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SpaceX CEO Elon Musk explains Starship’s ‘transpiring’ steel heat shield in Q&A

BFR's booster (Super Heavy) and spaceship (Starship) separate shortly after launch. (SpaceX)

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7 years ago

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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.

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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”.

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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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.

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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.

 

Check out Teslarati’s newsletters for prompt updates, on-the-ground perspectives, and unique glimpses of SpaceX’s rocket launch and recovery processes!

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Eric Ralph is Teslarati's senior spaceflight reporter and has been covering the industry in some capacity for almost half a decade, largely spurred in 2016 by a trip to Mexico to watch Elon Musk reveal SpaceX's plans for Mars in person. Aside from spreading interest and excitement about spaceflight far and wide, his primary goal is to cover humanity's ongoing efforts to expand beyond Earth to the Moon, Mars, and elsewhere.

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The Boring Company’s Vegas Loop moves 82k riders during CONEXPO

The Loop’s feat was highlighted by The Boring Company in a post on its official account on social media platform X.

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2 hours ago

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March 9, 2026

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Credit: The Boring Company/X

The Boring Company said its Vegas Loop system transported roughly 82,000 passengers during the recent CONEXPO-CON/AGG construction trade show in Las Vegas. The event was held at the Las Vegas Convention Center (LVCC) from March 3-7, 2026. 

The Loop’s feat was highlighted by The Boring Company in a post on its official account on social media platform X.

CONEXPO-CON/AGG 2026

CONEXPO-CON/AGG is one of the largest construction trade shows in North America. This year’s event was quite impressive, attracting more than 140,000 construction professionals from 128 countries across the world.

Considering the number of this year’s attendees, the LVCC Loop seemed to have proven itself to be a very useful transportation solution. A video posted by The Boring Company on its official X account featured attendees expressing their enthusiasm for the underground transport system, with some stating that they would like to see similar tunnels across Las Vegas. 

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The LVCC Loop is only part of the greater Vegas Loop network, which is actively under construction.

New Vegas Loop extensions

One of the newest additions is a station at the Fontainebleau Las Vegas resort on the Strip. The station is located on level V-1 of the resort’s south valet area, according to a report from the Las Vegas Review-Journal. From the Fontainebleau, passengers can travel free of charge to stations serving the Las Vegas Convention Center, as well as to Loop stations at Encore and Westgate.

The system is also expanding beyond the Strip corridor. In December, The Boring Company began offering Vegas Loop rides to and from Harry Reid International Airport. These trips include a limited above-ground segment after receiving approval from the Nevada Transportation Authority to allow surface street travel tied to Loop operations.

The Boring Company President Steve Davis previously told the Review-Journal that the University Center Loop segment, which is currently under construction, is expected to open in the first quarter of 2026. The extension would allow Loop vehicles to travel beneath Paradise Road between the convention center and the airport, with a planned station just north of Tropicana Avenue.

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Tesla preps to build its most massive Supercharger yet: 400+ V4 stalls

The project will be an expansion of the current Eddie World Supercharger in Yermo, California, and will take place in several stages.

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2 days ago

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March 7, 2026

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(Credit: Tesla)

Tesla is preparing to build its most massive Supercharger yet, as it recently submitted plans for an over 400-stall Supercharging station in California, which would dwarf its massive 168-stall location in Lost Hills, California.

The project will be an expansion of the current Eddie World Supercharger in Yermo, California, and will take place in several stages.

The expansion, adjacent to the existing Eddie World Supercharger, which is currently comprised of 22 older V2 and V3 stalls limited to 150 kW, unfolds across six phases.

Construction on Phase 1 begins later this year with 72 V4 stalls. Subsequent stages will progressively add hundreds more, culminating in over 400 next-generation chargers. Site plans label expansive parking arrays across Phases 1–5 along Calico Boulevard, with Phase 6 design still to be determined.

The project was first flagged by MarcoRP, a notable Tesla Supercharger watcher.

Strategically located midway on I-15 between Los Angeles and Las Vegas, the station targets heavy EV traffic on this high-demand corridor.

