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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
Starbase after dark: Musk’s latest photo captures a Spaceport on the brink of history
SpaceX’s Starbase city in Boca Chica, Texas is rapidly transforming the southern tip of the Lone Star State into one of the most ambitious launch complexes in history.
A striking nighttime photograph of SpaceX’s Starbase facility in Boca Chica, Texas, shared recently by Elon Musk on X, offers a dramatic glimpse of an operation that is rapidly transforming the southern tip of the Lone Star State into one of the most ambitious launch complexes in history.
The most immediately visible change in the photo is the presence of two fully erected Starship launch towers dominating the coastal skyline. The second orbital launch pad, known as Pad B, now features its fully erected tower, OLIT-3, which stands approximately 474 feet tall and incorporates an integrated water-cooled flame trench designed to minimize damage and reduce turnaround time between launches. The dual-tower silhouette against the night sky signals a decisive shift from experimental testing facility to high-cadence launch operations.
Grok Image concept of Elon Musk’s latest Starbase photo via X
Back at Starbase, Pad 2 is approaching hardware completion, with upgraded chopstick arms, a new chilldown vent system, and all 20 hold-down arms now fitted with protective doors to shield them from the intense exhaust of up to 33 Raptor 3 engines, according to a deeper dive by NASASpaceFlight.
SpaceX has also received approval to nearly double the footprint of the Starbase launch site, with groundwork already underway to add LNG liquefaction plants, expanded propellant storage, and additional ground support infrastructure.
The photo also carries a milestone civic dimension. Starbase officially became a Texas city in May 2025 after a community vote, with SpaceX employees elected as mayor and commissioners of the newly incorporated municipality. That legal status streamlines launch approvals and gives SpaceX direct control over local infrastructure decisions.
The FAA has approved an increase in launches from Starbase in Texas from five to twenty-five per year, clearing the runway for the kind of flight frequency needed to fulfill Starship’s ultimate mission of ferrying cargo and crew to the Moon, servicing the Department of Defense, deploying next-generation Starlink satellites, and eventually establishing Elon Musk’s long sought after goal of a self-sustaining human presence on Mars.
Seen from above in the dark, Starbase looks less like a test site and more like a spaceport.
News
Tesla loses Director who designed one of the company’s best features
Thomas Dmytryk, who has spent over 11 years with Tesla and helped to develop Over-the-Air updates and the company’s vehicles’ ability to utilize them to improve, has decided to leave.
Tesla has lost the director who designed one of the company’s best features: Over-the-Air updates.
Thomas Dmytryk, who has spent over 11 years with Tesla and helped to develop Over-the-Air updates and the company’s vehicles’ ability to utilize them to improve, has decided to leave. In a lengthy statement on LinkedIn, Dmytryk said that he’s “closing the book.” He had nothing but good things to say:
“After 11 incredible years at Tesla, I’m closing the book. It’s been the ride of a lifetime: always on the news, innovating relentlessly, constantly pushing the limits. Tesla is THE place for talented, passionate people. I feel insanely lucky to have been part in that culture for so long.”
It appears the intense lifestyle of developing and creating intensively for so long might have caught up to Dmytryk, who did not give his definitive plans for the future, and it appears he may be taking some time off before jumping into a new venture:
“The future? Extremely bright. Ambitions intact, just getting started as a transformative company that could elevate billions of lives. So why leave now?! Human life’s always been my North Star, right now I need to be with mines. I’ve always admired Tesla’s top leadership and vision. But what I’ve always found incredible is the tenacity, brilliance and devotion of people on the front line. YOU make Tesla unstoppable. I wish you all the best and of course EPIC wins.”
The move was first reported by NotaTeslaApp.
Over-the-Air updates are among Tesla’s best features. They are used to improve the Full Self-Driving suite, add features, remedy recalls, and more. Many vehicles have the ability to receive OTA updates, as I did in a Ford Bronco previous to my Model Y. However, Tesla does them better than anyone else: they’re seamless, effective, and frequent. Your car always improves.
