News
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’s surprise addition to the X Takeover lineup has fans talking
Elon Musk will join Saturday’s X Takeover at Giga Texas for a live virtual interview.
Elon Musk will join X Takeover at Giga Texas on Saturday for a live virtual interview, according to Sawyer Merritt, who shared the news late Thursday. Musk will not be on stage in Austin. The conversation is set to stream for free on the @teslaownersSV account on X.
Organizers had kept expectations in check. In a September update, Tesla Owners Silicon Valley said Musk had appeared at the event twice before but was not promising a third appearance, even as fans hoped he would walk the Giga Texas grounds in person. A virtual spot matches 2024, when Musk gave a surprise interview of about an hour to the crowd in San Luis Obispo, as Teslarati reported at the time.
Wasn’t expecting this 🫡
— Tesla Owners Silicon Valley (@teslaownersSV) October 9, 2026
This year’s edition is a first in several ways. It is the first X Takeover held outside California and the first at a Tesla facility, with tickets selling out in eight days. Tesla provides the venue, but the event is produced independently by Tesla Owners Silicon Valley. The main event runs from 10 a.m. to 6 p.m. CT, followed by a drone and light show at 9 p.m. Maye Musk is the keynote speaker, Franz von Holzhausen is set for a virtual keynote, and Nicki Minaj is the special guest. Joe Tegtmeyer, whose drone footage Teslarati used to track the Optimus factory steel frame at Giga Texas, is also on the speaker list.
Musk’s interview topics have not been revealed, but the backdrop is busy. Tesla doubled its Cybercab fleet in Austin in late September, and last week Musk explained why Robotaxi hours only moved from 10 p.m. to 11 p.m.. Merritt also reported Thursday that Texas DMV records now show 319 registered Cybercabs, up from 169. NHTSA’s deadline for Tesla’s sworn answers on Cybercab certification is October 30, and Tesla reports third quarter earnings on October 21.
Fans who cannot make it to Austin can watch the livestream on X. Musk tends to say more in unscripted settings than he does in prepared remarks, which is the reason this one is worth having open on Saturday.
News
It’s official: SpaceX takes aim at Verizon, AT&T, and T-Mobile
SpaceX is buying 800 MHz spectrum from Grain to turn Starlink Mobile into a carrier.
SpaceX has agreed to buy a nationwide block of low band wireless spectrum, a deal the company says will let Starlink Mobile operate as a full US carrier rather than a satellite add-on for someone else’s network.
The company announced the agreement on X on Thursday afternoon, saying it will “pave the way for @Starlink to become a major mobile carrier in the US.” The seller is Grain Management, a private investment firm that confirmed in a statement that SpaceX will acquire 100% of its nationwide 800 MHz portfolio. That covers up to 14 MHz of paired spectrum in the 817 to 824 MHz and 862 to 869 MHz bands. Neither side disclosed a price, and the deal still needs FCC approval.
We announced an agreement to acquire a nationwide low-band spectrum license portfolio that will pave the way for @Starlink to become a major mobile carrier in the US.
With this new spectrum and our Gen2 constellation, Starlink Mobile can ensure Americans have access to high-speed mobile broadband no matter where they are → https://t.co/1Uaf48v5pm
— SpaceX (@SpaceX) October 8, 2026
Grain only recently picked up the licenses itself. It bought the portfolio from T-Mobile in a transaction that closed in August, paying cash plus its own 600 MHz spectrum. Rival AST SpaceMobile had been testing satellites on the same bands before SpaceX stepped in.
SpaceX said its 2 GHz spectrum will handle high bandwidth capacity, while the new 800 MHz layer “ensures Starlink Mobile’s signal penetrates through obstacles, such as walls, and can provide service to customers’ devices even when they are in buildings.” The company added that most existing phones already support the band, so customers would not need new hardware to use it.
That 2 GHz spectrum came from SpaceX’s EchoStar acquisition last year, which gave the company exclusive S band rights in the US and global Mobile Satellite Service licenses. The Grain spectrum is different in an important way: it is tailored for service from ground towers, not satellites. SpaceX said that combination would make Starlink Mobile “the first network operator to deploy both satellite and terrestrial spectrum.”
