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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’s Cybercab has taken a significant step toward production with new technical details emerging from 2026 EPA certification documents.
The filings, which include a Certificate of Conformity issued in late May, provide the most comprehensive public look yet at the purpose-built autonomous vehicle designed for high-volume, low-cost ride-hailing operations.
At its core, the Cybercab is a front-wheel-drive electric vehicle powered by a single 163 kW (219 horsepower) AC permanent magnet motor. Despite its modest output, prioritizing efficiency and cost over neck-snapping acceleration, the vehicle boasts a strong power-to-weight ratio thanks to its lightweight curb weight of 3,113 pounds and a GVWR of 3,730 pounds.
It operates on a 326-volt electrical architecture with a compact ~48 kWh lithium-ion battery pack. The standout revelation is the vehicle’s exceptional efficiency, which Tesla has routinely flexed in the past.
EPA lab tests list an equivalent all-electric range of 418 miles combined and 375 miles on the highway. Tesla has previously targeted around 300 miles of real-world range, and analysts expect the final EPA-rated figure to land near 280-300 miles after adjustment factors.
At a certified 165 Wh/mi in earlier testing, the Cybercab is reportedly the most efficient EV ever produced, significantly outperforming vehicles like the Lucid Air Pure.
New information about @Tesla‘s Cybercab has been revealed in public EPA documents.
• Front-wheel drive
• Battery capacity: ~48 kWh
• 219 horsepower
• Curb weight: 3,113 lbs
• GVWR: 3,730 lbs
• Motor power: 163kW
• Voltage: 326vEquivalent All Electric Range is listed at… pic.twitter.com/D4gkJJTj25
— Sawyer Merritt (@SawyerMerritt) June 15, 2026
This efficiency stems from deliberate design choices tailored for robotaxi duty. The two-seater features a highly aerodynamic shape, minimal weight, which is aided by structural battery integration of what are likely 4680 cells, and no steering wheel or pedals in its fully autonomous configuration.
For ride-hailing fleets, where average trips are short, and can be just five or ten miles, the smaller battery enables faster charging cycles, lower material costs, and reduced vehicle price, a key to Tesla’s goal of a ~$30,000 production cost.
Implications for Autonomous Mobility
These specs underscore Tesla’s strategy: maximize utilization and minimize operating expenses. A ~48 kWh pack could support dozens of short rides per charge, with energy costs potentially dropping below 20 cents per mile at scale. Front-wheel drive simplifies manufacturing and maintenance compared to dual-motor AWD setups in passenger Teslas.
The 219 hp motor provides ample performance for urban and highway speeds without excess, addressing questions about why such power is needed in a “slow” autonomous vehicle. Quick merges and hill climbing still matter for safety and passenger comfort.
Production has already begun at Giga Texas, with EPA certification clearing the path for U.S. deployment. While unsupervised Full Self-Driving remains the critical hurdle, these details paint a compelling picture of a vehicle engineered from the ground up for the robotaxi future: affordable to build, cheap to run, and capable of delivering strong range on a fraction of the battery capacity found in today’s EVs.
As Tesla ramps toward volume output, the Cybercab could reshape urban transportation economics.
Tesla Cybercab, the all-electric ride-hailing-geared vehicle void of a steering wheel and pedals, has achieved a significant regulatory milestone. The vehicle has officially secured an EPA Certificate of Conformity for the 2026 Cybercab, classifying it as a battery electric Zero Emission Vehicle (ZEV).
This certification confirms full compliance with federal Clean Air Act emission standards, paving the way for legal sales and operation across the United States.
A Certificate of Conformity (CoC) is a critical document issued by the U.S. Environmental Protection Agency (EPA) to vehicle manufacturers. It certifies that a specific class of vehicles meets all applicable federal emission requirements for the model year.
We have reported on several of them in the past, and it’s a good sign that a vehicle is close to being available to the public.
Every vehicle sold in the U.S. must carry this approval, which covers exhaust emissions, evaporative emissions, and refueling standards. For battery electric vehicles like the Cybercab, it verifies zero tailpipe emissions and compliance with stringent testing protocols. The certificate, issued and effective May 26, 2026, was part of the EPA’s recent bi-weekly upload, detailing the Cybercab’s evaporative/refueling family and exhaust compliance.
