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”.
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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 Robotaxi services in Austin have been operating since last Summer, but Tesla has admittedly been delayed in its expansion of the geofence, fleet size, and other details in a bid to prioritize safety as new technology rolls out.
But those barriers are being broken with new guardrails being removed from the program.
Tesla has achieved a significant advancement in its autonomous ride-hailing program. As of May 4, the Robotaxi fleet in Austin, Texas, has begun operating unsupervised during evening hours for the first time. This expansion moves beyond previous limitations that restricted unsupervised service to daylight hours, typically ending in mid-afternoon.
Tesla Robotaxi in Austin is operating unsupervised in the evenings for the first time today.
Previously in Austin, unsupervised operation ended mid-afternoon
— Robotaxi Tracker (@RtaxiTracker) May 4, 2026
The change brings Austin in line with operations in Dallas and Houston. Those cities have supported evening unsupervised runs since their initial launches in April, and both recently received additions of new unsupervised vehicles to their fleets. This coordinated progress across Texas strengthens Tesla’s regional presence and provides a broader testing ground for the technology.
This milestone carries substantial weight in the development of autonomous vehicles. Extending operations into low-light conditions meaningfully expands the Robotaxi’s operational design domain (ODD)—the specific environments and scenarios in which the system is approved to operate safely without human intervention.
Nighttime driving presents unique technical demands: diminished visibility, headlight glare from oncoming traffic, reduced contrast for identifying pedestrians and lane markings, and greater variability in camera sensor exposure.
Tesla’s pure vision approach, powered by neural networks trained on vast real-world datasets rather than lidar or pre-mapped routes, must handle these variables reliably. Demonstrating consistent unsupervised performance after sunset validates the robustness of the end-to-end AI stack and its ability to generalize across diverse lighting conditions.
Beyond technical validation, the expansion holds important operational and economic implications. Evening hours often coincide with peak urban demand for rides, including commutes, dining, and entertainment outings.
Enabling service during these periods increases daily vehicle utilization, allowing each Robotaxi to generate more revenue while gathering additional high-value training data. Higher utilization accelerates the virtuous cycle of data collection, model improvement, and further ODD growth.
Looking ahead, this step paves the way for more ambitious rollouts. Success in low-light environments positions Tesla to pursue near-24-hour operations, potentially integrating highways and expanding into varied weather patterns. Regulators worldwide frequently demand evidence of safe performance across day-night cycles before granting wider approvals.
Proven capability in Texas could expedite deployments in planned cities such as Phoenix, Miami, Orlando, Tampa, and Las Vegas during the first half of 2026.
Tesla confirms Robotaxi expansion plans with new cities and aggressive timeline
Moreover, scaling evening service supports Tesla’s long-term vision of a high-efficiency robotaxi network. Greater fleet productivity lowers the cost per mile, making autonomous mobility more accessible and competitive against traditional ride-hailing.
As the company iterates on software updates informed by nighttime data, reliability is expected to compound rapidly, unlocking denser urban coverage and longer-distance trips.
In summary, the introduction of an unsupervised evening Robotaxi service in Austin represents more than an incremental schedule adjustment. It signals a critical maturation of the underlying technology and sets the foundation for broader geographic and temporal expansion.
With Texas operations gaining momentum, Tesla is steadily advancing toward transforming urban transportation at scale.
Cybertruck
Tesla Cybercab just rolled through Miami inside a glass box
Tesla paraded a Cybercab in a glass display at Miami’s F1 Grand Prix event this week.
Tesla set up an “Autonomy Pop-Up” at Lummus Park in Miami Beach from April 29 through May 3, 2026, embedded within the official F1 Miami Grand Prix Fan Fest. The centerpiece was a Cybertruck towing the Cybercab inside a glass display case marked “Future is Autonomous,” rolling through the beachfront crowd.
Miami is on Tesla’s confirmed list of cities for robotaxi expansion in the first half of 2026, making the promotion a strategic promotion that lays groundwork in a target market.
This was not Tesla’s first time using Miami as a showcase city. In December 2025, Tesla hosted “The Future of Autonomy Visualized” at its Miami Design District showroom, coinciding with Art Basel Miami Beach. That event featured the Cybercab prototype and Optimus robots interacting with attendees. The F1 pop-up this week marks Tesla’s return to Miami and follows a pattern Tesla has been running since early 2026. Just two weeks before Miami, Tesla stationed Optimus at the Tesla Boston Boylston Street showroom on April 19 and 20, directly on the final stretch of the Boston Marathon, letting tens of thousands of runners and spectators meet the robot for free, generating massive earned media at zero advertising cost.
