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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 gathers 93,000 FSD miles in a country where FSD isn’t approved – here’s how
Tesla has quietly logged an impressive 93,000 miles (roughly 150,000 km) of autonomous driving at its Giga Berlin factory—using Full Self-Driving (FSD) in a country where the technology remains unavailable to consumers on public roads.
Tesla has gathered 93,000 Full Self-Driving miles in a country where Full Self-Driving is not even approved. Here’s how.
Tesla has quietly logged an impressive 93,000 miles (roughly 150,000 km) of autonomous driving at its Giga Berlin factory—using Full Self-Driving (FSD) in a country where the technology remains unavailable to consumers on public roads.
The milestone, revealed alongside news that Giga Berlin has now built 750,000 Model Y vehicles, highlights how Tesla is putting its AI to work in one of the most controlled environments imaginable: it’s own factory floor.
Every Model Y that rolls off the final assembly line at Giga Berlin doesn’t need a human driver to reach the outbound lot. Instead, the freshly built vehicles engage FSD and navigate themselves across the factory campus.
The Tesla Model Ys rolling off the production line at Giga Berlin have now driven themselves on FSD a combined 93,000 miles from the end of the production line to the outbound lot. https://t.co/6RhL3W4q4p pic.twitter.com/DOKKHUcSSL
— Sawyer Merritt (@SawyerMerritt) May 11, 2026
The route—from the end of the production line through marked internal pathways to the staging area where cars await delivery or export—is entirely on private property. No public roads, no mixed traffic, and no regulatory hurdles for on-road autonomous operation.
It’s a closed-loop system: wide lanes, predictable layouts, minimal pedestrians, and consistent conditions that make it one of the simplest proving grounds for the software.
A short factory tour video shared by Tesla Manufacturing shows General Assembly team member Jan explaining the process. Gesturing beside a glossy black Model Y still wearing its protective wrap, he notes the cumulative distance the fleet has covered autonomously.
Tesla Giga Berlin seems to be using FSD Unsupervised to move Model Y units
The cars handle the short drive flawlessly, freeing up workers who would otherwise spend hours shuttling vehicles manually. For a high-volume plant like Giga Berlin, the time and labor savings add up quickly. Even small gains in cycle time per car can reclaim valuable space in the outbound lot and streamline logistics.
This internal deployment serves multiple purposes. First, it delivers zero-cost validation data. Each factory run exposes FSD to real-world physics—acceleration, steering precision, obstacle avoidance—in a repeatable setting far safer than public testing.
Second, it demonstrates the system’s readiness at scale. If FSD can reliably move thousands of brand-new cars without intervention inside a busy factory, it underscores the robustness of the vision-based, end-to-end neural network Tesla has been refining.
Critics often point to Europe’s cautious regulatory stance on unsupervised autonomy, yet Tesla has turned that limitation into an advantage. While owners in Germany still cannot activate consumer FSD on highways or city streets, the software is already proving its worth behind the factory gates.
The 93,000 miles represent not just internal efficiency gains but a subtle flex: the cars are manufactured ready to navigate autonomously, at least in the bounds of the factory. It’s a big feather in the cap of FSD, even if regulators have yet to green-light broader use.
As Giga Berlin continues ramping output, expect this autonomous logistics loop to grow. What began as a practical workaround for moving finished vehicles has quietly become one of the most compelling real-world showcases of FSD’s potential—right in the heart of regulated Europe. Tesla isn’t waiting for approval to perfect its autonomy; it’s already driving the future, one factory mile at a time.
Elon Musk
Elon Musk reveals how SpaceX is always on board Air Force One
Musk confirmed Tuesday that Starlink internet is live and kicking on Air Force One. Responding with a simple “Yup!” to a post showing him and Nvidia CEO Jensen Huang aboard the presidential jet en route to Beijing with President Trump, Musk proved the point: America’s most important aircraft now has seamless, high-speed satellite connectivity—even over the middle of the Pacific.
Air Force One, the official call sign for a U.S. Air Force aircraft carrying the President, now runs on SpaceX Starlink, CEO Elon Musk revealed.