It also revealed some other very important information, as the Cybercab’s “Charge Depleting Range” was rated at just over 418 miles. This was for city driving, while the highway range depletion test revealed just over 375 miles of range:
Highway miles for Charge Depleting Range was just over 375 miles
— TESLARATI (@Teslarati) June 15, 2026
This EPA approval is a foundational step for Tesla’s autonomous ambitions. While emission certification is standard for any new EV, it signals that the Cybercab is progressing through the full federal compliance process.
Tesla has already equipped prototypes with federal compliance stickers affirming adherence to safety, bumper, and theft-prevention standards via self-certification under FMVSS rules. This bypasses the traditional 2,500-vehicle exemption cap that previously constrained low-volume autonomous testing.
Production of the Cybercab ramped up at Giga Texas starting in early 2026, with volume targets aiming for hundreds of units per week and long-term ambitions of millions annually. The two-seater, steer-by-wire vehicle, lacking a steering wheel and pedals, features a sleek, minimalist design optimized for Robotaxi service.
Priced under $30,000 at unveiling, it promises operating costs as low as $0.20–$0.40 per mile once scaled. Tesla has routinely flexed it as one of the most efficient vehicles of all time.
Regulatory progress extends beyond the EPA. The NHTSA has streamlined approvals for control-free vehicles, benefiting the Cybercab. Tesla operates supervised and unsupervised Robotaxi services in Texas cities like Austin, Dallas, and Houston using its fleet. California recently updated rules for driverless operations, including enforcement mechanisms for violations. Additional state-by-state approvals will be needed for nationwide rollout.
This EPA green light reduces a key barrier, building confidence among regulators, partners, and investors.
It underscores Tesla’s strategy of designing the Cybercab from the ground up for full compliance rather than retrofitting existing platforms. Challenges remain in scaling unsupervised autonomy, mapping approvals, and public acceptance, but the certification marks tangible momentum toward transforming urban mobility.
With prototypes already testing on public roads and production accelerating, the Cybercab edges closer to redefining transportation. Tesla’s integrated approach—combining hardware simplicity, software prowess, and regulatory diligence—positions it uniquely in the robotaxi race.
SpaceX executed its first Falcon 9 launch since going public on June 15, a routine yet symbolically powerful Starlink mission from Vandenberg Space Force Base in California.
Liftoff of the Falcon 9 booster B1093, on its 14th flight, occurred at approximately 8:34 a.m. PDT from Space Launch Complex 4E (SLC-4E), deploying 24 Starlink V2 Mini Optimized satellites into low-Earth orbit.
The first stage successfully landed on the droneship “Of Course I Still Love You” in the Pacific Ocean, underscoring the company’s unmatched reusability track record.
Watch Falcon 9 launch 24 @Starlink satellites to orbit from California https://t.co/meDwb05qOE
— SpaceX (@SpaceX) June 15, 2026
This mission comes just three days after SpaceX’s historic IPO on June 12, which shattered records as the largest ever. The company raised $75 billion by pricing shares at $135, with trading under ticker SPCX on Nasdaq opening at $150 and closing at $160.95—a 19 percent gain—valuing SpaceX at over $2.1 trillion.
The launch highlights the seamless transition from private innovator to public powerhouse. SpaceX, founded in 2002, has revolutionized access to space with over 650 Falcon 9 flights and a massive Starlink constellation now serving millions globally.
As a public company, it faces new pressures: quarterly earnings, shareholder scrutiny, and expectations to accelerate Starship development for Mars ambitions and deeper NASA partnerships. Yet the market response signals strong confidence in its dominance, as launch costs are slashed by 95 percent, rapid satellite deployment, and a backlog of government and commercial contracts.
SpaceX maintains bold advertising push for Starlink, contrasting Tesla’s minimalistic approach
Analysts view today’s flight as business as usual, but it carries extra weight. With shares volatile in early trading days, successful operations reassure investors that core capabilities remain unaffected by public status.
SpaceX now operates under heightened transparency, potentially unlocking capital for ambitious goals like Starship orbital tests and global broadband expansion.
Challenges loom, including regulatory hurdles for megaconstellations, competition in reusable rockets, and orbital debris concerns. Nevertheless, this morning’s flawless execution reinforces SpaceX’s trajectory.
As Musk often notes, the company’s mission—to make humanity multiplanetary—now aligns with Wall Street’s growth demands. The stars, it seems, are aligning for both.
Tesla Cybercab specs revealed: range, curb weight, range ratings, and more
Tesla Cybercab snags huge regulatory green light that readies it for public roads
