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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 officially begins sunset of Model S and Model X

In the latest move to show Tesla is planning to eliminate the Model S and Model X from production, the company’s Korean arm has officially set a firm cutoff date of March 31, 2026, for new orders of both models.

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Credit: Tesla

Tesla has officially started its process of sunsetting the Model S and Model X just months after the company confirmed it would stop producing the two flagship vehicles in 2026.

This step marks the end of an era for the vehicles that helped establish not only Tesla’s prowess as an automaker but also its status as a disruptor in the entire car industry. While these two cars have done a tremendous amount for Tesla, the signal that it is time to wind down their production has evidently arrived.

In the latest move to show Tesla is planning to eliminate the Model S and Model X from production, the company’s Korean arm has officially set a firm cutoff date of March 31, 2026, for new orders of both models.

This is the first time Tesla has announced a hard global deadline for the Model S and X, as after that date, only existing inventory will be available in South Korea.

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The move to bring closure to the Model S and Model X aligns with CEO Elon Musk’s plans for Tesla moving forward. During the Q4 2025 Earnings Call in January, Musk said the two cars deserved an “honorable discharge” for what they have done for the company.

The long-running programs are primarily being removed so that manufacturing lines can be repurposed for high-volume manufacturing of the Optimus humanoid robot. Tesla is targeting a production rate of up to one million units each year.

The Model S and Model X being removed from Tesla’s plans is a tough choice, but it was one that was written on the wall. Sales of these premium models have declined sharply in recent years, and even with Plaid configurations that are performance-forward, the company still has had trouble getting them sold.

In 2025, the Model S and Model X together accounted for roughly 3 percent of Tesla’s global deliveries, down significantly from prior periods as competition intensified in the luxury EV segment and buyers shifted toward more affordable options like the Model 3 and Model Y.

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The Model S saw sales drop over 50 percent year-over-year in some quarters, while the Model X faced similar pressures from rivals, including the Rivian R1S and BMW iX.

Despite their dwindling volume, the Model S and Model X remain technological showcases. The Plaid variants deliver blistering acceleration, advanced Full Self-Driving capability, and luxurious interiors.

The phase-out paves the way for Tesla’s strategic pivot toward autonomy, robotics, and higher-volume vehicles.

Tesla brings closure to flagship ‘sentimental’ models, Musk confirms

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Fremont will continue producing the refreshed Model 3 and Model Y, ensuring the factory remains a key automotive hub while expanding into robotics. Tesla has stated that the shift is not expected to result in job losses and could increase headcount as Optimus production ramps up.

For Tesla fans, the sunset represents a bittersweet moment. The Model S, introduced in 2012, proved EVs could compete with luxury sedans, while the Falcon-wing-door Model X set new standards for family haulers. Owners can expect continued software support and service for years to come.

Many fans have pushed for the Model X to hang around due to its appeal for families.

With the two cars heading out, Tesla’s priority now becomes its future products, especially that of the Optimus robot, which is the main reason for the S/X platform’s conclusion.

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Tesla shows off mysterious vehicle at Giga Texas

The mysterious structure, partially unboxed amid construction materials, has sparked widespread speculation among Tesla enthusiasts and analysts. Many are convinced it is the long-rumored Model Y L, the extended-wheelbase variant already popular in China, now arriving in Texas for potential U.S. production.

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Credit: Joe Tegtmeyer | X

Tesla seemingly showed off a mysterious vehicle at Giga Texas, one that seems to be completely different than anything the company currently makes for the U.S. market.

The vehicle, which was spotted on the plant’s property, appears to be similar to the Model Y L that has not yet launched in North America, and is currently built at Gigafactory Shanghai in China.

Drone pilot Joe Tegtmeyer captured intriguing footage at Tesla’s Giga Texas on March 23, 2026, revealing what appears to be a large, blue plastic-wrapped vehicle body resting inside a wooden shipping crate outdoors.

The mysterious structure, partially unboxed amid construction materials, has sparked widespread speculation among Tesla enthusiasts and analysts. Many are convinced it is the long-rumored Model Y L, the extended-wheelbase variant already popular in China, now arriving in Texas for potential U.S. production.

