanding to more countries as of late.
Tesla Model Y is still China’s best-selling premium EV through October
Tesla holds a dominating lead in the United States with EV registrations, and performs incredibly well in several European countries.
With demand in China looking strong, it will be interesting to see how the company ends the year in terms of global deliveries.
Elon Musk and Tesla try to save legacy automakers from Déjà vu
Waymo driverless taxi drives directly into active LAPD standoff
