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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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SpaceX secures FAA approval for 44 annual Starship launches in Florida

The FAA’s environmental review covers up to 44 launches annually, along with 44 Super Heavy booster landings and 44 upper-stage landings.

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Credit: SpaceX

SpaceX has received environmental approval from the Federal Aviation Administration (FAA) to conduct up to 44 Starship-Super Heavy launches per year from Kennedy Space Center Launch Complex 39A in Florida. 

The decision allows the company to proceed with plans tied to its next-generation launch system and future satellite deployments.

The FAA’s environmental review covers up to 44 launches annually, along with 44 Super Heavy booster landings and 44 upper-stage landings. The approval concludes the agency’s public comment period and outlines required mitigation measures related to noise, emissions, wildlife, and airspace management.

Construction of Starship infrastructure at Launch Complex 39A is nearing completion. The site, previously used for Apollo and space shuttle missions, is transitioning to support Starship operations, as noted in a Florida Today report.

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If fully deployed across Kennedy Space Center and nearby Cape Canaveral Space Force Station, Starship activity on the Space Coast could exceed 120 launches annually, excluding tests. Separately, the U.S. Air Force has authorized repurposing Space Launch Complex 37 for potential additional Starship activity, pending further FAA airspace analysis.

The approval supports SpaceX’s long-term strategy, which includes deploying a large constellation of satellites intended to power space-based artificial intelligence data infrastructure. The company has previously indicated that expanded Starship capacity will be central to that effort.

The FAA review identified likely impacts from increased noise, nitrogen oxide emissions, and temporary airspace closures. Commercial flights may experience periodic delays during launch windows. The agency, however, determined these effects would be intermittent and manageable through scheduling, public notification, and worker safety protocols.

Wildlife protections are required under the approval, Florida Today noted. These include lighting controls to protect sea turtles, seasonal monitoring of scrub jays and beach mice, and restrictions on offshore landings to avoid coral reefs and right whale critical habitat. Recovery vessels must also carry trained observers to prevent collisions with protected marine species.

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Texas township wants The Boring Company to build it a Loop system

The township’s board unanimously approved an application to The Boring Company’s “Tunnel Vision Challenge.”

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Credit: The Boring Company

The Woodlands Township, Texas, has formally entered The Boring Company’s tunneling sweepstakes. 

The township’s board unanimously approved an application to The Boring Company’s “Tunnel Vision Challenge,” which offers up to one mile of tunnel construction at no cost to a selected community.

The Woodlands’ proposal, dubbed “The Current,” features two parallel 12-foot-diameter tunnels beneath the Town Center corridor near The Waterway. Teslas would shuttle passengers between Waterway Square, Cynthia Woods Mitchell Pavilion, Town Green Park and nearby hotels during concerts and large-scale events, as noted in a Chron report.

Township officials framed the tunnel as a solution for the township’s traffic congestion issues. The Pavilion alone hosts more than 60 shows each year and can accommodate crowds of up to 16,500, often straining Lake Robbins Drive and surrounding intersections.

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“We know we have traffic impacts and pedestrian movement challenges, especially in the Town Center area,” Chris Nunes, chief operating officer of The Woodlands Township, stated during the meeting.

“The Current” mirrors the Loop system operating beneath the Las Vegas Convention Center, where Tesla vehicles transport passengers through underground tunnels between venues and resorts.

The Boring Company issued its request for proposals (RFP) in mid-January, inviting cities and districts to pitch local uses for its tunneling technology. The Woodlands must submit its application by Feb. 23, though no timeline has been provided for when a winning community will be announced.

Nunes confirmed that the board has authorized a submission for “The Current’s” proposal, though he emphasized that the project is still in its preliminary stages.

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“The Woodlands Township Board of Directors has authorized staff to submit an application to The Boring Company, which has issued an RFP for communities interested in leveraging their technology to address community challenges,” he said in a statement. 

“The Board believes that an underground tunnel would provide a safe and efficient means to transport people to and from various high-use community amenities in our Town Center.”

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Tesla Model Y wins 2026 Drive Car of the Year award in Australia

The Model Y is already Australia’s best-selling EV in 2025 and the tenth best-selling vehicle overall.

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Credit: Tesla

The Tesla Model Y has been named 2026 Drive Car of the Year overall winner, taking the top honor after being judged as the vehicle that “moves the game forward the most for Australian new car buyers.” 

The Model Y is already Australia’s best-selling EV in 2025 and the tenth best-selling vehicle overall, but the vehicle’s Juniper update strengthened its case with new ownership benefits and expanded software capability.

Drive’s overall award compares category winners and looks at which model most significantly advances the local new car market. In 2026, judges pointed to the Model Y’s five-year warranty and the availability of Full Self-Driving (Supervised) as a monthly subscription as key differentiators.

Priced from AU$58,900 before on-road costs, the all-electric crossover SUV offers a lot of value compared to similarly sized petrol and hybrid rivals. The ability to access Tesla’s Supercharger network across Australia also reduces friction for buyers moving to EV ownership.

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Owners can add FSD (Supervised) for AU$149 per month. While it still requires driver oversight, the system expands the vehicle’s advanced driver-assistance capabilities and reflects Tesla’s software-first approach.

“The default choice for a reason. The Tesla Model Y makes the transition to electric both effortless and rewarding,” Drive wrote.

The 2025 Model Y facelift also sharpened the vehicle’s exterior, highlighted by a distinctive rear light bar that gives the crossover SUV a more modern road presence.

Drive described the Model Y as a benchmark for combining practicality, efficiency and technology at an accessible price point. With eligibility for federal Fringe Benefit Tax exemptions through novated leasing, its value proposition has improved for numerous buyers.

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For 2026, the Model Y’s combination of range efficiency, charging access and software capability proved decisive. Ultimately, the award all but cements the Model Y’s position as one of the most influential vehicles in Australia’s evolving new-car market today.

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