The images show an elongated silhouette that stands out from standard Model Y bodies. Side-by-side comparisons shared in replies to Tegtmeyer’s post highlight key differences: the rear door extends farther over the wheel arch than on a regular Model Y, and the rear glass appears to run all the way to the spoiler lip without the metal trim seen on shorter versions.

One overlay analysis noted that the visible proportions align precisely with the Chinese-market Model Y L, which measures approximately 4.98 meters long with a 3.04-meter wheelbase, which is about seven inches longer overall than the standard Model Y sold in the U.S.

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The vehicle is a bare “body-in-white” shell, typical of prototypes sent abroad for tooling validation and local manufacturing ramp-up. Tesla has already launched the six- and seven-seat Model Y L in China and other markets, where it offers roughly 10% more cargo space and greater family-friendly versatility.

This sighting fits Tesla’s broader strategy. Industry observers expect the company to localize Model Y L production at Giga Texas by mid-2026 to serve American families seeking extra room without stepping up to the larger Cybertruck or a future full-size SUV.

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Bringing the design stateside could add tens of thousands of annual deliveries while leveraging existing Model Y lines. People have been adamant that they want the Model Y L in the U.S., especially as Tesla plans to fade the Model X, the company’s most ideal vehicle for large families, out of production in the near future.

Tesla Model Y lineup expansion signals an uncomfortable reality for consumers

While Tesla has made no official comment, the timing, amid Giga Texas expansion and steady Model Y output, suggests the mysterious crate is more than a random prototype.

If confirmed as the Model Y L, it marks another step in Tesla’s effort to refresh its bestselling SUV for global demand. The vehicle would perform exceptionally well in the U.S., and despite the company’s rather mute stance on bringing it to America, this might be the biggest hint to date that it could be on the way.

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Tesla Cybertruck just won a rare and elusive crash safety honor

Only the most outstanding of performances in crash tests can warrant an IIHS Top Safety Pick+ award, as vehicles listed with that ranking must achieve “Good” ratings in the small overlap front, updated side, and updated moderate overlap front tests, along with “Acceptable” or “Good” headlights standard on all trims.

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(Credit: Tesla)

Tesla Cybertruck landed a rare and elusive safety honor from the Insurance Institute for Highway Safety (IIHS). It was the only pickup truck in the U.S. market to do so.

The IIHS rewarded the Cybertruck with the Top Safety Pick+ honors, the highest marks a vehicle can receive from the agency.

Only the most outstanding of performances in crash tests can warrant an IIHS Top Safety Pick+ award, as vehicles listed with that ranking must achieve “Good” ratings in the small overlap front, updated side, and updated moderate overlap front tests, along with “Acceptable” or “Good” headlights standard on all trims.

Cybertruck was the only truck to also win an NHTSA Five-Star Safety rating, making it the only pickup available on the market to be recognized with top marks from both agencies.

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There are a multitude of options for pickups in the U.S. market, as it is one of the most popular vehicle types for consumers in the country. Pickups are great vehicles for anyone who does any sort of hauling or is just looking for extra space for any variety of reasons.

Pickups are also inherently safer than other body types on the road, mostly because they are larger and heavier, making them more favorable against other vehicle types in the event of a collision. However, Tesla has a significant advantage in safety with its vehicles because it engineers them to not only be safer in collisions, but also easier to repair.

The Cybertruck managed to achieve “Good” ratings, the highest marks available by the IIHS, in all three Crashworthiness categories, as well as “Good” ratings in both Crash Avoidance and Mitigation assessments.

It also received “Good” ratings across all driver and pedestrian crash-test performance metrics, except for one, where it earned an “Acceptable” rating for rear passengers in the Chest category.

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The Cybertruck’s outstanding crash test performance has won it this incredible mark as the pickup still tends to be one of the more polarizing vehicle designs on the market.

It is no secret that Tesla has struggled with demand of the Cybertruck due to pricing, but the recent rollout of a trim that was temporarily priced at just $59,990 showed plenty of people want the all-electric pickup.

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