Musk confirmed Tuesday that Starlink internet is live and kicking on Air Force One. Responding with a simple “Yup!” to a post showing him and Nvidia CEO Jensen Huang aboard the presidential jet en route to Beijing with President Trump, Musk proved the point: America’s most important aircraft now has seamless, high-speed satellite connectivity—even over the middle of the Pacific.
Yup!
— Elon Musk (@elonmusk) May 13, 2026
The timing couldn’t be more symbolic. With trillion-dollar CEOs and the President sharing the cabin, Starlink wasn’t just a nice-to-have—it was mission-critical. No more spotty signals or dropped calls. Instead, real-time video conferences, secure data transfers, and global coordination at Mach speed.
Starlink’s aviation push has already transformed commercial and private flying. Dozens of major airlines have signed on or begun rollouts.
Hawaiian Airlines, United Airlines, Qatar Airways, Air France, SAS, WestJet, airBaltic, and Emirates (now equipping its Boeing 777 and A380 fleets) offer Starlink Wi-Fi to passengers. Lufthansa plans to follow in late 2026.
On private jets, the upgrade is even hotter: owners and charter companies report skyrocketing demand because Starlink turns cabins into flying boardrooms.
Starlink gets its latest airline adoptee for stable and reliable internet access
The advantages are massive. Traditional in-flight Wi-Fi relied on slow, high-latency geostationary satellites or ground-based systems that cut out over oceans and remote areas. Starlink’s low-Earth-orbit constellation delivers blazing speeds—often exceeding 200 Mbps download with latency as low as 25-60 milliseconds—gate-to-gate, from takeoff to landing.
Passengers stream 4K video, join Zoom calls, or work in the cloud without buffering. Pilots get real-time weather, NOTAM updates, and live ATC data. Even private-jet travelers get the benefits, as it means productivity that rivals the office.
On Air Force One, those benefits become strategic superpowers. The presidential aircraft demands unbreakable communications for national security, diplomacy, and crisis response. Starlink provides global coverage with no dead zones, offering redundancy against traditional systems that could fail in contested airspace or during long-haul flights.
It enables the President and staff to maintain secure links with the Pentagon, allies, or business leaders anywhere on Earth. During the Beijing trip, it likely facilitated direct coordination on trade, tech, and AI—proving the system’s reliability for the highest-stakes missions.
Critics once dismissed Starlink as a rich-person toy or military experiment. Now, it’s the backbone of commercial fleets, private aviation, and the world’s most visible symbol of American power, and it is providing stable internet to travelers.
With over 2,000 commercial aircraft committed and private-jet installations booming, Starlink is rewriting the rules of connected flight, and it seems like each week, a new airline is choosing to use it for on-flight connectivity.
For Air Force One, it’s more than faster Wi-Fi. It’s uninterrupted command-and-control in an increasingly connected world—ensuring the President never has to go dark at altitude. Elon Musk just made sure of it.
Elon Musk
SpaceX unveils sweeping Starship V3 upgrades ahead of May 19 launch
SpaceX has released a detailed list of changes for Starship Version 3, the next iteration of its fully reusable super-heavy-lift vehicle. Scheduled for its maiden flight as early as May 19 from Starbase in Texas, Starship V3 incorporates dozens of redesigns across the Super Heavy booster, Starship upper stage, Raptor 3 engines, and Launch Pad 2.
SpaceX has unveiled sweeping upgrades to its Starship v3 rocket ahead of the upcoming May 19 launch.
SpaceX has released a detailed list of changes for Starship Version 3, the next iteration of its fully reusable super-heavy-lift vehicle. Scheduled for its maiden flight as early as May 19 from Starbase in Texas, Starship V3 incorporates dozens of redesigns across the Super Heavy booster, Starship upper stage, Raptor 3 engines, and Launch Pad 2.
Elon Musk reveals date of SpaceX Starship v3’s maiden voyage
The updates focus on simplification, mass reduction, reliability, and enabling core capabilities like rapid reusability, in-orbit refueling, Starlink deployment, and crewed missions to the Moon and Mars.
