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
Elon Musk’s xAI and X to pay off $17.5B debt in full: report
The update was shared initially in a report from Bloomberg News, which cited people reportedly familiar with the matter.
Elon Musk’s social platform X and artificial intelligence startup xAI are reportedly preparing to repay approximately $17.5 billion in outstanding debt in full.
The update was shared initially in a report from Bloomberg News, which cited people reportedly familiar with the matter.
Morgan Stanley, which arranged the debt financing for both companies, has reportedly informed existing lenders that X and xAI plan to pay back the full amount of the $17.5 billion debt. Bloomberg’s sources did not disclose where the capital for the repayment would be coming from.
X, formerly known as Twitter, assumed roughly $12.5 billion in debt during Musk’s acquisition of the company. xAI separately borrowed about $5 billion through bonds and loans last June. The two firms merged last year under xAI Holdings.
Bloomberg noted that portions of the debt are relatively recent and may carry early repayment penalties. xAI’s $3 billion in high-yield bonds are expected to be redeemed at 117 cents on the dollar, reflecting a premium since the debt was expected to stay outstanding for at least two years.
X has been servicing tens of millions of dollars in monthly debt payments, while xAI has reportedly been burning approximately $1 billion in cash per month as it invests heavily in data centers, chips, and AI talent. That being said, xAI also concluded a funding round in January, where it raised $20 billion of new equity.
The repayment plans come as Musk consolidates several of his businesses. SpaceX recently acquired xAI, making it a subsidiary as the company explores plans for space-based data centers. The combined entity has been valued at approximately $1.25 trillion.
Bloomberg previously reported that SpaceX is targeting a confidential IPO filing as soon as this month, potentially positioning the private space firm for a public listing later this year. Representatives for Morgan Stanley declined to comment, and X and xAI did not immediately respond to requests for comment.
News
Tesla Giga Berlin head calls out Handelsblatt’s claimed 2025 production figures
Andre Thierig, Senior Director of Manufacturing at Giga Berlin, published a detailed post on LinkedIn challenging several points made in the publication’s coverage of the Grünheide facility.
Tesla Gigafactory Berlin’s plant manager has publicly pushed back against recent reporting by German business publication Handelsblatt, which cited reportedly erroneous data about the factory’s production figures and financial performance.
Andre Thierig, Senior Director of Manufacturing at Giga Berlin, published a detailed post on LinkedIn challenging several points made in the publication’s coverage of the Grünheide facility.
In his LinkedIn post, Thierig called out Handelsblatt’s claim that 149,000 Model Y vehicles were produced at Giga Berlin in 2025. He noted that “the article is simply filled from front to back with false information and claims!
“I have to set the record straight here! In the last article about Tesla in Grünheide, the Handelsblatt speaks e.g. of 149,000 Model Ys built in 2025. WRONG!
“In 2025, we again produced over 200,000 vehicles. And this despite the fact that we stopped production in Q1 for the changeover to the new Model Y and then ramped it up again to 5,000 units per week over several weeks,” Thierig wrote.
He added that production increased each quarter in 2025 compared to the prior quarter and stated that more than 700,000 Model Y units have been produced at Grünheide since manufacturing began in 2022. For the first quarter of 2026, he stated that the factory is planning another production increase compared to the fourth quarter of 2025.
Thierig also questioned Handelsblatt’s reported 0.74% profit margin, writing that how the publication calculated the figure “remains reserved for their secret ‘calculation skills.’”
Beyond production data, Thierig highlighted Tesla’s broader footprint in Germany, stating that the company has invested more than €5 billion in Grünheide since 2020 and created nearly 11,000 permanent, above-tariff jobs. He added that Tesla is currently investing nearly €100 million into battery cell production at the site, which is expected to generate several hundred additional positions.
In a follow-up comment, Thierig noted that he did communicate with the publication’s editor-in-chief in an effort to “start fresh,” but he was informed that Handelsblatt’s current approach works just fine.
“Last year, I spoke to a representative of the Handelsblatt editor-in-chief and suggested that we “start anew” again. Handelsblatt turned down this offer on the grounds that their current approach works well for them,” Thierig noted.
Sönke Iwersen, Head of Investigative Research at Handelsblatt, responded to Thierig’s post, stating that the newspaper’s figures were based on Tesla’s own annual financial statements for the Grünheide entity.
He cited reported 2024 revenue of €7.68 billion, operating profit of €156.8 million, and net income after taxes of €55.6 million. Iwersen also referenced prior public comments from Elon Musk about Cybertruck demand, noting the gap between reported pre-orders and subsequent annual sales figures.
He also stated that the works council election eligibility figures Giga Berlin had dropped to 10,703 employees today from 12,415 two years ago.
“As far as production figures are concerned, these are figures from the data service provider Inovev. This is also stated in the article. Please compare this with Elon Musk’s information on demand for the Cybertruck. According to Musk, there were one million pre-orders. In the first year, 39,000 units were sold, in the second year 20,000. How can this be explained? With a million pre-orders?
“You yourself have repeatedly pointed out in recent months that no jobs would be cut in Grünheide because Tesla is different from the competition. Now a new works council is being elected in Grünheide. 10,703 people are eligible to vote. Two years ago, 12,415 people were eligible to vote. So there were exactly 1712 fewer from 2024 to 2026,” Iwersen wrote.
News
I figured out how to charge my Tesla at my rented townhouse – Here’s how
I hope that this article is able to help the prospective EV buyer or the current Tesla owner who is living in a rental and does not have a straightforward solution to home charging. My situation will be presented in this article, and I will tell you why I went with the solution I went with, and alternatives, because there is more than one way to do this.
When I bought my Tesla Model Y Premium All-Wheel-Drive last year, I knew I would have to try to figure out a way not become totally reliant on Superchargers. After about six months of ownership, it came time to resolve that problem once and for good, and being a tenant in a rented townhouse community definitely added to my challenge.
Before I even bought my Tesla, I emailed my leasing office to see if the community had any plans to bring EV charging to the neighborhood. I had made myself available to them as I am familiar with a lot of the solutions out there and how much of an advantage this could be for the community, and attracting new tenants. After months of trying, I bought my Tesla in August anyway, and figured I’d be able to find an answer — whether positive or negative — and go from there.
I hope that this article is able to help the prospective EV buyer or the current Tesla owner who is living in a rental and does not have a straightforward solution to home charging. My situation will be presented in this article, and I will tell you why I went with the solution I went with, and alternatives, because there is more than one way to do this.
My Challenge with Home Charging
In a rental community, apartment complex, or even townhouse row, parking spots are a little complicated. I have assigned parking at my house, and unfortunately, my parking spot is not right in front of my front door. Instead, it is staggered, so my car is parked in front of my neighbor’s front door.
Initially, I had spoken to my neighbor whose spot is right in front of my front door and had gotten permission to park in their spot during the day while it is vacant. However, I was not going to be able to upgrade my outlet from a 110v-120v to the typical and suggested 220v-240v alternative.

