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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 taps Samsung for 5G modems amid plans of Robotaxi ramp: report
The move signals Tesla’s growing focus on supply-chain diversification and next-generation communications as it prepares to scale its autonomous driving and robotaxi operations.
A report from South Korea has suggested that Samsung Electronics is set to begin supplying 5G automotive modems to Tesla. If accurate, this would mark a major expansion of the two companies’ partnership beyond AI chips and into vehicle connectivity.
The move signals Tesla’s growing focus on supply-chain diversification and next-generation communications as it prepares to scale its autonomous driving and Robotaxi operations.
Samsung’s 5G modem
As per industry sources cited by TheElec, Samsung’s System LSI division has completed development of a dedicated automotive-grade 5G modem for Tesla. The 5G modem is reportedly in its testing phase. Initial supply is expected to begin in the first half of this year, with the first deployments planned for Tesla’s Robotaxi fleet in Texas. A wider rollout to consumer vehicles is expected to follow.
Development of the modem began in early 2024 and it required a separate engineering process from Samsung’s smartphone modems. Automotive modems must meet stricter durability standards, including resistance to extreme temperatures and vibration, along with reliability over a service life exceeding 10 years. Samsung will handle chip design internally, while a partner company would reportedly manage module integration.
The deal represents the first time Samsung has supplied Tesla with a 5G vehicle modem. Tesla has historically relied on Qualcomm for automotive connectivity, but the new agreement suggests that the electric vehicle maker may be putting in some serious effort into diversifying its suppliers as connectivity becomes more critical to autonomous driving.
Deepening Tesla–Samsung ties
The modem supply builds on a rapidly expanding relationship between the two companies. Tesla previously selected Samsung’s foundry business to manufacture its next-generation AI6 chips, a deal valued at more than 22.7 trillion won and announced in mid-2025. Together, the AI chip and 5G modem agreements position Samsung as a key semiconductor partner for Tesla’s future vehicle platforms.
Industry observers have stated that the collaboration aligns with Tesla’s broader effort to reduce reliance on Chinese and Taiwanese suppliers. Geopolitical risk and long-term supply stability are believed to be driving the shift in no small part, particularly as Tesla prepares for large-scale Robotaxi deployment.
Stable, high-speed connectivity is essential for Tesla’s Full Self-Driving system, supporting real-time mapping, fleet management, and continuous software updates. By pairing in-vehicle AI computing with a new 5G modem supplier, Tesla appears to be tightening control over both its hardware stack and its global supply chain.
Tesla’s new Full Self-Driving pricing strategy will eliminate one recurring complaint that many owners have had in the past: FSD transfers.
In the past, if a Tesla owner purchased the Full Self-Driving suite outright, the company did not allow them to transfer the purchase to a new vehicle, essentially requiring them to buy it all over again, which could obviously get pretty pricey.
This was until Q3 2023, when Tesla allowed a one-time amnesty to transfer Full Self-Driving to a new vehicle, and then again last year.
Tesla is now allowing it to happen again ahead of the February 14th deadline.
The program has given people the opportunity to upgrade to new vehicles with newer Hardware and AI versions, especially those with Hardware 3 who wish to transfer to AI4, without feeling the drastic cost impact of having to buy the $8,000 suite outright on several occasions.
Now, that issue will never be presented again.
Last night, Tesla CEO Elon Musk announced on X that the Full Self-Driving suite would only be available in a subscription platform, which is the other purchase option it currently offers for FSD use, priced at just $99 per month.
Tesla is shifting FSD to a subscription-only model, confirms Elon Musk
Having it available in a subscription-only platform boasts several advantages, including the potential for a tiered system that would potentially offer less expensive options, a pay-per-mile platform, and even coupling the program with other benefits, like Supercharging and vehicle protection programs.
While none of that is confirmed and is purely speculative, the one thing that does appear to be a major advantage is that this will completely eliminate any questions about transferring the Full Self-Driving suite to a new vehicle. This has been a particular point of contention for owners, and it is now completely eliminated, as everyone, apart from those who have purchased the suite on their current vehicle.
Now, everyone will pay month-to-month, and it could make things much easier for those who want to try the suite, justifying it from a financial perspective.
The important thing to note is that Tesla would benefit from a higher take rate, as more drivers using it would result in more data, which would help the company reach its recently-revealed 10 billion-mile threshold to reach an Unsupervised level. It does not cost Tesla anything to run FSD, only to develop it. If it could slice the price significantly, more people would buy it, and more data would be made available.
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Tesla Model 3 and Model Y dominates U.S. EV market in 2025
The figures were detailed in Kelley Blue Book’s Q4 2025 U.S. Electric Vehicle Sales Report.
Tesla’s Model 3 and Model Y continued to overwhelmingly dominate the United States’ electric vehicle market in 2025. New sales data showed that Tesla’s two mass market cars maintained a commanding segment share, with the Model 3 posting year-to-date growth and the Model Y remaining resilient despite factory shutdowns tied to its refresh.
The figures were detailed in Kelley Blue Book’s Q4 2025 U.S. Electric Vehicle Sales Report.
Model 3 and Model Y are still dominant
According to the report, Tesla delivered an estimated 192,440 Model 3 sedans in the United States in 2025, representing a 1.3% year-to-date increase compared to 2024. The Model 3 alone accounted for 15.9% of all U.S. EV sales, making it one of the highest-volume electric vehicles in the country.
The Model Y was even more dominant. U.S. deliveries of the all-electric crossover reached 357,528 units in 2025, a 4.0% year-to-date decline from the prior year. It should be noted, however, that the drop came during a year that included production shutdowns at Tesla’s Fremont Factory and Gigafactory Texas as the company transitioned to the new Model Y. Even with those disruptions, the Model Y captured an overwhelming 39.5% share of the market, far surpassing any single competitor.
Combined, the Model 3 and Model Y represented more than half of all EVs sold in the United States during 2025, highlighting Tesla’s iron grip on the country’s mass-market EV segment.
Tesla’s challenges in 2025
Tesla’s sustained performance came amid a year of elevated public and political controversy surrounding Elon Musk, whose political activities in the first half of the year ended up fueling a narrative that the CEO’s actions are damaging the automaker’s consumer appeal. However, U.S. sales data suggest that demand for Tesla’s core vehicles has remained remarkably resilient.
Based on Kelley Blue Book’s Q4 2025 U.S. Electric Vehicle Sales Report, Tesla’s most expensive offerings such as the Tesla Cybertruck, Model S, and Model X, all saw steep declines in 2025. This suggests that mainstream EV buyers might have had a price issue with Tesla’s more expensive offerings, not an Elon Musk issue.
Ultimately, despite broader EV market softness, with total U.S. EV sales slipping about 2% year-to-date, Tesla still accounted for 58.9% of all EV deliveries in 2025, according to the report. This means that out of every ten EVs sold in the United States in 2025, more than half of them were Teslas.
Tesla taps Samsung for 5G modems amid plans of Robotaxi ramp: report
Tesla Full Self-Driving pricing strategy eliminates one recurring complaint
