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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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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.

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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.

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.

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“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.

 


For prompt updates, on-the-ground perspectives, and unique glimpses of SpaceX’s rocket recovery fleet check out our brand new LaunchPad and LandingZone newsletters!

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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 launches first ‘true’ East Coast V4 Supercharger: here’s what that means

What truly distinguishes this installation from the hundreds of “V4” stalls already scattered across the network? Most existing V4 dispensers, rolled out since 2023, feature welcome upgrades like longer cables, built-in touchscreen displays, integrated credit-card readers for non-Tesla users, and improved ergonomics.

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Credit: Tesla Charging | X

Tesla has launched its first “true” V4 Supercharger on the East Coast, and while that may be sort of confusing, here’s what we mean by that.

Tesla has opened its first true V4 Supercharging station on the East Coast in Kissimmee, Florida, just south of Orlando.

The eight-stall site, powered by an advanced 1.2 MW V4 power cabinet, is capable of delivering up to 500 kW, making it one of only four fully operational 500 kW-capable V4 stations in the United States.

Pricing is dynamic and competitive, as Tesla owners pay $0.40 per kWh during peak hours (8 a.m. to midnight), dropping to an attractive $0.20/kWh off-peak (midnight to 8 a.m.).

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Non-Tesla EVs, which can now plug directly into the NACS ports thanks to the open standard, are charged a premium—$0.56/kWh peak and $0.28/kWh off-peak—reflecting Tesla’s strategy to monetize network access while rewarding its own customers.

What’s Makes This a “True” V4 Supercharger

What truly distinguishes this installation from the hundreds of “V4” stalls already scattered across the network? Most existing V4 dispensers, rolled out since 2023, feature welcome upgrades like longer cables, built-in touchscreen displays, integrated credit-card readers for non-Tesla users, and improved ergonomics.

Tesla confirms significant detail regarding V4 Supercharger

However, nearly all of these have been paired with legacy V3 power cabinets. These hybrid setups, sometimes informally called V3.5, deliver charging curves virtually identical to standard V3 stations, typically topping out at 250-325 kW depending on the vehicle and site conditions.

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In contrast, Kissimmee’s true V4 architecture incorporates next-generation 1.2 MW power cabinets. These support battery voltages up to 1,000 V (double the 500 V of V3 systems) and can push up to 500 kW per stall.

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One compact cabinet efficiently powers all eight stalls, slashing the physical footprint and reportedly keeping deployment costs under $40,000 per stall, far cheaper than earlier designs.

Right now, the primary beneficiary is the Cybertruck, which can achieve dramatically faster charging at low states of charge.

Everyday models like the Model 3 and Model Y see little immediate difference in peak speeds, but the hardware lays the groundwork for future vehicles with higher-voltage batteries.

Tesla launches faster Cybertruck charging at all V4 Superchargers

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This milestone signals Tesla’s accelerating push toward a high-power, future-proof Supercharger network.

As true V4 sites multiply, charging times will shrink, grid efficiency will improve, and the entire EV ecosystem, Tesla and non-Tesla alike, will benefit from the infrastructure lead Tesla continues to expand. For drivers in central Florida, the Kissimmee station is more than just another charging stop; it’s a glimpse of the faster, smarter charging era that’s finally arriving.

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Tesla reveals various improvements to the Semi in new piece with Jay Leno

Tesla Chief Designer Franz von Holzhausen and Semi Program Director Dan Priestley joined Leno in a 47-minute segment revealing all of the various things it did to make the Semi even better as it heads toward volume production this year.

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Credit: Jay Leno's Garage | YouTube

Tesla has revealed the various improvements it has made to the Semi with its redesign, which was unveiled late last year, on a new episode of Jay Leno’s Garage.

Tesla Chief Designer Franz von Holzhausen and Semi Program Director Dan Priestley joined Leno in a 47-minute segment revealing all of the various things it did to make the Semi even better as it heads toward volume production this year.

Last year, Tesla revealed it had updated the Semi design to fit the bill of its aesthetic, which, on its other vehicles, includes things like lightbars and a sleeker and more aerodynamic design. The changes were not all to appease the eye, but the drivers who will use the Semi on a daily basis to haul goods regionally as the program gets off the ground running.

Weight Reduction

Priestley revealed almost immediately that Tesla was able to cut out about 1,000 pounds of weight from the Semi compared to the previous version.

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This does several things, all of which are positive to the mission of a Class 8 truck, which is to haul goods and obtain more efficient travel to cut down on logistics costs.

Initially, this can increase payload capacity, which is often the biggest value driver for fleets that frequently hit gross vehicle weight limits. Tesla’s early Pilot Program members, like PepsiCo. and Frito-Lay, are large-scale companies. They will benefit from a decreased overall weight.

Lighter vehicles also require less energy to accelerate, climb hills, and maintain highway speeds. This new design has that advantage, and as Leno said in his first drive with the Semi as he hauled another unit behind, “I don’t feel like I’m pulling anything.”

