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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.
- A to-scale comparison of Falcon 1, Pegasus XL, MLV, and Falcon 9. (Teslarati/Stratolaunch/Wikipedia)
- 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.
- PGA’s first full-scale preburner seen during assembly. (Stratolaunch)
- PGA’s first full-scale preburner seen during assembly. (Stratolaunch)
- Jeff Thornburg stands in front of Stratolaunch’s NASA Stennis Space Center test stand. (Stratolaunch)
- The PGA preburner seen after installation at Stennis. (Stratolaunch)
- The control center. (Stratolaunch)
- MLV is released from Stratolauncher. (Stratolaunch)
- A concept video produced by Stratolaunch shows the Roc launching a Kraken rocket. (Stratolaunch, via Wired)
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Waymo scrutinized after self-driving taxis cause traffic jams during SF blackout
It’s not farfetched to speculate that it would have been a doomsday scenario for Tesla had FSD behaved this way.
A power outage across San Francisco over the weekend forced numerous Waymo self-driving taxis to stop at darkened intersections and cause traffic blockages in multiple locations across the city. The disruption left riders stranded, frustrated drivers blocked, and city officials stepping in as the Alphabet-owned company temporarily suspended service amid the widespread gridlock.
Needless to say, it would likely have been a doomsday scenario for Tesla had FSD behaved in a similar way, especially if fleets of its robotaxis blocked traffic for numerous drivers.
Power outage halts Waymo fleet
The outage knocked out electricity for tens of thousands of customers, leaving traffic signals dark across large parts of the city, as noted in a report from the New York Times. Waymo vehicles began stopping at intersections and remained stationary for extended periods, seemingly unable to operate. Tow truck operators worked through the night removing immobilized vehicles, while videos circulated online showing Waymos with hazard lights flashing as traffic backed up around them.
Waymo later confirmed that it had paused its Bay Area ride-hailing service after the San Francisco mayor’s office contacted the company about the congestion its vehicles were contributing to. Service began coming back online shortly after 3:30 p.m. local time, though some users still reported being unable to request rides. Waymo maintained that no injuries or accidents were reported during the outage.
Autonomous cars during emergencies
The incident surprised industry observers since autonomous vehicles are designed to function during signal outages and temporary connectivity losses. Waymo stated that its vehicles treat nonfunctional signals as four-way stops, but “the sheer scale of the outage led to instances where vehicles remained stationary longer than usual to confirm the state of the affected intersections. This contributed to traffic friction during the height of the congestion.” Experts suggested the problem may have been linked to the vehicles’ reliance on remote assistance teams, which help resolve complex situations the cars cannot handle independently.
“Yesterday’s power outage was a widespread event that caused gridlock across San Francisco, with non-functioning traffic signals and transit disruptions. While the failure of the utility infrastructure was significant, we are committed to ensuring our technology adjusts to traffic flow during such events,” the Waymo spokesperson stated, adding that it is “focused on rapidly integrating the lessons learned from this event, and are committed to earning and maintaining the trust of the communities we serve every day.”
News
Tesla aims to combat common Full Self-Driving problem with new patent
Tesla writes in the patent that its autonomous and semi-autonomous vehicles are heavily reliant on camera systems to navigate and interact with their environment.
Tesla is aiming to combat a common Full Self-Driving problem with a new patent.
One issue with Tesla’s vision-based approach is that sunlight glare can become a troublesome element of everyday travel. Full Self-Driving is certainly an amazing technology, but there are still things Tesla is aiming to figure out with its development.
Unfortunately, it is extremely difficult to get around this issue, and even humans need ways to combat it when they’re driving, as we commonly use sunglasses or sun visors to give us better visibility.
Cameras obviously do not have these ways to fight sunglare, but a new patent Tesla recently had published aims to fight this through a “glare shield.”
Tesla writes in the patent that its autonomous and semi-autonomous vehicles are heavily reliant on camera systems to navigate and interact with their environment.

