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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.
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- A to-scale comparison of Falcon 1, Pegasus XL, MLV, and Falcon 9. (Teslarati/Stratolaunch/Wikipedia)
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- 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.
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- PGA’s first full-scale preburner seen during assembly. (Stratolaunch)
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- PGA’s first full-scale preburner seen during assembly. (Stratolaunch)
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- Jeff Thornburg stands in front of Stratolaunch’s NASA Stennis Space Center test stand. (Stratolaunch)
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- The PGA preburner seen after installation at Stennis. (Stratolaunch)
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- The control center. (Stratolaunch)
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- MLV is released from Stratolauncher. (Stratolaunch)
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- A concept video produced by Stratolaunch shows the Roc launching a Kraken rocket. (Stratolaunch, via Wired)
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Tesla’s new Holiday perk is timed perfectly to make FSD a household name
Tesla AI4 owners get FSD (Supervised) through Christmas, New Year’s Eve and well into the post-holiday travel season.
Tesla quietly rolled out a free Full Self-Driving (Supervised) trial for roughly 1.5 million HW4 owners in North America who never bought the package, and the timing could very well be genius.
As it turns out, the trial doesn’t end after 30 days. Instead, it expires January 8, 2026, meaning owners get FSD (Supervised) through Christmas, New Year’s Eve and well into the post-holiday travel season. This extended window positions the feature for maximum word-of-mouth exposure.
A clever holiday gift
Tesla watcher Sawyer Merritt first spotted the detail after multiple owners shared screenshots showing the trial expiring on January 8. He confirmed with affected users that none had active FSD subscriptions before the rollout. He also observed that Tesla never called the promotion a “30-day trial,” as the in-car message simply reads “You’re Getting FSD (Supervised) For the Holidays,” which technically runs until after the new year.
The roughly 40-day period covers peak family travel and gatherings, giving owners ample opportunity to showcase the latest FSD V14’s capabilities on highway trips, crowded parking lots and neighborhood drives. With relatives riding along, hands-off highway driving and automatic lane changes could become instant conversation starters.
Rave reviews for FSD V14 highlight demo potential
FSD has been receiving positive reviews from users as of late. Following the release of FSD v14.2.1, numerous owners praised the update for its smoothness and reliability. Tesla owner @LactoseLunatic called it a “huge leap forward from version 14.1.4,” praising extreme smoothness, snappy lane changes and assertive yet safe behavior that allows relaxed monitoring.
-->Another Tesla owner, @DevinOlsenn, drove 600 km without disengagements, noting his wife now defaults to FSD for daily use due to its refined feel. Sawyer Merritt also tested FSD V14.2.1 in snow on unplowed New Hampshire roads, and the system stayed extra cautious without hesitation. Longtime FSD tester Chuck Cook highlighted improved sign recognition in school zones, showing better dynamic awareness. These reports of fewer interventions and a more “sentient” drive could turn family passengers into advocates, fueling subscriptions come January.
Elon Musk
Elon Musk predicts AI and robotics could make work “optional” within 20 years
Speaking on entrepreneur Nikhil Kamath’s podcast, Musk predicted that machines will soon handle most forms of labor, leaving humans to work only if they choose to.
Elon Musk stated that rapid advances in artificial intelligence and robotics could make traditional work unnecessary within two decades.
Speaking on entrepreneur Nikhil Kamath’s podcast, Musk predicted that machines will soon handle most forms of labor, leaving humans to work only if they choose to.
Work as a “hobby”
During the discussion, Musk said the accelerating capability of AI systems and general-purpose robots will eventually cover all essential tasks, making human labor a choice rather than an economic requirement. “In less than 20 years, working will be optional. Working at all will be optional. Like a hobby,” Musk said.
When Kamath asked whether this future is driven by massive productivity growth, Musk agreed, noting that people will still be free to work if they enjoy the routine or the challenge. He compared future employment to home gardening, as it is something people can still do for personal satisfaction even if buying food from a store is far easier.
“Optional” work in the future
Elon Musk acknowledged the boldness of his claim and joked that people might look back in 20 years and say he was wrong. That being said, the CEO noted that such a scenario could even happen sooner than his prediction, at least if one were to consider the pace of the advancements in AI and robotics.
-->“Obviously people can play this back in 20 years and say, ‘Look, Elon made this ridiculous prediction and it’s not true,’ but I think it will turn out to be true, that in less than 20 years, maybe even as little as ten or 15 years, the advancements in AI and robotics will bring us to the point where working is optional,” Musk said.
Elon Musk’s comments echo his previous sentiments at Tesla’s 2025 Annual Shareholder Meeting, where he noted that Optimus could ultimately eliminate poverty. He also noted that robots like Optimus could eventually provide people worldwide with the best medical care.
Elon Musk
Elon Musk reiterates why Tesla will never make an electric motorcycle
Tesla CEO Elon Musk preemptively shut down speculations about a Tesla road bike once more.
Tesla CEO Elon Musk preemptively shut down speculations about a Tesla road bike once more, highlighting that the electric vehicle maker has no plans to enter the electric motorcycle market.
Musk posted his clarification in a post on X.
Musk’s reply to a fun AI video
X user @Moandbhr posted an AI video featuring the Tesla CEO on the social media platform, captioning it with “Mr. Elon Musk Just Revealed the Game-Changing Tesla Motorcycle.” The short clip depicted Musk approaching a sleek, single-wheeled vehicle, stepping onto it, and gliding off into the distance amid cheers. The fun video received a lot of traction on X, gaining 3.1 million views as of writing.
Musk replied to the post, stating that a Tesla motorcycle is not going to happen. “Never happening, as we can’t make motorcycles safe. For Community Notes, my near death experience was on a road bike. Dirt bikes are safe if you ride carefully, as you can’t be smashed by a truck,” Musk wrote in his reply.
Musk’s Past Comments on Two-Wheelers
Musk also detailed his reservations about motorcycles in a December 2019 X post while responding to questions about Tesla’s potential ATV. At the time, he responded positively to an electric ATV, though he also opposed the idea of a Tesla road-going motorcycle. Musk did state that electric dirt bikes might be cool, since they do not operate in areas where large vehicles like Class 8 trucks are present.
-->“Electric dirt bikes would be cool too. We won’t do road bikes, as too dangerous. I was hit by a truck & almost died on one when I was 17,” Musk wrote in his post.
Considering Musk’s comments about dirt bikes, however, perhaps Tesla would eventually offer a road bike as a recreational vehicle. Such a two-wheeler would be a good fit for the Cybertruck, as well as future products like the Robovan, which could be converted into an RV.
Tesla’s new Holiday perk is timed perfectly to make FSD a household name
Elon Musk predicts AI and robotics could make work “optional” within 20 years
