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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.
Tesla owners have long griped about the wireless phone charger in the Model Y and other vehicles. It often turns smartphones into miniature ovens rather than reliably topping them up.
Software engineer and Model Y owner Michał Gapiński tackled this issue head-on with a clever DIY upgrade, swapping the cooled wireless charger pad from the China-made Model YL in for the one that came standard in his vehicle.
There are several key differences between the U.S.-built Model Y’s wireless charging pad and the one that Tesla has been installing in the Model YL. The one installed in U.S.-built vehicles lacks active cooling and relies on basic heat dissipation, leading to rapid temperature buildup during charging. In contrast, the Model YL integrates a small fan for active cooling.
Will it fit? Fingers crossed, I want a first YL charger deployed in the regular juniper pic.twitter.com/wWDqSNFVkW
— Michał Gapiński (@mikegapinski) June 2, 2026
This design maintains lower temperatures even in warm ambient conditions, though it does not support faster Qi2 charging on iPhones. The connector matches exactly, making physical swaps feasible on compatible consoles, but coding is required to enable full functionality.
Owners in the U.S. have complained about the wireless charging pad, with many reporting that overheating is fairly common. Within 20 or 30 minutes of placing a phone on the wireless charging pad, many have reported overheating messages on their phones, which halt charging and essentially turn the pad into a fancy place to rest your phone.
Many owners have opted to simply plug their phones into a charging cord. Tesla has acknowledged the problem by releasing several solutions for owners, including a relatively new feature that allows you to simply turn off the charging and simply act as a holder for your phone while driving.
Gapiński said that he sourced the cooled pad affordably from China, and it cost under $200 for the part.
He removed the existing console charger, swapped in the new unit, confirming a perfect connector fit, and handled the trim differences. Since the parameter isn’t fully secured, he enabled it through custom coding outside official Toolbox.
Connector is identical, she fits, now time to code it. https://t.co/Y9idgDrpCq pic.twitter.com/uwwgq6blg7
— Michał Gapiński (@mikegapinski) June 2, 2026
The fan activates quietly, blending with AC and seat cooling. He reported the installation was effective and the wireless charging pad worked perfectly; it even kept the phone cool as it stayed at just 86 degrees Fahrenheit. Many times, the wireless charging pad will bring the phone’s temperature well above 100 degrees, sometimes even being relatively hot to the touch.
The retrofit worked, no issues. First Model Y with a cooled wireless charger! No QI2/faster charging on the iPhone but it does not boil the phone even when it is 30 degrees outside.
The fan kicks in, it is not audible especially with the air conditioning and seat cooling. The… https://t.co/JOyR8Tb1Yo pic.twitter.com/kJcYhQIlYq
— Michał Gapiński (@mikegapinski) June 2, 2026
This retrofit highlighted an elegant, owner-driven solution to a factory shortcoming. It is expected that Tesla will begin installing the cooled charging pads into new cars in the U.S. soon, and hopefully, it will offer some sort of retrofit service or kit to owners here who want to use the charging pad effectively.
For those who love to tinker, it’s an accessible upgrade, proving that innovation thrives beyond the production line.
The Tesla Roadster unveiling could be coming “in a few weeks,” according to the company’s Chief Designer Franz von Holzhausen, who said at the Tesla Takeover Europe Event in Austria that the all-electric hypercar could finally make its way to the production line after years of anticipation.
Von Holzhausen delivered the news just days after The Information reported that Tesla planned to push the Roadster unveiling to August. It was slated for both April and May of this year, but now it seems the company is leaning toward a late Summer event to cap off the heat with perhaps its most anticipated vehicle of all-time.
🚨 Tesla Chief Designer Franz Von Holzhausen, speaking to the crowd at Tesla Takeover Europe, said at the event that the Roadster is coming “in a few weeks,”
Multiple attendees have confirmed this pic.twitter.com/B1v6yb2Geq
— TESLARATI (@Teslarati) June 6, 2026
Franz has been with Tesla since 2008, and has played a pivotal role in the iconic design language the company has utilized with its vehicles. Speaking to the crowd in Austria virtually, von Holzhausen’s comments injected fresh excitement into a project that has been plagued by delays for nine years.
The second-generation Roadster promises to redefine supercar standards. Tesla’s website still highlights ambitious targets: 0-60 mph in under 1.9 seconds (with optional SpaceX thruster pack potentially achieving 1.1 seconds or less), a top speed exceeding 250 mph, and a range of about 620 miles.
Equipped with a tri-motor all-wheel-drive setup delivering over 1,000 horsepower, the four-seater aims to blend blistering acceleration, everyday usability, and innovative features like cold gas thrusters for short-hop capabilities, technology that will combine the project with SpaceX.
But years after the company promised to start production, which was slated for 2020, the timeline for the Roadster has continued to shift.
Tesla has strung along those who have put $50,000 deposits down, as well as fans and enthusiasts of the company who have been long awaiting the company to bring forth a car truly designed for the human driver, and not autonomy. The Roadster is more than just a halo vehicle for Tesla; it showcases the company’s ability to push the boundaries while incorporating synergies from other Musk companies.
However, it has to make it to production, which is something Musk and Co. have pushed back repeatedly.
As Tesla navigates Robotaxi development and broader autonomy goals, the Roadster serves as a reminder of its performance roots. If von Holzhausen’s timeline holds, fans could witness this engineering marvel by late June or early July 2026. Whether a full unveiling, demo, or initial deliveries, it marks a milestone for electric supercars.
Tesla has reportedly pushed the unveiling of the Roadster once again, but there are also evidently new details about the event that the company plans to show off.
The Information reported this morning that Tesla will now unveil, for the second time, the next-generation Roadster in August, a further delay from the multiple timeline that the company had previously stated.
The report has not been confirmed or denied by Tesla at any capacity.
It also states the unveiling event will take place in Texas, the same place that Tesla executives revealed in May would be the place of manufacture for the company’s highly-anticipated supercar, which boasts a top speed of over 250 MPH and 650 miles of range, according to its website.
Tesla is also expected to showcase the SpaceX package, which will be used for faster acceleration and potentially hovering capabilities, at the unveiling event, the report states. Musk has always planned for this to happen, but now it seems it is more realistic than ever
The report also states the Roadster unveiling is planned for August pic.twitter.com/By26XZIJzU
— TESLARATI (@Teslarati) June 5, 2026
The Roadster has had its unveiling date and manufacturing date pushed back on many occasions. It was set to start production in 2020, but the COVID-19 pandemic crippled supply chain operations, forcing Tesla to push its timeline back considerably.
However, COVID has been over for some time, and Tesla has still not managed to successfully schedule and execute an unveiling event, which is something fans and enthusiasts, as well as those who have put down a $50,000 deposit, have been waiting for.
The vehicle was close to completion last year, but Musk truly wanted Lars Moravy and Franz von Holzhausen to push the limits of the Roadster. In July of last year, Moravy said:
“Roadster is definitely in development. We did talk about it last Sunday night. We are gearing up for a super cool demo. It’s going to be mind-blowing; We showed Elon some cool demos last week of the tech we’ve been working on, and he got a little excited.”
It is important to note two things: Tesla has not confirmed these details, and the company has regularly pushed these dates back. Until Tesla sends out formal invitations with a concrete date, taking any unveiling event reports with a grain of salt is a good idea.
Tesla owner fixes common feature complaint with crafty DIY retrofit
Tesla exec says Roadster unveil is soon — for real this time
