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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 Semi gets strange-but-understandable comparison from Jay Leno
In a recent interview with MotorTrend, legendary comedian and automotive enthusiast Jay Leno shared his impressions after driving Tesla’s long-range Semi truck, offering one of the most vivid descriptions to date:
The Tesla Semi recently received a strange-but-understandable comparison from automotive enthusiast and former long-time late-night television show host Jay Leno.
In a recent interview with MotorTrend, legendary comedian and automotive enthusiast Jay Leno shared his impressions after driving Tesla’s long-range Semi truck, offering one of the most vivid descriptions to date:
“It’s like driving an office building.”
The comparison may seem quirky—office buildings evoke images of immobility rather than motion—but it aptly conveys the experience of commanding a massive 23,000-pound Class 8 electric truck that delivers sports-car acceleration.
Lenotested the production-spec Long Range model, which is rated for up to 500 miles of range. He was visibly impressed by its performance, noting how the enormous vehicle moves with surprising urgency.
“It’s as fast as a Tesla, but it’s like driving an office building,” he remarked. “It’s this huge thing that moves like right now. You go 500 miles. You get 60% charge in 30 minutes. You’re saving on fuel costs. It seems quite good.”
Jay Leno in new interview on what it’s like to drive the @Tesla Semi:
“I was quite impressed with that. It’s a fast as a Tesla, but it’s like driving an office building. It’s this huge thing that moves like right now. You go 500 miles. You get 60% charge in 30 mins. You’re… pic.twitter.com/YU7tk6a6pV
— Sawyer Merritt (@SawyerMerritt) May 8, 2026
The reaction highlights the cognitive dissonance at the core of the Tesla Semi. Traditional diesel semi-trucks are slow, noisy, and expensive to run. The Semi rewrites the rules with instant torque from its tri-motor electric powertrain, producing up to 800 kW.
Despite its size, the truck feels agile thanks to full electric steering assist, upgraded actuators borrowed from the Cybertruck, and a 48-volt electrical architecture that improves responsiveness and efficiency.
Tesla reports real-world energy consumption below 1.7 kWh per mile for the Long Range version. Megacharger stations can deliver a 60% charge in roughly 30 minutes, making the truck suitable for long-haul operations.
Additional features include an electric Power Take-Off (ePTO) capable of 25 kW for trailer refrigeration or other equipment, and a driver-focused cab with a central seating position for optimal visibility and a quiet, high-tech interior.
Fleet operators stand to benefit significantly from the economics. Diesel trucks often cost nearly one dollar per mile when including fuel, maintenance, and downtime.
Tesla projects the Semi can reduce operating costs to as low as 15 cents per mile through cheaper electricity, regenerative braking that minimizes brake wear, and reduced service requirements. While early deployments, like Pepsi’s, focused on shorter routes, the 500-mile variant targets cross-country applications.
Obstacles remain. A fully loaded tractor-trailer can reach 80,000 pounds, which reduces real-world range compared to the unloaded test conditions. Building out a nationwide Megacharger network will be essential for broader adoption. The Semi also carries a higher upfront price than conventional diesels, though total cost of ownership and available incentives frequently tip the scales in its favor over time.
Tesla Semi hauls fresh Cybercab batch as Robotaxi era takes hold
Leno’s “office building” description resonates because it captures the unexpected thrill of piloting something so large yet so capable. As the trucking industry faces pressure to cut emissions and control rising fuel expenses, the Semi offers a compelling alternative that excels in performance, comfort, and efficiency.
Coming from a man who has driven everything from vintage classics to modern hypercars, Leno’s genuine enthusiasm adds weight to the verdict.
The Tesla Semi is emerging as more than an experimental EV—it represents a practical vision for the future of heavy-duty transport where massive rigs accelerate instantly, and the numbers finally make sense. If fleet results continue to validate the claims, the era of diesel dominance could be drawing to a close.
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Tesla expands its mass-market color palette in the U.S.
Delivering a fresh splash of color to its lineup, Tesla is giving U.S. buyers two stunning new blue options that are already turning heads.
Tesla has expanded the color palette it offers on its mass market vehicles in the United States, giving buyers of the Model 3 and Model Y a few additional options than before.
Delivering a fresh splash of color to its lineup, Tesla is giving U.S. buyers two stunning new blue options that are already turning heads. Starting on May 8, the automaker updated its North American configurator to introduce Marine Blue on Model Y Premium trims and Frost Blue exclusively on the Model 3 Performance.
Tesla Model Y and Model 3 Premium get Marine Blue for $1000 in the U.S.!
What do you think? pic.twitter.com/3FqMXcnmru
— TESLARATI (@Teslarati) May 8, 2026
The move replaces the long-running Deep Blue Metallic, a staple for over eight years, and brings previously exclusive shades stateside.
