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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 launches first ‘true’ East Coast V4 Supercharger: here’s what that means
What truly distinguishes this installation from the hundreds of “V4” stalls already scattered across the network? Most existing V4 dispensers, rolled out since 2023, feature welcome upgrades like longer cables, built-in touchscreen displays, integrated credit-card readers for non-Tesla users, and improved ergonomics.
Tesla has launched its first “true” V4 Supercharger on the East Coast, and while that may be sort of confusing, here’s what we mean by that.
Tesla has opened its first true V4 Supercharging station on the East Coast in Kissimmee, Florida, just south of Orlando.
The eight-stall site, powered by an advanced 1.2 MW V4 power cabinet, is capable of delivering up to 500 kW, making it one of only four fully operational 500 kW-capable V4 stations in the United States.
Pricing is dynamic and competitive, as Tesla owners pay $0.40 per kWh during peak hours (8 a.m. to midnight), dropping to an attractive $0.20/kWh off-peak (midnight to 8 a.m.).
Non-Tesla EVs, which can now plug directly into the NACS ports thanks to the open standard, are charged a premium—$0.56/kWh peak and $0.28/kWh off-peak—reflecting Tesla’s strategy to monetize network access while rewarding its own customers.
What’s Makes This a “True” V4 Supercharger
What truly distinguishes this installation from the hundreds of “V4” stalls already scattered across the network? Most existing V4 dispensers, rolled out since 2023, feature welcome upgrades like longer cables, built-in touchscreen displays, integrated credit-card readers for non-Tesla users, and improved ergonomics.
However, nearly all of these have been paired with legacy V3 power cabinets. These hybrid setups, sometimes informally called V3.5, deliver charging curves virtually identical to standard V3 stations, typically topping out at 250-325 kW depending on the vehicle and site conditions.
In contrast, Kissimmee’s true V4 architecture incorporates next-generation 1.2 MW power cabinets. These support battery voltages up to 1,000 V (double the 500 V of V3 systems) and can push up to 500 kW per stall.
NEWS: Tesla has opened its first true V4 Supercharging station on the East Coast, capable of delivering up to 500 kW charging speeds.
• Location: Kissimmee, Florida (near Orlando)
• 8 charging stalls
• Fees for Tesla owners: $0.40/kWh ($0.20/kWh off-peak)
• Fees for all… pic.twitter.com/E8AkaibWsC— Sawyer Merritt (@SawyerMerritt) March 19, 2026
One compact cabinet efficiently powers all eight stalls, slashing the physical footprint and reportedly keeping deployment costs under $40,000 per stall, far cheaper than earlier designs.
Right now, the primary beneficiary is the Cybertruck, which can achieve dramatically faster charging at low states of charge.
Everyday models like the Model 3 and Model Y see little immediate difference in peak speeds, but the hardware lays the groundwork for future vehicles with higher-voltage batteries.
Tesla launches faster Cybertruck charging at all V4 Superchargers
This milestone signals Tesla’s accelerating push toward a high-power, future-proof Supercharger network.
As true V4 sites multiply, charging times will shrink, grid efficiency will improve, and the entire EV ecosystem, Tesla and non-Tesla alike, will benefit from the infrastructure lead Tesla continues to expand. For drivers in central Florida, the Kissimmee station is more than just another charging stop; it’s a glimpse of the faster, smarter charging era that’s finally arriving.
Elon Musk
Tesla reveals various improvements to the Semi in new piece with Jay Leno
Tesla Chief Designer Franz von Holzhausen and Semi Program Director Dan Priestley joined Leno in a 47-minute segment revealing all of the various things it did to make the Semi even better as it heads toward volume production this year.
Tesla has revealed the various improvements it has made to the Semi with its redesign, which was unveiled late last year, on a new episode of Jay Leno’s Garage.
Tesla Chief Designer Franz von Holzhausen and Semi Program Director Dan Priestley joined Leno in a 47-minute segment revealing all of the various things it did to make the Semi even better as it heads toward volume production this year.
Last year, Tesla revealed it had updated the Semi design to fit the bill of its aesthetic, which, on its other vehicles, includes things like lightbars and a sleeker and more aerodynamic design. The changes were not all to appease the eye, but the drivers who will use the Semi on a daily basis to haul goods regionally as the program gets off the ground running.
Weight Reduction
Priestley revealed almost immediately that Tesla was able to cut out about 1,000 pounds of weight from the Semi compared to the previous version.
This does several things, all of which are positive to the mission of a Class 8 truck, which is to haul goods and obtain more efficient travel to cut down on logistics costs.
Initially, this can increase payload capacity, which is often the biggest value driver for fleets that frequently hit gross vehicle weight limits. Tesla’s early Pilot Program members, like PepsiCo. and Frito-Lay, are large-scale companies. They will benefit from a decreased overall weight.
Lighter vehicles also require less energy to accelerate, climb hills, and maintain highway speeds. This new design has that advantage, and as Leno said in his first drive with the Semi as he hauled another unit behind, “I don’t feel like I’m pulling anything.”
