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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 and SpaceX shares fell on Wednesday after Democrats swept both chambers of Congress. The decline stood out as broader market securities recovered and turned positive, while both of Musk’s publicly traded companies lagged.
CEO Elon Musk already joked about the unsuccessful campaigning for the Republicans, but now the new party will make pretty drastic changes to how it handles Tesla and SpaceX, and those companies will adjust their outlook.
Let’s take a deeper look.
Tesla ($TSLA)
Tesla shares traded lower during the regular session after Democrats secured both the House and Senate. The stock was down 2.32 percent at around 1:45 p.m. on the East Coast, trading at around $389.30.
The pressure is tied to more than the raw scale of Musk’s political spending, estimated at $450–474 million this cycle with roughly $224 million directed at Texas. In that state, Tesla now faces a Democratic governor and a Democratic senator after Gina Hinojosa unseated Greg Abbott and James Talarico defeated Ken Paxton.
The Austin Gigafactory, Robotaxi pilot programs in multiple Texas cities, and any related AI compute expansion sit under a new state executive who campaigned against certain corporate subsidies and floated a moratorium on new data-center construction.
Federally, Democratic control of key committees opens the door to deeper examination of Tesla’s autonomous-driving safety record, federal energy-storage and manufacturing incentives, and the national-security implications of any combination with SpaceX.
Investors are also weighing whether the company’s historically close alignment with the prior Republican leadership will invite slower permitting, additional hearings, or tighter rules on Full Self-Driving deployment.
For Tesla, the political shift adds near-term friction around state permitting and federal regulatory approvals for autonomy and energy storage. A potential merger with SpaceX may face slower review even if it proceeds.
Core growth drivers such as vehicle deliveries, energy deployments, and robotaxi rollout remain intact, yet the stock now carries a higher political-risk premium that could weigh on valuation until the company demonstrates workable relationships with the new Texas leadership and congressional majorities.
SpaceX ($SPCX)
SpaceX shares also declined in live trading on November 4 following the Democratic midterm sweep. The stock traded at $134.97, down 4.49 percent. The drop occurred even as broader indexes stabilized, highlighting a company-specific reaction to the election outcome.
Musk’s large contributions, concentrated in Texas races that both companies lost, place SpaceX’s Starbase launch facility and headquarters under a new Democratic governor.
At the federal level, Democratic control of Congress enables greater scrutiny of NASA, the Department of Defense, and other contracts that support a meaningful share of revenue, along with reviews of Starlink national-security uses and any Tesla merger. Analysts have noted that empowered committees can hold hearings and request documents on these relationships.
For SpaceX, the results raise the risk of delayed contract awards, higher compliance costs, and tighter constraints on AI and satellite infrastructure expansion, particularly in Texas where a data-center moratorium has been discussed.
A merger with Tesla could encounter political friction that slows integration of launch, connectivity, and autonomy capabilities.
While Starlink growth and launch cadence continue as primary drivers, the company faces a more contested path for federal funding and state-level operations, requiring management to rebuild ties with the new congressional majorities and Texas leadership to limit the overhang.
Tesla’s new vehicle registrations in Germany rose sharply in October, nearly quadrupling from the same month a year earlier. That’s according to data from the KBA, Germany’s federal motor transport authority.
The KBA reported 2,932 Tesla vehicles registered in October, a 290.9 percent year-over-year- increase. For the first ten months of the year, Tesla’s cumulative registrations reached 47,742 units. This number is up 206.1 percent compared with the January-October period of 2025. These gains occurred against a backdrop of strong overall growth in the BEV sector as a whole.
Germany registered 94,086 new BEVs in October, a 79.5 percent rise that brought the BEV share of the passenger car market to 37 percent of the 254,492 total cars registered that month.
🇩🇪 Tesla’s new registrations in Germany nearly quadrupled in October, according to KBA data.
October: 2,932 units, +290.9% YoY Jan–Oct: 47,742 units, +206.1%
Germany’s overall BEV market grew 79.5% to 94,086 units last month. https://t.co/GMwNqsFAOC
— TESLARATI (@Teslarati) November 4, 2026
Despite the percentage surge, Tesla’s absolute numbers left it with a 1.2 percent share of all new car registrations for October. Chinese competitors did record higher volumes, as BYD registered 5,173 vehicles, a 2 percent share, Leapmotor with 3,661 cars, which equates to 1.4 percent, and Xpeng had a 0.5 percent share.
Year-to-date through October, BYD edged ahead of Tesla with 47,961 registrations versus Tesla’s 47,742.
The October results follow a notably strong September for Tesla in Germany, when it registered 12,552 vehicles, an increase of roughly 269 percent year-over-year and one of its strongest monthly totals on record in the country. That month, the Model Y led all EVs and ranked among the top-selling vehicles of any powertrain.
