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.
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Tesla appears to be making a change to its exterior side repeater cameras, which are used for the company’s Full Self-Driving suite, and other features, like Sentry Mode.
The change appears to be a potential upgrade in preparation for the AI5 suite, which CEO Elon Musk said will be present on a handful of vehicles next year, but will not be widely implemented until 2027.
Currently, Tesla uses a Sony sensor lens with the model number IMX963, a 5-megapixel camera with better dynamic range and low-light performance over the past iteration in Hardware 3 vehicles. Cameras in HW3 cars were only 1.2 megapixels.
However, Tesla is looking to upgrade, it appears, as Tesla hacker greentheonly has spotted a new sensor model in its firmware code, with the model number IMX00N being explicitly mentioned:
Looks like Tesla is changing (upgrading?) cameras in (some?) new cars produced.
Where as HW4 to date used exterior cameras with IMX963, now they (might potentially) have something called IMX00N— green (@greentheonly) December 1, 2025
Sony has not announced any formal specifications for the IMX00N model, and although IMX963 has been used in AI4/HW4 vehicles, it only makes sense that Tesla would prepare to upgrade these external cameras once again in preparation for what it believes to be the second hardware iteration capable of fully autonomous self-driving.
Tesla has maintained that AI4/HW4 vehicles are capable of self-driving operation, but AI5 will likely help the company make significant strides, especially in terms of overall performance and data collection.
Tesla last updated its exterior cameras on its vehicles back in early 2023, as it transitioned to the 5-megapixel IMX963. It also added additional cameras to its vehicles in January with the new Model Y, which featured an additional lens on the front bumper to help with Full Self-Driving.
Tesla’s new self-driving computer (HW4): more cameras, radar, and more
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Tesla launched the Model Y Standard as an attempt to offer affordable electric vehicles to consumers now that the $7,500 EV tax credit is gone. We were able to spend four days with the car, and it was more than enough time to determine whether or not the car was worth the $9,000 discount compared to the Premium All-Wheel-Drive configuration, which is what I drive daily.
The Model Y Standard was stripped of some of the features that are present in the Premium trims of the Model Y: no glass roof, a sound system with roughly half the speakers, fewer acoustic-lined glass windows, less storage, and less functionality from an interior standpoint.
However, there are some real advantages to purchasing a Standard Model Y, and there are a handful of situations where this car would be well-suited.
Do I think it is worth the lower price? Well, I’ll get to that later in this article.
Initial Thoughts
In my first impressions review of the Model Y Standard, I talked about the face-value differences between my Model Y Premium and the new, more affordable trim. You will first notice the lack of storage between the front two seats, as the cupholder and additional storage bin sliding doors are void. You still get the cupholders, but they are exposed, which isn’t a huge deal, but it definitely takes away from the sleek look the Premium trim offers.
-->Additionally, the textile seats replace those of the vegan leather that is available in the upper-level trims. I mentioned previously that I could take or leave the vegan leather for the textile seats, as they are easy to clean, quick drying, and hide oils from your skin much better than leather does.
However, there comes one big sacrifice that I have been spoiled by, as the textile seats are not ventilated, so say goodbye to cooling your keister in the Summertime.
The lack of a glass roof is something many owners might not even notice. However, I have been spoiled by the glass roof in my car, and I look out of it every time I’m in my car. It is one of my favorite features, without a doubt. While it would not be a dealbreaker for me, it would be something I would miss terribly.
Things I Noticed After Several Days
Cabin Noise
One of the biggest things I noticed after the first two days in the Model Y Standard is that the cabin is much louder than the Premium. This is because Tesla did not acoustically line all of the glass in the Standard configuration, as it did in the Premium. The side windows are not treated, just the windshields. Therefore, you notice the noise level in the cabin is louder than in the Premium.
If you had not been driving in a Premium trim for a few months, you might not notice it. However, it is something that is a big sacrifice when moving to a different trim level, especially one that is less premium than what you might currently drive.
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I have always been so shocked at how amazingly quiet the Premium trim’s cabin is; my Model Y is extremely peaceful, even when I’m sitting in bumper-to-bumper traffic, and people have modified mufflers and exhaust systems, tractor-trailers are going by, or crotchrockets are zipping by on the interstate.
This is a huge difference between the two cars, and it is something that is really hard to get used to. I know, first-world problems, right? But when you’re paying between $39,990 and $48,990 for a car, those little things truly do matter.
Stereo System Differences
Another thing I was very aware of was how weak the sound system is. I think if I had bought a Standard Model Y, I would have looked at having the speakers and subwoofers upgraded; I was almost disappointed in how much of a change it was between the two cars.
