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Ex-SpaceX engineer leads Stratolaunch to major rocket engine test milestone

Stratolaunch has successfully completed the first full-scale test of its 200,000-lbf thrust PGA rocket engine. (Stratolaunch)

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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.

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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.

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.

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“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.

 


For prompt updates, on-the-ground perspectives, and unique glimpses of SpaceX’s rocket recovery fleet check out our brand new LaunchPad and LandingZone newsletters!

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Eric Ralph is Teslarati's senior spaceflight reporter and has been covering the industry in some capacity for almost half a decade, largely spurred in 2016 by a trip to Mexico to watch Elon Musk reveal SpaceX's plans for Mars in person. Aside from spreading interest and excitement about spaceflight far and wide, his primary goal is to cover humanity's ongoing efforts to expand beyond Earth to the Moon, Mars, and elsewhere.

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Tesla unveils mysterious prototype at Giga Texas: Is the Model Y L coming to America?

The Model Y L has been available in China for some time, but Americans are wondering when it will potentially come to the United States, offering a larger version of the best-selling vehicle in the world, as the Model X is officially phased out.

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Credit: Joe Tegtmeyer | X

Tesla unveiled a mysterious prototype, covered up between a Model Y and a Cybertruck at Gigafactory Texas, perhaps giving yet another hint that the Model Y L is coming to America.

The Model Y L has been available in China for some time, but Americans are wondering when it will potentially come to the United States, offering a larger version of the best-selling vehicle in the world, as the Model X is officially phased out.

Giga Texas observer and drone operator Joe Tegtmeyer captured an image of the vehicle on May 6, showing a fully-covered prototype parked alongside a standard Model Y and a Cybertruck.

From top-down and angled views, the prototype appears nearly identical in scale to the Model Y but reveals noticeably distinct rear proportions—an elongated rear door that stretches farther over the wheel arch and rear glass that flows uninterrupted to the spoiler lip.

The side-by-side placement provides an immediate size reference. The mystery vehicle sits comfortably between the compact Model Y and the massive Cybertruck, suggesting it occupies a practical middle ground for families seeking more interior room without jumping to a full-size pickup.

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Enthusiasts quickly took to social media with guesses ranging from an extended-wheelbase Model Y to a potential station-wagon variant.

The sight of this prototype follows an earlier look at another shrouded body-in-white resting in a wooden shipping crate at the Giga Texas plant in late March.

That prototype appeared to display an elongated silhouette. Some analysis seems to show nearly exact dimensions as to what is reported for the Model Y L in the Chinese market, approximately 4.98 meters long with a 3.04-meter wheelbase, roughly seven inches longer overall than the U.S.-spec Model Y. The rear-door extension and glass-to-spoiler design were identical to the current sighting:

Tesla shows off mysterious vehicle at Giga Texas

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The Model Y L has already proven popular in China, where it launched in six- and seven-seat configurations and quickly ranked among the top-selling mid-to-large SUVs. Owners enjoy roughly 10 percent more cargo space and enhanced family versatility.

Tesla has remained silent on U.S. plans other than CEO Elon Musk saying it could come in late 2026, but localizing production at Giga Texas would make strategic sense.

With the Model X phase-out and steady Model Y output already humming along expanded lines, a longer-wheelbase variant could add tens of thousands of annual deliveries without major retooling.

The latest sighting arrives amid Tesla’s broader push to refresh its lineup. Whether this prototype represents the long-rumored Model Y L, a subtle Juniper-style update, or something entirely new remains unconfirmed.

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Yet the consistent visual cues—precise dimensional match, distinctive rear styling, and strategic placement at Giga Texas—point strongly toward an extended Model Y designed for American families who want extra space without sacrificing the Model Y’s efficiency and affordability.Tesla watchers will be monitoring future drone flights closely.

If the prototype is indeed the Model Y L, it could mark a significant expansion of the company’s best-selling vehicle and deliver the extra room many U.S. buyers have been requesting for years. For now, the blue tarp keeps its secrets—but the clues are getting harder to hide.

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Tesla Roadster gets an update, but not the one fans were looking for

Tesla has quietly filed a new trademark application for its next-generation Roadster, giving enthusiasts their first official glimpse of fresh branding for the long-teased electric supercar.

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Credit: Dan Burkland

Tesla has been slow to show its hand regarding the massive project that is the Roadster, but it is now coming forth with a new update.

However, it is probably not the one fans were looking for.

Tesla has quietly filed a new trademark application for its next-generation Roadster, giving enthusiasts their first official glimpse of fresh branding for the long-teased electric supercar.

The February 3 filing includes an inverted triangular badge with the word “ROADSTER” centered above four vertical lines that, according to the application, represent “speed, propulsion, heat, or wind.”

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A sleek, angular wordmark and a minimalist curved-line silhouette hinting at the car’s aerodynamic shape round out the trio of marks.