Tesla is sending its humanoid Optimus robot to the Boston Marathon
Tesla has confirmed plans to expand its robotaxi service to seven cities in the first half of 2026, including Dallas, Houston, Phoenix, Miami, Orlando, Tampa, and Las Vegas, building on the unsupervised service already running in Austin. Musk has said he expects robotaxis to cover between a quarter and half of the United States by end of year. On the production side, Musk told shareholders that the Cybercab manufacturing process could eventually produce up to 5 million vehicles per year, targeting a cycle time of one unit every ten seconds. Scaling robotaxis to 10 million operational units over the next ten years is a key condition of his compensation package, alongside selling 20 million passenger vehicles.
As for the Cybercab’s price, Musk has said buyers will be able to purchase one for under $30,000, with an average operating cost around $0.20 per mile. Whether those numbers hold through full production remains to be seen.
Cybercab at F1 Fan Fest in Miami
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News
Tesla Semi gets new product launch as mass manufacturing hits Plaid Mode
While the 1.2 MW Megacharger handles quick 30-minute en-route boosts, the Basecharger serves as a reliable overnight solution for longer dwell times at warehouses, distribution centers, fleet yards, and even, potentially, homes.
The Tesla Semi is getting a new production launch as mass manufacturing on the all-electric truck is gearing up to hit Plaid Mode.
Tesla has introduced a game-changing addition to its commercial charging lineup with the new 125 kW Basecharger for Semi. Launched this week as part of the new “Semi Charging for Business” program, this compact unit is purpose-built for depot and overnight charging of Tesla Semi trucks.
While the 1.2 MW Megacharger handles quick 30-minute en-route boosts, the Basecharger serves as a reliable overnight solution for longer dwell times at warehouses, distribution centers, fleet yards, and even, potentially, homes.
Our new 125 kW Basecharger is designed for longer dwell times and overnight charging of Semis. It’s the “home charging” for heavy-duty fleets.
It features a fully integrated design that eliminates the need for a separate AC-to-DC cabinet, simplifying installation. The 6 meter… https://t.co/ovy1C4PsRW pic.twitter.com/vBUCNMzs57
— Tesla Charging (@TeslaCharging) May 1, 2026
Delivering up to 60 percent of the Semi’s range in roughly four hours, perfect for overnight top-ups during mandated driver rest periods or while trucks are loaded or unloaded. Its fully integrated design eliminates the need for bulky separate AC-to-DC cabinets.
Tesla engineers tucked one of the power modules from a V4 Supercharger Cabinet directly inside the sleek post, resulting in a compact footprint. It also features a six-meter cable for layout flexibility. This is one thing that must have been learned through the V4 Supercharger rollout.
Installation and operating costs drop dramatically thanks to daisy-chaining. Up to three Basechargers can share a single 125 kVA breaker, slashing electrical infrastructure requirements. The unit outputs 150 amps continuous across an 180–1,000 VDC range, matching the Semi’s high-voltage architecture while supporting the MCS 3.2 standard.
Tesla Semi sends clear message to Diesel rivals with latest move
Priced from $40,000 for a minimum order of two units, the Basecharger is far more affordable than the $188,000 Megacharger setup for two posts. Deliveries begin in early 2027. Buyers also receive Tesla’s full network-level software, remote monitoring, maintenance, and a guaranteed 97 percent or higher uptime—critical for fleet reliability.
This launch arrives as Tesla accelerates high-volume Semi production at its Nevada factory, targeting 50,000 units annually. By pairing affordable depot charging with ultra-fast highway options, Tesla removes one of the biggest obstacles to electrifying Class 8 trucking: infrastructure cost and complexity.
Fleet operators stand to gain lower electricity rates during off-peak hours, dramatically reduced maintenance compared to diesel, and quieter yards at night. The Basecharger isn’t just another charger—it’s the practical bridge that makes large-scale electric semi adoption economically viable.
With the Basecharger handling “home” duties and Megachargers powering the road, Tesla is delivering a complete ecosystem that could finally tip the scales toward zero-emission freight. For trucking companies ready to go electric, the future just got a whole lot more charger-friendly.
Tesla Robotaxi service in Austin achieves monumental new accomplishment
Tesla Cybercab just rolled through Miami inside a glass box