Drag Coefficient
Franz said one of the goals of the Semi was to get the drag coefficient down below that of a Bugatti Veyron. This would increase efficiency tremendously, a major need with a large truck like a Semi.
Drag coefficient is extremely valuable when it comes to electric vehicles, because the displacement of air is incredibly important for range ratings.
Franz said aerodynamic efficiency has been improved by 7 percent compared to the last model. He says the coefficient is around 0.4.
New Features and Improvements
Priestley shed some additional light on the Semi and some of the improvements the company has made under the hood.
These include:
- Fully Electric Steering Assist
- Cybertruck actuators are being used for more strength
- Tesla included a 48-volt architecture
- Semi will utilize 4680 battery cells, which are designed to last 1 million miles
These changes come after Tesla rolled out the Semi to various companies for its Pilot Program, which yielded tremendous results. Due to the years it has been working with those companies, it knew what things it had to change and what it had to improve upon before selling the Semi openly.
Fleet Data
The fleet data Tesla has gathered from the Pilot Program has been one of the most widely discussed parts of the Semi program.
Franz and Priestley said that there are currently a few hundred Semi units in the real world, and Tesla has gathered 13.5 million miles. One of those units has traveled over 440,000 miles in the years it has been on the road.
Tesla Semi’s latest adoptee will likely encourage more of the same
Pilot Program members have reported an uptime of 95 percent, and Tesla’s maintenance and Service teams have kept things running:
“80% of breakdowns if you have one, are returned back to the customer in less than 24 hours, and half are back in less than 1 hour.”
Demand
Priestley says demand for the Semi has never been higher, and due to the recent political climate and the impact things have had on gas prices, Tesla has never received more inquiries for the Semi than it has recently.
Many companies will be surprised to hear that the Semi Pilot Program has been an overwhelming success. As Tesla begins to build out the infrastructure for the vehicle, it will only benefit the all-electric Class 8 trucks that keep things moving.
CEO Elon Musk said Tesla plans to start high-volume production this year. The company also plans to start deliveries this year.
News
Tesla launches amazing new feature for shared vehicles
Tesla has quietly introduced one of its most practical software features yet in update 2026.8: real-time visibility of the active driver profile directly in the Tesla mobile app. Available under the Security & Drivers section, this new tool lets owners see exactly who is behind the wheel or who last drove the vehicle.
Tesla is launching an amazing new feature for shared vehicles, giving owners more transparency when they choose to have a Tesla ownership experience with another driver.
This is one of the many advantages of having a Tesla. New features are constantly rolled out through software updates and Over-the-Air fixes, which download directly to the car with an internet connection.
Tesla has quietly introduced one of its most practical software features yet in update 2026.8: real-time visibility of the active driver profile directly in the Tesla mobile app. Available under the Security & Drivers section, this new tool lets owners see exactly who is behind the wheel or who last drove the vehicle.
The feature works seamlessly. While the car is driving, the app displays the name of the currently selected driver profile in real time.
When the vehicle is parked or asleep, it shows the last active profile.
Requiring both the 2026.8 vehicle software and the latest Tesla app, the update brings this capability to every model in the lineup, including legacy Model S and Model X vehicles, which are unfortunately being phased out of the company lineup later this year.
Tesla makes latest move to remove Model S and Model X from its lineup
The feature was first reported on by Not a Tesla App.
Tesla driver profiles have always excelled at personalization, automatically adjusting seat positions, mirrors, steering wheel height, climate settings, navigation recents and favorites, and media preferences.
These profiles link to specific phone keys for automatic activation and support PIN protection for privacy and security. Restricted profiles for teens can also limit speed or features.
This feature shines brightest in single-car households with multiple drivers. Families, couples, and roommates frequently share one Tesla, leading to constant adjustments and questions about settings. Now, a quick app check reveals the current profile, allowing users to anticipate seat configurations or confirm usage without entering the vehicle.
Tesla’s cloud-synced driver profiles to bring custom settings across multiple cars
Parents particularly benefit: they can verify that teens are driving under their assigned (and possibly restricted) profiles, adding a layer of safety oversight and peace of mind. Teslas are already so incredibly safe that many parents dream of putting their kids in one.
Two kids around the same age could now share a Tesla, and this feature would make that effort, which is likely to be a difficult one at times, more seamless.
Beyond convenience, it promotes accountability and reduces everyday friction. No more manual profile switching or arguments over mirror positions. Before approaching the car, anyone can check the app and know exactly what to expect, no more wasted minutes readjusting everything.
In multi-driver setups, it transforms the shared EV into a truly intelligent, user-aware machine that respects individual preferences while keeping the primary owner informed.
Tesla’s commitment to over-the-air updates continues to enhance ownership value years after purchase.
This small but significant addition highlights how software can solve real-world problems in multi-user environments, making Tesla vehicles more family-friendly and practical than ever. For the millions of owners sharing a single car, the 2026.8 update delivers transparency, time savings, enhanced safety, and effortless personalization. It is a great new feature that is rolling out to vehicles now.
Tesla launches first ‘true’ East Coast V4 Supercharger: here’s what that means
Tesla reveals various improvements to the Semi in new piece with Jay Leno
