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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 made two big interior changes to several Model Y vehicles in its lineup, and the changes come just as the new model year begins production.
Last year, Tesla launched the Model Y Standard, which separated the previous models into the “Premium” category. The Standard vehicles lack several features, including more premium interior materials, acoustic-lined glass, and storage.
@teslarati There are some BIG differences between the Tesla Model Y Standard and Tesla Model Y Premium #tesla #teslamodely ♬ Sia – Xeptemper
The Model Y “Premium” trims are now getting several new upgrades, which come after the company launched a seven-seat configuration of the vehicle last night in the North American market for an upcharge of $2,500.
The new Model Y seven-seat configuration did not come with just an additional row of seating; it also came with a slew of other goodies that now come standard and were previously only available on the Model Y Performance, which was launched late last year.
All Black Headliner
The new Tesla Model Y Premium trims will now come standard with a black headliner, something that many owners have been requesting for some time.
The previous grey headliner and trim within the vehicle is now gone; it will be all black on all of the Premium trims from here on out, a welcome change:
Credit: Tesla
Larger and Higher Resolution Center Touchscreen
The center touchscreen in the new Model Y Premium configuration is now larger and has a higher resolution than the previous version.
In last year’s Model Y configurations (apart from the Performance), the center touchscreen was 15.4″. Now, Tesla has decided to go with the 16″ version across all Premium trims, which is a nice step up. It was nice to see this in the Performance, but it is really great to see Tesla include this in the Model Y’s more Premium trim levels.
Tesla Model Y Seven Seater
Tesla launched the latest iteration of the seven-seater for the Model Y on Monday night. Traditionally, the Model Y seats five passengers in total, but there were calls for a more spacious version several years ago.
Tesla released it, but it was extremely tight in the back, basically reserving those back seats for only small people or children.
Credit: Tesla
The new configuration looks to be slightly more spacious in the third row, but not as much space as most would require or want. Instead,
Elon Musk
Lufthansa Group to equip Starlink on its 850-aircraft fleet
Under the collaboration, Lufthansa Group will install Starlink technology on both its existing fleet and all newly delivered aircraft, as noted by the group in a press release.
Lufthansa Group has announced a partnership with Starlink that will bring high-speed internet connectivity to every aircraft across all its carriers.
This means that aircraft across the group’s brands, from Lufthansa, SWISS, and Austrian Airlines to Brussels Airlines, would be able to enjoy high-speed internet access using the industry-leading satellite internet solution.
Starlink in-flight internet
Under the collaboration, Lufthansa Group will install Starlink technology on both its existing fleet and all newly delivered aircraft, as noted by the group in a press release.
Starlink’s low-Earth orbit satellites are expected to provide significantly higher bandwidth and lower latency than traditional in-flight Wi-Fi, which should enable streaming, online work, and other data-intensive applications for passengers during flights.
Starlink-powered internet is expected to be available on the first commercial flights as early as the second half of 2026. The rollout will continue through the decade, with the entire Lufthansa Group fleet scheduled to be fully equipped with Starlink by 2029. Once complete, no other European airline group will operate more Starlink-connected aircraft.
Free high-speed access
As part of the initiative, Lufthansa Group will offer the new high-speed internet free of charge to all status customers and Travel ID users, regardless of cabin class. Chief Commercial Officer Dieter Vranckx shared his expectations for the program.
“In our anniversary year, in which we are celebrating Lufthansa’s 100th birthday, we have decided to introduce a new high-speed internet solution from Starlink for all our airlines. The Lufthansa Group is taking the next step and setting an essential milestone for the premium travel experience of our customers.
“Connectivity on board plays an important role today, and with Starlink, we are not only investing in the best product on the market, but also in the satisfaction of our passengers,” Vranckx said.
Elon Musk
Tesla locks in Elon Musk’s top problem solver as it enters its most ambitious era
The generous equity award was disclosed by the electric vehicle maker in a recent regulatory filing.
Tesla has granted Senior Vice President of Automotive Tom Zhu more than 520,000 stock options, tying a significant portion of his compensation to the company’s long-term performance.
The generous equity award was disclosed by the electric vehicle maker in a recent regulatory filing.
Tesla secures top talent
According to a Form 4 filing with the U.S. Securities and Exchange Commission, Tom Zhu received 520,021 stock options with an exercise price of $435.80 per share. Since the award will not fully vest until March 5, 2031, Zhu must remain at Tesla for more than five years to realize the award’s full benefit.
Considering that Tesla shares are currently trading at around the $445 to $450 per share level, Zhu will really only see gains in his equity award if Tesla’s stock price sees a notable rise over the years, as noted in a Sina Finance report.
Still, even at today’s prices, Zhu’s stock award is already worth over $230 million. If Tesla reaches the market cap targets set forth in Elon Musk’s 2025 CEO Performance Award, Zhu would become a billionaire from this equity award alone.
Tesla’s problem solver
Zhu joined Tesla in April 2014 and initially led the company’s Supercharger rollout in China. Later that year, he assumed the leadership of Tesla’s China business, where he played a central role in Tesla’s localization efforts, including expanding retail and service networks, and later, overseeing the development of Gigafactory Shanghai.
Zhu’s efforts helped transform China into one of Tesla’s most important markets and production hubs. In 2023, Tesla promoted Zhu to Senior Vice President of Automotive, placing him among the company’s core global executives and expanding his influence beyond China. He has since garnered a reputation as the company’s problem solver, being tapped by Elon Musk to help ramp Giga Texas’s vehicle production.
With this in mind, Tesla’s recent filing seems to suggest that the company is locking in its top talent as it enters its newest, most ambitious era to date. As could be seen in the targets of Elon Musk’s 2025 pay package, Tesla is now aiming to be the world’s largest company by market cap, and it is aiming to achieve production levels that are unheard of. Zhu’s talents would definitely be of use in this stage of the company’s growth.
Tesla makes two big interior changes to several Model Y vehicles
Lufthansa Group to equip Starlink on its 850-aircraft fleet