When I finally picked up my Model Y Premium on Friday (which had been detailed by the awesome team at Tesla Mechanicsburg), the first thing I did was crank up the volume and listen to some music. I really missed having a premium sound system.
Ride Quality
There are virtually no differences between the two cars in terms of ride quality. They are both extremely fun to drive, and the suspension in the Model Y Standard feels perhaps a little bit stiffer than the Premium. Regardless, I didn’t truly notice all that much of a change.
-->Driving this car around windy roads and tight turns was just as fun as my Model Y Premium. It was a blast to test out, and the slight change in feel was welcome. It’s always fun to drive new cars.
Performance
This is the first EV I’ve ever ridden in where I did not feel that awesome sensation of instant torque. It’s still a quick car, but it is missing that pep in its step that many of us have become accustomed to.
If you want to get someone’s true reaction to EV acceleration, let me just put it this way: This is not the car to do it in.
Some Little-Known Facts About the Model Y Standard
Most of us know that the Model Y Standard has a glass roof, but it is opaque, so even if you took out the headliner, you still would not see out of it. However, there is an interesting little tidbit from a Service perspective that does not make much sense.
If the Model Y glass roof cracks or is broken and needs to be replaced, Service is required to pull off the entire headliner and topside interior to access the glass. It cannot be replaced from the outside. In the Premium, because the glass is exposed, it is a much simpler process to replace the glass. This was an interesting thing I learned.
-->Additionally, the seat controls are only available on the center screen, which makes it difficult to adjust the seat if you are larger than the person who sat in the car previously. In order to adjust the seat, you’ll have to lean over the chair, access the controls from the screen, and adjust it manually before getting in.
Is the Tesla Model Y Standard Worth the Cheaper Price?
For an additional $9,000 to buy the Model Y Premium AWD, you would get a more capable powertrain, a quieter cabin, better performance, an upgraded interior, more storage, a better sound system, and more luxury features.
To me, the Standard is a car that seems extremely ideal for a teenager’s first vehicle (I got a $1,500 1998 VW Jetta K2 with 200,000 miles when I was 16), or a fleet vehicle. This would be the perfect car for salespeople to use: it does not have all the bells and whistles, it is efficient, and it is just what is needed to drive around to meetings.
For a personal car, it really depends on what you think you need. Admittedly, I’ve been spoiled by the Premium configuration, and personally, I wouldn’t go down to the Standard after owning a Premium trim.
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Tesla’s new Holiday perk is timed perfectly to make FSD a household name
Tesla AI4 owners get FSD (Supervised) through Christmas, New Year’s Eve and well into the post-holiday travel season.
Tesla quietly rolled out a free Full Self-Driving (Supervised) trial for roughly 1.5 million HW4 owners in North America who never bought the package, and the timing could very well be genius.
As it turns out, the trial doesn’t end after 30 days. Instead, it expires January 8, 2026, meaning owners get FSD (Supervised) through Christmas, New Year’s Eve and well into the post-holiday travel season. This extended window positions the feature for maximum word-of-mouth exposure.
A clever holiday gift
Tesla watcher Sawyer Merritt first spotted the detail after multiple owners shared screenshots showing the trial expiring on January 8. He confirmed with affected users that none had active FSD subscriptions before the rollout. He also observed that Tesla never called the promotion a “30-day trial,” as the in-car message simply reads “You’re Getting FSD (Supervised) For the Holidays,” which technically runs until after the new year.
The roughly 40-day period covers peak family travel and gatherings, giving owners ample opportunity to showcase the latest FSD V14’s capabilities on highway trips, crowded parking lots and neighborhood drives. With relatives riding along, hands-off highway driving and automatic lane changes could become instant conversation starters.
Rave reviews for FSD V14 highlight demo potential
FSD has been receiving positive reviews from users as of late. Following the release of FSD v14.2.1, numerous owners praised the update for its smoothness and reliability. Tesla owner @LactoseLunatic called it a “huge leap forward from version 14.1.4,” praising extreme smoothness, snappy lane changes and assertive yet safe behavior that allows relaxed monitoring.
-->Another Tesla owner, @DevinOlsenn, drove 600 km without disengagements, noting his wife now defaults to FSD for daily use due to its refined feel. Sawyer Merritt also tested FSD V14.2.1 in snow on unplowed New Hampshire roads, and the system stayed extra cautious without hesitation. Longtime FSD tester Chuck Cook highlighted improved sign recognition in school zones, showing better dynamic awareness. These reports of fewer interventions and a more “sentient” drive could turn family passengers into advocates, fueling subscriptions come January.
Tesla is making a change to its exterior cameras with a potential upgrade
Tesla Model Y Standard Full Review: Is it worth the lower price?
