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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.
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Tesla is building a massive Cybercab car wash in Las Vegas
Tesla quietly filed plans to build the Cybercab car wash, and on May 12, the company submitted a permit to begin renovating the “Tesla Center Cybercab Phase 2 Car Wash,” documents show.
Tesla is beginning to construct what will be an incredibly unique project, as it is now building a 36,000-square-foot car wash just for the Cybercab in Clark County, Nevada, near Las Vegas.
Tesla quietly filed plans to build the Cybercab car wash, and on May 12, the company submitted a permit to begin renovating the “Tesla Center Cybercab Phase 2 Car Wash,” documents show.
This is not just some ordinary car wash. Instead, it’s a dedicated, high-tech maintenance hub built specifically for Tesla’s ride-hailing vehicle and the many units that will be in the fleet.
According to the permit documents, which were first spotted by MarcoRP, a Supercharger observer on X, the work involves upgrading and updating the interior and exterior of an existing 36,000-square-foot facility. Crews will construct a full car-wash enclosure, relocate tire-service equipment, and install new power raceways.
Tesla has reportedly submitted plans for a carwash dedicated for Robotaxis in Las Vegas. The permit, filed with Clark County on May 12th, describes “Tesla Center Cybercab Phase 2 Car Wash.”
According to the project description, the work involves interior and exterior… pic.twitter.com/BayBYP7kSv
— Sawyer Merritt (@SawyerMerritt) May 14, 2026
Every camera on a Tesla Cybercab must stay clean, and without a human driver to perform manual maintenance on the vehicle, this Cybercab-specific car wash will be crucial in keeping the fleet operational, safe, and effective.
Tesla has spent years perfecting unsupervised FSD, and the Cybercab – unveiled last year as a driverless, two-seater purpose-built for ride-hailing – is the physical embodiment of that vision. Industry skeptics have long questioned how a massive Robotaxi network could scale without drivers handling basic upkeep.
Tesla just answered them with a permit filing. Sources close to the project suggest this could be the first of several such hubs, with whispers of similar plans already surfacing in Texas.
A purpose-built Robotaxi wash station means fleets can cycle vehicles through cleaning, charging, and minor servicing at lightning speed with almost no human intervention. Optimus robots could eventually handle the physical work, turning the entire operation into a lights-out, 24/7 machine.
Las Vegas, with its endless tourist traffic and wide-open roads, is the perfect proving ground. Imagine stepping out of a gleaming Cybercab after a night on the Strip, knowing the same vehicle will be sparkling clean and ready for the next rider within minutes.
California hits Tesla Cybercab and Robotaxi driverless cars with new law
Critics who claimed Robotaxis would get filthy and unreliable now look shortsighted. However, it will be interesting to see how many of these types of facilities the company establishes, especially as it plans for the Robotaxi fleet to be available everywhere.
If the permit moves forward as expected, Las Vegas could witness the first large-scale, fully autonomous taxi operation complete with its own cleaning infrastructure. As soon as Tesla solves wireless charging, we’re looking at a very capable and potentially fully autonomous ride-sharing business from A to Z.
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Tesla puts Giga Berlin in Plaid Mode with new massive investment
The facility, Tesla’s first in Europe, opened in 2022 and has become a cornerstone for Model Y production and, increasingly, in-house battery manufacturing. Recent announcements highlight a dual focus on scaling vehicle output and advancing vertical integration through 4680 battery cells.
Tesla is pushing forward with significant upgrades at its Gigafactory Berlin-Brandenburg in Grünheide, Germany, signaling renewed confidence in its European operations despite past market challenges.
The facility, Tesla’s first in Europe, opened in 2022 and has become a cornerstone for Model Y production and, increasingly, in-house battery manufacturing. Recent announcements highlight a dual focus on scaling vehicle output and advancing vertical integration through 4680 battery cells.
In April, plant manager André Thierig announced a 20 percent increase in Model Y production starting in July, following a record Q1 output of more than 61,000 vehicles. To support the ramp-up, Tesla plans to hire approximately 1,000 new employees beginning in May and convert 500 temporary workers to permanent positions.
