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Ex-SpaceX engineer leads Stratolaunch to major rocket engine test milestone
Led by rocket propulsion expert Jeff Thornburg, Stratolaunch – famous for owning the largest fixed-wing aircraft ever built – has completed the first hot-fire test of a full-scale rocket engine component known as the preburner, a major milestone in the development of any launch vehicle or propulsion system.
Despite the significant size and power of the component, destined to support an engine that will generate 200,000 pounds (~900 kN) of thrust, Thornburg and his team of engineers and technicians have managed to go from designing the preburner to successfully hot-firing a full-scale test article, an extraordinary achievement by any measure.
The team made amazing progress this week! Check out the #PGAEngine preburner’s first hot-fire test at @NASAStennis. #NewUSEngine pic.twitter.com/kKTnf0bj1S
— Stratolaunch (@Stratolaunch) November 6, 2018
Aside from SpaceX, Blue Origin, and Aerojet-Rocketdyne, Stratolaunch is the only private entity developing – let alone testing full-scale parts for – a liquid-fueled rocket engine as large as PGA. Shorthand for the Stratolaunch’s late founder and bankroller Paul G. Allen, PGA is a fuel-rich staged combustion cycle engine that uses liquid hydrogen and oxygen (hydrolox) fuel and oxidizer, typically resulting in high efficiency. In terms of scale and thrust, PGA is very closely comparable to SpaceX’s Merlin 1D engine, which uses kerosene instead of hydrogen but produces roughly 190,000 lbf (850 kN) of thrust and stands 4 feet (1.2m) wide and ~10 feet (~3m) tall.
Another major difference between PGA and Merlin 1D is the fact Merlin 1D’s nozzle is largely optimized for sea level while PGA is being built for a rocket that will be “launched” from a massive plane flying around 35,000 feet (~10.5 km), ultimately resulting in a nozzle that is much wider and longer, featuring nearly the same proportions as fully vacuum-optimized engines like SpaceX’s MVac. By widening the nozzle relative to the rest of the engine, rocket engines are able to operate far more efficiently at higher altitudes, where Earth’s atmosphere thins and exerts less pressure on the escaping exhaust gases. This is visualized well by the visible expansion of rocket exhausts during launches, morphing from a straight cylinder to a massive teardrop-shaped plume. At lower altitudes (and thus higher atmospheric pressures), wider nozzles can produce extreme turbulence and will ultimately shake themselves to destruction, preventing their usage on ground-launched rocket boosters.
Judging from official renders of the engine, PGA’s in-atmosphere variant appears to utilize a form of regenerative nozzle cooling very similar to that used on M1D, where liquid propellant flows through thin capillaries sandwiched between two or more layers of metal to cool the nozzle much like cold water chills the skin of an uninsulated water bottle.
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- A to-scale comparison of Falcon 1, Pegasus XL, MLV, and Falcon 9. (Teslarati/Stratolaunch/Wikipedia)
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- A render of Stratolaunch’s impressive PGA engine. Note the giant nozzle relative to the throat. (Stratolaunch)
Testing rocket engine preburners
In the case of staged combustion cycle hydrolox rocket engines, a small portion of liquid oxygen and all of the liquid hydrogen (hence “fuel-rich”) are mixed and combusted to generate hot gas that then spools up the engine’s primary turbopump(s), ultimately drawing fuel and oxidizer into the combustion quickly enough to ignite the engine and generate sustained thrust. The components that get those main turbopumps started are known collectively as the preburner, which is what Stratolaunch successfully tested – at full-scale – for the first time ever last week. For any liquid rocket engine that cannot solely rely on propellant tank pressure to deliver fuel to the combustion chamber, full-scale tests of preburners or gas-generators effectively mark the moment that engines truly become real.
“This is the first step in proving the performance and highly efficient design of the PGA engine. The hot-fire test is an incredible milestone for both the propulsion team and Stratolaunch.” – Jeff Thornburg, VP of Propulsion, Stratolaunch
Stratolaunch’s propulsion team will continue to test the preburner for longer durations and at higher power levels over the next several months, likely optimizing operations and tweaking or upgrading the preburner’s hardware as real tests produce valuable lessons-learned. Built entirely with additive manufacturing (3D printing), the team should be able to rapidly iterate on the physical design of the engine, a rarity in a field where traditional fabrication methods can take weeks or months to produce complex turbomachinery components with mercilessly strict tolerances.
