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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.

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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 Full Self-Driving lands in a new country, its 7th

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56 minutes ago

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November 23, 2025

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Credit: Tesla Korea

Tesla Full Self-Driving has officially landed in a new country today, its seventh overall after it launched in both Australia and New Zealand earlier this year.

On Sunday, Tesla owners in South Korea reported that the company’s Full Self-Driving (Supervised) had started arriving in their vehicles. Owners reported that it was v14.1.4, which is not the latest version available in other countries, but is one of the most recent releases Tesla has deployed to drivers:

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This marks the seventh country in which Tesla has enabled its Full Self-Driving suite, following the United States and Puerto Rico, Canada, China, Mexico, Australia, and New Zealand.

Tesla launched Full Self-Driving most recently in Australia and New Zealand about three months ago. The expansion is a major breakthrough for the company as it aims to launch Full Self-Driving on a global scale.

However, the company’s biggest challenge thus far has been getting European regulatory agencies to handle the red tape that has inhibited Tesla from launching its semi-autonomous driving suite on the continent. Recently, it admitted that it sees a pathway through Dutch regulatory bodies, which seem to be the most willing to work with Tesla to get FSD in Europe.

Tesla Full Self-Driving appears to be heading to Europe soon

The company said that it has driven over 1 million kilometers safely on European roads across 17 different countries in internal testing. But its path to success will be by “partnering with the Dutch approval authority RDW to gain exemption for the feature. This involves proving compliance with existing regulations (UN-R-171 DCAS) + filing an exemption (EU Article 39) for yet-to-be-regulated behaviors like Level 2 systems off-highway, system-initiated lane changes with hands-off the wheel, etc.”

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Perhaps the expansion into Europe will be the biggest challenge for Tesla, but it could also yield major results and advantages for the company moving forward. Tesla said it hopes to have FSD available in Europe sometime early next year.

For now, the expansion in South Korea is the latest win for Tesla and its self-driving efforts. In the U.S., it now turns its focus toward fully autonomous operation, as it works with state agencies to launch Robotaxi outside of Texas, California, and most recently, Arizona.

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Tesla CEO Elon Musk teases insane capabilities of next major FSD update

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20 hours ago

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November 22, 2025

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Credit: Tesla China/Weibo

Tesla CEO Elon Musk teased the insane capabilities of the next major Full Self-Driving update just hours after the company rolled out version 14.2 to owners.

Tesla Full Self-Driving v14.2 had some major improvements from the previous iteration of v14.1.x. We were on v14.1.7, the most advanced configuration of the v14.1 family, before Tesla transitioned us and others to v14.2.

However, Musk has said that the improvements coming in the next major update, which will be v14.3, will be where “the last big piece of the puzzle finally lands.”

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There were some major improvements with v14.2, most notably, Tesla seemed to narrow in on the triggers that caused issues with hesitation and brake stabbing in v14.1.x.

One of the most discussed issues with the past rollout was that of brake stabbing, where the vehicle would contemplate proceeding with a route as traffic was coming from other directions.

We experienced it most frequently at intersections, especially four-way stop signs.

Elon Musk hints at when Tesla can fix this FSD complaint with v14

In our review of it yesterday, it was evident that this issue had been resolved, at least to the extent that we had no issues with it in a 62-minute drive, which you can watch here.

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Some owners also reported a more relaxed driver monitoring system, which is something Tesla said it was working on as it hopes to allow drivers to text during operation in the coming months. We did not test this, as laws in Pennsylvania prohibit the use of phones at any time due to the new Paul Miller’s Law, which took effect earlier this year.

However, the improvements indicate that Tesla is certainly headed toward a much more sentient FSD experience, so much so that Musk’s language seems to be more indicative of a more relaxed experience in terms of overall supervision from the driver, especially with v14.3.

Musk did not release or discuss a definitive timeline for the release of v14.3, especially as v14.2 just rolled out to Early Access Program (EAP) members yesterday. However, v14.1 rolled out to Tesla owners just a few weeks ago in late 2025. There is the potential that v14.3 could be part of the coming Holiday Update, or potentially in a release of its own before the New Year.

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Tesla Full Self-Driving v14.2 – Full Review, the Good and the Bad

Published

1 day ago

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November 22, 2025

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Credit: Teslarati

Tesla rolled out Full Self-Driving version 14.2 yesterday to members of the Early Access Program (EAP). Expectations were high, and Tesla surely delivered.

With the rollout of Tesla FSD v14.2, there were major benchmarks for improvement from the v14.1 suite, which spanned across seven improvements. Our final experience with v14.1 was with v14.1.7, and to be honest, things were good, but it felt like there were a handful of regressions from previous iterations.

While there were improvements in brake stabbing and hesitation, we did experience a few small interventions related to navigation and just overall performance. It was nothing major; there were no critical takeovers that required any major publicity, as they were more or less subjective things that I was not particularly comfortable with. Other drivers might have been more relaxed.

With v14.2 hitting our cars yesterday, there were a handful of things we truly noticed in terms of improvement, most notably the lack of brake stabbing and hesitation, a major complaint with v14.1.x.

However, in a 62-minute drive that was fully recorded, there were a lot of positives, and only one true complaint, which was something we haven’t had issues with in the past.

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The Good

Lack of Brake Stabbing and Hesitation

Perhaps the most notable and publicized issue with v14.1.x was the presence of brake stabbing and hesitation. Arriving at intersections was particularly nerve-racking on the previous version simply because of this. At four-way stops, the car would not be assertive enough to take its turn, especially when other vehicles at the same intersection would inch forward or start to move.

This was a major problem.

However, there were no instances of this yesterday on our lengthy drive. It was much more assertive when arriving at these types of scenarios, but was also more patient when FSD knew it was not the car’s turn to proceed.

This improvement was the most noticeable throughout the drive, along with fixes in overall smoothness.

Speed Profiles Seem to Be More Reasonable

There were a handful of FSD v14 users who felt as if the loss of a Max Speed setting was a negative. However, these complaints will, in our opinion, begin to subside, especially as things have seemed to be refined quite nicely with v14.2.

Freeway driving is where this is especially noticeable. If it’s traveling too slow, just switch to a faster profile. If it’s too fast, switch to a slower profile. However, the speeds seem to be much more defined with each Speed Profile, which is something that I really find to be a huge advantage. Previously, you could tell the difference in speeds, but not in driving styles. At times, Standard felt a lot like Hurry. Now, you can clearly tell the difference between the two.

It seems as if Tesla made a goal that drivers should be able to tell which Speed Profile is active if it was not shown on the screen. With v14.1.x, this was not necessarily something that could be done. With v14.2, if someone tested me on which Speed Profile was being used, I’m fairly certain I could pick each one.

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Better Overall Operation

I felt, at times, especially with v14.1.7, there were some jerky movements. Nothing that was super alarming, but there were times when things just felt a little more finicky than others.

v14.2 feels much smoother overall, with really great decision-making, lane changes that feel second nature, and a great speed of travel. It was a very comfortable ride.

The Bad

Parking

It feels as if there was a slight regression in parking quality, as both times v14.2 pulled into parking spots, I would have felt compelled to adjust manually if I were staying at my destinations. For the sake of testing, at my first destination, I arrived, allowed the car to park, and then left. At the tail-end of testing, I walked inside the store that FSD v14.2 drove me to, so I had to adjust the parking manually.

This was pretty disappointing. Apart from parking at Superchargers, which is always flawless, parking performance is something that needs some attention. The release notes for v14.2. state that parking spot selection and parking quality will improve with future versions.

However, this was truly my only complaint about v14.2.

You can check out our full 62-minute ride-along below:

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