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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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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.

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.

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“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.

 

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.

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“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.

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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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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Tesla Diner becomes latest target of gloom and doom narrative

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tesla diner
Credit: Tesla

The Tesla Diner has been subject to many points of criticism since its launch in mid-2025, and skeptics and disbelievers claim the company’s latest novel concept is on its way down, but there’s a lot of evidence to state that is not the case.

The piece cites anecdotal evidence like empty parking lots, more staff than customers during a December visit, removed novelty items, like Optimus robot popcorn service and certain menu items, the departure of celebrity chef Eric Greenspan in November 2025, slow service, high prices, and a shift in recent Google/Yelp reviews toward disappointment.

The piece frames this as part of broader Tesla struggles, including sales figures and Elon Musk’s polarizing image, calling it a failed branding exercise rather than a sustainable restaurant.

This narrative is overstated and sensationalized, and is a good representation of coverage on Tesla by today’s media.

Novelty Fade is Normal, Not Failure

Any hyped launch, especially a unique Tesla-branded destination blending dining, Supercharging, and a drive-in theater, naturally sees initial crowds taper off after the “Instagram effect” wears down.

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Tesla makes major change at Supercharger Diner amid epic demand

This is common for experiential spots in Los Angeles, especially pop-up attractions or celebrity-backed venues. The article admits early success with massive lines and social media buzz, but treats the return to normal operations as “dying down.”

In reality, this stabilization is a healthy sign of transitioning from hype-driven traffic to steady patronage.

Actual Performance Metrics Contradict “Ghost Town” Claims

  • In Q4 2025, the Diner generated over $1 million in revenue, exceeding the average McDonald’s location
  • It sold over 30,000 burgers and 83,000 fries in that quarter alone. These figures indicate a strong ongoing business, especially for a single-location prototype focused on enhancing Supercharger experiences rather than competing as a mass-market chain

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Conflicting On-the-Ground Reports

While the article, and other similar pieces, describe a half-full parking lot and sparse customers during specific off-peak visits, other recent accounts push back:

  • A January 2026 X post noted 50 of 80 Supercharger stalls were busy at 11 a.m., calling it “the busiest diner in Hollywood by close to an order of magnitude

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  • Reddit discussions around the same time describe it as not empty when locals drive by regularly, with some calling the empty narrative “disingenuous anti-Tesla slop.”

Bottom Line

The Tesla Diner, admittedly, is not the nonstop circus it was at launch–that was never sustainable or intended. But, it’s far from “dying” or an “empty pit stop.”

It functions as a successful prototype: boosting Supercharger usage, generating solid revenue, and serving as a branded amenity in the high-traffic EV market of Los Angeles.

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Tesla stands to win big from potential adjustment to autonomous vehicle limitations

Enabling scale, innovation, and profitability in a sector that is growing quickly would benefit Tesla significantly, especially as it has established itself as a leader.

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Credit: Patrick Bean | X

Tesla stands to be a big winner from a potential easing of limitations on autonomous vehicle development, as the United States government could back off from the restrictions placed on companies developing self-driving car programs.

The U.S. House Energy and Commerce subcommittee will hold a hearing later this month that will aim to accelerate the deployment of autonomous vehicles. There are several key proposals that could impact the development of self-driving cars and potentially accelerate the deployment of this technology across the country.

These key proposals include raising the NHTSA’s exemption cap from 2,500 to 90,000 vehicles per year per automaker, preempting state-level regulations on autonomous vehicle systems, and mandating NHTSA guidelines for calibrating advanced driver assistance systems (ADAS).

Congress, to this point, has been divided on AV rules, with past bills like the 2017 House-passed measure stalling in the Senate. Recent pushes come from automakers urging the Trump administration to act faster amid competition from Chinese companies.

Companies like Tesla, who launched a Robotaxi service in Austin and the Bay Area last year, and Alphabet’s Waymo are highlighted as potential beneficiaries from lighter sanctions on AV development.

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The NHTSA recently pledged to adopt a quicker exemption review for autonomous vehicle companies, and supporters of self-driving tech argue this will boost U.S. innovation, while critics are concerned about safety and job risks.

How Tesla Could Benefit from the Proposed Legislation

Tesla, under CEO Elon Musk’s leadership, has positioned itself as a pioneer in autonomous driving technology with its Full Self-Driving software and ambitious Robotaxi plans, including the Cybercab, which was unveiled in late 2024.

The draft legislation under consideration by the U.S. House subcommittee could provide Tesla with significant advantages, potentially transforming its operational and financial landscape.

NHTSA Exemption Cap Increase

First, the proposed increase in the NHTSA exemption cap from 2,500 to 90,000 vehicles annually would allow Tesla to scale up development dramatically.

