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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.
Tesla has finally announced the features for the 2025 Holiday Update, which includes a wide variety of new inclusions that are both functional and just for fun.
The new features are plentiful, but there were a handful of things we were expecting to see based on what we know. We don’t want to sound ungrateful, because there are a lot of great new things on the way with this update.
Here’s what was included:
Grok with Navigation Commands (Beta)
Grok will now have the ability to add and edit navigation destinations, which is a drastic improvement considering Tesla owners had to use their standard voice commands for this in the past.
The utilization of Grok will likely improve the navigation experience by offering some insight into your destination, including reviews and other points of interest nearby.
It will be enabled by using Grok’s “Assistant” personality.
Tesla Photobooth
“Turn your car into a photobooth! Take selfies from inside your Tesla & give yourself a makeover with fun filters, stickers, and emojis. Share with others right from the Tesla app.”
This feature will be available within the Toybox.
Dog Mode Live Activity
When using Dog Mode to keep your four-legged friend comfortable in the car, you’ll now be able to check in on them as it will share periodic snapshots of the cabin, along with live updates on temperature, battery, and climate conditions.
Dashcam Viewer Update
Dashcam clips are awesome, but they’re void of a lot of information, which could be useful in some instances, especially if there is an accident.
Now, there will be additional details included on each Dashcam clip, like speed, steering wheel angle, and Self-Driving state.
Santa Mode
New graphics, trees, and a lock chime are now available.
Light Show Update
A new Light Show, called Jingle Rush, will be available.
Custom Wraps and License Plates in Colorizer
Colorizer will now be known as “Paint Shop” in the Toybox. You will now be able to personalize your Tesla Avatar with window tints, custom wraps, and license plates. Preloaded designs will be available, but owners will be able to use their USB Flash Drives to create one that suits their style.
Navigation Improvements
Changing the order of your destinations will be easier through a new “Favorites” tab, and Home and Work can now be set by dropping a pin.
There will also be “Suggested Destinations,” which will be determined through recent trips and habits while parked.
Supercharger Site Map
Perhaps the most significant feature of the Holiday Update, Tesla is adding a 3D view of select Tesla Superchargers by tapping “View Site Map.”
When navigating to a location with this capability, the site layout, live occupancy, and nearby amenities will be available. Drivers will also be able to choose which stall to Supercharge.
This is only available at a handful of locations currently, but it will expand to more Superchargers as it becomes more robust.
Automatic Carpool Lane Routing
Navigation will include an option to utilize carpool lanes. Your route will automatically choose the carpool lane when eligible.
Phone Left Behind Chime
If the in-car occupant detection system does not see anyone in the car and there is a phone key, or if a phone is left inside the cabin, your Tesla will chime a few seconds after the doors close.
Charge Limit Per Location
You can now save a charge limit for the current location while parked and it will be applied automatically the next time you charge there.
ISS Docking Simulator
In a SpaceX collaboration, Tesla has added this game to its in-car Arcade:
“Become an astronaut and prove your skills by docking with the International Space Station. Control & guide the rocket in this 3D docking simulator game using a set of controls based on actual interfaces used by NASA astronauts.”
Additional Improvements
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Enable or disable wireless phone charging pads in Controls > Charging (S3XY) or Controls > Outlets & Mods (Cybertruck)
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Add Spotify tracks to your queue right from the search screen & scroll through large Spotify playlists, albums, podcasts, audiobooks & your library seamlessly, without paging
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Take the vibes up another level with rainbow colors during Rave Cave. Accent lights color will change along with the beats of your music. App Launcher > Toybox > Light Sync
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Lock Sound now includes Light Cycle from Tron Mode. Toybox > Boombox > Lock Sound
What’s Missing
There are a handful of features we expected to see with the Holiday Update, but were not included.
Banish Feature
Tesla has been teasing the Banish functionality for quite a few years, but evidently, it is not quite there yet.
Banish will allow owners to get out of their vehicle at the entrance of their destination, and the car will go find a spot and park itself. Some refer to it as “Reverse Summon.”
Apple CarPlay
With all of the rumors regarding Apple CarPlay and then the evidence that Tesla was working to bring CarPlay to vehicles, we really expected it to come with the Holiday Update.
We’re not upset it’s not here, though. Tesla’s in-car UI is significantly better, at least in our opinion.
Parking Spot Selection
One of the biggest gripes about the new Arrival Features with Full Self-Driving v14 is that choosing a set parking spot is not available. This is especially frustrating for Tesla owners who rent or live in townhouse neighborhoods or apartment complexes with assigned parking.
Tesla seems to be working on this based on the release notes for v14.2, where it said future capabilities would include Parking Spot Selection.
