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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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7 years ago

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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.

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.

“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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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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Tesla makes big Full Self-Driving change to reflect future plans

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13 hours ago

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January 23, 2026

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tesla interior operating on full self driving
Credit: TESLARATI

Tesla made a dramatic change to the Online Design Studio to show its plans for Full Self-Driving, a major part of the company’s plans moving forward, as CEO Elon Musk has been extremely clear on the direction moving forward.

With Tesla taking a stand and removing the ability to purchase Full Self-Driving outright next month, it is already taking steps to initiate that with owners and potential buyers.

On Thursday night, the company updated its Online Design Studio to reflect that in a new move that now lists the three purchase options that are currently available: Monthly Subscription, One-Time Purchase, or Add Later:

This change replaces the former option for purchasing Full Self-Driving at the time of purchase, which was a simple and single box to purchase the suite outright. Subscriptions were activated through the vehicle exclusively.

However, with Musk announcing that Tesla would soon remove the outright purchase option, it is clearer than ever that the Subscription plan is where the company is headed.

The removal of the outright purchase option has been a polarizing topic among the Tesla community, especially considering that there are many people who are concerned about potential price increases or have been saving to purchase it for $8,000.

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This would bring an end to the ability to pay for it once and never have to pay for it again. With the Subscription strategy, things are definitely going to change, and if people are paying for their cars monthly, it will essentially add $100 per month to their payment, pricing some people out. The price will increase as well, as Musk said on Thursday, as it improves in functionality.

Those skeptics have grown concerned that this will actually lower the take rate of Full Self-Driving. While it is understandable that FSD would increase in price as the capabilities improve, there are arguments for a tiered system that would allow owners to pay for features that they appreciate and can afford, which would help with data accumulation for the company.

Musk’s new compensation package also would require Tesla to have 10 million active FSD subscriptions, but people are not sure if this will move the needle in the correct direction. If Tesla can potentially offer a cheaper alternative that is not quite unsupervised, things could improve in terms of the number of owners who pay for it.

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Tesla Model S completes first ever FSD Cannonball Run with zero interventions

The coast-to-coast drive marked the first time Tesla’s FSD system completed the iconic, 3,000-mile route end to end with no interventions.

Published

17 hours ago

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January 23, 2026

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A Tesla Model S has completed the first-ever full Cannonball Run using Full Self-Driving (FSD), traveling from Los Angeles to New York with zero interventions. The coast-to-coast drive marked the first time Tesla’s FSD system completed the iconic, 3,000-mile route end to end, fulfilling a long-discussed benchmark for autonomy.

A full FSD Cannonball Run

As per a report from The Drive, a 2024 Tesla Model S with AI4 and FSD v14.2.2.3 completed the 3,081-mile trip from Redondo Beach in Los Angeles to midtown Manhattan in New York City. The drive was completed by Alex Roy, a former automotive journalist and investor, along with a small team of autonomy experts.

Roy said FSD handled all driving tasks for the entirety of the route, including highway cruising, lane changes, navigation, and adverse weather conditions. The trip took a total of 58 hours and 22 minutes at an average speed of 64 mph, and about 10 hours were spent charging the vehicle. In later comments, Roy noted that he and his team cleaned out the Model S’ cameras during their stops to keep FSD’s performance optimal. 

History made

The historic trip was quite impressive, considering that the journey was in the middle of winter. This meant that FSD didn’t just deal with other cars on the road. The vehicle also had to handle extreme cold, snow, ice, slush, and rain. 

As per Roy in a post on X, FSD performed so well during the trip that the journey would have been completed faster if the Model S did not have people onboard. “Elon Musk was right. Once an autonomous vehicle is mature, most human input is error. A comedy of human errors added hours and hundreds of miles, but FSD stunned us with its consistent and comfortable behavior,” Roy wrote in a post on X.

Roy’s comments are quite notable as he has previously attempted Cannonball Runs using FSD on December 2024 and February 2025. Neither were zero intervention drives.

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Tesla removes Autopilot as standard, receives criticism online

The move leaves only Traffic Aware Cruise Control as standard equipment on new Tesla orders.

Published

18 hours ago

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January 23, 2026

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Credit: Tesla Malaysia/X

Tesla removed its basic Autopilot package as a standard feature in the United States. The move leaves only Traffic Aware Cruise Control as standard equipment on new Tesla orders, and shifts the company’s strategy towards paid Full Self-Driving subscriptions.

Tesla removes Autopilot

As per observations from the electric vehicle community on social media, Tesla no longer lists Autopilot as standard in its vehicles in the U.S. This suggests that features such as lane-centering and Autosteer have been removed as standard equipment. Previously, most Tesla vehicles came with Autopilot by default, which offers Traffic-Aware Cruise Control and Autosteer.

The change resulted in backlash from some Tesla owners and EV observers, particularly as competing automakers, including mainstream players like Toyota, offer features like lane-centering as standard on many models, including budget vehicles.

That being said, the removal of Autopilot suggests that Tesla is concentrating its autonomy roadmap around FSD subscriptions rather than bundled driver-assistance features. It would be interesting to see how Tesla manages its vehicles’ standard safety features, as it seems out of character for Tesla to make its cars less safe over time. 

Musk announces FSD price increases

Following the Autopilot changes, Elon Musk stated on X that Tesla is planning to raise subscription prices for FSD as its capabilities improve. In a post on X, Musk stated that the current $99-per-month price for supervised FSD would increase over time, especially as the system itself becomes more robust.

“I should also mention that the $99/month for supervised FSD will rise as FSD’s capabilities improve. The massive value jump is when you can be on your phone or sleeping for the entire ride (Unsupervised FSD),” Musk wrote. 

At the time of his recent post, Tesla still offers FSD as a one-time purchase for $8,000, but Elon Musk has confirmed that this option will be discontinued on February 14, leaving subscriptions as the only way to access the system.

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