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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.
A new report claims that Apple is in the process of developing what would be the missing link for Tesla to get CarPlay.
Apple and Tesla have been reportedly working together for some time to give Tesla owners the opportunity to utilize CarPlay within their vehicles. While many owners are more than happy with Tesla’s in-house UI, which is seamless, effective, and smooth, some still want CarPlay, which does have its advantages.
A report from 9to5Mac now states that a new CarPlay technology that was highlighted during the Worldwide Developers Conference (WWDC) would potentially be the bridge between Tesla and Apple. With the addition of a feature known as “Route Sharing,” which gives a navigation app the ability to share routing data with the vehicle, Tesla would be able to launch CarPlay in its vehicles, the report states.
CarPlay has not been a priority for Tesla because it has done extremely well with its in-house UI, but some drivers are just used to it. Additionally, it could improve Tesla’s subpar Navigation or offer improved app capabilities, especially with iMessage.
Route Sharing is an intended addition to CarPlay’s iteration in iOS 26.4, which was released in March:
The addition of CarPlay would undoubtedly be welcome, but at the same time, it seems like Tesla realizes it is not of the utmost priority. There are so many things that Tesla is working on currently within its own vehicles, especially attempting to solve self-driving.
Back in February, Bloomberg had reported that Tesla was still working on bringing CarPlay to its vehicles, but it had not due to app compatibility issues and incredibly low adoption rates of iOS 26.
This bottleneck could buy Tesla the proper amount of time to develop CarPlay for its vehicles. It would be a welcome addition, and could be brought on with either the Summer or Fall 2026 Software Updates.
Tesla deliveries got a big boost in expectations from Wall Street firm Goldman Sachs, who believes the company will report some stronger-than-expected numbers when the second quarter comes to an end in the coming weeks.
Goldman Sachs has raised its vehicle delivery forecast for Tesla (NASDAQ: TSLA) in the second quarter of 2026, signaling growing confidence in the electric vehicle leader’s near-term momentum despite mixed market signals. Analyst Mark Delaney lifted the bank’s Q2 estimate to 420,000 units from a previous 405,000, surpassing the Visible Alpha consensus estimate of 400,000.
The upward revision stems from stronger-than-expected sales data across key regions. Europe stands out with projected year-over-year growth of 85-90 percent, driven by robust demand for Tesla’s Model Y and refreshed offerings. China posted high single-digit gains, while markets like South Korea and Australia also contributed positive momentum. These gains help offset mid-teens declines in U.S. deliveries through May, where broader EV market headwinds and competition persist.
Goldman extended its optimism to the full year, increasing its 2026 delivery projection to 1.73 million vehicles from 1.72 million. Longer-term forecasts remain unchanged, with 1.88 million units expected in 2027 and 1.96 million in 2028. The bank also nudged its 2026 earnings-per-share estimate higher to $1.35 from $1.30, reflecting anticipated margin benefits from higher volumes and operational efficiencies.
Despite these positive adjustments, Goldman maintained its Neutral rating and $375 price target on Tesla shares. At current trading levels near $411, the stock sits about 8-9 percent above the target, highlighting ongoing valuation concerns even as delivery momentum builds. Tesla’s Q1 2026 deliveries totaled 358,023 units, setting a baseline for recovery expectations in the current period.
This update arrives as Tesla prepares to report official Q2 figures shortly after June 30. Investors and analysts will closely watch not only headline delivery numbers but also regional breakdowns, average selling prices, and progress on energy storage deployments and autonomous technology initiatives.
The move by Goldman Sachs underscores a broader narrative for Tesla: while legacy auto markets face softening demand and tariff uncertainties, Tesla’s global footprint and product pipeline provide resilience. Europe’s surge reflects pent-up demand and policy support for EVs, while China’s steady growth highlights Tesla’s competitive positioning against local rivals.
