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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.
Elon Musk
SpaceX’s next Starship flight set to make history on Friday the 13th
SpaceX is targeting Friday, November 13 for Starship Flight 15 and its first ship catch.
SpaceX is targeting Friday, November 13 for Starship Flight 15, the mission the company plans to use for its first attempt at catching the ship itself with the launch tower.
SpaceX Vice President of Launch Kiko Dontchev shared the date on stage at the UP.Summit on Thursday, according to Ars Technica’s Eric Berger, who was in attendance. It is the first launch target to come directly from a SpaceX executive. Until now, the public schedule had relied on FAA air traffic planning slides, which listed Flight 15 for no earlier than November 8 and later November 12. SpaceX has not posted an official mission page yet, and no launch time has been shared.
The date lands inside the window Elon Musk sketched out last month. Speaking at Giga Texas on October 10, Musk said the flight would “probably launch a little bit before Thanksgiving,” as Teslarati reported. On SpaceX’s third quarter earnings call ten days later, he confirmed that Flight 15 would try to catch both the Super Heavy booster and the ship, and put the odds of a successful ship catch at “more likely than not.” SpaceX also aired an animation of the maneuver during that webcast, showing the ship swinging vertical over Starbase before dropping into the tower’s chopsticks.
The hardware is ready. Booster 22 fired all 33 of its Raptor engines for a full duration static fire at Pad 2 on October 25. Ship 42 followed with a single engine burn simulating a deorbit maneuver on October 26 and a 60 second firing of all six engines the next day, according to NASASpaceflight. Ship 42 had already rehearsed the catch in September, when the Pad 2 arms lifted it into position and crews connected the quick disconnect arm while the vehicle hung from the tower.
The remaining hurdle is regulatory. The FAA’s Starship page does not yet list a Flight 15 license. SpaceX President Gwynne Shotwell said in October that, after “significant constructive engagement with the FAA,” she expects the license to cover a return to the launch site and a tower catch for both stages. Bringing the ship home means a reentry path that heads toward land, rather than ending over open ocean as every Starship flight so far has.
SpaceX has caught Super Heavy three times, on Flights 5, 7 and 8, but the ship comes back from orbital velocity and has never been caught. Flight 14 on September 28 was the first Starship to reach orbit, deploying 26 Starlink V3 satellites before splashing down despite an early engine shutdown that Musk blamed on engine computer software.
Musk has called a successful ship catch “the first time that there’s been full recovery of an orbital class rocket,” and he has already named the step after it: a Flight 16 where both the booster and the ship fly again. NASASpaceflight reports that Ship 43, the next vehicle in line, is set for static fire testing in December.
EVgo has tapped Tesla Superchargers for its most recent efforts to expand its charging presence in the United States, a move that seems logical based on the effectiveness of the automaker’s own infrastructure.
EVgo opened its first Supercharger site in Illinois, a 12-stall station near downtown Chicago at 3145 South Ashland Avenue in the Riverside Square & River’s Edge center, right beside a grocery store. This marks the start of the company’s plan to deploy hundreds of Supercharger stalls across the United States, primarily at grocery-anchored Regency Centers properties where drivers can shop, eat, or run errands while they charge.
We’ve opened our first EVgo Supercharger location in Illinois, marking the start of our plan to add hundreds of Supercharger stalls across the U.S.
Designed for both NACS and CCS vehicles with Magic Dock technology, these new sites help make fast charging more accessible and convenient for all EV drivers. Learn more: https://t.co/V92t5FDryQ
— EVgo Fast Charging Network (@evgonetwork) November 5, 2026
The new location uses Tesla’s Magic Dock technology so both NACS and CCS vehicles can plug in natively without drivers needing to carry their own adapters. Peak power reaches 325 kW at this site, with pricing set between $0.25 and $0.35 per kWh depending on the hour—the same rate for Tesla and non-Tesla drivers.
