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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 just raised Model Y prices for the first time in two years, with the largest increase being $1,000.
The move signals shifting dynamics in the competitive electric vehicle market as the company continues to work on balancing demand, profitability, and accessibility.
The new pricing affects premium trims while leaving entry-level options unchanged. The Model Y Premium Rear-Wheel Drive (RWD) now starts at $45,990, a $1,000 increase.
The Model Y Premium All-Wheel Drive (AWD)—previously referred to in the post as simply “Model Y AWD”—rises to $49,990, also up $1,000. The top-tier Model Y Performance sees a more modest $500 bump, bringing its starting price to $57,990.
Tesla Model Y prices just went up:
New prices:
🚗 Model Y Premium RWD: $45,990 – up $1,000
🚗 Model Y AWD: $49,990 – up $1,000
🚗 Model Y Performance: $57,990 – up $500 https://t.co/e4GhQ0tj4H pic.twitter.com/TCWqr3oqiV— TESLARATI (@Teslarati) May 16, 2026
Base models remain untouched to preserve affordability. The entry-level Model Y RWD holds steady at $39,990, and the base Model Y AWD stays at $41,990. This selective approach keeps the crossover accessible for budget-conscious buyers while extracting more revenue from higher-margin configurations.
After years of aggressive price cuts to stimulate volume amid slowing EV adoption and rising competition from rivals like BYD, Ford, and GM, Tesla appears confident in underlying demand. Recent lineup refreshes for the 2026 Model Y, including refreshed styling and efficiency gains, have helped maintain its status as America’s best-selling EV.
By protecting base prices, Tesla avoids alienating price-sensitive customers while improving margins on the more popular variants.
Tesla Model Y ownership review after six months: What I love and what I don’t
For consumers, the changes are relatively modest—under 3% on affected trims—and still position the Model Y competitively against gas-powered SUVs in the same class. Federal tax credits and potential state incentives may further offset costs for eligible buyers.
This marks a subtle but notable shift from the deep discounting era that defined much of 2024 and 2025. As the EV market matures into 2026, Tesla’s pricing strategy will be closely watched for clues about production ramps, new variants like the rumored longer-wheelbase Model Y, and broader profitability goals.
In short, today’s adjustment reflects a company that remains dominant yet pragmatic—willing to test higher pricing where demand supports it. It is unlikely to deter consumers from choosing other options.
Elon Musk cannot be fired from SpaceX, and there’s a reason for that.
In a blunt post on X on Friday, Elon Musk confirmed plans to structurally shield his leadership at SpaceX, ensuring he cannot be fired while tying a potential trillion-dollar compensation package to the company’s long-term goal of establishing a self-sustaining colony on Mars.
Yes, I need to make sure SpaceX stays focused on making life multiplanetary and extending consciousness to the stars, not pandering to someone’s bullshit quarterly earnings bonus!
Obviously, IF SpaceX succeeds in this absurdly difficult goal, it will be worth many orders of…
— Elon Musk (@elonmusk) May 15, 2026
The revelation stems from a Financial Times report detailing SpaceX’s intention to restructure its governance and compensation framework. The moves are designed to protect Musk’s control and align his incentives with the company’s founding mission rather than short-term financial pressures. Musk’s reply left no ambiguity:
“Yes, I need to make sure SpaceX stays focused on making life multiplanetary and extending consciousness to the stars, not pandering to someone’s bullshit quarterly earnings bonus!”
He added that success in this “absurdly difficult goal” would generate value “many orders of magnitude more than the economy of Earth,” though he cautioned that the journey will not be smooth. “Don’t expect entirely smooth sailing along the way,” Musk wrote.
The strategy reflects Musk’s deep concerns about how public-market expectations could derail SpaceX’s core objective. Founded in 2002, SpaceX has repeatedly stated its purpose is to reduce the cost of space travel and ultimately make humanity a multiplanetary species.
Unlike Tesla, which went public in 2010 and has faced repeated battles over Musk’s compensation and board influence, SpaceX remains privately held. Musk has long resisted taking the rocket company public precisely to avoid the quarterly earnings treadmill that forces most CEOs to prioritize short-term stock performance over ambitious, high-risk projects.
