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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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7 years ago

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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 plans for largest Australian Supercharger yet

The company has a 20-stall site in the city of Goulburn in New South Wales, which is an ideal location for trips between Sydney and Canberra, two major cities.

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2 hours ago

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March 16, 2026

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Credit: Tesla

Tesla is planning to build its largest Supercharger in Australia yet, expanding on the infrastructure the company has built for electric vehicles.

The company has a 20-stall site in the city of Goulburn in New South Wales, which is an ideal location for trips between Sydney and Canberra, two major cities.

However, according to The Driven, a new Australian Supercharger is on the way, and it is going to be the biggest in the country, accounting for more than 25 stalls total. They will likely be V4 Superchargers, Tesla’s fastest piles that enable some serious range for cars that will plug in.

Tesla is operating 148 active Supercharger sites in Australia, with 80 of those being available to non-Tesla EVs as a part of the company’s initiative to make things accessible for all electric vehicle owners.

The expansion of Tesla Superchargers is welcome for all EV owners, especially as there are so many automakers that have access to the network. It is widely reliable and extremely dependable; it is tough to find a Supercharger location that is completely out of service.

The opening of the stalls will be welcome for the Tesla owners of Australia, especially as the Model Y continues to be a major contributor to the company’s prowess in the market.

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Tesla’s sales performance in Australia showed a mixed but challenging picture in 2025, with the company delivering 28,856 new vehicles, marking a significant 24.8% decline from 38,347 units in 2024.

This represented the brand’s largest annual drop on record and the second consecutive year of decline, amid intensifying competition from Chinese EV makers like BYD and shifting buyer preferences toward SUVs. The Tesla Model Y remained a standout performer and Australia’s best-selling electric vehicle, with 22,239 deliveries, up 4.6percent year-over-year, accounting for about 77 percent of Tesla’s total sales.

The mid-year launch of the updated “Juniper” Model Y helped sustain momentum in the popular mid-size SUV segment.

In contrast, the Model 3 sedan struggled sharply, plummeting 61.3 percent to just 6,617 units, as consumers favored SUVs and faced growing options in the sedan category.

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Despite the overall dip, Tesla held onto leadership in the EV segment, capturing roughly 28 percent of the BEV market. Australia’s EV market grew robustly, surpassing 156,000 sales and reaching 13 percent market share, up 38.7 percent from 2024, highlighting strong broader adoption even as Tesla faced headwinds.

Early 2026 data suggests a rebound, with EV sales nearly doubling year-over-year in February and the Model Y showing strong gains, positioning Tesla for potential recovery amid ongoing competition.

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Tesla Model Y L gets new entertainment feature

Beyond audio quality, Immersive Sound X aligns with Tesla’s ecosystem of over-the-air updates, potentially allowing future refinements.

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6 hours ago

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March 16, 2026

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Credit: Tesla China

Tesla is including a new entertainment feature in the Model Y L, improving the vehicle even further and making it what appears to be the best configuration of the all-electric crossover globally.

Unfortunately, we in the U.S. do not yet have access to the vehicle, and the plans for it to enter the market remain up in the air, as CEO Elon Musk has said it could appear late this year. However, there is nothing concrete at this time.

Tesla’s latest enhancement to the Model Y L is a new Immersive Sound X feature, exclusive to the Model Y L.

It aims to transform the in-car listening experience into something truly cinematic. First introduced by Tesla China in October 2025, this advanced audio mode is now rolling out to deliveries in Australia and New Zealand, highlighting Tesla’s approach to region-specific premium upgrades.

At its core, Immersive Sound X leverages real-time sound extraction technology to create a customizable 3D soundstage. Using advanced algorithms, it analyzes audio tracks to separate direct sounds, such as vocals or lead instruments, from ambient elements like echoes and reverb.

The system then positions direct sounds front and center while diffusing ambient sounds to the side and rear speakers, simulating an expansive virtual environment. This results in a heightened sense of depth and spatial awareness, making listeners feel as if they’re in a concert hall or studio.

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What sets Immersive Sound X apart from the standard Immersive Sound found in other Tesla models is its hardware dependency and enhanced processing. The Model Y L boasts an 18-speaker system with a subwoofer, compared to the 15-speaker setup, plus a subwoofer, in the Model Y Long Range’s previous premium audio configuration.