The stalls also appear in Tesla’s in-car navigation and Trip Planner, making them easy for Tesla owners to find and route to. Illinois has seen EV registrations rise nearly 60 percent over the past two years, and EVgo’s broader network has experienced more than 700 percent growth in charging demand over three years, so the timing fits the market’s trajectory.
Choosing Tesla hardware through the Supercharger for Business program turns out to have been a smart, practical move.
Tesla’s V4 stalls and cabinets deliver high, reliable power with a proven track record of strong uptime, while Magic Dock delivers true dual-standard compatibility in one package. Because the sites show up in Tesla’s navigation tools, EVgo instantly gains visibility among millions of existing Tesla drivers, which should raise utilization and help the company double its addressable market as more vehicles adopt NACS. EVgo still owns the stations and sets pricing, yet benefits from Tesla’s established hardware, longer cables, and operational support.
The result is faster, lower-risk infrastructure expansion that serves every EV driver—Tesla or otherwise—with convenient, high-power charging at everyday retail locations. For drivers, that means fewer adapters, more predictable stops, and a denser network just as electric vehicles become everyday transportation.
Tesla’s Austin Gigafactory is reportedly shifting to round-the-clock vehicle production through the end of 2026, according to longtime drone observer Joe Tegtmeyer.
In his November 2 update, Tegtmeyer, widely regarded as one of the most reliable independent sources on Giga Texas activity (we call him the Drone GOAT), stated that the plant has added a night shift, creating two 12-hour production shifts.
Tegtmeyer said in his video:
“Now, I do have some interesting news about that when it comes to the production schedule here at Giga Texas, and things are actually looking pretty good, especially when you think about what the demand is and the delivery numbers that they’re looking for and what they’re expecting. So, normally they have shifts Monday through Friday. It’s a day shift and it’s about 10 hours long or so, give or take. But now they’re on day and night shifts and they’re going to 12-hour days. So they’re going to be adding or they have another shift. They have 12 hours for both of them. In addition to that, the typical downtime that we’re going to be seeing around the holidays, specifically Thanksgiving and Christmas to the New Year time frame is actually changed. And we’re not going to see those big several day events where there is no production. At least that’s what the plan is right now. So, it’s really a great sign, I think, when we consider what they’ve done in the past and what production and the deliveries have been so far. So, maybe it’s shaping up to be a really strong quarter.”
Previously, General Assembly typically operated on a single roughly 10-hour day shift, Monday through Thursday or Friday. The new arrangement keeps General Assembly on its Monday-to-Thursday schedule while adding overnight capacity, and most other areas of the factory continue working the full week with some weekend activity.
Notably, the plant is also forgoing the multi-day shutdowns around Thanksgiving and the Christmas–New Year period that have occurred in prior years
Giga Texas currently builds the Model Y, the larger Model Y L, the Cybertruck, and the Cybercab robotaxi. Tesla has not confirmed the shift change or specified which lines will receive the extra output. Recent comments suggest Cybercab production has been constrained by the pace at which the Robotaxi fleet can absorb new vehicles, making the Model Y and Model Y L the more likely beneficiaries as the company works through order backlogs.
Tegtmeyer’s November 2 footage and commentary also highlighted broader site progress. Cortex 2 continues to expand, with additional compute coming online, a roughly 25 percent lengthening of the structure on the north end, and work on a third cooling plant.
The Boring Company tunnel site showed increased activity in the large launch pit, while the Advanced Technology Chip Fab (a SpaceX–Tesla joint R&D facility) continued steel superstructure and heavy truss installation, along with concrete pours.
The reported capacity increase arrives as Tesla aims for a strong fourth quarter following solid third-quarter results. While unconfirmed by the company, the information aligns with Tegtmeyer’s consistent track record of accurate on-site observations.
If Tesla makes the decision to sustain the all-day production plans, the dual 12-hour shifts would meaningfully raise weekly output potential at one of Tesla’s most important manufacturing hubs.
SpaceX’s next Starship flight set to make history on Friday the 13th
EVgo taps Tesla Superchargers for mass charging expansion