By embedding protections against his removal and linking any outsized pay package to verifiable milestones—such as a functioning Mars colony—SpaceX aims to insulate its leadership from activist investors or board members who might demand faster profits or safer bets.
Musk has referenced past experiences, including his ouster from OpenAI and shareholder lawsuits at Tesla, as cautionary tales. In those cases, he argued, external pressures risked diluting the original vision.
Critics may view the arrangement as excessive, especially given Musk’s already substantial voting power and wealth. Supporters, however, argue it is a necessary safeguard for a company pursuing goals measured in decades rather than quarters. Achieving a Mars colony would require sustained investment in Starship development, orbital refueling, life-support systems, and in-situ resource utilization—technologies that may deliver no immediate financial return.
Musk’s post underscores a broader philosophical point: true breakthrough innovation often demands tolerance for volatility and a willingness to ignore conventional business wisdom. As SpaceX prepares for increasingly ambitious Starship test flights and eventual crewed missions, the new governance structure signals that the company’s North Star remains unchanged—humanity’s expansion beyond Earth.
Whether the trillion-dollar package materializes depends on execution, but Musk’s message is clear: SpaceX exists to reach the stars, not to chase the next earnings beat. For investors or employees who share that vision, the protections are not a perk—they are a prerequisite for success.
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Tesla discloses two Robotaxi crashes to NHTSA
Newly unredacted data filed with the National Highway Traffic Safety Administration (NHTSA) reveals the two incidents.
Tesla has disclosed information on two low-speed crashes that occurred in Austin with its Robotaxi platform. These incidents occurred with teleoperators steering the vehicle, and there were no passengers in the car at the time they happened.
Newly unredacted data filed with the National Highway Traffic Safety Administration (NHTSA) reveals the two incidents.
The first crash took place in July 2025, shortly after Tesla launched its nascent Robotaxi network in Austin. The ADS reportedly struggled to move forward while stopped on a street. A teleoperator assumed control, gradually accelerating and turning left toward the roadside. The vehicle then mounted the curb and struck a metal fence.
In the second incident, in January 2026, the ADS was traveling straight when the safety monitor requested navigation support. The teleoperator took over from a stop, continued forward, and collided with a temporary construction barricade at approximately 9 mph, scraping the front-left fender and tire.
Tesla Robotaxi service in Austin achieves monumental new accomplishment
Tesla has previously told lawmakers that teleoperators are authorized to pilot vehicles remotely—but only at speeds below 10 mph, as the only maneuvers they were approved to perform were repositioning in awkward areas.
“This capability enables Tesla to promptly move a vehicle that may be in a compromising position, thereby mitigating the need to wait for a first responder or Tesla field representative to manually recover the vehicle,” the company stated in filings earlier this year.
Before this week, Tesla redacted the NHTSA reports, but they decided to reveal all 17 Robotaxi incidents recorded since the launch in Austin last Summer. Most of the other crashes involved the Tesla being struck by other road users and were not caused by the self-driving suite itself.
There were other incidents, including two additional self-caused accidents involving the ADS clipping side mirrors on parked cars. In September 2025, one Robotaxi struck a dog that darted into the roadway (the dog escaped unharmed), while another made an unprotected left turn into a parking lot and hit a metal chain.
Although Waymo and Zoox have reported more total crashes, Tesla operates at a far smaller scale. The cautious pace reflects the company’s broader safety concerns; it has been very slow with the Robotaxi rollout to ensure the suite is ready for operation.
Last month, CEO Elon Musk acknowledged that “making sure things are completely safe” remains the primary bottleneck to expanding the network, describing the company’s approach as “very cautious.”
The unredacted filings arrive amid heightened regulatory scrutiny of autonomous vehicles. NHTSA recently closed a separate probe into Tesla’s Full Self-Driving software repeatedly striking parking-lot obstacles such as bollards and chains—a problem that also prompted a recall at Waymo last year.
Tesla Robotaxi has been a widely successful program in its early days of operation, and the transparency Tesla brings here is greatly appreciated. Incidents will happen, of course, but the honesty gives customers and regulators a sense of where Tesla is in terms of developing its self-driving and fully autonomous ride-hailing suite.
Tesla Model Y prices just went up for the first time in two years
Elon Musk explains why he cannot be fired from SpaceX