According to Thornburg, the ultimate goal is to continue that additive-manufacturing-only strategy throughout the development of this rocket engine, theoretically enabling unprecedented design flexibility while also slashing production time throughout. PGA will ultimately power the creatively-named Medium Launch Vehicle (MLV), a small-ish air-launched rocket designed to place a respectable 3400 kg into low Earth orbit (LEO) as early as 2022, as well as a Heavy version of MLV and, potentially, a reusable spaceplane somewhere down the line.
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- PGA’s first full-scale preburner seen during assembly. (Stratolaunch)
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- PGA’s first full-scale preburner seen during assembly. (Stratolaunch)
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- Jeff Thornburg stands in front of Stratolaunch’s NASA Stennis Space Center test stand. (Stratolaunch)
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- The PGA preburner seen after installation at Stennis. (Stratolaunch)
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- The control center. (Stratolaunch)
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- MLV is released from Stratolauncher. (Stratolaunch)
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- A concept video produced by Stratolaunch shows the Roc launching a Kraken rocket. (Stratolaunch, via Wired)
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Tesla Cybercab units finally got a definitive date for when they will be able to be purchased by consumers, ending speculation regarding whether the fully autonomous vehicle would be available in the near term.
During Tesla’s third-quarter 2026 earnings call on October 21, Vice President of Engineering Lars Moravy said the company is aiming to begin delivering its purpose-built Cybercab robotaxi to customers before year-end.
🚨 In short, Cybercabs are slated to go to customers by end of the year. All units are going into Robotaxi fleet currently, per @larsmoravy
Cybercab will be “transport-as-a-service,” but vast majority of Cybercab will be “Tesla-owned,” @elonmusk says https://t.co/R8Qu8QWdmp
— TESLARATI (@Teslarati) October 21, 2026
“We’re trying to get Cybercabs to customers by the end of this year, 2026,” Moravy said. He added that production is underway on the line at Gigafactory Texas, but “all of those are currently going to our own internal Robotaxi fleet.”
Moravy explained that as operations scale, Tesla will “mainly deliver fully designed autonomous vehicles to our customers,” with the Cybercab as the first such vehicle. Initial customer deliveries will start small while the company gains experience with delivery logistics, ownership models, fleet management, and operating autonomous vehicles outside its direct control.
CEO Elon Musk reinforced the limited nature of private sales, describing the Cybercab primarily as a “transport-as-a-service” offering rather than a personal ownership vehicle like the Model 3, Model Y, or upcoming Roadster. “The vast majority of the Cybercab stuff will be Tesla-owned and transport-as-a-service,” Musk said.
The Cybercab is a two-seater vehicle developed by Tesla without a steering wheel or pedals. It relies completely on Tesla’s Full Self-Driving suite and has been in production since February. Early units have been put in Tesla’s Robotaxi service as of early September, when the company launched rides to the public. Tesla previously indicated it would aim to sell Cybercabs for about $30,000.
Unsupervised Full Self-Driving is expected to ship to consumer cars during Q2 2027, Ashok Elluswamy, Tesla’s Head of AI, indicated during the call. Early buyers or fleet operators may receive vehicles whose autonomous operation remains geographically restricted due to lagging regulatory agencies. There are some hurdles that remain ahead of Cybercab deliveries.
Tesla (NASDAQ: TSLA) reported its earnings for the third quarter of 2026, marking a reasonable performance on the various financial metrics. Tesla still plans to hold a call that will field investor questions at 5:30 p.m. ET, 4:30 p.m. CT.
Here’s where Earnings came in:
- Total Revenues: $28.046 reported vs. $28.34B expected
- Non-GAAP EPS: $0.48 reported vs. $0.45 expected
- Operating Margin: 2.6 % reported vs. 2.5% expected
- Operating Income: $718M reported vs. $721M expected
- Free Cash Flow: $1.531B reported vs. ~-$4.51B expected
Tesla $TSLA Earnings Results:
Revenues: $28.046B
Non-GAAP EPS: $0.48
Operating Margin: 2.6%
Operating Income: $718M
FCF: $1.531B— TESLARATI (@Teslarati) October 21, 2026
Major Takeaways
Full Self-Driving (Supervised)
“FSD (Supervised)⁴ attach rate continued to grow, reaching over 75% of new vehicle deliveries in North America – our most mature market – a nearly twenty percentage point sequential increase. We believe that FSD is driving demand in markets where it is available, and we continue to work with regulators to get it approved in other markets.”