Tesla still has its work cut out for it, including U.S. price sensitivity and intensifying competition. Yet Goldman’s revision adds to a series of analyst notes suggesting Q2 could mark a turning point. As Tesla pushes toward higher production rates at facilities in Fremont, Shanghai, and Berlin, sustained execution will be key to validating these higher forecasts.
We have said numerous times that deliveries are becoming a less important metric in the grand scheme of things, as AI truly takes precedence in the company’s thesis.
For Tesla bulls, the Goldman note reinforces faith in underlying demand trends. For skeptics, the unchanged rating serves as a reminder that delivery beats alone may not immediately resolve valuation debates in a high-interest-rate environment. Tesla’s stock reaction will likely hinge on the official numbers and management commentary in the coming weeks.
SpaceX has exercised its option to acquire Cursor, the innovative AI coding company, in an all-stock transaction valued at $60 billion. The deal, announced on June 16, marks a significant step in SpaceX’s expansion into advanced artificial intelligence, building on months of close collaboration between the companies.
Cursor, officially operated by Anysphere, Inc., is an AI-native code editor and coding agent designed to transform software development. Founded in 2022 by a group of MIT graduates in San Francisco, Cursor builds on the familiar foundation of Visual Studio Code but integrates powerful AI capabilities directly into the core experience.
Unlike traditional code editors or simple extensions, Cursor functions as a full “coding agent” that turns natural-language instructions into actionable code.
SpaceX has exercised the option to acquire @cursor_ai in an all-stock transaction with the goal of building the world’s most useful AI models.
For the past few months, SpaceXAI has been jointly training a model with Cursor, which will be released in Cursor and Grok Build soon.… https://t.co/X5mepgXgjJ
— SpaceX (@SpaceX) June 16, 2026
Developers interact with Cursor through features like its Composer agent, which can search entire codebases, edit multiple files, run terminal commands, debug issues, and complete complex multi-step programming tasks autonomously.
Users describe high-level goals, such as “build a scalable API endpoint with authentication,” and the AI plans, implements, tests, and refines the solution while the human oversees decisions. Additional tools include advanced autocomplete (Tab), context-aware chat, and infrastructure for handling billions of daily requests.
The platform has gained considerable traction, surpassing $3 billion in annual recurring revenue by early 2026 and earning adoption by over half of the Fortune 500 companies. Its agentic approach accelerates development dramatically, allowing engineers to focus on architecture and creativity rather than repetitive coding.
The acquisition integrates Cursor’s leading product, expert team of roughly 300 engineers, and distribution network among top software developers with SpaceX’s unparalleled computational resources. SpaceX’s Colossus supercomputer, equivalent to a million H100 GPUs, has already powered joint training of next-generation models. These models are expected to launch soon within Cursor and SpaceX’s Grok Build environment.
This combination positions SpaceX to develop the world’s most capable AI systems for coding and knowledge work. Access to Cursor’s real-world usage data from millions of professional developers provides unparalleled feedback loops for model improvement. Training on Colossus enables rapid iteration on massive datasets, potentially creating AI that outperforms current leaders in reliability, context handling, and complex reasoning.
For SpaceX, the benefits extend far beyond software tools. Rocket engineering, satellite constellation management, autonomous flight systems, and Starship development involve millions of lines of highly specialized, safety-critical code.
Cursor’s AI agents, supercharged by proprietary models trained on SpaceX’s domain expertise, could slash development timelines, reduce errors, and enable faster innovation cycles. This vertical integration of AI tooling strengthens SpaceX’s competitive edge in both aerospace and the broader AI race, complementing its xAI initiatives.
The deal reflects the exploding value of AI-native developer platforms. By owning Cursor outright, SpaceX secures a strategic talent pool and product pipeline that will accelerate internal projects while potentially offering enhanced tools to the wider engineering community. As AI continues reshaping software creation, this acquisition underscores SpaceX’s commitment to leveraging cutting-edge technology for ambitious goals, from Mars colonization to global connectivity.
Apple is developing the missing link for Tesla to get CarPlay: report
Tesla deliveries get a big boost in expectations from Wall Street
