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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 has officially launched its first branded Supercharger just months after initiating a new program that allows third-party companies to brand their own charging piles.
The site opened in Land O’ Lakes, Florida, and features eight V4 Supercharging stalls offering up to 325 kW of charging speed. It appears it was purchased by a company called Suncoast Credit Union. This particular branch is located Northeast of Tampa, which is on the Gulf of Mexico.
It features graphics of Florida animals, like alligators:
Here’s a video of the graphics being installed on the Tesla Superchargers at this site: https://t.co/oIfEPNZjAH pic.twitter.com/ENWakZ2qT9
— TESLARATI (@Teslarati) November 20, 2025
Tesla launched this program back in September, and it basically was a way to expand its Supercharger presence and also allow companies to pay for the infrastructure. Tesla maintains it. When it announced the “Supercharger for Business,” it said:
“Purchase and install Superchargers at your business. Superchargers are compatible with all electric vehicles, bringing EV drivers to your business by offering convenient, reliable charging.”
The program does a few things. Initially, it expands EV charging infrastructure and makes charging solutions more readily available for drivers. It can also attract people to those businesses specifically.
Tesla launches new Supercharger program that business owners will love
The chargers can also be branded with any logo that the business chooses, which makes them more personalized and also acts as an advertisement.
The best part is that the customers do not have to maintain anything about the Supercharger. Tesla still takes care of it and resolves any issues:
“We treat your site like we treat our sites. By providing you with a full-service package that includes network operations, preventative maintenance, and driver support, we’re able to guarantee 97% uptime–the highest in the industry.”
It appears the Superchargers will also appear within the in-car nav during routing, so they’ll be publicly available to anyone who needs to use them. They are still available to all EVs that have worked with Tesla to utilize its infrastructure, and they are not restricted to people who are only visiting the business.
Tesla has revealed its Cybertruck light bar installation fix after a recall exposed a serious issue with the accessory.
Tesla and the National Highway Traffic Safety Administration (NHTSA) initiated a recall of 6,197 Cybertrucks back in October to resolve an issue with the Cybertruck light bar accessory. It was an issue with the adhesive that was provided by a Romanian company called Hella Romania S.R.L.
Tesla recalls 6,197 Cybertrucks for light bar adhesive issue
The issue was with the primer quality, as the recall report from the NHTSA had stated the light bar had “inadvertently attached to the windshield using the incorrect surface primer.”
Instead of trying to adhere the light bar to the Cybertruck with an adhesive, Tesla is now going to attach it with a bracketing system, which will physically mount it to the vehicle instead of relying on adhesive strips or glue.
Tesla outlines this in its new Service Bulletin, labeled SB-25-90-001, (spotted by Not a Tesla App) where it shows the light bar will be remounted more securely:
The entire process will take a few hours, but it can be completed by the Mobile Service techs, so if you have a Cybertruck that needs a light bar adjustment, it can be done without taking the vehicle to the Service Center for repair.
However, the repair will only happen if there is no delamination or damage present; then Tesla could “retrofit the service-installed optional off-road light bar accessory with a positive mechanical attachment.”
The company said it would repair the light bar at no charge to customers. The light bar issue was one that did not result in any accidents or injuries, according to the NHTSA’s report.
This was the third recall on Cybertruck this year, as one was highlighted in March for exterior trim panels detaching during operation. Another had to do with front parking lights being too bright, which was fixed with an Over-the-Air update last month.
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Tesla is already expanding its Rental program aggressively
The program has already launched in a handful of locations, specifically, it has been confined to California for now. However, it does not seem like Tesla has any interest in keeping it restricted to the Golden State.
Tesla is looking to expand its Rental Program aggressively, just weeks after the program was first spotted on its Careers website.
Earlier this month, we reported on Tesla’s intention to launch a crazy new Rental program with cheap daily rates, which would give people in various locations the opportunity to borrow a vehicle in the company’s lineup with some outrageous perks.
Along with the cheap rates that start at about $60 per day, Tesla also provides free Full Self-Driving operation and free Supercharging for the duration of the rental. There are also no limits on mileage or charging, but the terms do not allow the renter to leave the state from which they are renting.
🚨🚨 If you look up details on the Tesla Rental program on Google, you’ll see a bunch of sites saying it’s because of decreasing demand 🤣 pic.twitter.com/WlSQrDJhMg
— TESLARATI (@Teslarati) November 10, 2025
The program has already launched in a handful of locations, specifically, it has been confined to California for now. However, it does not seem like Tesla has any interest in keeping it restricted to the Golden State.
Job postings from Tesla now show it is planning to launch the Rental program in at least three new states: Texas, Tennessee, and Massachusetts.
The jobs specifically are listed as a Rental Readiness Specialist, which lists the following job description:
“The Tesla Rental Program is looking for a Rental Readiness Specialist to work on one of the most progressive vehicle brands in the world. The Rental Readiness Specialist is a key contributor to the Tesla experience by coordinating the receipt of incoming new and used vehicle inventory. This position is responsible for fleet/lot management, movement of vehicles, vehicle readiness, rental invoicing, and customer hand-off. Candidates must have a high level of accountability, and personal satisfaction in doing a great job.”
It also says that those who take the position will have to charge and clean the cars, work with clients on scheduling pickups and drop-offs, and prepare the paperwork necessary to initiate the rental.
The establishment of a Rental program is big for Tesla because it not only gives people the opportunity to experience the vehicles, but it is also a new way to rent a car.
Just as the Tesla purchasing process is more streamlined and more efficient than the traditional car-buying experience, it seems this could be less painful and a new way to borrow a car for a trip instead of using your own.
Tesla launches its new branded Supercharger for Business with first active station
Tesla reveals its Cybertruck light bar installation fix