Marine Blue, a deep, rich oceanic hue formerly limited to Europe and Asia-Pacific markets, is now available on Model 3 and Model Y RWD and Long Range AWD Premium variants. Priced at a $1,000 upgrade—standard for Tesla’s premium paints—it delivers a sophisticated, metallic finish that shifts beautifully under light.
Tesla Model Y and Model 3 Premium get Marine Blue for $1000 in the U.S.!
What do you think? pic.twitter.com/3FqMXcnmru
— TESLARATI (@Teslarati) May 8, 2026
Tesla North America highlighted the change directly in an official post, confirming Marine Blue as the new flagship blue for non-Performance models.
Frost Blue, on the other hand, is the real crowd-pleaser for enthusiasts. Previously reserved for the flagship Model S and Model X, this lighter, icy metallic shade is now offered at no extra cost on Model 3 Performance and Model Y Performance trims.
Frost Blue now available on Tesla Model 3 Performance 😤 pic.twitter.com/rLOEh4pTkp
— TESLARATI (@Teslarati) May 8, 2026
Performance buyers effectively get a premium color included in the base price, a smart perk that Tesla has extended to higher-end variants across the board. Early in-person sightings and configurator renders show Frost Blue’s cool, modern vibe popping against the cars’ sleek lines, especially with black wheels and red brake calipers.
The timing couldn’t be better. With Tesla pushing refreshed Model 3 and Model Y refreshes amid growing competition, these updates add visual excitement without major redesigns.
Deep Blue Metallic orders are being transitioned to the new shades, according to customer reports and Tesla communications. In the U.S., Puerto Rico, and Mexico, the options are live now; Canada sees limited Frost Blue availability on the Model 3 Performance.
Tesla’s color strategy continues to evolve, borrowing from higher-end models to refresh mass-market EVs. Now that we bid farewell to the Model S and Model X, some of their colors might be available on the more widely available Model 3 and Model Y.
Elon Musk
Tesla Semi’s official battery capacity leaked by California regulators
A California regulatory filing just confirmed the exact battery size inside each Tesla Semi variant.
A regulatory filing published by the California Air Resources Board in April 2026 has put official numbers on what Tesla Semi owners and fleet buyers have long wanted confirmed: the exact battery capacities of both the Long Range and Standard Range Semi truck variants. CARB is California’s independent air quality regulator, and it certifies zero-emission powertrains before they can be sold or operated in the state. When a manufacturer submits a vehicle for certification, the resulting executive order becomes a public document, making it one of the most reliable sources for confirmed production specs on any EV.
The document lists two certified powertrain configurations. The Long Range Semi carries a usable battery capacity of 822 kWh, while the Standard Range version comes in at 548 kWh. Both use lithium-ion NCMA chemistry and share the same peak and steady-state motor output ratings of 800 kW and 525 kW respectively. Cross-referencing Tesla’s published efficiency figure of approximately 1.7 kWh per mile under full load, the 822 kWh pack supports roughly 480 miles of real-world range, which aligns closely with Tesla’s advertised 500-mile figure for the Long Range trim. The 548 kWh Standard Range pack works out to approximately 320 miles, again consistent with Tesla’s stated 325-mile target.
Here is a direct comparison of the two versions based on the CARB filing and published specs:
| Tesla Semi Spec | Long Range | Standard Range |
| Battery Capacity | 822 kWh | 548 kWh |
| Battery Chemistry | NCMA Li-Ion | NCMA Li-Ion |
| Peak Motor Power | 800 kW | 525 kW |
| Estimated Range | ~500 miles | ~325 miles |
| Efficiency | ~1.7 kWh/mile | ~1.7 kWh/mile |
| Est. Price | ~$290,000 | ~$260,000 |
| GVW Rating | 82,000 lbs | 82,000 lbs |
The timing of this certification is not incidental. On April 29, 2026, Semi Programme Director Dan Priestley confirmed on X that high-volume production is now ramping at Tesla’s dedicated 1.7-million-square-foot facility in Sparks, Nevada. A key advantage of the Nevada location is vertical integration: the 4680 battery cells powering the Semi are manufactured in the same complex, eliminating the supply chain bottleneck that had delayed the program for years.
Tesla’s long-term goal is to reach a production capacity of 50,000 trucks annually at the Nevada factory, which would represent roughly 20 percent of the entire North American Class 8 market. With CARB certification now in hand and the production line running, the regulatory and manufacturing groundwork for that target is in place.
Tesla Semi gets strange-but-understandable comparison from Jay Leno
Tesla expands its mass-market color palette in the U.S.
