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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 FSD mocks BMW human driver: Saves pedestrian from near miss

Tesla FSD anticipated a BMW driver’s lane drift before the human behind the wheel could react.

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A video posted to r/TeslaFSD this week put a sharp spotlight on Tesla’s Full Self-Driving (FSD) software being able to react to pedestrian intent than an actual human driver behind the wheel. In the Reddit clip, a BMW driver can be seen rolling through a neighborhood street completely unaware of a pedestrian stepping in to cross. At the same time, a Tesla  driving on FSD had already begun slowing down before the pedestrian even began their attempt to cross the street The BMW kept moving, prompting the pedestrian to hop back, while the Tesla came to a stop and provide right-of-way for the human to safely cross.

That gap between what the BMW driver saw and what FSD had already processed is the story. Tesla FSD wasn’t reacting to a person in the street, rather it was reading the signals that a person was about to enter it based on the pedestrian’s movement, trajectory, and their trajectory to telegraph intent.

Tesla’s FSD is now built on an end-to-end neural network trained on billions of real-world miles, learning to interpret subtle human behavioral cues the same way an experienced human driver does instinctively. The difference is consistency. A human driver distracted for two seconds misses what FSD does not.

Tesla sues California DMV over Autopilot and FSD advertising ruling

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Reddit commenters in the thread were blunt about the BMW driver’s failure, with several pointing out that the pedestrian was visible well before the crossing. One response put it plainly that the car on FSD saw the situation developing before the human in the other car had registered there was a situation at all.

Tesla has published data showing FSD (Supervised) is 54% safer than a human driver, accumulated across billions of miles driven on the system. Elon Musk has said FSD v14 will outperform human drivers by a factor of two to three, and that v15 has “a shot” at a 10x improvement. Pedestrian safety is where the stakes are highest, and where intent prediction closes the gap fastest. At 30 mph, a car covers roughly 44 feet per second. An extra second of awareness from reading a person’s body language rather than waiting for them to step out is often the difference between a near miss and a fatality.

Video and community discussion: r/TeslaFSD on Reddit

FSD saves man from becoming a pancake. BMW driver nearly flattens him.
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Tesla Robotaxi gets a small but significant change

In the world of Tesla, where billion-dollar battery breakthroughs and autonomy milestones dominate headlines, a quiet design update can still pack a punch.

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Credit: David Moss | X

In the world of Tesla, where billion-dollar battery breakthroughs and autonomy milestones dominate headlines, a quiet design update can still pack a punch.

Last week in downtown Austin, sharp-eyed observers spotted a subtle but telling evolution on the Cybercab: a new “ROBOTAXI” logo graphic now graces the vehicle’s doors at Tesla’s Autonomy Popup.

What looks at first glance like a minor stylistic choice is, in fact, a deliberate rebranding move that hints at how the company envisions its robotaxi fleet fitting into everyday life.

The updated lettering is bold, graffiti-inspired, and unapologetically street-smart. Rendered in black with dripping white accents and a glowing yellow outline, the font evokes urban energy and playful irreverence.

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Gone is the sleek, minimalist typography that defined earlier Cybercab prototypes. In its place is something more human, almost rebellious.

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The new logo pops against the Cybercab’s smooth, metallic body, turning the autonomous pod into a rolling piece of public art rather than just another futuristic taxi.

Designers know that fonts are silent brand ambassadors. They shape perception before a single ride is taken. Tesla’s classic sans-serif aesthetic screams precision engineering and Silicon Valley cool.

The new Robotaxi script leans into accessibility and fun, suggesting the vehicle is approachable, not intimidating. For a product meant to ferry strangers through city streets 24/7, that matters. It signals that the robotaxi isn’t reserved for tech elites; it’s for everyone.

Tesla Cybercab spotted next to Model Y shows size comparison

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The timing is no accident. With regulatory approvals for unsupervised autonomy advancing and Tesla preparing to scale Cybercab production, the company is shifting from prototype showcase to fleet deployment.

A fresh logo helps differentiate the vehicles visually in dense urban environments—crucial for rider recognition and brand recall. It also aligns with Elon Musk’s long-standing ethos: make the future feel exciting, not sterile.

Small changes like this often foreshadow a larger strategy. Tesla has always obsessed over details—door handles, screen interfaces, even the curvature of a steering wheel.

Updating the Robotaxi font reflects the same meticulous care now applied to consumer-facing autonomy. It’s not just paint on metal; it’s a statement that the ride of the future should feel personal, memorable, and undeniably cool.

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In an industry racing toward self-driving fleets, Tesla’s willingness to evolve even the smallest visual cues shows confidence. A font won’t launch the robotaxi network, but it might just help millions climb aboard with a smile.

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Tesla makes latest announcement on Model S and Model X

The announcement follows Tesla CEO Elon Musk’s statement on the Q4 2025 earnings call in late January. Musk described the decision as an “honorable discharge” for the two vehicles, noting that production would wind down in Q2 2026.

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Credit: Tesla

Tesla has officially begun winding down production of its flagship Model S and Model X in the United States, notifying owners via email that the long-running models will soon reach the end of the line.

The email, sent to U.S. customers on March 27, opens with gratitude. “Model S and Model X marked the beginning of the world’s transition to electric transportation,” it reads. “These vehicles also made it possible for Tesla to develop the technology that would move our world toward autonomy.”

Tesla officially begins sunset of Model S and Model X

It then delivers the news directly: “As we make way for this autonomous future, Model S and Model X production will be ending. If you’d like to bring home a new Model S or Model X, order yours soon from our limited inventory.”

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The message closes with a simple thank-you: “Thank you for being part of our journey.”

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The announcement follows Tesla CEO Elon Musk’s statement on the Q4 2025 earnings call in late January. Musk described the decision as an “honorable discharge” for the two vehicles, noting that production would wind down in Q2 2026.

The move frees factory floor space at Fremont, California, for next-generation manufacturing, including Optimus humanoid robots and the upcoming Robotaxi platform.

Introduced in 2012 and 2015, respectively, the Model S and Model X were Tesla’s original halo cars. They proved EVs could outperform gasoline luxury vehicles in acceleration, range, and tech features while pioneering over-the-air updates and early autonomy hardware.

Although they never matched the volume of the Model 3 and Model Y, their engineering breakthroughs laid the foundation for the company’s current lineup and full self-driving development.

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Early adopters highlighted how the cars convinced them to invest in Tesla stock and the EV movement. Some U.S. owners who had not yet received the note voiced mild frustration, and international customers confirmed the outreach remains U.S.-only for now.

Tesla has not detailed an exact final production date beyond the Q2 2026 target or confirmed immediate replacements. Speculation continues about a possible Cybertruck-derived SUV, but the company’s public focus has shifted squarely to autonomy and robotics.

For buyers still interested in the S or X, the window is closing. Inventory is described as limited, and Tesla’s Korean division has already set a March 31 cutoff for new orders in that market. The email serves as both a farewell and final sales push, an elegant close to a chapter that helped define modern electric driving.

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