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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 Model Y and Model 3 named safest vehicles tested by ANCAP in 2025
According to ANCAP in a press release, the Tesla Model Y achieved the highest overall weighted score of any vehicle assessed in 2025.
The Tesla Model Y recorded the highest overall safety score of any vehicle tested by ANCAP in 2025. The Tesla Model 3 also delivered strong results, reinforcing the automaker’s safety leadership in Australia and New Zealand.
According to ANCAP in a press release, the Tesla Model Y achieved the highest overall weighted score of any vehicle assessed in 2025. ANCAP’s 2025 tests evaluated vehicles across four key pillars: Adult Occupant Protection, Child Occupant Protection, Vulnerable Road User Protection, and Safety Assist technologies.
The Model Y posted consistently strong results in all four categories, distinguishing itself through a system-based safety approach that combines structural crash protection with advanced driver-assistance features such as autonomous emergency braking, lane support, and driver monitoring.
This marked the second time the Model Y has topped ANCAP’s annual safety rankings. The Model Y’s previous version was also ANCAP’s top performer in 2022.
The Tesla Model 3 also delivered a strong performance in ANCAP’s 2025 tests, contributing to Tesla’s broader safety presence across segments. Similar to the Model Y, the Model 3 also earned impressive scores across the ANCAP’s four pillars. This made the vehicle the top performer in the Medium Car category.
ANCAP Chief Executive Officer Carla Hoorweg stated that the results highlight a growing industry shift toward integrated safety design, with improvements in technologies such as autonomous emergency braking and lane support translating into meaningful real-world protection.
“ANCAP’s testing continues to reinforce a clear message: the safest vehicles are those designed with safety as a system, not a checklist. The top performers this year delivered consistent results across physical crash protection, crash avoidance and vulnerable road user safety, rather than relying on strength in a single area.
“We are also seeing increasing alignment between ANCAP’s test requirements and the safety technologies that genuinely matter on Australian and New Zealand roads. Improvements in autonomous emergency braking, lane support, and driver monitoring systems are translating into more robust protection,” Hoorweg said.
News
Tesla Sweden uses Megapack battery to bypass unions’ Supercharger blockade
Just before Christmas, Tesla went live with a new charging station in Arlandastad, outside Stockholm, by powering it with a Tesla Megapack battery.
Tesla Sweden has successfully launched a new Supercharger station despite an ongoing blockade by Swedish unions, using on-site Megapack batteries instead of traditional grid connections. The workaround has allowed the Supercharger to operate without direct access to Sweden’s electricity network, which has been effectively frozen by labor action.
Tesla has experienced notable challenges connecting its new charging stations to Sweden’s power grid due to industrial action led by Seko, a major Swedish trade union, which has blocked all new electrical connections for new Superchargers. On paper, this made the opening of new Supercharger sites almost impossible.
Despite the blockade, Tesla has continued to bring stations online. In Malmö and Södertälje, new Supercharger locations opened after grid operators E.ON and Telge Nät activated the sites. The operators later stated that the connections had been made in error.
More recently, however, Tesla adopted a different strategy altogether. Just before Christmas, Tesla went live with a new charging station in Arlandastad, outside Stockholm, by powering it with a Tesla Megapack battery, as noted in a Dagens Arbete (DA) report.
Because the Supercharger station does not rely on a permanent grid connection, Tesla was able to bypass the blocked application process, as noted by Swedish car journalist and YouTuber Peter Esse. He noted that the Arlandastad Supercharger is likely dependent on nearby companies to recharge the batteries, likely through private arrangements.
Eight new charging stalls have been launched in the Arlandastad site so far, which is a fraction of the originally planned 40 chargers for the location. Still, the fact that Tesla Sweden was able to work around the unions’ efforts once more is impressive, especially since Superchargers are used even by non-Tesla EVs.
Esse noted that Tesla’s Megapack workaround is not as easily replicated in other locations. Arlandastad is unique because neighboring operators already have access to grid power, making it possible for Tesla to source electricity indirectly. Still, Esse noted that the unions’ blockades have not affected sales as much.
“Many want Tesla to lose sales due to the union blockades. But you have to remember that sales are falling from 2024, when Tesla sold a record number of cars in Sweden. That year, the unions also had blockades against Tesla. So for Tesla as a charging operator, it is devastating. But for Tesla as a car company, it does not matter in terms of sales volumes. People charge their cars where there is an opportunity, usually at home,” Esse noted.
Elon Musk
Elon Musk’s X goes down as users report major outage Friday morning
Error messages and stalled loading screens quickly spread across the service, while outage trackers recorded a sharp spike in user reports.
Elon Musk’s X experienced an outage Friday morning, leaving large numbers of users unable to access the social media platform.
Error messages and stalled loading screens quickly spread across the service, while outage trackers recorded a sharp spike in user reports.
Downdetector reports
Users attempting to open X were met with messages such as “Something went wrong. Try reloading,” often followed by an endless spinning icon that prevented access, according to a report from Variety. Downdetector data showed that reports of problems surged rapidly throughout the morning.
As of 10:52 a.m. ET, more than 100,000 users had reported issues with X. The data indicated that 56% of complaints were tied to the mobile app, while 33% were related to the website and roughly 10% cited server connection problems. The disruption appeared to begin around 10:10 a.m. ET, briefly eased around 10:35 a.m., and then returned minutes later.
Previous disruptions
Friday’s outage was not an isolated incident. X has experienced multiple high-profile service interruptions over the past two years. In November, tens of thousands of users reported widespread errors, including “Internal server error / Error code 500” messages. Cloudflare-related error messages were also reported.
In March 2025, the platform endured several brief outages spanning roughly 45 minutes, with more than 21,000 reports in the U.S. and 10,800 in the U.K., according to Downdetector. Earlier disruptions included an outage in August 2024 and impairments to key platform features in July 2023.
Tesla Model Y and Model 3 named safest vehicles tested by ANCAP in 2025
Tesla Sweden uses Megapack battery to bypass unions’ Supercharger blockade
