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.
Despite many recent rumors and various reports, Elon Musk confirmed today that SpaceX is not developing a phone based on Starlink, not once, but twice.
Today’s report from Reuters cited people familiar with the matter and stated internal discussions have seen SpaceX executives mulling the idea of building a mobile device that would connect directly to the Starlink satellite constellation.
Musk did state in late January that SpaceX developing a phone was “not out of the question at some point.” However, He also said it would have to be a major difference from current phones, and would be optimized “purely for running max performance/watt neural nets.”
Not out of the question at some point. It would be a very different device than current phones. Optimized purely for running max performance/watt neural nets.
— Elon Musk (@elonmusk) January 30, 2026
While Musk said it was not out of the question “at some point,” that does not mean it is currently a project SpaceX is working on. The CEO reaffirmed this point twice on X this afternoon.
Musk said, “Reuters lies relentlessly,” in one post. In the next, he explicitly stated, “We are not developing a phone.”
Reuters lies relentlessly
— Elon Musk (@elonmusk) February 5, 2026
We are not developing a phone
— Elon Musk (@elonmusk) February 5, 2026
Musk has basically always maintained that SpaceX has too many things going on, denying that a phone would be in the realm of upcoming projects. There are too many things in the works for Musk’s space exploration company, most notably the recent merger with xAI.
SpaceX officially acquires xAI, merging rockets with AI expertise
A Starlink phone would be an excellent idea, especially considering that SpaceX operates 9,500 satellites, serving over 9 million users worldwide. 650 of those satellites are dedicated to the company’s direct-to-device initiative, which provides cellular coverage on a global scale.
Nevertheless, there is the potential that the Starlink phone eventually become a project SpaceX works on. However, it is not currently in the scope of what the company needs to develop, so things are more focused on that as of right now.
Tesla has added a notable improvement to its Dashcam feature after complaints from owners have pushed the company to make a drastic change.
Perhaps one of the biggest frustrations that Tesla owners have communicated regarding the Dashcam feature is the lack of ability to retain any more than 60 minutes of driving footage before it is overwritten.
It does not matter what size USB jump drive is plugged into the vehicle. 60 minutes is all it will hold until new footage takes over the old. This can cause some issues, especially if you were saving an impressive clip of Full Self-Driving or an incident on the road, which could be lost if new footage was recorded.
This has now been changed, as Tesla has shown in the Release Notes for an upcoming Software Update in China. It will likely expand to the U.S. market in the coming weeks, and was first noticed by NotaTeslaApp.
The release notes state:
“Dashcam Dynamic Recording Duration – The dashcam dynamically adjusts the recording duration based on the available storage capacity of the connected USB drive. For example, with a 128 GB USB drive, the maximum recording duration is approximately 3 hours; with a 1 TB or larger USB drive, it can reach up to 24 hours. This ensures that as much video as possible is retained for review before it gets overwritten.”
Tesla Adds Dynamic Recording
Instead of having a 60-minute cap, the new system will now go off the memory in the USB drive. This means with:
- 128 GB Jump Drive – Up to Three Hours of Rolling Footage
- 1TB Jump Drive – Up to 24 Hours of Rolling Footage
This is dependent on the amount of storage available on the jump drive, meaning that if there are other things saved on it, it will take away from the amount of footage that can be retained.
While the feature is just now making its way to employees in China, it will likely be at least several weeks before it makes its way to the U.S., but owners should definitely expect it in the coming months.
It will be a welcome feature, especially as there will now be more customization to the number of clips and their duration that can be stored.
With the news of a merger between SpaceX and xAI being confirmed earlier this week by CEO Elon Musk directly, the first moves of an umbrella company that combines all of the serial tech entrepreneur’s companies have been established.
The move aims to combine SpaceX’s prowess in launches with xAI’s expanding vision in artificial intelligence, as Musk has detailed the need for space-based data centers that will require massive amounts of energy to operate.
It has always been in the plans to bring Musk’s companies together under one umbrella.
“My companies are, surprisingly in some ways, trending toward convergence,” Musk said in November. With SpaceX and xAI moving together, many are questioning when Tesla will be next. Analysts believe it is a no-brainer.
SpaceX officially acquires xAI, merging rockets with AI expertise
Dan Ives of Wedbush wrote in a note earlier this week that there is a “growing chance” Tesla could be merged in some form with the new conglomeration over the next 12 to 18 months.
“In our view, there is a growing chance that Tesla will eventually be merged in some form into SpaceX/xAI over time. The viewis this growing AI ecosystem will focus on Space and Earth together… and Musk will look to combine forces,” Ives said.