For a program that began with Elon Musk’s 2017 reveal, this is tangible forward motion. The original Roadster proved EVs could be thrilling; the next generation aims higher, with promises of sub-two-second 0-60 mph acceleration and, in its most extreme configuration, optional SpaceX cold-gas thrusters for rocket-like thrust.

The new trademarks suggest Tesla is now locking down the visual identity that will accompany those headline specs, as well as a small hint that maybe we’re finally getting close. However, the company has not revealed any progress on the vehicle itself or its specs to the public.

It continues to tease with developments like this one.

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That said, the update lands with a familiar bittersweet note. Fans have waited nearly a decade since the initial unveiling. Production was once eyed for 2020, then 2021, then later still. In the intervening years, Tesla has delivered the Model Y, Cybertruck, Semi, and major autonomy advances while scaling its energy business.

The Roadster has taken a back seat, and the delays have been genuinely disappointing. Many longtime supporters have grown frustrated watching renderings and hearsay while other marques roll out ever-faster electric sports cars.

Elon Musk talks Tesla Roadster’s future

Yet, the Roadster program itself still sparks genuine excitement. It represents the purest expression of Tesla’s “accelerate the world’s transition to sustainable energy” mission—pushing performance boundaries to prove EVs can outperform anything with an engine.

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The new branding, modest as it is, keeps that promise alive. It tells owners and prospective buyers that Tesla hasn’t forgotten the car that started it all.

No one would blame fans for wanting more than a logo right now. But in an industry where many concepts never leave the drawing board, the fact that Tesla continues to invest in and protect the Roadster’s identity is reason for measured optimism.

The wait has tested patience, but when the next-generation Roadster finally arrives, the new badge may well adorn one of the most exciting cars ever built. For those who have followed the journey this far, that payoff still feels worth it.

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Tesla gets a massive order for the Semi: 370 units and $100M

WattEV, a leading provider of electric freight operations and charging infrastructure in the United States, has announced one of the largest deployments of electric Class 8 trucks in California history: an order for 370 Tesla Semi vehicles.

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Credit: Tesla

Tesla just got a massive order for the Semi, and it is its largest by a long shot.

WattEV, a leading provider of electric freight operations and charging infrastructure in the United States, has announced one of the largest deployments of electric Class 8 trucks in California history: an order for 370 Tesla Semis.

Valued at approximately $100 million, this marks the state’s biggest single electric truck order to date and signals accelerating momentum for zero-emission long-haul freight.

Credit: Tesla

Deliveries are set to begin with the first 50 Tesla Semis in 2026, with the full fleet operational by the end of 2027. More than 300 of these trucks will support a joint program with the Port of Oakland, helping electrify drayage and regional freight routes. The initiative aligns with California’s ambitious goals to transition to carbon-neutral freight operations.

Salim Youssefzadeh, CEO of WattEV, said at the annual ACT Expo industry event that the Semi was the easiest choice:

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“We selected the Tesla Semi based on cost, performance, and availability after issuing a public request for proposals…With the Tesla Semi now entering mass production and drawing strong reviews from fleet operators nationwide, WattEV’s vertically integrated model – combining vehicle deployment, megawatt-class charging infrastructure, and full-service leasing – offers a turn-key path for carriers without any capital risk.”

Critical to the rollout are new Megawatt Charging System (MCS) hubs in Oakland, Fresno, Stockton, and Sacramento. These stations will deliver up to 300 miles of range in roughly 30 minutes—comparable to a traditional diesel fill-up. The Oakland depot, where WattEV recently broke ground, will serve as a cornerstone for northern and central California corridors, connecting ports to inland hubs and beyond.

This deployment builds on WattEV’s existing experience. The company has already logged millions of electric miles in Southern California, including early Tesla Semi deployments at the Ports of Long Beach and Los Angeles. By combining high-efficiency electric trucks with strategically placed fast-charging depots, WattEV aims to prove that battery-electric long-haul trucking can match—or exceed—diesel economics while slashing emissions.

The order arrives as Tesla ramps up Semi production at its Nevada factory, targeting higher volumes in 2026. Fleet operators nationwide have praised the Semi’s real-world performance, including strong torque, low operating costs, and advanced safety features. For California, the project supports air quality improvements around ports and highways while demonstrating scalable infrastructure for heavy-duty electrification.

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Industry observers see this as a pivotal step toward broader adoption. With diesel trucks facing rising fuel and regulatory costs, turnkey electric solutions like WattEV’s could accelerate the shift. As the first 50 Semis hit the road in 2026, they will not only move freight but also help build the charging network that paves the way for even larger fleets.

This landmark order underscores Tesla’s growing footprint in commercial trucking and California’s leadership in sustainable transportation. For WattEV and its partners, it’s more than a vehicle purchase—it’s the foundation of a zero-emission freight network connecting Northern and Central California.

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