The move is expected to lift weekly production significantly, addressing rebounding demand in Europe after a challenging 2025.
Today, we announced a $ 250m investment for our Giga Berlin Cell factory. This will enable 18GWh of annual 4680 cell production and create more than 1500 new jobs. Good news during challenging times for the German industry. pic.twitter.com/ou4SWMfWh9
— André Thierig (@AndrThie) May 12, 2026
The expansion builds on earlier progress. In 2025, Tesla secured partial approvals to add roughly 2 million square feet of factory space, raising potential annual vehicle capacity from around 500,000 toward 800,000 units, with longer-term ambitions approaching one million vehicles per year. Logistical improvements, new infrastructure, and battery-related facilities are already underway on company-owned land.
Battery production is the latest major focus. On May 12, Thierig revealed an additional $250 million investment in the on-site cell factory. This more than doubles the planned 4680 battery cell capacity to 18 gigawatt-hours annually—up from the 8 GWh target set in December 2025—while creating over 1,500 new battery-related jobs.
Total cell investments at the site now exceed previous figures, bringing the factory closer to full vertical integration: cells, packs, and vehicles produced under one roof. Tesla describes this as unique in Europe and a step toward stronger supply chain resilience.
The plans come amid regulatory and community hurdles. Earlier expansion proposals faced protests over environmental concerns and water usage, leading to phased approvals beginning in 2024. Tesla has navigated these by emphasizing sustainable practices and economic benefits, including thousands of local jobs in Brandenburg.
With nearly 12,000 employees already on site and production steadily climbing, Gigafactory Berlin is poised for growth. The combined vehicle and battery expansions position the plant as a key hub for Tesla’s European ambitions, potentially making it one of the continent’s largest manufacturing complexes if local support continues.
As EV demand recovers, these investments underscore Tesla’s commitment to scaling efficiently in Germany while addressing regional supply chain needs.
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Honda gives up on all-EV future: ‘Not realistic’
Mibe believes the demand for its gas vehicles is certainly strong enough and has changed “beyond expectations.” As many drivers went for EVs a few years back, hybrids are becoming more popular for consumers as they offer the best of both worlds.
Honda has given up on a previous plan to completely changeover to EVs by 2040, a new report states. The company’s CEO, Toshihiro Mibe, said that the idea is “not realistic.”
Mibe believes the demand for its gas vehicles is certainly strong enough and has changed “beyond expectations.” As many drivers went for EVs a few years back, hybrids are becoming more popular for consumers as they offer the best of both worlds.
Mibe said (via Motor1):
“Because of the uncertainty in the business environment and also the customer demand, is changing beyond our expectation and, therefore, we have judged that it’ll be difficult to achieve. That ratio [100-percent electric in 2040] is not realistic as of now. We have withdrawn this target.”
Instead of going all-electric, Honda still wants to oblige by its hopes to be net carbon neutral by 2050. It will do this by focusing on those popular hybrid powertrains, planning to launch 15 of them by March 2030.
Honda will invest 4.4 trillion yen, or almost $28 billion, to build hybrid powertrains built around four and six-cylinder gas engines.
There are so many companies abandoning their all-electric ambitions or even slowing their roll on building them so quickly. Ford, General Motors, Mercedes, and Nissan have all retreated from aggressive EV targets by either cancelling, delaying, or pausing the development of electric models.
Hyundai’s 2030 targets rely on mixed offerings of electric, hybrid & hydrogen vehicles
Early-decade pledges from multiple brands proved overly ambitious as infrastructure lags, battery costs remain high in some markets, and many buyers prefer hybrids for their convenience and range. Toyota has long championed hybrids, while others have quietly extended internal-combustion timelines.
For Honda—historically known for reliable gasoline engines—this shift leverages its core strengths while buying time to refine electric technology. Whether the hybrid-heavy strategy will protect market share in an increasingly competitive landscape remains to be seen, but one thing is clear: the gas engine is far from dead at Honda, unfortunately.
Tesla is building a massive Cybercab car wash in Las Vegas
Tesla puts Giga Berlin in Plaid Mode with new massive investment