The surrounding 20-mile stretch already hosts over 200 high-power stalls (including 40 at 250 kW, 120 at 325 kW, and more), plus 96 in nearby Baker—yet bottlenecks persist during peak travel.

In scale, it eclipses all existing Tesla Superchargers. The current record holder, the solar- and Megapack-powered “Project Oasis” in Lost Hills, California, offers 164 stalls. Barstow’s former leader had 120. Eddie World 2 will be more than double that size, cementing Tesla’s dominance in ultra-high-capacity charging.

Tesla finishes its biggest Supercharger ever with 168 stalls

Development blends charging with convenience. Architectural drawings show integrated retail: a 10,100 square foot Cracker Barrel, a 4,300 square foot McDonald’s, a 3,800 square foot convenience store, additional restaurants, drive-thrus, outdoor dining, and lease space.

EV-centric features include pull-through bays for Cybertrucks and trailers, ensuring accessibility for larger vehicles and future Semi trucks.

This phased approach minimizes disruption while scaling capacity. It supports Tesla’s broader vision amid rising EV adoption, Robotaxi corridors, and long-haul needs. Once complete, Eddie World 2 won’t just charge vehicles; it will redefine highway stops, turning a dusty desert exit into a futuristic EV oasis.
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Tesla makes latest move to remove Model S and Model X from its lineup

Tesla’s latest decisive step toward phasing out its flagship sedan and SUV was quietly removing the Model S and Model X from its U.S. referral program earlier this week.

Published

3 days ago

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March 6, 2026

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Credit: Tesla

Tesla has made its latest move that indicates the Model S and Model X are being removed from the company’s lineup, an action that was confirmed by the company earlier this quarter, that the two flagship vehicles would no longer be produced.

Tesla has ultimately started phasing out the Model S and Model X in several ways, as it recently indicated it had sold out of a paint color for the two vehicles.

Now, the company is making even more moves that show its plans for the two vehicles are being eliminated slowly but surely.

Tesla’s latest decisive step toward phasing out its flagship sedan and SUV was quietly removing the Model S and Model X from its U.S. referral program earlier this week.

The change eliminates the $1,000 referral discount previously available to new buyers of these vehicles. Existing Tesla owners purchasing a new Model S or Model X will now only receive a halved loyalty discount of $500, down from $1,000.

The updates extend beyond the two flagship vehicles. New Cybertruck buyers using a referral code on Premium AWD or Cyberbeast configurations will no longer get $1,000 off. Instead, both referrer and buyer receive three months of Full Self-Driving (Supervised).

The loyalty discount for Cybertruck purchases, excluding the new Dual Motor AWD trim level, has also been cut to $500.

These adjustments apply only in the United States, and reflect Tesla’s broader strategy to optimize margins while boosting adoption of its autonomous driving software.

The timing is no coincidence. Tesla confirmed earlier this year that Model S and Model X production will end in the second quarter of 2026, roughly June, as the company reallocates factory capacity toward its Optimus humanoid robot and next-generation vehicles.

With annual sales of the low-volume flagships already declining (just 53,900 units in 2025), incentives are no longer needed to drive demand. Production is winding down, and Tesla expects strong remaining interest without subsidies.

Industry observers see this as the clearest sign yet of an “end-of-life” phase for the vehicles that once defined Tesla’s luxury segment. Community reactions on X range from nostalgia, “Rest in power S and X”, to frustration among long-time owners who feel perks are eroding just as the models approach discontinuation.

Some buyers are rushing orders to lock in final discounts before they vanish entirely.

Doug DeMuro names Tesla Model S the Most Important Car of the last 30 years

For Tesla, the move prioritizes efficiency: fewer discounts on outgoing models, a stronger push for FSD subscriptions, and a focus on high-margin Cybertruck trims amid surging orders.

Loyalists still have a narrow window to purchase a refreshed Plaid or Long Range model with remaining incentives, but the message is clear: Tesla’s lineup is evolving, and the era of the original flagships is drawing to a close. 

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