The announcement also follows a key regulatory win. Earlier this week, the FCC approved SpaceX’s plan to deploy 15,000 second generation Starlink Mobile satellites, which the company has said will carry up to 100 times the data density of the current system, as Teslarati previously reported.
Shares of AT&T, Verizon and T-Mobile fell in extended trading after the announcement. T-Mobile is currently SpaceX’s launch partner for Starlink Mobile in the US, which makes its position the most complicated of the three.
SpaceX has not been subtle about its plans. During the company’s August earnings call, President and COO Gwynne Shotwell said she expected Starlink Mobile to win over customers from the major carriers. “I anticipate us to be able to acquire quite a few of their customers because I think our service will be better,” she said, pointing to dead zone coverage and resilience during disasters. Shotwell also described plans for low cost cellular base stations that could pair with existing Starlink dishes.
SpaceX has targeted 2027 for deployment of its next generation Starlink Mobile satellites, with upgraded service expected by the end of that year. The FCC review of the Grain deal now determines when the terrestrial half of that network can come online.
Elon Musk
Trump presents Elon Musk with National Medal of Science, calls him “modern-day Thomas Edison”
Trump gave Elon Musk the National Medal of Science and compared him to Thomas Edison.
Elon Musk now has the highest honor the U.S. government gives to scientists and engineers. President Donald Trump presented him with the National Medal of Science on Thursday at the White House’s “Science: A New Golden Age” summit, held at the Institute of Peace in Washington, according to the White House.
Trump called Musk a “national treasure” and “our modern-day Thomas Edison.” “Few Americans in history have done more to advance America’s national interest than Elon in one field after another,” the president said. He also described Musk as an “industrial titan, brilliant engineer and one of the greatest technology founders to ever live.”
The official citation credits Musk “for engineering achievements of extraordinary ambition and scale that have pushed the frontiers of space exploration, intelligent systems, communications, and beyond, renewing American technological leadership and opening a new chapter in American manufacturing.” Tesla is not named in it, but “intelligent systems” and “American manufacturing” cover a lot of ground that Tesla and the Terafab chip project occupy.
Google co-founder Sergey Brin, Nvidia CEO Jensen Huang and AMD CEO Lisa Su received the same medal. Microsoft CEO Satya Nadella and Dell Technologies CEO Michael Dell were given the National Medal of Technology and Innovation. It was the first time Trump has handed out either award in his two terms. As Teslarati noted when the list was first reported on Wednesday, the National Science Foundation says 529 people have received the Medal of Science since Congress created it in 1959.
🚨 IT’S OFFICIAL: President Trump just PERSONALLY presented Elon Musk the National Medal of Science for his INCREDIBLE contributions to our nation
I can’t think of ANYONE who deserves this honor more 👏🏻
Congratulations, @elonmusk! https://t.co/GkAaVp9wb9
— Nick Sortor (@nicksortor) October 8, 2026
The ceremony closes a loop that opened in 2025, when Musk left DOGE and criticized the “Big Beautiful Bill,” sparking a public feud. Al Jazeera noted that Musk was the largest contributor to Trump’s 2024 campaign, and CNBC reported that all of the honorees have given financially to Trump or Republican causes in some form. The reconciliation has moved quickly in recent weeks. Musk sat at Trump’s left at the September 29 White House AI lunch, was named to help lead the Pentagon’s Project Meridian study on the future of warfare, and adopted the administration’s “super intelligence” wording when he said SpaceXAI will become SpaceXSI.
For Tesla and SpaceX shareholders, the practical question is what the closer relationship means for federal approvals. Tesla’s Robotaxi and Cybercab expansion depends on national autonomy rules, and SpaceX’s Starship and Starlink plans run through the FAA, FCC and NASA. Thursday’s ceremony did not change any of that directly.
Elon Musk’s surprise addition to the X Takeover lineup has fans talking
It’s official: SpaceX takes aim at Verizon, AT&T, and T-Mobile
Trump presents Elon Musk with National Medal of Science, calls him “modern-day Thomas Edison”
The Pentagon taps Elon Musk to design the battlefield of the future
Tesla Roadster’s new patent preps white-knuckle speeds, keeping it grounded
