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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
Elon Musk launches TERAFAB: The $25B Tesla-SpaceXAI chip factory that will rewire the AI industry
Tesla, SpaceX, and xAI unveiled TERAFAB, a $25B chip factory targeting one terawatt of AI compute annually.
Elon Musk took the stage over the weekend at the defunct Seaholm Power Plant in Austin, Texas, to officially unveil TERAFAB, a $20-25 billion joint venture between Tesla, SpaceX, and xAI that he described as “the most epic chip building exercise in history by far.” The announcement marks the most ambitious infrastructure bet Musk has made since Gigafactory 1 in Sparks, Nevada, and it fuses three of his companies into a single, vertically integrated AI hardware machine for the first time.
TERAFAB is designed to consolidate every stage of semiconductor production under one roof, including chip design, lithography, fabrication, memory production, advanced packaging, and testing. At full capacity, the facility would scale to roughly 70% of the global output from the current world’s largest semiconductor foundry from Taiwan Semiconductor Manufacturing Company (TSMC).
Elon Musk’s stated goal is one terawatt of computing power annually, split between Tesla’s AI5 inference chips for vehicles and Optimus robots, and D3 chips built specifically for SpaceXAI’s orbital satellite constellation.
Tesla Terafab set for launch: Inside the $20B AI chip factory that will reshape the auto industry
The logic behind the merger of these three entities is rooted in a supply chain crisis Musk has been signaling for over a year. At Tesla’s Q4 2025 earnings call, he warned investors that external chip capacity from TSMC, Samsung, and Micron would hit a ceiling within three to four years. “We’re very grateful to our existing supply chain, to Samsung, TSMC, Micron and others,” Musk acknowledged at the Terafab event, “but there’s a maximum rate at which they’re comfortable expanding.” Building in-house was, in his framing, not a strategic option, but a necessity.
The space angle is where the announcement becomes genuinely unprecedented. Musk said 80% of Terafab’s compute output would be directed toward space-based orbital AI satellites, arguing that solar irradiance in space is roughly 5x greater than at Earth’s surface, and that heat rejection in vacuum makes thermal scaling viable. This directly feeds the SpaceXAI vision, which is betting that within two to three years, running AI workloads in orbit will be cheaper than doing so on the ground. The satellites, powered by constant solar energy, would effectively turn low Earth orbit into the world’s largest data center.
Will Tesla join the fold? Predicting a triple merger with SpaceX and xAI
Historically, this announcement threads together every major Musk initiative of the past two years: the xAI-SpaceX merger, Tesla’s $2.9 billion solar equipment talks with Chinese suppliers, the 100 GW domestic solar manufacturing push, the Optimus humanoid robot program, and Starship’s development. TERAFAB is the capstone that ties them into a single coherent architecture — chips made on Earth, launched by SpaceX, powered by Tesla solar, run by xAI, and ultimately extended to the Moon.
“I want us to live long enough to see the mass driver on the moon, because that’s going to be incredibly epic,”Musk said during the presentation.
Announcing TERAFAB: the next step towards becoming a galactic civilization https://t.co/IDKey07mJa
— Tesla (@Tesla) March 22, 2026
News
Rolls-Royce makes shocking move on its EV future
When Rolls-Royce unveiled its first all-electric model, the Spectre, in 2022, former CEO Torsten Müller-Ötvös declared the brand would cease production of internal combustion engine vehicles by the end of the decade.
Rolls-Royce made a shocking move on its EV future after planning to go all-electric by the end of the decade. Now, the company is tempering its expectations for electric vehicles, and its CEO is aiming to lean on its legacy of high-powered combustion engines to lead it into the future.
In a significant reversal, Rolls-Royce Motor Cars has scrapped its ambitious plan to become an all-electric manufacturer by 2030. The luxury British marque announced the decision amid sustained customer demand for traditional combustion engines and shifting regulatory landscapes.
When Rolls-Royce unveiled its first all-electric model, the Spectre, in 2022, former CEO Torsten Müller-Ötvös declared the brand would cease production of internal combustion engine vehicles by the end of the decade.
The move aligned with the industry’s broader push toward electrification, promising silent, effortless power befitting the “Rolls-Royce of cars.”
However, new CEO Chris Brownridge, who assumed the role in late 2023, has reversed course. “We can respond to our client demand … we build what is ordered,” Brownridge stated.
The company will continue offering its iconic V12 engines, which remain a cornerstone of its heritage and appeal to discerning buyers who appreciate the distinctive sound and character. He noted the original pledge was “right at the time,” but “the legislation has changed.”