Drag Coefficient

Franz said one of the goals of the Semi was to get the drag coefficient down below that of a Bugatti Veyron. This would increase efficiency tremendously, a major need with a large truck like a Semi.

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Drag coefficient is extremely valuable when it comes to electric vehicles, because the displacement of air is incredibly important for range ratings.

Franz said aerodynamic efficiency has been improved by 7 percent compared to the last model. He says the coefficient is around 0.4.

New Features and Improvements

Priestley shed some additional light on the Semi and some of the improvements the company has made under the hood.

These include:

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  • Fully Electric Steering Assist
  • Cybertruck actuators are being used for more strength
  • Tesla included a 48-volt architecture
  • Semi will utilize 4680 battery cells, which are designed to last 1 million miles

These changes come after Tesla rolled out the Semi to various companies for its Pilot Program, which yielded tremendous results. Due to the years it has been working with those companies, it knew what things it had to change and what it had to improve upon before selling the Semi openly.

Fleet Data

The fleet data Tesla has gathered from the Pilot Program has been one of the most widely discussed parts of the Semi program.

Franz and Priestley said that there are currently a few hundred Semi units in the real world, and Tesla has gathered 13.5 million miles. One of those units has traveled over 440,000 miles in the years it has been on the road.

Tesla Semi’s latest adoptee will likely encourage more of the same

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Pilot Program members have reported an uptime of 95 percent, and Tesla’s maintenance and Service teams have kept things running:

“80% of breakdowns if you have one, are returned back to the customer in less than 24 hours, and half are back in less than 1 hour.”

Demand

Priestley says demand for the Semi has never been higher, and due to the recent political climate and the impact things have had on gas prices, Tesla has never received more inquiries for the Semi than it has recently.

Many companies will be surprised to hear that the Semi Pilot Program has been an overwhelming success. As Tesla begins to build out the infrastructure for the vehicle, it will only benefit the all-electric Class 8 trucks that keep things moving.

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CEO Elon Musk said Tesla plans to start high-volume production this year. The company also plans to start deliveries this year.

 

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Tesla launches amazing new feature for shared vehicles

Tesla has quietly introduced one of its most practical software features yet in update 2026.8: real-time visibility of the active driver profile directly in the Tesla mobile app. Available under the Security & Drivers section, this new tool lets owners see exactly who is behind the wheel or who last drove the vehicle.

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Credit: Tesla

Tesla is launching an amazing new feature for shared vehicles, giving owners more transparency when they choose to have a Tesla ownership experience with another driver.

This is one of the many advantages of having a Tesla. New features are constantly rolled out through software updates and Over-the-Air fixes, which download directly to the car with an internet connection.

Tesla has quietly introduced one of its most practical software features yet in update 2026.8: real-time visibility of the active driver profile directly in the Tesla mobile app. Available under the Security & Drivers section, this new tool lets owners see exactly who is behind the wheel or who last drove the vehicle.

The feature works seamlessly. While the car is driving, the app displays the name of the currently selected driver profile in real time.

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When the vehicle is parked or asleep, it shows the last active profile.

Requiring both the 2026.8 vehicle software and the latest Tesla app, the update brings this capability to every model in the lineup, including legacy Model S and Model X vehicles, which are unfortunately being phased out of the company lineup later this year.

Tesla makes latest move to remove Model S and Model X from its lineup

The feature was first reported on by Not a Tesla App.

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Tesla driver profiles have always excelled at personalization, automatically adjusting seat positions, mirrors, steering wheel height, climate settings, navigation recents and favorites, and media preferences.

These profiles link to specific phone keys for automatic activation and support PIN protection for privacy and security. Restricted profiles for teens can also limit speed or features.

This feature shines brightest in single-car households with multiple drivers. Families, couples, and roommates frequently share one Tesla, leading to constant adjustments and questions about settings. Now, a quick app check reveals the current profile, allowing users to anticipate seat configurations or confirm usage without entering the vehicle.

Tesla’s cloud-synced driver profiles to bring custom settings across multiple cars

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Parents particularly benefit: they can verify that teens are driving under their assigned (and possibly restricted) profiles, adding a layer of safety oversight and peace of mind. Teslas are already so incredibly safe that many parents dream of putting their kids in one.

Two kids around the same age could now share a Tesla, and this feature would make that effort, which is likely to be a difficult one at times, more seamless.

Beyond convenience, it promotes accountability and reduces everyday friction. No more manual profile switching or arguments over mirror positions. Before approaching the car, anyone can check the app and know exactly what to expect, no more wasted minutes readjusting everything.

In multi-driver setups, it transforms the shared EV into a truly intelligent, user-aware machine that respects individual preferences while keeping the primary owner informed.

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Tesla’s commitment to over-the-air updates continues to enhance ownership value years after purchase.

This small but significant addition highlights how software can solve real-world problems in multi-user environments, making Tesla vehicles more family-friendly and practical than ever. For the millions of owners sharing a single car, the 2026.8 update delivers transparency, time savings, enhanced safety, and effortless personalization. It is a great new feature that is rolling out to vehicles now.

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