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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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Elon Musk put a number on where he thinks SpaceX’s Starship program is headed by 2030, replying on X a day after President Trump signed a memo pushing the country toward 1,000 space launches and reentries a year.
The exchange started when Aaron Burnett, co-founder of propulsion startup Mach 33, posted that “1,000 launches/reentries is the goal,” quoting White House science adviser Michael Kratsios on the newly signed National Space Transportation Policy. Burnett noted that the FAA’s own bull-case forecast reached only 385 annual launches by 2030, while his firm’s conservative model already put SpaceX alone near 940. Musk responded, “We’re aiming to reach 30+ Starship launches/day in 2030, which is ~10k annualized. Still tiny numbers compared to airplane flights!”
We’re aiming to reach 30+ Starship launches/day in 2030, which is ~10k annualized.
Still tiny numbers compared to airplane flights!
— Elon Musk (@elonmusk) August 21, 2026
That figure is specific to Starship, the rocket SpaceX is still developing for orbital and lunar missions, not the Falcon 9 fleet that carries most of the company’s current launch volume. Starship has flown twice this year, a slower pace than the four and five flights SpaceX managed in 2024 and 2025. Getting from two flights a year to 30 a day is the scale of jump the new federal policy is meant to clear regulatory room for.
Trump’s memo, signed Thursday, directs agencies to identify new launch and reentry sites on federal land, including a new reentry site within 90 days, and to speed up the permitting and environmental reviews that have long slowed cadence growth. It also sets a goal of returning American astronauts to the moon by 2028 and placing initial lunar base elements by 2030, tying the launch buildout directly to NASA’s Artemis program.
SpaceX has already been pushing the FAA toward higher numbers on its own. The agency approved up to 44 annual Starship launches from Kennedy Space Center in February, on top of a 2024 review that raised the cap at Starbase in Texas to 25 a year. Those approvals cover a fraction of the 10,000 annual flights Musk is now describing, which shows how far current permitting still sits from the administration’s stated target.
The near-term test of all this is more modest. SpaceX cleared a full-duration, six-engine static fire on its next Starship vehicle this week, the last major hardware checkpoint before Flight 14, which is targeting no earlier than August 28 and is expected to attempt the vehicle’s first full orbital mission. Musk said last week that a tower catch of the upper stage is still probably months away, a reminder that the immediate roadmap remains far more incremental than the daily launch numbers he just posted.
Tesla will resolve its massive recall of nearly three million vehicles in China with stickers and a software update.
On Friday, Chinese regulators filed recall plans against Tesla, Xiaomi, Leapmotor, Xpeng, Chery, Geely, Dongfeng, Arcfox, and FAW to resolve what is essentially a carbon-copy issue throughout each of the companies’ vehicle models: emergency door release latches are simply not visible enough.
Tesla door handle saga gets its latest chapter and a big change is coming
The companies will be required to add things that will make these latches, which will open the door in the event of an emergency, more visible. Of the 7 million vehicles impacted, Tesla accounts for 2,975,910 units. More than 1.9 million of those are Model Y vehicles, with the rest, just over 970,000, being Model 3s.
To resolve the issue, Tesla is going to add warning labels to the emergency latches free of charge, and then utilize an Over-the-Air update to add a post-crash window-lowering strategy, according to CNEVpost.
This massive effort to fix the all-electric Model Y and Model 3’s emergency latch system comes just months after several probes across various markets identified the trouble some had identifying this latch. Those who had gotten involved in car accidents that stripped the vehicle of its power were not aware that every Tesla has emergency door latches.
China’s State Administration for Market Regulation (SAMR) said that severe crashes that disable a vehicle’s low-voltage system could not only hinder occupants from getting out, but also make it more difficult for emergency response workers to gain entry.
SAMR is starting to tighten the regulations it has on door handles on vehicles. A new mandatory national standard will take effect for all models starting January 1, 2027, and will require all doors to be equipped with mechanical release mechanisms. This will effectively end purely electronic door handles. Models already on sale with type approval have been granted a two-year transition period, which will enable things to change until January 2029.
Tesla has officially confirmed plans to bring its all-electric Semi truck to Europe, with full specifications and market-launch details set for unveiling at the IAA Transportation trade fair in Hannover, Germany.
The event runs September 15–20, with a possible press preview on September 14. The announcement, shared via Tesla’s Semi account, marks a significant expansion beyond North America nearly nine years after the truck’s original 2017 reveal.
🚨 Tesla Semi is coming to Europe!
Sustainable logistics is a huge market internationally, and now Tesla is involved in it outside of the U.S. market! https://t.co/q3hjX6ybMv pic.twitter.com/mxTaVY3UsE
— TESLARATI (@Teslarati) August 20, 2026
In the United States, the Semi’s path has been gradual. Limited pilot production and customer deliveries began in late 2022, primarily to fleets such as PepsiCo. After years of refinement, high-volume manufacturing started on April 29, 2026, at a dedicated facility adjacent to Gigafactory Nevada.
The plant targets an annual capacity of 50,000 units, though the ramp is expected to be gradual, with “many thousands” of trucks projected by the end of 2026.
Demand is building, with recent orders including 500 units for Einride (deliveries starting September 2026, serving Amazon and others) and hundreds more from operators such as WattEV. Pricing stands at approximately $260,000 for the Standard Range and $290,000 for the Long Range before incentives.
Tesla Semi pricing revealed after company uncovers trim levels
Earlier in 2026, Tesla finalized production specifications that incorporated substantial updates. In February, the company detailed two variants designed for a full 82,000-pound gross combination weight.
The Standard Range offers about 325 miles of range with a 548 kWh battery and curb weight under 20,000 pounds. The Long Range delivers roughly 500 miles with an 822 kWh pack and a 23,000-pound curb weight. Both use three independent rear-axle motors producing up to 800 kW (about 1,073 horsepower), achieve energy consumption of around 1.7 kWh per mile, and support megawatt-class charging at up to 1.2 MW—recovering about 60 percent of range in 30 minutes through the MCS standard.
Additional refinements include a roughly 1,000-pound weight reduction versus earlier prototypes, improved aerodynamics, a 48-volt electrical architecture, electric power take-off up to 25 kW for refrigerated trailers, and fleet management software with over-the-air updates.
These advances position the Semi as a competitive option against diesel trucks on operating costs and performance. For Europe, adaptations such as lighting, cab configurations (including potential sleeper options), and regulatory compliance are anticipated.
With series production underway in Nevada and major fleet commitments secured, the upcoming IAA reveal will clarify timelines, European-specific specs, and pricing, potentially accelerating electrification of heavy-duty freight on both continents.
SpaceX and a new Trump order that could rewrite the next decade of launches
Tesla will resolve massive China recall with stickers and a software update