I knew that this would mean I would need to be in my permanent spot because charging sufficiently, especially in preparation for trips or errands, would require overnight charging.
The Tesla Mobile Connector is 20 feet long, which is sufficient for most applications. Mine, however, required about 30 feet, maybe even a little more, to charge.
My Options
I had a few options: Use the Mobile Connector and park in my neighbor’s spot and charge when I could, buy an 8 or 10-gauge extension cord that could handle moving power from the Mobile Connector to my car, or buy an NACS to NACS extension cord.
I didn’t really want to do the first option, considering I knew that spot would only be available when my neighbor was not there. It didn’t seem like a viable option, and I figured it would be better to figure out something from my personal, permanent parking spot anyway.
The 10-gauge extension cord option was what I first considered: it was less expensive than buying an NACS extension, it was more readily available, and it was the first thing my friends who are electricians recommended.
However, running this option would have put the Mobile Connector in the grass or on the ground, and I was not interested in doing that. Running the risk of having that $300 connector that came with the car in the grass and exposing it to dew, dogs, and various other things just did not seem like the best idea.

I looked around for some NACS to NACS connectors, and there are a lot of options. Given that this was something that was going to plug into a $50,000 car, I chose to spend the additional money on one that was not from Amazon, and I went with this one from A2Z, which was recommended by other owners, and their reputation seemed more than positive. I was leaning toward this option anyway because it would keep the Mobile Connector off the ground, and it gave me an additional 16 feet of length to work with.
This was the solution.
Putting It Into Action
It was a relatively simple process: Plug the Mobile Connector into my house, plug the NACS to NACS extension into the Mobile Connector, plug the NACS extension into the car. It all worked immediately, but there are some things you should know if you are also planning to do this.
The first is that you should be very aware that these cables are going to be a target of thieves. I don’t have too much of an issue with this in my area, but if you’re in a place where copper wiring is heavily sought after, be sure to keep these in a place where they won’t be stolen. I put mine away when they’re not charging, and at night, they’re visible from my Ring camera, so I’m not overly concerned. Definitely be aware of it, though.
Additionally, if you’re going to run it across the sidewalk like I am, you’re going to want to pick up some sort of cable cover from a local hardware store. I picked up this one from Amazon because it was a little more heavy-duty, and it was big enough to cover the thicker gauge of the NACS to NACS extension:
I’ve considered picking up a second one for the visible cable, but I am undecided.
So far, I’ve been able to add some range to my car three times using this strategy, and while it is very slow, it is definitely worth it. It’s better than it sitting there stagnant.
Speed of Charging
Tesla says the Mobile Connector will provide you with between 3 and 5 miles of range per hour when plugged into a typical wall outlet. That is about what I’ve gotten with it. From 30 percent to 80 percent, be aware that it will take well over 24 hours to charge your car.

I plan to cover some additional details on this as time goes on, including any troubleshooting I might have to do, how much my electric bill goes up, and whether or not I run into any issues with my neighbors or my leasing office.
If you’re looking for some help on an at-home charging solution or have any questions about my setup, please email me at joey@teslarati.com.
🚨 I FINALLY figured out a way to charge my Tesla at home as a renter — Using Superchargers exclusively was inconvenient, tough on the battery, and expensive
Here’s how I did it: https://t.co/TZokpc6Fh3 pic.twitter.com/UtRYKLvB2Y
— TESLARATI (@Teslarati) March 2, 2026