The ability to see surroundings is crucial for accurate performance, and glare is one element of interference that has yet to be confronted.
Tesla described the patent, which will utilize “a textured surface composed of an array of micro-cones, or cone-shaped formations, which serve to scatter incident light in various directions, thereby reducing glare and improving camera vision.”

The patent was first spotted by Not a Tesla App.
The design of the micro-cones is the first element of the puzzle to fight the excess glare. The patent says they are “optimized in size, angle, and orientation to minimize Total Hemispherical Reflectance (THR) and reflection penalty, enhancing the camera’s ability to accurately interpret visual data.”
Additionally, there is an electromechanical system for dynamic orientation adjustment, which will allow the micro-cones to move based on the angle of external light sources.
This is not the only thing Tesla is mulling to resolve issues with sunlight glare, as it has also worked on two other ways to combat the problem. One thing the company has discussed is a direct photon count.
CEO Elon Musk said during the Q2 Earnings Call:
“We use an approach which is direct photon count. When you see a processed image, so the image that goes from the sort of photon counter — the silicon photon counter — that then goes through a digital signal processor or image signal processor, that’s normally what happens. And then the image that you see looks all washed out, because if you point the camera at the sun, the post-processing of the photon counting washes things out.”
Future Hardware iterations, like Hardware 5 and Hardware 6, could also integrate better solutions for the sunglare issue, such as neutral density filters or heated lenses, aiming to solve glare more effectively.
Elon Musk
Delaware Supreme Court reinstates Elon Musk’s 2018 Tesla CEO pay package
The unanimous decision criticized the prior total rescission as “improper and inequitable,” arguing that it left Musk uncompensated for six years of transformative leadership at Tesla.
The Delaware Supreme Court has overturned a lower court ruling, reinstating Elon Musk’s 2018 compensation package originally valued at $56 billion but now worth approximately $139 billion due to Tesla’s soaring stock price.
The unanimous decision criticized the prior total rescission as “improper and inequitable,” arguing that it left Musk uncompensated for six years of transformative leadership at Tesla. Musk quickly celebrated the outcome on X, stating that he felt “vindicated.” He also shared his gratitude to TSLA shareholders.
Delaware Supreme Court makes a decision
In a 49-page ruling Friday, the Delaware Supreme Court reversed Chancellor Kathaleen McCormick’s 2024 decision that voided the 2018 package over alleged board conflicts and inadequate shareholder disclosures. The high court acknowledged varying views on liability but agreed rescission was excessive, stating it “leaves Musk uncompensated for his time and efforts over a period of six years.”
The 2018 plan granted Musk options on about 304 million shares upon hitting aggressive milestones, all of which were achieved ahead of time. Shareholders overwhelmingly approved it initially in 2018 and ratified it once again in 2024 after the Delaware lower court struck it down. The case against Musk’s 2018 pay package was filed by plaintiff Richard Tornetta, who held just nine shares when the compensation plan was approved.
A hard-fought victory
As noted in a Reuters report, Tesla’s win avoids a potential $26 billion earnings hit from replacing the award at current prices. Tesla, now Texas-incorporated, had hedged with interim plans, including a November 2025 shareholder-approved package potentially worth $878 billion tied to Robotaxi and Optimus goals and other extremely aggressive operational milestones.
The saga surrounding Elon Musk’s 2018 pay package ultimately damaged Delaware’s corporate appeal, prompting a number of high-profile firms, such as Dropbox, Roblox, Trade Desk, and Coinbase, to follow Tesla’s exodus out of the state. What added more fuel to the issue was the fact that Tornetta’s legal team, following the lower court’s 2024 decision, demanded a fee request of more than $5.1 billion worth of TSLA stock, which was equal to an hourly rate of over $200,000.
Delaware Supreme Court Elon Musk 2018 Pay Package by Simon Alvarez