Let’s take a look at the potential.
The Case for Synergies – Building the Ultimate AI Ecosystem
A triple merger would create a unified “Musk Trinity,” blending Tesla’s physical AI with Robotaxi, Optimus, and Full Self-Driving, SpaceX’s orbital infrastructure through Starlink and potential space-based computer, and xAI’s advanced models, including Grok.
This could accelerate real-world AI applications, more specifically, ones like using satellite networks for global autonomy, or even powering massive training through solar-optimized orbital data centers.
The FCC welcomes and now seeks comment on the SpaceX application for Orbital Data Centers.
The proposed system would serve as a first step towards becoming a Kardashev II-level civilization and serve other purposes, according to the applicant. pic.twitter.com/TDnUPuz9w7
— Brendan Carr (@BrendanCarrFCC) February 4, 2026
This would position the entity, which could ultimately be labeled “X,” as a leader in multiplanetary AI-native tech.
It would impact every level of Musk’s AI-based vision for the future, from passenger use to complex AI training models.
Financial and Structural Incentives — and Risks
xAI’s high cash burn rate is now backed by SpaceX’s massive valuation boost, and Tesla joining the merger would help the company gain access to private funding channels, avoiding dilution in a public-heavy structure.
The deal makes sense from a capital standpoint, as it is an advantage for each company in its own specific way, addressing specific needs.
Because xAI is spending money at an accelerating rate due to its massive compute needs, SpaceX provides a bit of a “lifeline” by redirecting its growing cash flows toward AI ambitions without the need for constant external fundraising.
Additionally, Tesla’s recent $2 billion investment in xAI also ties in, as its own heavy CapEx for Dojo supercomputers, Robotaxis, and Optimus could potentially be streamlined.
Musk’s stake in Tesla and SpaceX, after the xAI merger, is also uneven. His ownership in Tesla equates to about 13 percent, only increasing as he achieves each tranche of his most recent compensation package. Meanwhile, he owns about 43 percent of the private SpaceX.
A triple merger between the three companies could boost his ownership in the combined entity to around 26 percent. This would give Musk what he wants: stronger voting power and alignment across his ventures.
It could also be a potential facilitator in private-to-public transitions, as a reverse merger structure to take SpaceX public indirectly via Tesla could be used. This avoids any IPO scrutiny while accessing the public markets’ liquidity.
Timeline and Triggers for a Public Announcement
As previously mentioned, Ives believes a 12-18 month timeline is realistic, fueled by Musk’s repeated hints at convergence between his three companies. Additionally, the recent xAI investment by Tesla only points toward the increased potential for a conglomeration.
Of course, there is speculation that the merger could happen in the shorter term, before June 30 of this year, which is a legitimate possibility. While this possibility exists but remains at low probability, especially when driven by rapid AI/space momentum, longer horizons, like 2027 or later, allow for key milestones like Tesla’s Robotaxi rollout and Cybercab ramp-up, Optimus scaling, or regulatory clarity under a favorable administration.
Credit: Grok Imagine
The sequencing matters: SpaceX-xAI merger as “step one” toward a unified stack, with a potential SpaceX IPO setting a valuation benchmark before any Tesla tie-up.
Full triple convergence could follow if synergies prove out.
Prediction markets are also a reasonable thing to look at, just to get an idea of where people are putting their money. Polymarket, for example, sits at between a 12 and 24 percent chance that a Tesla-SpaceX merger is officially announced before June 30, 2026.
Looking Ahead
The SpaceX-xAI merger is not your typical corporate shuffle. Instead, it’s the clearest signal yet that Musk is architecting a unified “Muskonomy” where AI, space infrastructure, and real-world robotics converge to solve humanity’s biggest challenges.
Yet the path is fraught with execution risks that could turn this visionary upside into a major value trap. Valuation mismatches remain at the forefront of this skepticism: Tesla’s public multiples are unlike any company ever, with many believing they are “stretched.” On the other hand, SpaceX-xAI’s private “marked-to-muth” pricing hinges on unproven synergies and lofty projects, especially orbital data centers and all of the things Musk and Co. will have to figure out along the way.
Ultimately, the entire thing relies on a high-conviction bet on Musk’s ability to execute at scale. The bullish case is transformative: a vertically integrated AI-space-robotics giant accelerates humanity toward abundance and multi-planetary civilization faster than any siloed company could.
Elon Musk confirms SpaceX is not developing a phone
Tesla adds notable improvement to Dashcam feature
