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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 influencers argue company’s polarizing Full Self-Driving transfer decision
Tesla maintains it will honor transfers for orders with initial delivery windows before the deadline and offers full deposit refunds otherwise, citing longstanding fine print that the program is “subject to change at any time.”
Tesla’s decision to tighten its Full Self-Driving (FSD) transfer promotion has ignited fierce debate among owners and enthusiasts.
The company quietly updated its terms in late February 2026, changing the eligibility from “order by March 31, 2026” to “take delivery by March 31, 2026.”
What began as a flexible incentive to boost sales, allowing buyers to transfer their paid FSD (Supervised) to a new vehicle, now excludes many, particularly Cybertruck owners facing delivery delays into summer or later.
Tesla maintains it will honor transfers for orders with initial delivery windows before the deadline and offers full deposit refunds otherwise, citing longstanding fine print that the program is “subject to change at any time.”
The reversal has polarized the Tesla community, with accusations of a “bait-and-switch” clashing against defenses of corporate pragmatism. Many owners who placed orders under the original wording feel betrayed, especially as production backlogs and new unsupervised FSD rollout complicate timelines.
However, Tesla has allowed them to cancel their orders and receive a refund.
Critics of the decision argue that the change disadvantages loyal customers who helped fund FSD development, calling it poor communication and a revenue grab as Tesla pivots toward subscriptions.
Popular influencers have amplified the divide. Whole Mars Catalog struck a measured but firm tone, acknowledging the original “order by” language but emphasizing Tesla’s right to adjust terms. He has continued to defend Tesla in this particular issue:
Sad to see so many fans trashing Tesla with such extreme language.
LIARS!!! PATHETIC!!! And if you aren’t as furious and angry as they are they are you’re “worshipping” and saying “they can do no wrong”.
Let’s get real here. They’re not liars. They offered FSD transfer to us… https://t.co/3Ay7vGaVR6
— Whole Mars Catalog (@wholemars) March 3, 2026
He criticized extreme backlash as “dramatization” and “spoiled kids,” noting the unsupervised FSD era and broader sales challenges make blanket transfers financially risky. Whole Mars advocated for polite outreach to CEO Elon Musk over the issue.
Rather than “calling them out”, I would simply say “Hey Elon, really hoped to be able to do FSD transfer on my cybertruck but the terms changed. Would really appreciate if Tesla could extend this to everyone who ordered before the terms changes”
that would probably work
— Whole Mars Catalog (@wholemars) March 3, 2026
In a contrasting perspective, Dirty TesLA voiced sharper frustration, posting that blocking transfers feels “crazy” and distancing himself from “people that want to worship a corporation and say they can do no wrong.” His stance resonated with owners who view the policy flip as disrespectful to early adopters.
Popular Tesla influencer Sawyer Merritt captured the frustration felt by thousands. In a widely shared thread viewed over 700,000 times, Merritt detailed how pre-change Cybertruck orders now risk losing FSD eligibility unless their initial delivery window falls before March 31.
It’s not a contradiction, it’s a change in policy that Tesla just made an hour ago. I am trying to check if the change is retroactive to all existing orders, including Cybertruck AWD orders, because if it is, that sucks big time.
— Sawyer Merritt (@SawyerMerritt) February 28, 2026
The controversy underscores deeper tensions—between Tesla’s need for revenue discipline and owners’ expectations of goodwill. As FSD evolves toward unsupervised capability, the community remains split: some see the change as necessary business, others as a broken promise. Whether Tesla reconsiders under pressure or holds firm remains to be seen, but it does not appear they are planning to budge.
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Tesla Semi’s latest adoptee will likely encourage more of the same
Public visibility matters. When shoppers see a trusted name like Ralph’s running clean, high-tech trucks on public roads, skepticism fades. Competitors such as Albertsons, which pre-ordered Semis years ago, and other chains chasing ESG targets now have proof that electric autonomy works in real-world grocery fleets.
The latest adoptee of the Tesla Semi will likely encourage more businesses in the same realm to adopt the all-electric Class 8 truck, as a new company utilizing the Semi has been spotted in Southern California.
A sleek, futuristic Tesla Semi truck branded for Ralph’s Supermarkets was spotted cruising a Los Angeles highway in a viral 13-second dashcam video posted March 2, by X user ChargePozitive.
Tesla Semi Truck in the wild pic.twitter.com/SnQY8ShMMJ
— ChargePozitive ⚡️➕ (@ChargePozitive) March 2, 2026
This sighting confirms Kroger’s March 2025 partnership with Tesla to deploy up to 500 autonomous electric Semis.
While the initial announcement targeted Midwest supply chains, the California appearance under the Ralph’s banner shows the program expanding to Kroger’s West Coast operations. Ralph’s, a staple for millions of Southern California shoppers, is now hauling groceries with the Semi, which has zero tailpipe emissions and claims up to 500 miles of range per charge.
