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”.
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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.
SpaceX announced today that it would expand its launch capabilities into a new U.S. state: Louisiana.
Today, SpaceX, in conjunction with the Louisiana Economic Development Office, said that it will establish a new launch facility, which it will call Starbase, Louisiana. It will be located near Vermilion Parish, supporting thousands of launches each year, at least eventually.
CEO Elon Musk commented by stating, “Starbase Louisiana will ultimately have over a dozen launch towers, enabling more than 30 Starship flights per day and making it the biggest launch site on Earth!”
Starbase Louisiana will ultimately have over a dozen launch towers, enabling more than 30 Starship flights per day and making it the biggest launch site on Earth!
SpaceX makes sci-fi real. https://t.co/C7Ht0U12ba
— Elon Musk (@elonmusk) August 25, 2026
The expansion is SpaceX’s latest move to push its launch cadence to be more frequent than ever. SpaceX said that Starbase, Louisiana, will be built to “support thousands of Starship flights a year,” with the first coming in 2029.
SpaceX announced the new facility in partnership with the Louisiana Economic Development Office as it will bring a major influx of jobs and investments into the area. Currently, it will produce more than 3,000 new jobs in Louisiana, and SpaceX plans to invest at least $100 billion into the entire facility, ensuring that many jobs are created as a result.
Environmental Responsibility
SpaceX acknowledges the impact launches could have on marshlands, local wildlife, and water sources. Here’s how the company plans to help with the issues in Vermilion Parish:
- Restoring the Shoreline: “In Vermilion Parish, the shoreline is eroding between 3.3 and 23 feet per year. We’re partnering with state and federal agencies to expand Louisiana’s Coastal Master Plan and Coastal Wetlands Planning, Protection and Restoration Act projects, including Gulf shoreline protection breakwaters designed to reduce wave energy and slow loss along the Gulf edge.”
- Rebuilding the Marshlands: “In working with the state, we’re planning thousands of acres of marsh creation using beneficial-use placement of dredged material and offshore sediment sources. Restoration will also include interior marsh bank stabilization and rebuilding marsh in remnant canals. These projects can reconnect fragmented wetlands, restore natural buffers against storms, and return habitat that has been lost to erosion and historic canalization.”
- Preserving Coastal Wildlife: “Pecan Island and nearby wetlands are high-value habitat for migratory waterfowl, shorebirds, wading birds, and other coastal wildlife. SpaceX is not developing the full footprint of the land and will preserve wetlands and wildlife habitat. At existing launch sites, waterfowl and other birds continue to use nearby habitat during operations. Working with wildlife agencies, landowners, and conservation groups, SpaceX will support monitoring and management so this habitat stays productive and hunting, fishing, birding, and other recreational activities that are part of this coast’s culture can continue.”
SpaceX shares rose about 2.5 percent on the news.
Tesla Cybertruck trims saw a big price change, at least on two of the three available to consumers, as demand for the all-electric pickup appears to be increasing.
Tesla bumped up its Base All-Wheel-Drive trim level up to $74,990 from $69,990 and the Premium All-Wheel-Drive configuration from $79,990 to $84,990. The Cyberbeast price remains unchanged at $99,990.
🚨 Cybertruck prices went up as Tesla bumped them 7%
– Tesla Cybertruck AWD is now $74,990
– Tesla Cybertruck Premium AWD now $84,990
– Tesla Cyberbeast now $99,990 https://t.co/MYJbaw56GL— TESLARATI (@Teslarati) August 25, 2026
Despite questions of demand for the truck, Tesla is bumping its two least expensive trims up $5,000 to signal that there are plenty of buyers. Although SpaceX has been buying Tesla Cybertruck units to utilize as company vehicles, it is no secret that the Cybertruck is among the most sought-after Tesla models out there.
The issue has always been pricing, at least for the most part. When Tesla initially launched the Cybertruck AWD at $59,990 a few months back, the company stated that price would remain intact for just ten days due to the influx of orders it received.
Cybertruck Sales: Is It the Product or Pricing?
Depending on who you ask, you will likely hear one of two explanations for relatively low Cybertruck sales: either the product itself or the pricing.
Yes, this is the best-selling all-electric pickup on the market. However, there are people who simply hate the look of it, which I understand, but do not agree with. Look is totally subjective, and I love the look of the Cybertruck.
Some people will not buy the Cybertruck because of the look, but I am under the impression that sales would be much better if this truck were priced lower; something that might not be possible considering Tesla’s need to make money on its products. When it was unveiled in 2019, its most expensive trim level was $69,990. Now, the cheapest trim level is more expensive than that.
I would be in a Cybertruck if it were more affordable. I LOVE my Model Y, but Cybertruck is the best vehicle Tesla makes, and it’s not particularly close. Even in the base model, the steer-by-wire, the space, storage, and performance make it more desirable than the Model Y to me. I cannot be the only Tesla owner without a Cybertruck who feels this way.
If you’re interested in buying a Tesla vehicle, use my referral link.
Energy
Tesla Semi factory is getting a celebration nobody expected
Tesla will inaugurate its Nevada Semi factory September 24, five months after production quietly began ramping.
Tesla says it will officially inaugurate its new Semi factory in Nevada next month. The Tesla Semi account posted the announcement on X, sharing a graphic titled “Semi Rollout” with a date of September 24. No further details were given about the format of the event or who would attend.
While Tesla’s dedicated Semi plant in Sparks, adjacent to Gigafactory Nevada, opened back in April, with the first trucks rolling off the high volume line on April 29, the timing for the factory inauguration comes at a surprise. The ribbon cutting event five months into production is a break from how Tesla has usually handled its other factories, where the first truck or car off the line typically served as the milestone moment.
Inauguration of new Semi factory in Nevada next month pic.twitter.com/a8kAlxrOOn
— Tesla Semi (@tesla_semi) August 24, 2026
The 1.7 million square foot factory was built as part of a $3.6 billion expansion Tesla announced in early 2023, and it shares a site with the battery cell lines that feed the Semi’s structural pack, a decision meant to remove the supply bottleneck that delayed the truck for years. The plant is designed for 50,000 trucks a year at full ramp. Semi program director Dan Priestley has said production “is now ramping” rather than claiming it has reached scale.
Nine years passed between the Semi’s 2017 unveiling and this stage of production, with the truck slipping from an original 2019 target through hand built pilot units for PepsiCo and a slow build out of the Nevada plant. An inauguration event now gives Tesla a stage to talk up that ramp and reset expectations for how many trucks it can begin delivering at scale.
The September date also lines up with the Semi’s next milestone. Tesla confirmed the truck is heading to Europe with a full unveiling at the IAA Transportation trade show in Hannover, Germany, running September 15 through 20. Between the Nevada event and the Hannover reveal, Tesla has roughly a week and a half in September to make the case that the Semi is now a truck being built and sold on two continents rather than tested in a handful of fleets.
SpaceX announces new Starbase for ‘thousands of Starship launches annually’
Tesla just made Cybertruck more expensive