News
Man credits Grok AI with saving his life after ER missed near-ruptured appendix
The AI flagged some of the man’s symptoms and urged him to return to the ER immediately and demand a CT scan.
A 49-year-old man has stated that xAI’s Grok ended up saving his life when the large language model identified a near-ruptured appendix that his first ER visit dismissed as acid reflux.
After being sent home from the ER, the man asked Grok to analyze his symptoms. The AI flagged some of the man’s symptoms and urged him to return immediately and demand a CT scan. The scan confirmed that something far worse than acid reflux was indeed going on.
Grok spotted what a doctor missed
In a post on Reddit, u/Tykjen noted that for 24 hours straight, he had a constant “razor-blade-level” abdominal pain that forced him into a fetal position. He had no fever or visible signs. He went to the ER, where a doctor pressed his soft belly, prescribed acid blockers, and sent him home.
The acid blockers didn’t work, and the man’s pain remained intense. He then decided to open a year-long chat he had with Grok and listed every detail that he was experiencing. The AI responded quickly. “Grok immediately flagged perforated ulcer or atypical appendicitis, told me the exact red-flag pattern I was describing, and basically said “go back right now and ask for a CT,” the man wrote in his post.
He copied Grok’s reasoning, returned to the ER, and insisted on the scan. The CT scan ultimately showed an inflamed appendix on the verge of rupture. Six hours later, the appendix was out. The man said the pain has completely vanished, and he woke up laughing under anesthesia. He was discharged the next day.
How a late-night conversation with Grok got me to demand the CT scan that saved my life from a ruptured appendix (December 2025)
byu/Tykjen ingrok
AI doctors could very well be welcomed
In the replies to his Reddit post, u/Tykjen further explained that he specifically avoided telling doctors that Grok, an AI, suggested he get a CT scan. “I did not tell them on the second visit that Grok recommended the CT scan. I had to lie. I told them my sister who’s a nurse told me to ask for the scan,” the man wrote.
One commenter noted that the use of AI in medicine will likely be welcomed, stating that “If AI could take doctors’ jobs one day, I will be happy. Doctors just don’t care anymore. It’s all a paycheck.” The Redditor replied with, “Sadly yes. That is what it felt like after the first visit. And the following night could have been my last.”
Elon Musk has been very optimistic about the potential of robots like Tesla Optimus in the medical field. Provided that they are able to achieve human-level articulation in their hands, and Tesla is able to bring down their cost through mass manufacturing, the era of AI-powered medical care could very well be closer than expected.
News
Tesla expands Model 3 lineup in Europe with most affordable variant yet
The Model 3 Standard still delivers more than 300 miles of range, potentially making it an attractive option for budget-conscious buyers.
Tesla has introduced a lower-priced Model 3 variant in Europe, expanding the lineup just two months after the vehicle’s U.S. debut. The Model 3 Standard still delivers more than 300 miles (480 km) of range, potentially making it an attractive option for budget-conscious buyers.
Tesla’s pricing strategy
The Model 3 Standard arrives as Tesla contends with declining registrations in several countries across Europe, where sales have not fully offset shifting consumer preferences. Many buyers have turned to options such as Volkswagen’s ID.3 and BYD’s Atto 3, both of which have benefited from aggressive pricing.
By removing select premium finishes and features, Tesla positioned the new Model 3 Standard as an “ultra-low cost of ownership” option of its all-electric sedan. Pricing comes in at €37,970 in Germany, NOK 330,056 in Norway, and SEK 449,990 in Sweden, depending on market. This places the Model 3 Standard well below the “premium” Model 3 trim, which starts at €45,970 in Germany.
Deliveries for the Standard model are expected to begin in the first quarter of 2026, giving Tesla an entry-level foothold in a segment that’s increasingly defined by sub-€40,000 offerings.
Tesla’s affordable vehicle push
The low-cost Model 3 follows October’s launch of a similarly positioned Model Y variant, signaling a broader shift in Tesla’s product strategy. While CEO Elon Musk has moved the company toward AI-driven initiatives such as robotaxis and humanoid robots, lower-priced vehicles remain necessary to support the company’s revenue in the near term.
Reports have indicated that Tesla previously abandoned plans for an all-new $25,000 EV, with the company opting to create cheaper versions of existing platforms instead. Analysts have flagged possible cannibalization of higher-margin models, but the move aims to counter an influx of aggressively priced entrants from China and Europe, many of which sell below $30,000. With the new Model 3 Standard, Tesla is reinforcing its volume strategy in Europe’s increasingly competitive EV landscape.
Tesla 2025 Holiday Update: Here’s what it includes, and what it’s missing
Man credits Grok AI with saving his life after ER missed near-ruptured appendix
