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”.
-
- Starhopper and SpaceX’s spartan assembly facilities are pictured here, showing the inside of the aft section and a completed tank dome. (Austin Barnard)
-
- 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.
-
- Starship’s first full-scale prototype is being rapidly assembled in South Texas. (NASASpaceflight – bocachicagal)
-
- Starship’s first full-scale prototype is being rapidly assembled in South Texas. (NASASpaceflight – bocachicagal)
-
- Meanwhile, giant 9m-diameter tank domes are being assembled and welded together a few hundred feet away from Starhopper. (NSF – bocachicagal)
-
- SpaceX’s Starhopper seen in a January render and a January photo. (SpaceX/Elon Musk)
-
- BFS seen standing vertically on the pads of its tripod fins. (SpaceX)
-
- 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
Tesla makes Elon Musk’s new compensation package official
This is an important thing to note, as much of the media coverage regarding Musk’s pay package seems to indicate that the company and the shareholders are simply giving the CEO the money. He has to come through on each of these tranches to unlock the $1 trillion.
Tesla has made CEO Elon Musk’s new compensation package official, as it filed a Form 4 with the Securities and Exchange Commission (SEC) on Monday.
The package officially gives Musk the opportunity to acquire over 423 million shares of Tesla stock (NASDAQ: TSLA), dependent on his ability to achieve twelve performance-based tranches that will bring growth to the company and its shareholders.
Tesla (TSLA) shareholders officially approve Elon Musk’s 2025 performance award
Musk’s new compensation package was approved by investors last Thursday at the company’s Annual Shareholder Meeting, as over 75 percent of voters supported the CEO’s new plan, which could be valued at over $1 trillion if he is able to come through on all twelve tranches.
The twelve tranches include growth goals related to vehicle deliveries, the Optimus humanoid robot project, and Tesla’s valuation. If Musk is able to achieve each tranche, he would help Tesla achieve an over $8 trillion market cap.
The 12 tranches include:
-
$2 trillion market cap + Deliver 20 million Tesla vehicles cumulatively
-
$2.5 trillion market cap + Reach 10 million active Full Self-Driving (FSD) subscriptions
-
$3 trillion market cap + Deliver 1 million Optimus humanoid robots
-
$3.5 trillion market cap + Operate 1 million Robotaxis commercially
-
$4 trillion market cap + Hit $50 billion in adjusted EBITDA (earnings before interest, taxes, etc.)
-
$4.5 trillion market cap + Hit $80 billion in adjusted EBITDA
-
$5 trillion market cap + Hit $130 billion in adjusted EBITDA
-
$5.5 trillion market cap + Hit $210 billion in adjusted EBITDA
-
$6 trillion market cap + Hit $300 billion in adjusted EBITDA
-
$6.5 trillion market cap + Hit $400 billion in adjusted EBITDA
-
$7.5 trillion market cap + Hit $400 billion in adjusted EBITDA for four straight quarters in a row
-
$8.5 trillion market cap + Hit $400 billion in adjusted EBITDA for four straight quarters in a row
Achieving the twelve levels of the new compensation package would also give Musk what he’s really after: a larger ownership share in Tesla, which would help him achieve more control, something he feels is necessary for the rollout of the Optimus robot “army.”
Musk does not earn a dime if he does not achieve any of the tranches above.
This is an important thing to note, as much of the media coverage regarding Musk’s pay package seems to indicate that the company and the shareholders are simply giving the CEO the money. He has to come through on each of these tranches to unlock the $1 trillion.
News
Tesla provides vehicles for German firefighters’ EV training program
The sessions were aimed at improving emergency services for accidents involving electric vehicles.
Firefighters from across Germany recently gathered at Tesla Gigafactory Berlin-Brandenburg to practice emergency procedures on electric vehicles. The first training session last weekend focused on dismantling Tesla vehicles using spreaders, shears, and saws, giving responders hands-on experience with modern EV construction and safety features.
The sessions were aimed at improving emergency services for accidents involving electric vehicles, which, while less likely to catch fire than conventional cars, require special handling.
Challenges for first responders
During the exercises, firefighters discovered that Tesla vehicles’ sturdy, unified body panels, which are among the reasons why they are among the safest cars on the road, made cutting doors and roofs more difficult than in older vehicles, as noted in an rbb24 report.
“It was a real eye-opener,” firefighter Martin Haschick said, adding that his first attempt showed him “how not to do it, because we are also trained on older vehicles, and that took longer than I expected.” Tesla trainers demonstrated proper techniques to safely dismantle vehicles, emphasizing differences between older combustion-engine cars and today’s EVs.
