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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 put a number on where he thinks SpaceX’s Starship program is headed by 2030, replying on X a day after President Trump signed a memo pushing the country toward 1,000 space launches and reentries a year.
The exchange started when Aaron Burnett, co-founder of propulsion startup Mach 33, posted that “1,000 launches/reentries is the goal,” quoting White House science adviser Michael Kratsios on the newly signed National Space Transportation Policy. Burnett noted that the FAA’s own bull-case forecast reached only 385 annual launches by 2030, while his firm’s conservative model already put SpaceX alone near 940. Musk responded, “We’re aiming to reach 30+ Starship launches/day in 2030, which is ~10k annualized. Still tiny numbers compared to airplane flights!”
We’re aiming to reach 30+ Starship launches/day in 2030, which is ~10k annualized.
Still tiny numbers compared to airplane flights!
— Elon Musk (@elonmusk) August 21, 2026
That figure is specific to Starship, the rocket SpaceX is still developing for orbital and lunar missions, not the Falcon 9 fleet that carries most of the company’s current launch volume. Starship has flown twice this year, a slower pace than the four and five flights SpaceX managed in 2024 and 2025. Getting from two flights a year to 30 a day is the scale of jump the new federal policy is meant to clear regulatory room for.
Trump’s memo, signed Thursday, directs agencies to identify new launch and reentry sites on federal land, including a new reentry site within 90 days, and to speed up the permitting and environmental reviews that have long slowed cadence growth. It also sets a goal of returning American astronauts to the moon by 2028 and placing initial lunar base elements by 2030, tying the launch buildout directly to NASA’s Artemis program.
SpaceX has already been pushing the FAA toward higher numbers on its own. The agency approved up to 44 annual Starship launches from Kennedy Space Center in February, on top of a 2024 review that raised the cap at Starbase in Texas to 25 a year. Those approvals cover a fraction of the 10,000 annual flights Musk is now describing, which shows how far current permitting still sits from the administration’s stated target.
The near-term test of all this is more modest. SpaceX cleared a full-duration, six-engine static fire on its next Starship vehicle this week, the last major hardware checkpoint before Flight 14, which is targeting no earlier than August 28 and is expected to attempt the vehicle’s first full orbital mission. Musk said last week that a tower catch of the upper stage is still probably months away, a reminder that the immediate roadmap remains far more incremental than the daily launch numbers he just posted.
Tesla will resolve its massive recall of nearly three million vehicles in China with stickers and a software update.
On Friday, Chinese regulators filed recall plans against Tesla, Xiaomi, Leapmotor, Xpeng, Chery, Geely, Dongfeng, Arcfox, and FAW to resolve what is essentially a carbon-copy issue throughout each of the companies’ vehicle models: emergency door release latches are simply not visible enough.
Tesla door handle saga gets its latest chapter and a big change is coming
The companies will be required to add things that will make these latches, which will open the door in the event of an emergency, more visible. Of the 7 million vehicles impacted, Tesla accounts for 2,975,910 units. More than 1.9 million of those are Model Y vehicles, with the rest, just over 970,000, being Model 3s.
To resolve the issue, Tesla is going to add warning labels to the emergency latches free of charge, and then utilize an Over-the-Air update to add a post-crash window-lowering strategy, according to CNEVpost.
This massive effort to fix the all-electric Model Y and Model 3’s emergency latch system comes just months after several probes across various markets identified the trouble some had identifying this latch. Those who had gotten involved in car accidents that stripped the vehicle of its power were not aware that every Tesla has emergency door latches.
China’s State Administration for Market Regulation (SAMR) said that severe crashes that disable a vehicle’s low-voltage system could not only hinder occupants from getting out, but also make it more difficult for emergency response workers to gain entry.
SAMR is starting to tighten the regulations it has on door handles on vehicles. A new mandatory national standard will take effect for all models starting January 1, 2027, and will require all doors to be equipped with mechanical release mechanisms. This will effectively end purely electronic door handles. Models already on sale with type approval have been granted a two-year transition period, which will enable things to change until January 2029.
Tesla has officially confirmed plans to bring its all-electric Semi truck to Europe, with full specifications and market-launch details set for unveiling at the IAA Transportation trade fair in Hannover, Germany.
The event runs September 15–20, with a possible press preview on September 14. The announcement, shared via Tesla’s Semi account, marks a significant expansion beyond North America nearly nine years after the truck’s original 2017 reveal.
🚨 Tesla Semi is coming to Europe!
Sustainable logistics is a huge market internationally, and now Tesla is involved in it outside of the U.S. market! https://t.co/q3hjX6ybMv pic.twitter.com/mxTaVY3UsE
— TESLARATI (@Teslarati) August 20, 2026
In the United States, the Semi’s path has been gradual. Limited pilot production and customer deliveries began in late 2022, primarily to fleets such as PepsiCo. After years of refinement, high-volume manufacturing started on April 29, 2026, at a dedicated facility adjacent to Gigafactory Nevada.
The plant targets an annual capacity of 50,000 units, though the ramp is expected to be gradual, with “many thousands” of trucks projected by the end of 2026.
Demand is building, with recent orders including 500 units for Einride (deliveries starting September 2026, serving Amazon and others) and hundreds more from operators such as WattEV. Pricing stands at approximately $260,000 for the Standard Range and $290,000 for the Long Range before incentives.
Tesla Semi pricing revealed after company uncovers trim levels
Earlier in 2026, Tesla finalized production specifications that incorporated substantial updates. In February, the company detailed two variants designed for a full 82,000-pound gross combination weight.
The Standard Range offers about 325 miles of range with a 548 kWh battery and curb weight under 20,000 pounds. The Long Range delivers roughly 500 miles with an 822 kWh pack and a 23,000-pound curb weight. Both use three independent rear-axle motors producing up to 800 kW (about 1,073 horsepower), achieve energy consumption of around 1.7 kWh per mile, and support megawatt-class charging at up to 1.2 MW—recovering about 60 percent of range in 30 minutes through the MCS standard.
Additional refinements include a roughly 1,000-pound weight reduction versus earlier prototypes, improved aerodynamics, a 48-volt electrical architecture, electric power take-off up to 25 kW for refrigerated trailers, and fleet management software with over-the-air updates.
These advances position the Semi as a competitive option against diesel trucks on operating costs and performance. For Europe, adaptations such as lighting, cab configurations (including potential sleeper options), and regulatory compliance are anticipated.
With series production underway in Nevada and major fleet commitments secured, the upcoming IAA reveal will clarify timelines, European-specific specs, and pricing, potentially accelerating electrification of heavy-duty freight on both continents.
SpaceX and a new Trump order that could rewrite the next decade of launches
Tesla will resolve massive China recall with stickers and a software update
