News
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”.
- Starhopper and SpaceX’s spartan assembly facilities are pictured here, showing the inside of the aft section and a completed tank dome. (Austin Barnard)
- 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.
- Starship’s first full-scale prototype is being rapidly assembled in South Texas. (NASASpaceflight – bocachicagal)
- Starship’s first full-scale prototype is being rapidly assembled in South Texas. (NASASpaceflight – bocachicagal)
- Meanwhile, giant 9m-diameter tank domes are being assembled and welded together a few hundred feet away from Starhopper. (NSF – bocachicagal)
- SpaceX’s Starhopper seen in a January render and a January photo. (SpaceX/Elon Musk)
- BFS seen standing vertically on the pads of its tripod fins. (SpaceX)
- 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.

News
Tesla Theater might be getting plenty more streaming platforms
The in-car Tesla Theater is among the most unique features available within the cars. When charging, parked, camping, or just hanging out, vehicle occupants can access a variety of streaming platforms on the large center screen, helping keep them entertained during downtime.
However, the Theater might be getting plenty more streaming platforms, something that owners have requested for some time.
Tesla owners recently discovered that visiting Apple TV in the vehicle browser can launch a fullscreen interface that looks and behaves like a dedicated application rather than an ordinary webpage:
Today I learned that if you go to Apple TV in the Tesla browser, it will open up an actual Apple TV app, fully functional. Not just the site.
Apparently there are more apps than just the few that show on the apps page. pic.twitter.com/os1Ypfm4JR
— Jason W (@jmwilt21) August 20, 2026
The experience drops the usual address bar and browser chrome, presenting catalogs, continue watching rows, and playback controls in the same window Tesla Theater already uses for its listed services. Independent testers soon found similar treatment for HBO Max, Paramount+, Peacock, Disney+, and Prime Video when those sites are opened from the car browser.
This shift is a plausible early signal that Tesla is widening Theater support without a formal software note. Theater has long been a set of web views rather than native applications, so recognizing extra domains and stripping the browser frame is a small server-side change that can expand the catalog quickly.
Owners still lack permanent Theater icons for the newly recognized services, and video remains limited to Park, yet the smoother launch is a meaningful step toward a broader lounge while charging.
Tesla Theater arrived with software version 10 in September 2019. The first video services were Netflix, YouTube, and Hulu, available only while parked and originally tied to WiFi. Spotify arrived in the same era as music rather than Theater video. Disney+ joined officially in July 2021 with the 2021.24 update, giving owners another major catalog on the center screen. Twitch and TikTok later appeared among the default Theater tiles, and Tesla Tutorials remained a persistent educational tile.
Not every addition stayed put. In December 2023, a Holiday software build removed the Disney+ tile for many United States owners after a public dispute involving advertising on X. Hulu stayed visible even though Disney owned it. Visiting disneyplus.com in the browser often restored the tile, which suggested the removal was a recognition list change rather than a complete block. Owners have also reported occasional blank Theater grids after updates, usually fixed by language toggles, resets, or later firmware.
Tesla axes Disney+ from vehicles with Musk-Iger rivalry, but there’s a workaround
Code archives from 2024 listed many unused source names, including Apple TV and Prime Video, that never became official icons, which now looks like groundwork for the current fullscreen browser behavior.
Now that this hint toward an expanded Theater experience has been recognized, Tesla could follow through with these additional shortcuts as a sign that more streaming platforms are available in Teslas than ever before.
News
Tesla Semi’s biggest adoptee gives an update on production timeline
Tesla recently received its largest order for the all-electric Semi from Einride, a Swedish transport service, for 500 units, a groundbreaking invoice to receive before the first deliveries begin.
Even more remarkable, Einride CEO Roozbeh Charli said in a recent interview that he expects his company to take delivery of all 500 — the entire order — before the end of 2027. He even expects to have 75 Tesla Semi units in the Einride fleet before the end of this year.
🚨 Einride CEO Roozbeh Charli on the Tesla Semi partnership:
“If we start with the Amazon announcement that we did earlier this year, that was on the back of having gone through a proving period together with them and proving out our technology. Then we took that next step in… pic.twitter.com/oazkXjwoig
— TESLARATI (@Teslarati) August 28, 2026
Charli said the Tesla partnership was part of a broader push, along with its earlier partnership with Amazon. Einride is assisting Amazon with the use of its Saga AI platform, which helps eliminate questions about budgeting and forecasting for logistics companies.
The Semi, as well as Tesla’s production and subsequent delivery of the units to Einride, will help the company “to have a good supply of vehicles that we can deploy on the [Saga AI] platform,” Charli said. “Tesla is also a relationship we’ve had for a while, and as the Tesla Semi deliveries are firming up, we decided to do a larger commitment to that and deploy that on our platform.”
In its initial announcement, Einride said it anticipated taking delivery of the trucks over the next two years, but now it appears the company is expecting all 500 units within the next 16 months.
Built at a dedicated factory in Sparks, Nevada, the Tesla Semi has been perhaps the biggest and most intensive testing process the company has ever had for a single vehicle model. For the past several years, Tesla has been working with many companies, most notably Frito-Lay and PepsiCo, to gain knowledge on the performance on regional routes.
Tesla plans to launch the Semi officially on September 24, five months after production started ramping.
Additionally, drivers have said they are happy about the Semi’s performance and that its numerous safety and productivity features have made their jobs and routes much easier.
News
Tesla Cybercab uses a unique strategy for picking up the right rider
Tesla Cybercab is using a unique strategy for picking up the correct rider, which is a crucial part of ride-hailing to ensure people end up in the right place and are charged the correct price.
Cybercab will utilize an RGB strip in its front light bar that will illuminate in a variety of different colors to mark itself.
This identifying mark will also appear in the Robotaxi app, giving riders in the same location a notable distinction in an effort to avoid any confusion regarding who should get in each vehicle.
🚨 Tesla is using different light bar colors to help riders understand which vehicle is theirs
Pretty cool strategy pic.twitter.com/eGMpEMeRpc
— TESLARATI (@Teslarati) August 27, 2026
Other ride-hailing services use similar strategies: Lyft and Uber rides are recognizable through driver identity, vehicle type and color, as well as license plate. Waymo will display the rider’s initials on top of the vehicle, letting them know that the specific vehicle for them has arrived.
Tesla’s strategy is unique and interesting, but there are some flaws. Cybercab’s main purpose is aimed toward being an autonomous ride for all, including those who have disabilities like being blind or even color blind.
Tesla will likely have something in the pipeline for those who cannot see colors or have limited vision. There will definitely be multiple ways to identify which vehicle is the one that “you” specifically ordered.
Cybercab is set to start giving public rides next Thursday, September 3, in Austin, as it announced a dedicated event last week and invited many members of the Tesla community.
Additionally, members of the public will be invited as well. Tesla has been offering employee rides in Cybercab for nearly two months.







