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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 arsonist who burned Cybertruck sees end of FAFO journey
The man has now reached the “Find Out” stage.
A Mesa, Arizona man has been sentenced to five years in federal prison for setting fire to a Tesla location and vehicle in a politically motivated arson attack, federal prosecutors have stated.
The April 2025 incident destroyed a Tesla Cybertruck, endangered first responders, and triggered mandatory sentencing under federal arson laws.
A five-year sentence
U.S. District Judge Diane J. Humetewa sentenced Ian William Moses, 35, of Mesa, Arizona, to 5 years in prison followed by 3 years of supervised release for maliciously damaging property and vehicles by means of fire. Moses pleaded guilty in October to all five counts brought by a federal grand jury. Restitution will be determined at a hearing scheduled for April 13, 2026.
As per court records, surveillance footage showed Moses arriving at a Tesla store in Mesa shortly before 2 a.m. on April 28, 2025, carrying a gasoline can and backpack. Investigators stated that he placed fire starter logs near the building, poured gasoline on the structure and three vehicles, and ignited the fire. The blaze destroyed a Tesla Cybertruck. Moses fled the scene on a bicycle and was arrested by Mesa police about a quarter mile away, roughly an hour later.
Authorities said Moses was still wearing the same clothing seen on camera at the time of his arrest and was carrying a hand-drawn map marking the dealership’s location. Moses also painted the word “Theif” on the walls of the Tesla location, prompting jokes from social media users and Tesla community members.
The “Finding Out” stage
U.S. Attorney Timothy Courchaine noted that Moses’ sentence reflects the gravity of his crime. He also highlighted that arson is never acceptable.
“Arson can never be an acceptable part of American politics. Mr. Moses’ actions endangered the public and first responders and could have easily turned deadly. This five-year sentence reflects the gravity of these crimes and makes clear that politically fueled attacks on Arizona’s communities and businesses will be met with full accountability.”
Maricopa County Attorney Rachel Mitchell echoed the same sentiments, stating that regardless of Moses’ sentiments towards Elon Musk, his actions are not defensible.
“This sentence sends a clear message: violence and intimidation have no place in our community. Setting fire to a business in retaliation for political or personal grievances is not protest, it is a crime. Our community deserves to feel safe, and this sentence underscores that Maricopa County will not tolerate political violence in any form.”
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Tesla says its Texas lithium refinery is now operational and unlike anything in North America
Elon Musk separately described the site as both the most advanced and the largest lithium refinery in the United States.
Tesla has confirmed that its Texas lithium refinery is now operational, marking a major milestone for the company’s U.S. battery supply chain. In a newly released video, Tesla staff detailed how the facility converts raw spodumene ore directly into battery-grade lithium hydroxide, making it the first refinery of its kind in North America.
Elon Musk separately described the site as both the most advanced and the largest lithium refinery in the United States.
A first-of-its-kind lithium refining process
In the video, Tesla staff at the Texas lithium refinery near Corpus Christi explained that the facility processes spodumene, a lithium-rich hard-rock ore, directly into battery-grade lithium hydroxide on site. The approach bypasses intermediate refining steps commonly used elsewhere in the industry.
According to the staff, spodumene is processed through kilns and cooling systems before undergoing alkaline leaching, purification, and crystallization. The resulting lithium hydroxide is suitable for use in batteries for energy storage and electric vehicles. Tesla employees noted that the process is simpler and less expensive than traditional refining methods.
Staff at the facility added that the process eliminates hazardous byproducts typically associated with lithium refining. “Our process is more sustainable than traditional methods and eliminates hazardous byproducts, and instead produces a co-product named anhydrite, used in concrete mixes,” an employee noted.
Musk calls the facility the largest lithium refinery in America
The refinery’s development timeline has been very impressive. The project moved from breaking ground in 2023 to integrated plant startup in 2025 by running feasibility studies, design, and construction in parallel. This compressed schedule enabled the fastest time-to-market for a refinery using this type of technology. This 2026, the facility has become operational.
Elon Musk echoed the significance of the project in posts on X, stating that “the largest Lithium refinery in America is now operational.” In a separate comment, Musk described the site as “the most advanced lithium refinery in the world” and emphasized that the facility is “very clean.”
By bringing large-scale lithium hydroxide production online in Texas, Tesla is positioning itself to reduce reliance on foreign refining capacity while supporting its growth in battery and vehicle production. The refinery also complements Tesla’s nascent domestic battery manufacturing efforts, which could very well be a difference maker in the market.
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Tesla Optimus V3 gets early third-party feedback, and it’s eye-opening
Jason Calacanis’ remarks, which were shared during a discussion at CES 2026, offered one of the first third-party impressions of the yet-to-be-unveiled robot
Angel investor and entrepreneur Jason Calacanis shared some insights after he got an early look at Tesla’s upcoming Optimus V3. His remarks, which were shared during a discussion at CES 2026, offered one of the first third-party impressions of the yet-to-be-unveiled robot.
Calacanis’ comments were shared publicly on X, and they were quite noteworthy.
The angel investor stated that he visited Tesla’s Optimus lab on a Sunday morning and observed that the place was buzzing with energy. The investor then shared a rare, shocking insight. As per Calacanis, Optimus V3 will be so revolutionary that people will probably not even remember that Tesla used to make cars in the future.
“I don’t want to name drop, but two Sundays ago, I went to Tesla with Elon and I went and visited the Optimus lab. There were a large number of people working on a Sunday at 10 a.m. and I saw Optimus 3. I can tell you now, nobody will remember that Tesla ever made a car,” he noted.
The angel investor also reiterated the primary advantage of Optimus, and how it could effectively change the world.
“They will only remember the Optimus and that he is going to make a billion of those, and it is going to be the most transformative technology product ever made in the history of humanity, because what LLMs are gonna enable those products to do is understand the world and then do things in the world that we don’t want to do. I believe there will be a 1:1 ratio of humans to Optimus, and I think he’s already won,” he said.
While Calacanis’ comments were clearly opinion-driven, they stood out as among the first from a non-Tesla employee about Optimus V3. Considering his reaction to the humanoid robot, perhaps Elon Musk’s predictions for Optimus V3 might not be too far-fetched at all.
Tesla has been careful with its public messaging around Optimus V3’s development stage. Musk has previously stated on X that Optimus V3 has not yet been revealed publicly, clarifying that images and videos of the robot online still show Optimus V2 and V2.5, not the next-generation unit. As for Calacanis’ recent comments, however, Musk responded with a simple “Probably true” in a post on X.
Tesla arsonist who burned Cybertruck sees end of FAFO journey
Tesla says its Texas lithium refinery is now operational and unlike anything in North America