Tesla Semi
“We began volume production of Tesla Semi, our Class 8 heavy-duty truck. The top variant can go 500 miles at full 82,000 lbs gross combination weight while achieving an efficiency of 1.7 kWh/mile. That efficiency allows the Tesla Semi to use a third of the energy used by a comparable diesel truck to haul the same payload. In a transportation market where energy is one of the largest components of total cost per mile, this will provide a meaningful advantage to Tesla Semi operators.”
SI Compute
“We plan to reach 400 MW of SI training compute by the end of the year, supporting the development of both vehicle and humanoid robot autonomy software. Additionally, we continued construction for the Austin Fab, where we plan to start commissioning equipment in 2027.”
Robotaxi
“We began deployment of Cybercab into our Robotaxi fleet in Austin. We reached nearly two million cumulative unsupervised miles for our Robotaxi service as of the end of the quarter. Operating hours in Austin are now 6am to midnight, and we expect to reduce wait times via increased fleet supply and improvement of Robotaxi orchestration algorithms. Grok is available in Cybercab with access to Grok Bot and Connectors, which allows users to manage their inbox, calendars, files, chats and tasks – all hands free via voice command – making Cybercab a mode of transport, a productivity space and, with our entertainment options, a second living room.”
Interested in ordering a Tesla? Use my referral code for three free months of Full Self-Driving (Supervised) here.
Tesla (NASDAQ: TSLA) reports its earnings for Q3 today. Here’s what to expect, as the company will reveal its balance sheet after the market closes on Wednesday.
Tesla already reported deliveries just after Q3 ended, and it demolished Wall Street consensus estimates of roughly 462,000 vehicles. Tesla delivered 486,532 cars in the third quarter, which was a big beat, but was down 2.1 percent from the same quarter last year. Energy storage deployments were 13.7 GWh, up year-over-year.
Tesla showrooms picked clean ahead of Q3 end as demand looks strong
For the quarter, analysts have already compiled their predictions for what Tesla will report this afternoon:
- Total Revenues: $28.34B
- Non-GAAP EPS: $0.43
- Operating Margin: 2.5%
- Operating Income: $721M
- Free Cash Flow: ~-$4.51B
Here are a few things we are looking forward to hearing about on the call:
Automotive Gross Margin and Overall Profitability
This was 16.3 percent in Q2, down from 19.2 percent in Q1, and was impacted by warranty charges and some fading regulatory credits. Consensus implies overall gross margin near 18 percent, but a miss here would potentially reinforce concerns about pricing pressure on its vehicles.
Pay attention to energy storage margins as well, especially since Tesla missed GWh expectations, although it was still a strong quarter.
Robotaxi/Cybercab, Unsupervised FSD, and Optimus Progress
The Say questions from retail investors usually focus on these types of projects, and this quarter is no different. Scaling the Cybercab fleet beyond Austin amid the open NHTSA safety review, timeline for Unsupervised FSD in customer cars, Robotaxi unit economics, and Optimus cost per unit plus when it could start generating revenue, are all things to be looking for.
Any concrete timelines or regulatory path details will likely move the stock more than the near-term numbers. SpaceX merger speculation, which was detailed during SpaceX’s earnings call last night, may also surface, although the key details were shared last night.
Elon Musk just confirmed the Tesla and SpaceX merger step everyone was waiting for
Say Investor Questions
- How does the Cybercab fleet scale past Austin, and what’s the regulatory path outside Texas given NHTSA’s open safety review?
- When can we anticipate FSD unsupervised in customer cars?
- When will the CyberCab be available for customer purchase/ownership?
- What’s the unit economics per paid robotaxi mile, and how does it compare to the thirty-cent target?
- Tesla has acknowledged that HW3 vehicles cannot support unsupervised FSD. When will owners know whether they can upgrade their hardware for free, and when will Tesla provide a clear plan?
The full Earnings Call will be streamed this evening after market close around 5 p.m. this evening.
Tesla Cybercab gets a for sale date at last
Tesla Q3 2026 Earnings results: in-line revenues, slight beat on EPS
