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Ex-SpaceX engineer leads Stratolaunch to major rocket engine test milestone
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.
The team made amazing progress this week! Check out the #PGAEngine preburner’s first hot-fire test at @NASAStennis. #NewUSEngine pic.twitter.com/kKTnf0bj1S
— Stratolaunch (@Stratolaunch) November 6, 2018
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.
- A to-scale comparison of Falcon 1, Pegasus XL, MLV, and Falcon 9. (Teslarati/Stratolaunch/Wikipedia)
- A render of Stratolaunch’s impressive PGA engine. Note the giant nozzle relative to the throat. (Stratolaunch)
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.
“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.
- PGA’s first full-scale preburner seen during assembly. (Stratolaunch)
- PGA’s first full-scale preburner seen during assembly. (Stratolaunch)
- Jeff Thornburg stands in front of Stratolaunch’s NASA Stennis Space Center test stand. (Stratolaunch)
- The PGA preburner seen after installation at Stennis. (Stratolaunch)
- The control center. (Stratolaunch)
- MLV is released from Stratolauncher. (Stratolaunch)
- A concept video produced by Stratolaunch shows the Roc launching a Kraken rocket. (Stratolaunch, via Wired)
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Elon Musk
SpaceX and xAI tapped by Pentagon for autonomous drone contest
The six-month competition was launched in January and is said to carry a $100 million award.
SpaceX and its AI subsidiary xAI are reportedly competing in a new Pentagon prize challenge focused on autonomous drone swarming technology, as per a report from Bloomberg News.
The six-month competition was launched in January and is said to carry a $100 million award.
Bloomberg reported that SpaceX and xAI are among a select group invited to participate in the Defense Department’s effort to develop advanced drone swarming capabilities. The goal is reportedly to create systems that can translate voice commands into digital instructions and manage fleets of autonomous drones.
Neither SpaceX, xAI, nor the Pentagon’s Defense Innovation Unit has commented on the report, and Reuters said it could not independently verify the details.
The development follows SpaceX’s recent acquisition of xAI, which pushed the valuation of the combined companies to an impressive $1.25 trillion. The reported competition comes as SpaceX prepares for a potential initial public offering later this year.
The Pentagon has been moving to speed up drone deployment and expand domestic manufacturing capacity, while also seeking tools to counter unauthorized drone activity around airports and major public events. Large-scale gatherings scheduled this year, including the FIFA World Cup and America250 celebrations, have heightened focus on aerial security.
The reported challenge aligns with broader Defense Department investments in artificial intelligence. Last year, OpenAI, Google, Anthropic, and xAI secured Pentagon contracts worth up to $200 million each to advance AI capabilities across defense applications.
Elon Musk previously joined AI and robotics researchers in signing a 2015 open letter calling for a ban on offensive autonomous weapons. In recent years, however, Musk has spoken on X about the strengths of drone technologies in combat situations.
News
Doug DeMuro names Tesla Model S the Most Important Car of the last 30 years
In a recent video, the noted reviewer stated that the choice was “not even a question.”
Popular automotive reviewer and YouTuber Doug DeMuro has named the 2012 Tesla Model S as the most important car of the last 30 years.
In a recent video, the noted reviewer stated that the choice was “not even a question,” arguing that the Model S did more to change the trajectory of the auto industry than any other vehicle released since the mid-1990s.
“Unquestionably in my mind, the number one most important car of the last 30 years… it’s not even a question,” DeMuro said. “The 2012 Tesla Model S. There is no doubt that that is the most important car of the last 30 years.”
DeMuro acknowledged that electric vehicle adoption has faced recent headwinds. Still, he maintained that long-term electrification is inevitable.
“If you’re a rational person who’s truthful with yourself, you know that the future is electric… whether it’s 10, 20, 30 years, the future will be electric, and it was the Model S that was the very first car that did that truthfully,” he said.
While earlier EVs like the Nissan Leaf and Chevrolet Volt arrived before the Model S, DeMuro argued that they did not fundamentally shift public perception. The Model S proved that EVs “could be cool, could be fast, could be luxurious, could be for enthusiasts.” It showed that buyers did not have to make major compromises to drive electric.
He also described the Model S as a cultural turning point. Tesla became more than a car company. The brand expanded into Superchargers, home energy products, and a broader tech identity.
DeMuro noted that the Leaf and Volt “made a huge splash and taught us that it was possible.” However, he drew a distinction between being first and bringing a technology into the mainstream.
“It’s rarely about the car that does it first. It’s about the car that brings it into the mainstream,” he said. “The Model S was the car that actually won the game even though the Leaf and Volt scored the first.”
He added that perhaps the Model S’ most surprising achievement was proving that a new American automaker could succeed. For decades, industry observers believed the infrastructure and capital requirements made that nearly impossible.
“For decades, it was generally agreed that there would never be another competitive American car company because the infrastructure and the investment required to start up another American car company as just too challenging… It was just a given basically that you couldn’t do it. And not only did they go it, but they created a cultural icon… That car just truly changed the world,” he said.
Elon Musk
Elon Musk doubles down on Tesla Cybercab timeline once again
“Cybercab, which has no pedals or steering wheel, starts production in April,” Musk said.
CEO Elon Musk doubled down once again on the timeline of production for the Tesla Cybercab, marking yet another example of the confidence he has in the company’s ability to meet the aggressive timeline for the vehicle.
It is the third time in the past six months that Musk has explicitly stated Cybercab will enter production in April 2026.
On Monday morning, Musk reiterated that Cybercab will enter its initial manufacturing phase in April, and that it would not have any pedals or a steering wheel, two things that have been speculated as potential elements of the vehicle, if needed.
Cybercab, which has no pedals or steering wheel, starts production in April https://t.co/yShxZ2HJqp
— Elon Musk (@elonmusk) February 16, 2026
Musk has been known to be aggressive with timelines, and some products have been teased for years and years before they finally come to fruition.
One of perhaps the biggest complaints about Musk is the fact that Tesla does not normally reach the deadlines that are set: the Roadster, Semi, and Unsupervised Full Self-Driving suite are a few of those that have been given “end of this year” timelines, but have not been fulfilled.
Nevertheless, many are able to look past this as part of the process. New technology takes time to develop, but we’d rather not hear about when, and just the progress itself.
However, the Cybercab is a bit different. Musk has said three times in the past six months that Cybercab will be built in April, and this is something that is sort of out of the ordinary for him.
In December 2025, he said that Tesla was “testing the production system” of the vehicle and that “real production ramp starts in April.
Elon Musk shares incredible detail about Tesla Cybercab efficiency
On January 23, he said that “Cybercab production starts in April.” He did the same on February 16, marking yet another occasion that Musk has his sights set on April for initial production of the vehicle.
Musk has also tempered expectations for the Cybercab’s initial production phase. In January, he noted that Cybercab would be subjected to the S-curve-type production speed:
“…initial production is always very slow and follows an S-curve. The speed of production ramp is inversely proportionate to how many new parts and steps there are. For Cybercab and Optimus, almost everything is new, so the early production rate will be agonizingly slow, but eventually end up being insanely fast.”
Cybercab will be a huge part of Tesla’s autonomous ride-sharing plans moving forward.








