News
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 reportedly pushed the unveiling of the Roadster once again, but there are also evidently new details about the event that the company plans to show off.
The Information reported this morning that Tesla will now unveil, for the second time, the next-generation Roadster in August, a further delay from the multiple timeline that the company had previously stated.
The report has not been confirmed or denied by Tesla at any capacity.
It also states the unveiling event will take place in Texas, the same place that Tesla executives revealed in May would be the place of manufacture for the company’s highly-anticipated supercar, which boasts a top speed of over 250 MPH and 650 miles of range, according to its website.
Tesla is also expected to showcase the SpaceX package, which will be used for faster acceleration and potentially hovering capabilities, at the unveiling event, the report states. Musk has always planned for this to happen, but now it seems it is more realistic than ever
The report also states the Roadster unveiling is planned for August pic.twitter.com/By26XZIJzU
— TESLARATI (@Teslarati) June 5, 2026
The Roadster has had its unveiling date and manufacturing date pushed back on many occasions. It was set to start production in 2020, but the COVID-19 pandemic crippled supply chain operations, forcing Tesla to push its timeline back considerably.
However, COVID has been over for some time, and Tesla has still not managed to successfully schedule and execute an unveiling event, which is something fans and enthusiasts, as well as those who have put down a $50,000 deposit, have been waiting for.
The vehicle was close to completion last year, but Musk truly wanted Lars Moravy and Franz von Holzhausen to push the limits of the Roadster. In July of last year, Moravy said:
“Roadster is definitely in development. We did talk about it last Sunday night. We are gearing up for a super cool demo. It’s going to be mind-blowing; We showed Elon some cool demos last week of the tech we’ve been working on, and he got a little excited.”
It is important to note two things: Tesla has not confirmed these details, and the company has regularly pushed these dates back. Until Tesla sends out formal invitations with a concrete date, taking any unveiling event reports with a grain of salt is a good idea.
Tesla is offering a tasty Supercharging incentive on certain Model 3 trims, but the company has officially put a concrete end date on it, so those interested should act fast.
Tesla is offering Free Supercharging for One Year on the Model 3 Premium and Performance trims, the top two offerings of the all-electric sedan. There are three trims of the Model 3 that will have the Free Supercharging offer attached:
- Premium Rear-Wheel-Drive – $42,490
- Premium All-Wheel-Drive – $47,490
- Performance – $54,990
Tesla has now announced that this offer will expire on June 15, giving potential buyers about ten days to take advantage of the incentive.
This could be an additional incentive for car buyers to transition to electric vehicles. Many states are showing gas prices well over $4 per gallon, with the national average currently sitting at $4.22, according to AAA.
A free year of Supercharging miles would allow people to charge and travel for free, other than routine maintenance, which is already incredibly cheap compared to a gas car.
🚨 Tesla is now showing that it’s Free Supercharging offer for Model 3 Premium and Performance trims ends June 15 pic.twitter.com/VCLeddNSj8
— TESLARATI (@Teslarati) June 5, 2026
At Tesla Superchargers, peak rates, meaning prices between 8 a.m. and 10 p.m., average between $0.45 and $0.60. One year of driving at an average of 12,000 miles would cost between $1,000 and $1,500 at $0.50 per kWh. It’s a pretty good deal.
Supercharging prices have also increased recently:
Many of the Superchargers in my area just had their peak rates increased from $0.44 per kWh to $0.49, $0.52, and $0.54 per kWh
If you’re looking to save on your commute/travel for the next year, this Model 3 Free Supercharging incentive might not be a bad idea https://t.co/YDwwl4xxHk pic.twitter.com/DleURW7eqa
— TESLARATI (@Teslarati) June 5, 2026
Tesla has used Free Supercharging to move units in the past, and it’s a great strategy for those who plan to use the car for longer commutes, cross-country drives, or do not have reliable access to home charging.
It should be noted that Tesla recommends that Supercharging be used at a minimum to preserve the life of the battery, as fast-charging is more stressful on the cells.
However, some people might not have an option, so the Free Supercharging incentive could truly be a great reason for many people to charge their cars.
The Supercharging incentive is short-term, and it is pretty rare that Tesla utilizes it, so once this offer is gone, we probably will not see it on the Model 3 for some time.
Ferrari CEO Benedetto Vigna revealed that the Italian automaker’s future will not involve self-driving, a point that echoes that of Tesla CEO Elon Musk’s — sort of.
You might be thinking, “Are you insane? Musk has been so incredibly hellbent on delivering self-driving vehicles to the public, so much so that he has even hinted that Tesla won’t need the ever-popular and widely-requested Model Y L in the U.S.”
However, when it comes to electric supercars with high-performance specs and lofty price tags, Vigna’s stance is exactly what Musk wants for Tesla’s own hypercar project, the Tesla Roadster.
🚨 Tesla Roadster vs. Ferrari Luce
Price – $250,000 vs. $640,000
Horsepower – 1,000+ vs. 1,035
0-60 MPH – 1.1s OR 1.9s vs. 2.4s
Top Speed – 250+ MPH vs. 194 MPH
Range – 620 miles vs. 280 miles https://t.co/uEgswwVLeD pic.twitter.com/XcP58ZRO6Z— TESLARATI (@Teslarati) June 5, 2026
In a new interview with Australian media outlet Drive, Vigna made it clear that Ferrari’s ambitions for the future do not involve autonomy, simply because the company’s cars are not designed for anything but manual, spirited driving.
He said:
“We will not make fully autonomous cars — loud and clear. We want the people to have fun, not the [computer] chips. We want to have a steering wheel and a man or a woman behind the steering wheel. Otherwise, why do you buy a Ferrari?”
This seems to be a reasonable assertion. Ferraris are not made for daily commutes, cross-country road trips, or bumper-to-bumper traffic. They’re made for fast, spirited driving, and many of their buyers will only put a few thousand miles on them throughout their lifetime. True, exciting, fun driving is meant to be done manually.
That is not to say Full Self-Driving or other semi-autonomous suites are not “fun,” but they are meant to take the stress out of driving. They are made for the daily commutes, the rush hour traffic, and the parking lots and garages. It’s made to take the stress out of driving.
Tesla Full Self-Driving attempts 150-mile stress test: the good and the bad
Musk had stated in an interview in early 2026 that the Roadster would also be geared toward fun, manually-controlled driving. On the Moonshots podcast with Peter Diamandis, Musk said about the Roadster:
“This is not a…safety is not the main goal. If you buy a Ferrari, safety is not the number one goal. I say, if safety is your number one goal, do not buy the Roadster…We’ll aspire not to kill anyone in this car. It’ll be the best of the last of the human-driven cars. The best of the last.”
There are cars out there that simply are meant to be driven by humans, and Ferraris and Roadsters are a few of them. Ferrari has no true advantage in developing self-driving; their cars sell at low volumes with high price tags, and their performance specs and engineering are all geared toward spirited driving.
Tesla Roadster unveiling gets pushed again, but new event details emerge
Tesla Model 3 has a tasty Supercharging incentive, but it’s ending soon