The move is a blow to Tesla, of course, considering Dmytryk’s massive contribution to the company and extremely long tenure spent, but not something that is overwhelmingly detrimental. Tesla deals with a lot of extremely intelligent people, some of whom are the best in their field, so they are sure to find a suitable replacement.
However, it’s no secret that the company has been losing some of its top talent, some of whom were in executive roles. Some have left to take on new projects, and others have not revealed their career plans.
It seems at least some of those employees are simply deciding to walk away and try new things after working so hard for so long. According to Dmytryk’s LinkedIn, he also played a large part in Musk’s acquisition of X, as he stated he “worked at Twitter/X ~45/week while working at the same pace for Tesla.”
That averages a 13-hour day, seven days a week, or 18 hours for the normal five-day work week.
News
Tesla’s most wanted Model Y heads to new region with no sign of U.S. entry
Unlike the standard Model Y, the “L” stretches the wheelbase by roughly 150 mm and the overall length by about 177 mm to 4,976 mm. The result is a genuine 2-2-2 seating layout that gives six adults proper legroom and cargo space — a true family hauler without the cramped third-row compromises of many three-row SUVs.
Tesla’s most wanted Model Y configuration is heading to a new region, and although U.S. fans and owners have requested the vehicle since its release last year, it appears the company has no plans to bring it to the market.
According to fresh regulatory filings, the six-seat Model Y L is coming to South Korea with signs indicating an imminent launch. The extended-wheelbase configuration, already a hit in China, just cleared energy-efficiency certification from the Korea Energy Agency, paving the way for deliveries as early as the first half of 2026.
The vehicle is already built at Tesla’s Giga Shanghai facility in China, making it an ideal candidate for the Asian market, as well as the European one, as the factory has been known as a bit of an export hub in the past.
$TSLA
BREAKING: The official launch of Tesla Model Y L in S.Korea seems to be quite imminent.Additional credentials related to Model YL were released today.
✅ Battery Manufacturer: LG Energy Solutions
✅ Number of passengers: 6 people
✅ Total battery capacity: 97.25 kWh… pic.twitter.com/hmy64XYi80— Tsla Chan (@Tslachan) March 6, 2026
It seems like Tesla was prepping for this release anyway, as the timing was no accident. A camouflaged Model Y L prototype was spotted testing on Korean highways the same day the certification dropped. Tesla has already secured similar approvals for Australia and New Zealand, with both markets expecting the larger Model Y in 2026.
Unlike the standard Model Y, the “L” stretches the wheelbase by roughly 150 mm and the overall length by about 177 mm to 4,976 mm. The result is a genuine 2-2-2 seating layout that gives six adults proper legroom and cargo space — a true family hauler without the cramped third-row compromises of many three-row SUVs.
South Korean filings list it as an all-wheel-drive imported electric passenger vehicle with a 97.25 kWh total battery capacity supplied by LG Energy Solution. Local tests show an impressive 543 km (337 miles) combined range at room temperature and 454 km (282 miles) in colder conditions, easing one of the biggest concerns for Korean EV buyers.
Tesla Model Y lineup expansion signals an uncomfortable reality for consumers
But for U.S. fans, things are not looking good for a launch in the market.
CEO Elon Musk has been blunt. The six-seater “wouldn’t arrive in the U.S. until late 2026, if ever,” he said, pointing to the company’s heavy bet on unsupervised Full Self-Driving and robotaxi platforms like the Cybercab. With the Model X slated for discontinuation, many families hoped the stretched Model Y would slide into the lineup as an affordable three-row bridge. So far, that hope remains unfulfilled.
For now, South Korean drivers will be among the first buyers outside China to enjoy the spacious, efficient Model Y L. Tesla continues its global rollout strategy, tailoring vehicles to regional tastes while North American customers keep refreshing their apps and crossing their fingers.
The Model Y L proves the appetite for practical, family-sized electric SUVs is stronger than ever. Hopefully, Tesla will listen to its fans and bring the vehicle to the U.S. where it would likely sell well.
Starbase after dark: Musk’s latest photo captures a Spaceport on the brink of history
Tesla loses Director who designed one of the company’s best features