Collectively, these modifications mark a major step-change. By reducing dry mass, improving thermal protection, and integrating systems for orbital operations, Starship V3 aims to transition from test vehicle to operational infrastructure.
Here is an explicit, broken-down list of the key changes, first starting with the changes to Super Heavy V3:
- Grid Fin Redesign: Reduced from four fins to three. Each fin is now 50% larger and stronger, repositioned for better catching and lifting performance. Fins are lowered on the booster to reduce heat exposure during hot staging, with hardware moved inside the fuel tank for protection.
- Integrated Hot Staging: Eliminates the old disposable interstage shield. The booster dome is now directly exposed to upper-stage engine ignition, protected by tank pressure and steel shielding. Interstage actuators retract after separation.
- New Fuel Transfer System: Massive redesign of the fuel transfer tube—roughly the size of a Falcon 9 first stage—enables simultaneous startup of all 33 Raptors for faster, more reliable flip maneuvers.
- Engine Bay / Thermal Protection: Engine shrouds removed entirely; new shielding added between engines. Propulsion and avionics are more tightly integrated. CO₂ fire suppression system deleted for a simpler, lighter aft section.
- Propellant Loading Improvements: Switched from one quick disconnect to two separate systems for added redundancy and reduced pad complexity.
Next, we have the changes to Starship V3:
- Completely Redesigned Propulsion System: Clean-sheet redesign supports new Raptor startup, larger propellant volume, and an improved reaction control system while reducing trapped or leaked propellant risk.
- Aft Section Simplification: Fluid and electrical systems rerouted; engine shrouds and large aft cavity deleted.
- Flap Actuation Upgrade: Changed from two actuators per flap to one actuator with three motors for better redundancy, mass efficiency, and lower cost.
- Faster Starlink Deployment: Upgraded PEZ dispenser enables quicker satellite release.
- Long-Duration Spaceflight Capability: New systems for long orbital coasts, orbital refueling, cryogenic fluid management, vacuum-insulated header tanks, and high-voltage cryogenic recirculation.
- Ship-to-Ship Docking + Refueling: Four docking drogues and dedicated propellant transfer connections added to support in-space refueling architecture.
- Avionics Upgrades: 60 custom avionics units with integrated batteries, inverters, and high-voltage systems (9 MW peak power). New multi-sensor navigation for precision autonomous flight. RF sensors measure propellant in microgravity. ~50 onboard camera views and 480 Mbps Starlink connectivity for low-latency communications.
Next are the changes to the Raptor 3 Engine:
- Higher Thrust: Sea-level Raptors increased from 230 tf (507k lbf) to 250 tf (551k lbf); vacuum Raptors from 258 tf (568k lbf) to 275 tf (606k lbf).
- Lower Mass: Sea-level engine mass reduced from 1630 kg to 1525 kg.
- Simpler Design: Sensors and controllers integrated into the engine body; shrouds eliminated; new ignition system for all variants. Results in ~1 ton of vehicle-level weight savings per engine.
Finally, the upgrades to Launch Pad 2 are as follows:
- Faster propellant loading via larger farm and more pumps.
- Chopstick improvements: shorter arms, electromechanical actuators (replacing hydraulic) for reliability.
- Stronger quick-disconnect arm that swings farther away.
- Redesigned launch mount for better load handling and protection.
- New bidirectional flame diverter eliminates post-launch ablation and refurbishment.
- Hardened propellant systems with separated methane/oxygen lines and protected valves/filters.
SpaceX states these elements “are designed to enable a step-change in Starship capabilities and aim to unlock the vehicle’s core functions, including full and rapid reuse, in-space propellant transfer, deployment of Starlink satellites and orbital data centers, and the ability to send people and cargo to the Moon and Mars.”
With these upgrades, Starship V3 is poised for an epic test flight that could accelerate humanity’s multiplanetary future. The rapid pace of iteration underscores SpaceX’s relentless drive toward making life multiplanetary. Launch watchers are in for a spectacular show.
Tesla gathers 93,000 FSD miles in a country where FSD isn’t approved – here’s how
Elon Musk reveals how SpaceX is always on board Air Force One