The figures form part of a broader recovery in Tesla’s European registrations after an extended period of softer demand. While monthly volumes remain subject to typical quarter-end patterns and competitive pressure from both established European brands and rapidly expanding Chinese manufacturers, the year-to-date growth indicates improved traction in Europe’s largest car market.
Tesla’s Gigafactory Berlin-Brandenburg continues to supply the region, positioning the company to capture a share of the expanding German BEV market as overall EV adoptions looks to be accelerating.
In the early hours of Wednesday following the 2026 midterm elections, Elon Musk took to X with a characteristically irreverent reaction to the results.
“Guess my election-interfering space lasers didn’t work this time,” the Tesla and SpaceX CEO posted, generating hundreds of thousands of likes and widespread attention.
The quip landed after Democrats secured control of both the House and Senate in a sweeping victory. Musk, the largest individual donor of the cycle, had directed an estimated $440–474 million toward Republican candidates and aligned groups—more than any non-candidate in modern history.
Much of the spending targeted Texas, where Musk’s companies have significant operations. There, Democrat Gina Hinojosa defeated incumbent Gov. Greg Abbott, and James Talarico ousted Ken Paxton in the Senate race.
Musk’s “space lasers” joke playfully referenced conspiracy theories that have circulated since the 2024 election, falsely claiming he used Starlink satellites or other technology to influence vote totals. By leaning into the accusation with a shrug emoji, he turned potential criticism into self-deprecating humor:
St. Clair says Musk told her he knew the 2024 election’s outcome erlier in the day — claiming he had “lasers in space” and had unleashed an “anomaly in the matrix.”
(She says she didn’t press for details, worried she’d later be deposed about it.)
(2/7)
— Matt Rivera (@rivera) September 16, 2026
According to .@nytimes reporting by .@KirstenGrind and .@mega2e, after appearing on stage with Trump on Oct 5, Musk texted someone close to him:
“I’m feeling more optimistic after tonight. Tomorrow we unleash the anomaly in the matrix.”
Then, an hour later:
“This isn’t something on the chessboard, so they’ll be quite surprised. ‘Lasers’ from space.”Important to remember that Musk just admitted to winning the election for Trump, that the House would be blue, and the Senate would be 51–49 for the Democrats.
It’s also important to remember that just days before the election Musk activated 265 low Earth orbit (LEO) V2 Mini satellites, each equipped with Direct-to-Cell (DTC) technology capable of processing, routing, and manipulating real-time data, including voting data, through his satellite network.
Now Trump is forcing countries to sign Starlink contracts in exchange for tariff relief. Do Democrats understand where this is heading? Does anyone in Congress tune in to .@jimstewartson? This isn’t just policy—it’s Musk and Thiel’s global heist of democracy. And Dems are out here sending texts asking people to chip in for midterms?
What midterms? A vote-flipping algorithm just WON the 2024 election. We have the data.
We have constitutional avenues to remove this entire illegitimate administration. Stealing an election is an act of rebellion against the Constitution—and nearly every individual currently serving has previously sworn an oath to uphold and defend it. Do you see where I’m going here?
See Starlink op-ed, attached.
This is not HUMAN generated data..@AmyMcGrathKY .@YourAnonCentral .@ellenbarkin .@JasonBassler1 .@SenDuckworth
— This Will Hold (@This_Will_Hold) June 8, 2025
He followed up with another post observing that “Data centers in space looking pretty appealing right now,” a pointed nod to possible regulatory and infrastructure challenges for data-center projects in Texas under the new Democratic leadership.
Critics quickly highlighted the scale of the spending relative to the outcome. One reply noted that Musk had “dropped half a fucking BILLION on this shit and got dog walked,” underscoring the disconnect between financial outlay and electoral returns. Musk later shared a vintage-style “technical difficulties” image, extending the humorous tone.
The posts arrived as markets reacted: shares of Tesla and SpaceX-related entities dipped in premarket trading amid concerns over heightened scrutiny and shifting state-level politics. Democrats had previously signaled plans to examine Musk’s government ties, DOGE involvement, and business conflicts if they regained congressional majorities.
Musk’s response stands out for its light touch amid high-stakes political setbacks. Rather than offering a detailed defense of his spending or a sober analysis of voter sentiment, he chose sarcasm—consistent with his long-standing style of public communication.
Whether the comments signal a retreat from large-scale political donations ahead of 2028 or simply a momentary shrug remains unclear, but they captured the attention of millions in the immediate aftermath of election night.
Musk’s Tesla and SpaceX decline after Democratic Midterm sweep
Tesla registrations in Germany nearly quadruple in October