This upgrade provides more “kick” and precision, enabling finer control over the soundstage. Unlike traditional surround sound, which requires multi-channel mixes like Dolby Atmos, Immersive Sound X works with any stereo source from platforms like Spotify or Apple Music, so every owner will be able to use it.

Tesla Model Y lineup expansion signals an uncomfortable reality for consumers

You can fine-tune the experience via an adjustable immersion slider, scaling the “size” of the virtual space to personal preferences. This caters to a more custom sound.

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An Auto mode intelligently adapts based on media type, whether it’s music, podcasts, or videos, ensuring optimal immersion without manual tweaks. This feature is unavailable on standard Model Y variants (with 7 or 15 speakers) or Model 3 trims, underscoring Tesla’s strategy to differentiate higher trims through superior hardware and software integration.

Beyond audio quality, Immersive Sound X aligns with Tesla’s ecosystem of over-the-air updates, potentially allowing future refinements.

For audiophiles and casual listeners alike, it elevates mundane commutes into immersive journeys, proving Tesla’s commitment to blending cutting-edge tech with user-centric design.

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Elon Musk teases crazy outlook for xAI against its competitors

Musk’s response was vintage hyperbole, designed to rally supporters and dismiss doubters, something his responses on social media often do.

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7 hours ago

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March 16, 2026

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Credit: NVIDIA

Elon Musk has never been one to shy away from crazy timelines, massive expectations, and outrageous outlooks. However, his recent plans for xAI and where he believes it will end up compared to its competitors are sure to stimulate conversation.

In a bold and characteristic response on X, Elon Musk fired back at a recent analysis that positioned his AI venture, xAI, as lagging behind industry frontrunners.

The post, from March 14, came as a direct reply to forecaster Peter Wildeford’s assessment, which drew from benchmarks and reporting to rank AI developers.

Wildeford placed Anthropic, Google, and OpenAI in a virtual tie at the top, with xAI and Meta trailing by about seven months. Chinese players like Moonshot, Deepseek, zAI, and Alibaba were estimated to be nine months behind, while France’s Mistral lagged by about a year and a half.

Musk’s response was vintage hyperbole, designed to rally supporters and dismiss doubters, something his responses on social media often do.

He claimed xAI would “catch up this year,” meaning by the end of 2026, erasing that seven-month deficit against the leaders. But he didn’t stop there.

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Musk escalated his vision to 2029, predicting xAI would “exceed them all by such a long distance” that observers would need the James Webb Space Telescope, NASA’s orbiting observatory stationed about 930,000 miles from Earth, to spot whoever lands in second place. This analogy underscores Musk’s confidence in xAI’s trajectory, implying an astronomical lead that could redefine the AI landscape.

Breaking down these claims reveals Musk’s strategic optimism. First, the short-term catch-up: xAI, launched in 2023, has already released models like Grok, but recent benchmarks, including those for Grok 4.2, have shown it falling short in capabilities compared to rivals.

Anthropic’s Claude series, Google’s Gemini, and OpenAI’s GPT models dominate in areas like reasoning, coding, and multimodal tasks. Musk’s assertion suggests aggressive scaling in compute, talent, or architecture, perhaps leveraging xAI’s ties to Tesla’s Dojo supercomputers or Musk’s vast resources, to close the gap swiftly.

The longer-term dominance by 2029 paints an even more audacious picture. Musk envisions xAI not just parity but supremacy, outpacing competitors in innovation speed and model sophistication.

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This could involve breakthroughs in energy-efficient training, real-world integration, like Tesla’s robotics, or ethical AI alignment, aligning with Musk’s stated goal of “understanding the universe.”

Critics, however, point to parallels with Tesla’s Full Self-Driving delays; one reply highlighted Musk’s 2023 promise of FSD readiness. Musk has made this promise for many years, and although the system has been strong and improving, it is still a ways off from the completely autonomous operation that was expected by now.

Tesla Full Self-Driving v14.2.2.5 might be the most confusing release ever

Musk’s comment highlights the intensifying U.S.-centric AI race, with xAI challenging the “three-way” dominance noted by Wharton professor Ethan Mollick, whom Wildeford quoted. As geopolitical tensions rise—evident in the Chinese firms’ lag—Musk’s tease could spur investment and talent wars.

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Yet, it also invites scrutiny: Will xAI deliver, or is this another telescope-needed mirage? In an industry where timelines slip but stakes soar, Musk’s words keep the spotlight on xAI’s ambitious path forward.

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