Patrick Fath, head of the Tesla plant fire brigade, explained that hands-on experience with current EVs is critical, as scrap cars typically used in training do not reflect modern material strengths or technological design.
“They naturally have a completely different level of technology and different material strengths. But what can happen to us in everyday life – on the highway, on the roads, involves modern vehicles,” Fath stated.
Future training programs
Tesla plans to continue offering training for regional fire departments and state fire service schools, with the Brandenburg Ministry of the Interior observing the initial sessions to provide feedback. Exercises currently avoid live fires or fluid leaks due to the factory’s location in a drinking water protection zone. Tesla covers the costs of these programs, aiming to enhance first responders’ knowledge of modern EV safety and accident procedures.
In a comment, Fath highlighted that electric vehicle fires should not be too much of a problem, considering that the vehicles don’t catch fire as often as their combustion-powered counterparts. “Studies and experience from recent years have already shown that electric vehicles catch fire far less often than conventional vehicles. We have far fewer flammable materials, no gasoline or diesel tank, and therefore fewer ignition sources,” Fath stated.
Authorities have announced similar conclusions. The German Insurance Association (GDV) has confirmed that EVs catch fire significantly less often than combustion-powered cars, with statistics showing that around 14,200 vehicles caught fire in Germany in 2023. At the time, no higher fire risk was found in EVs. Data from the US National Transportation Safety Board (NTSB) from 2024 also showed that about 25 out of 100,000 EVs catch fire, which is notably fewer than the 1,530 out of 100,000 combustion-powered vehicles that catch fire.
Elon Musk
SpaceX’s next project will produce Starships at a level that sounds impossible
1,000 rockets per year is an insane number, especially considering Starship’s sheer size.
Elon Musk has revealed bold plans for SpaceX’s newest Starbase facility in Texas, predicting it will become a birthplace for “so many spaceships.” The upcoming “Gigabay,” a massive $250 million production hub in Starbase, Texas, is designed to manufacture up to 1,000 Starship rockets per year.
That’s an insane number of rockets for a single facility, especially considering Starship’s sheer size.
One of the world’s largest industrial structures
SpaceX’s Gigabay is expected to stand roughly 380 feet tall and enclose 46.5 million cubic feet of interior space, making it one of the largest industrial structures to date. The facility will feature 24 dedicated work cells for assembling and refurbishing Starship and Super Heavy vehicles, complete with heavy-duty cranes capable of lifting up to 400 U.S. tons, as noted in a Times of India report.
Construction crews have already placed four tower cranes on-site, with completion targeted for December 2026. Once operational, the Gigabay is expected to boost SpaceX’s launch cadence dramatically, as it would be able to build up to 1,000 reusable Starships per year, as noted in a report from the Dallas Express. Musk stated that the Gigabay will be “one of the biggest structures in the world” and hinted that it represents a major leap in Starbase’s evolution from test site to full-scale production hub.
A key step toward Mars and beyond
Starship is SpaceX’s heavy-lift rocket system, and it remains a key part of Elon Musk’s vision of a multiplanetary future. The vehicle can carry 100–150 tonnes to low Earth orbit and up to 250 tonnes in expendable mode. With several successful flights to date, including a perfect 11th test flight, the Starship program continues to refine its reusable launch system ahead of crewed lunar missions under NASA’s Artemis initiative.
Starship is unlike any other spacecraft that has been produced in the past. As per Elon Musk, Starship is a “planet-colonizer” class rocket, as the magnitude of such a task “makes other space transport task trivial.” Considering Starship’s capabilities, it could indeed become the spacecraft that makes a Moon or Mars base feasible.
Tesla makes Elon Musk’s new compensation package official
Tesla provides vehicles for German firefighters’ EV training program
SpaceX’s next project will produce Starships at a level that sounds impossible
-
News4 days agoTesla shares rare peek at Semi factory’s interior
-
Elon Musk4 days agoTesla says texting and driving capability is coming ‘in a month or two’
-
News3 days agoTesla makes online ordering even easier
-
News3 days agoTesla Model Y Performance set for new market entrance in Q1
-
News4 days agoTesla Cybercab production starts Q2 2026, Elon Musk confirms
-
News4 days agoTesla China expecting full FSD approval in Q1 2026: Elon Musk
-
News5 days agoTesla Model Y Performance is rapidly moving toward customer deliveries
-
News2 days agoTesla is launching a crazy new Rental program with cheap daily rates