Currently, regulatory hurdles limit how many fully autonomous vehicles can hit the roads without exhaustive approvals. For Tesla, this means accelerating the rollout of its robotaxi fleet, which Musk envisions as a network of millions of vehicles generating recurring revenue through ride-hailing. With Tesla’s vast existing fleet of over 6 million vehicles equipped with FSD hardware, a higher cap could enable rapid conversion and deployment, turning parked cars into profit centers overnight.

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Preempting State Regulations

A united Federal framework would be created if it could preempt State regulations, eliminating the patchwork of rules that currently complicate interstate operations. Tesla has faced scrutiny and restrictions in states like California, especially as it has faced harsh criticism through imposed testing limits.

A federal override of State-level rules would reduce legal battles, compliance costs, and delays, allowing Tesla to expand services nationwide more seamlessly.

This is crucial for Tesla’s growth strategy, as it operates in multiple markets and aims for a coast-to-coast Robotaxi network, competing directly with Waymo’s city-specific expansions.

Bringing Safety Standards to the Present Day

Innovation in the passenger transportation sector has continued to outpace both State and Federal-level legislation, which has caused a lag in the development of many things, most notably, self-driving technology.

Updating these outdated safety standards, especially waiving requirements for steering wheels or mirrors, directly benefits Tesla’s innovative designs. Tesla wanted to ship Cybertruck without side mirrors, but Federal regulations required the company to equip the pickup with them.

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Cybercab is also planned to be released without a steering wheel or pedals, and is tailored for full autonomy, but current rules would mandate human-ready features.

Streamlined NHTSA reviews would further expedite approvals, addressing Tesla’s complaints about bureaucratic slowdowns. In a letter written in June to the Trump Administration, automakers, including Tesla, urged faster action, and this legislation could deliver it.

In Summary

This legislation represents a potential regulatory tailwind for Tesla, but it still relies on the government to put forth action to make things easier from a regulatory perspective. Enabling scale, innovation, and profitability in a sector that is growing quickly would benefit Tesla significantly, especially as it has established itself as a leader.

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Nvidia CEO Jensen Huang explains difference between Tesla FSD and Alpamayo

“Tesla’s FSD stack is completely world-class,” the Nvidia CEO said.

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Credit: Grok Imagine

NVIDIA CEO Jensen Huang has offered high praise for Tesla’s Full Self-Driving (FSD) system during a Q&A at CES 2026, calling it “world-class” and “state-of-the-art” in design, training, and performance. 

More importantly, he also shared some insights about the key differences between FSD and Nvidia’s recently announced Alpamayo system. 

Jensen Huang’s praise for Tesla FSD

Nvidia made headlines at CES following its announcement of Alpamayo, which uses artificial intelligence to accelerate the development of autonomous driving solutions. Due to its focus on AI, many started speculating that Alpamayo would be a direct rival to FSD. This was somewhat addressed by Elon Musk, who predicted that “they will find that it’s easy to get to 99% and then super hard to solve the long tail of the distribution.”

During his Q&A, Nvidia CEO Jensen Huang was asked about the difference between FSD and Alpamayo. His response was extensive:

“Tesla’s FSD stack is completely world-class. They’ve been working on it for quite some time. It’s world-class not only in the number of miles it’s accumulated, but in the way it’s designed, the way they do training, data collection, curation, synthetic data generation, and all of their simulation technologies. 

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“Of course, the latest generation is end-to-end Full Self-Driving—meaning it’s one large model trained end to end. And so… Elon’s AD system is, in every way, 100% state-of-the-art. I’m really quite impressed by the technology. I have it, and I drive it in our house, and it works incredibly well,” the Nvidia CEO said. 

Nvidia’s platform approach vs Tesla’s integration

Huang also stated that Nvidia’s Alpamayo system was built around a fundamentally different philosophy from Tesla’s. Rather than developing self-driving cars itself, Nvidia supplies the full autonomous technology stack for other companies to use.

“Nvidia doesn’t build self-driving cars. We build the full stack so others can,” Huang said, explaining that Nvidia provides separate systems for training, simulation, and in-vehicle computing, all supported by shared software.

He added that customers can adopt as much or as little of the platform as they need, noting that Nvidia works across the industry, including with Tesla on training systems and companies like Waymo, XPeng, and Nuro on vehicle computing.

“So our system is really quite pervasive because we’re a technology platform provider. That’s the primary difference. There’s no question in our mind that, of the billion cars on the road today, in another 10 years’ time, hundreds of millions of them will have great autonomous capability. This is likely one of the largest, fastest-growing technology industries over the next decade.”

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He also emphasized Nvidia’s open approach, saying the company open-sources its models and helps partners train their own systems. “We’re not a self-driving car company. We’re enabling the autonomous industry,” Huang said.

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