Tesla Semi pricing revealed after company uncovers trim levels
The timing could not be better for sustainable logistics. Traditional trucking accounts for a massive share of retail emissions, but Tesla’s Semi slashes fuel and maintenance costs while leveraging full autonomy to ease driver shortages and improve safety.
Tesla’s expanding Megacharger network, including new sites along major freight corridors and partnerships like the recently-announced one with Pilot Travel Centers, is removing range anxiety and making nationwide scaling realistic. There’s still a long way to go, but things are moving in the right direction.
Public visibility matters. When shoppers see a trusted name like Ralph’s running clean, high-tech trucks on public roads, skepticism fades. Competitors such as Albertsons, which pre-ordered Semis years ago, and other chains chasing ESG targets now have proof that electric autonomy works in real-world grocery fleets.
PepsiCo’s successful pilots already demonstrated viability, and Ralph’s sighting adds retail credibility.
As Tesla ramps high-volume Semi production through 2026, this isn’t an isolated curiosity. Instead, it’s a catalyst. More grocers adopting the platform will accelerate industry-wide decarbonization, cut operating expenses, and deliver tangible environmental wins.
The future of sustainable supply chains is already on the highway, and Ralph’s just made it impossible to ignore.
Moving forward, Tesla hopes to expand the Semi program into other regions, including Europe, which CEO Elon Musk recently said is a total possibility next year.
Elon Musk
Tesla ramps Cybercab test manufacturing ahead of mass production
Tesla still has plans for volume production, which remains between four and eight weeks away, aligning with Musk’s statements that early ramps would be deliberately measured given the Cybercab’s novel architecture and full reliance on Tesla’s vision-based Full Self-Driving technology.
Tesla is seemingly ramping Cybercab test manufacturing ahead of mass production, which is scheduled to begin next month, the company said.
At Tesla’s Gigafactory Texas, production of the Cybercab, the company’s groundbreaking purpose-built Robotaxi vehicle, is accelerating markedly. Drone footage from Joe Tegtmeyer captured striking aerial footage today, revealing what appears to be the largest public sighting of Cyebrcabs to date.
A total of 25 units were observed by Tegtmeyer across the Gigafactory Texas property, marking a clear step-up in testing and validation activities as Tesla prepares for a broader output.
Tesla Cybercab production begins: The end of car ownership as we know it?
In the footage, 14 metallic gold Cybercabs were parked in a tight formation outside the factory exit, showcasing their sleek, autonomous-only design with no steering wheels, pedals, or traditional controls. Another 9 units sat at the crash testing facility, likely undergoing structural and safety validations, while two more appeared at the west end-of-line area for final checks.
Big day for Cybercab at Giga Texas today! Actually, yesterday to kick off March, the production line went into a higher volume & today we see 25 at three main locations, and there were several others I observed driving around too!
I think this may be the largest single grouping… pic.twitter.com/HZDMNv57lJ
— Joe Tegtmeyer 🚀 🤠🛸😎 (@JoeTegtmeyer) March 3, 2026
Tegtmeyer noted additional Cybercabs driving around the complex, hinting at active movement and real-world testing beyond static parking.
This surge follows the first production Cybercab rolling off the line in mid-February 2026, several weeks ahead of the originally anticipated April start.
That milestone, celebrated by Tesla employees and confirmed by CEO Elon Musk, kicked off low-volume builds on the dedicated “unboxed” manufacturing line, a modular process designed to slash costs, reduce factory footprint, and enable faster assembly compared to conventional methods.
Industry observers interpret the jump to dozens of visible units in early March as evidence that Tesla has transitioned into higher-volume test manufacturing.
Tesla still has plans for volume production, which remains between four and eight weeks away, aligning with Musk’s statements that early ramps would be deliberately measured given the Cybercab’s novel architecture and full reliance on Tesla’s vision-based Full Self-Driving technology.
The Cybercab, envisioned as a sub-$30,000 autonomous two-seater for robotaxi fleets, represents Tesla’s bold pivot toward scalable autonomy and robotics.
Tesla fans and enthusiasts on X praised the imagery, with many expressing excitement over the visible progress toward deployment. While challenges remain, including software maturity, regulatory hurdles, and supply chain scaling, the increased factory activity underscores Tesla’s momentum in turning the Cybercab vision into reality.
As Giga Texas continues expanding and refining the manufacturing process of the Cybercab, the coming months will prove to be a pivotal time in determining how quickly this revolutionary vehicle reaches roads in the U.S. and internationally.
Tesla influencers argue company’s polarizing Full Self-Driving transfer decision
Tesla Semi’s latest adoptee will likely encourage more of the same