While not abandoning electric vehicles entirely, the Spectre remains in production, with an electric Cullinan option forthcoming; the decision marks the end of a strict all-EV timeline. Relaxed emissions regulations and slowing EV demand, evidenced by a 47 percent drop in Spectre sales to 1,002 units in 2025, forced the reconsideration.
It was a sign that perhaps Rolls-Royce owners were not inclined to believe that the company’s all-EV future was the right move.
Rolls-Royce joins a growing roster of automakers reevaluating aggressive electrification targets.
Fellow luxury brand Bentley has pushed its full electrification from 2030 to 2035, while continuing to offer hybrids and ICE models. Mercedes-Benz walked back its 2030 all-EV goal, now aiming for about 50% electrified sales while keeping combustion engines into the 2030s. Porsche has abandoned its 80% EV sales target by 2030, delaying models and extending hybrids.
Mainstream giants are following suit. Honda canceled its U.S. EV plans, including the 0-Series and Acura RSX, facing a $15.7 billion hit as it doubles down on hybrids. Ford and General Motors have incurred tens of billions in writedowns, canceling models and pivoting to hybrids amid an industry total exceeding $70 billion in charges.
This trend reflects a pragmatic shift driven by infrastructure gaps, consumer preferences, and policy changes. In the ultra-luxury segment, where emotional connection reigns, automakers are prioritizing flexibility over rigid deadlines, ensuring brands like Rolls-Royce evolve without alienating their core clientele.
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Elon Musk teases expectations for Tesla’s AI6 self-driving chip
This optimistic timeline for tape-out—the stage where chip design is finalized before manufacturing—signals Tesla’s push to rapidly advance its silicon capabilities.
Tesla CEO Elon Musk is outlining expectations for the AI6 self-driving chip, which is still two generations away. Despite this, it is already in the plans of the company and its serial entrepreneur CEO, who has high expectations for it.
Musk provided fresh details on the company’s aggressive AI hardware roadmap, spotlighting the upcoming AI6 chip designed to supercharge Tesla’s self-driving tech, humanoid robots, and data center operations.
In a post on X dated March 19, Musk stated, “With some luck and acceleration using AI, we might be able to tape out AI6 in December.”
With some luck and acceleration using AI, we might be able to tape out AI6 in December
— Elon Musk (@elonmusk) March 19, 2026
This optimistic timeline for tape-out—the stage where chip design is finalized before manufacturing—signals Tesla’s push to rapidly advance its silicon capabilities.
The announcement builds on progress with the predecessor AI5. Earlier in January, Musk announced that the AI5 design was “in good shape” and “almost done,” describing it as an “existential” project for the company that demanded his personal attention on weekends.
He characterized AI5 as roughly equivalent to Nvidia’s Hopper class performance in a single system-on-chip (SoC) and Blackwell-level as a dual configuration, but at significantly lower cost and power usage.
Elon Musk is setting high expectations for Tesla AI5 and AI6 chips
Musk highlighted that AI5 “will punch far above its weight” thanks to Tesla’s co-designed AI software and hardware stack, making maximal use of every circuit. While capable of data center training tasks, it is primarily optimized for edge computing in Optimus robots and Robotaxi vehicles.
For AI6, Musk envisions substantial gains. “In the same half reticle and same process node, we think a single AI6 chip has the potential to match a dual SoC AI5,” he explained.
The company is targeting ambitious nine-month development cycles for future chips, allowing rapid iteration to AI7, AI8, and beyond. AI5/AI6 engineering remains Musk’s top time allocation at Tesla, with the CEO calling AI5 “good” and AI6 “great.”
Samsung is expected to manufacture the AI6 chips, following deals worth billions, while AI5 will leverage TSMC and Samsung production. These chips will form the backbone of Tesla’s Full Self-Driving system, enabling safer and more capable autonomy, alongside powering dexterous movements in Optimus bots and efficient inference in expanding data centers.
Tesla to discuss expansion of Samsung AI6 production plans: report
Musk has also restarted work on the Dojo 3 supercomputer project now that AI5 is progressing. Long-term plans include in-house manufacturing via the Terafab facility.
By accelerating chip development with AI tools, Tesla aims to reduce dependence on third-party GPUs and deliver high-performance, energy-efficient solutions tailored to its ecosystem. Success with AI6 could mark a major milestone in Tesla’s journey toward full autonomy and robotics leadership, though timelines remain subject to manufacturing realities.
Elon Musk launches TERAFAB: The $25B Tesla-SpaceXAI chip factory that will rewire the AI industry
Rolls-Royce makes shocking move on its EV future
