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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 Cybercab is using a unique strategy for picking up the correct rider, which is a crucial part of ride-hailing to ensure people end up in the right place and are charged the correct price.
Cybercab will utilize an RGB strip in its front light bar that will illuminate in a variety of different colors to mark itself.
This identifying mark will also appear in the Robotaxi app, giving riders in the same location a notable distinction in an effort to avoid any confusion regarding who should get in each vehicle.
🚨 Tesla is using different light bar colors to help riders understand which vehicle is theirs
Pretty cool strategy pic.twitter.com/eGMpEMeRpc
— TESLARATI (@Teslarati) August 27, 2026
Other ride-hailing services use similar strategies: Lyft and Uber rides are recognizable through driver identity, vehicle type and color, as well as license plate. Waymo will display the rider’s initials on top of the vehicle, letting them know that the specific vehicle for them has arrived.
Tesla’s strategy is unique and interesting, but there are some flaws. Cybercab’s main purpose is aimed toward being an autonomous ride for all, including those who have disabilities like being blind or even color blind.
Tesla will likely have something in the pipeline for those who cannot see colors or have limited vision. There will definitely be multiple ways to identify which vehicle is the one that “you” specifically ordered.
Cybercab is set to start giving public rides next Thursday, September 3, in Austin, as it announced a dedicated event last week and invited many members of the Tesla community.
Additionally, members of the public will be invited as well. Tesla has been offering employee rides in Cybercab for nearly two months.
Tesla has said goodbye to one customization option for its vehicles: the wrap service it launched several years ago.
After launching an in-house wrap service in August 2020 for the first time in China. In the U.S., it launched in October 2023. Tesla continued to expand the program and adjust it with better pricing and fewer options for the Cybertruck.
By December 2023, it was giving owners of the Model 3, Model Y, and the Cybertruck the opportunity to give their vehicle a fresh look with a vinyl wrap.
Tesla revamps in-house vinyl wrap service with better pricing
It was only available in five locations: Costa Mesa, Oceanside, Santa Clara, West Covina, all in California, and Seattle, Washington.
However, Tesla made some big adjustments to its shop, and the wrap service is officially gone:
Tesla has made a LOT of changes to its online shop recently — price increases, price cuts, new options, and several products being removed entirely.
Some of the biggest increases are wheel covers. 👀
📈 PRICE INCREASES
• 2017-2023 | Model 3 Aero Wheel Cover — Style: Refresh…— Phoenix Self-Driving 🐦🔥 (@PhoenixFSD) August 25, 2026
Wraps are very popular across the Tesla lineup, especially since the company offers relatively few colors. Many choose to wrap their Teslas with interesting colors, patterns, or even finishes, turning their cars from glossy to satin or matte.
However, Tesla’s wrap service was so limited geographically that it never really had a chance to get off the ground or compete with local shops. Every area in the United States is now overflowing with detailing shops, mobile detailers, and other automotive specialists, many of whom perform wrap services.
Tesla’s service was confined to the Pacific time zone and only spanned across two states. It was never going to be something Tesla was a major competitor in, nor was it going to disrupt the wrapping industry. Now that the program has ended, it seems pretty ideal to believe it was always going to be a short-term thing.
Along with the wrap service, Tesla removed several other products, but nothing too crazy. The Model 3 Door Pocket and Cupholder Liners, the Model S 19″ Magnetite Wheel and Winter Tire Package, Model X/Y Ski/Snowboard Carrier for Hitch Rack, Tesla’s Electric Summer Party Tee, and the Electric Summer Tee were the other items the company totally eliminated from its online shop.
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Tesla Robotaxi fleet gets a brain upgrade ahead of Cybercab launch event
Tesla’s Robotaxi service now runs longer hours nationwide as its unsupervised fleet quietly grows larger.
Tesla’s Robotaxi service just got easier to catch, with the company’s official Robotaxi account noting that rides are now available from 6 a.m. to 10 p.m., seven days a week, across its operating footprint. The account also said its unsupervised fleet is “a lot bigger” than before, though without specifics. The bigger change is what Tesla says upgraded intelligence in vehicle distribution and routing is what’s actually cutting wait times, not a new Full Self-Driving version.
While Tesla did not name the team behind the upgrade, the language points to its AI and fleet software group rather than the driving stack itself. Vehicle distribution and routing in Robotaxi has functioned mostly as a dispatch problem with the software deciding which idle car goes to which rider, and how far it has to travel to get there. “Upgraded intelligence” suggests a smarter version of that dispatch logic, likely using demand forecasting to position idle cars near where riders are about to request them rather than reacting once a request comes in. Tesla’s AI division has built similar prediction systems for other parts of the business, including the neural networks that power FSD itself, so applying that same approach to fleet logistics would be a natural extension rather than a new discipline for the team.
Robotaxi now runs 6am to 10pm, 7 days/week
Unsupervised fleet is a lot bigger
Also, upgraded intelligence in vehicle distribution & routing means you wait less pic.twitter.com/UFZ4bqg2dZ
— Tesla Robotaxi (@robotaxi) August 26, 2026
Tesla is also about a week away from a separate robotaxi milestone. The company plans to launch Cybercab, its purpose built two seat robotaxi with no steering wheel or pedals, in Austin on September 3. Cybercab has been giving employees rides on public and private roads for weeks, and the September event is expected to fold those vehicles into the existing Robotaxi fleet within days of the launch.
Thank you so much @Tesla for inviting us to the Cybercab launch in Austin! 🤠 pic.twitter.com/F1rAR8zd5O
— TESLARATI (@Teslarati) August 22, 2026
Austin previously ran Robotaxi from 6 a.m. to 2 a.m. as of last September, a schedule set before the service expanded into Dallas, Houston, Miami, Tampa, Orlando and the Bay Area. Wednesday’s post did not specify whether that extended overnight window still applies in Austin specifically or whether 6 a.m. to 10 p.m. is now the standard across every market. Tesla’s post, visible on its official Robotaxi account, framed the change simply as fewer riders waiting around for a car.
Whether the wider hours hold once Cybercab enters the fleet next week is the next thing worth watching. Tesla has tended to expand Robotaxi in increments, first geofence, then hours, then fleet size, and each step so far has arrived without much advance notice.
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Tesla Cybercab uses a unique strategy for picking up the right rider
