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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Investor's Corner
Elon Musk confirms SpaceX IPO is on the way
However, it appears Musk is ready for SpaceX to go public, as Ars Technica Senior Space Editor Eric Berger wrote an op-ed that indicated he thought SpaceX would go public soon. Musk replied, basically confirming it.
Elon Musk confirmed through a post on X that a SpaceX initial public offering (IPO) is on the way after hinting at it several times earlier this year.
It also comes one day after Bloomberg reported that SpaceX was aiming for a valuation of $1.5 trillion, adding that it wanted to raise $30 billion.
Musk has been transparent for most of the year that he wanted to try to figure out a way to get Tesla shareholders to invest in SpaceX, giving them access to the stock.
He has also recognized the issues of having a public stock, like litigation exposure, quarterly reporting pressures, and other inconveniences.
However, it appears Musk is ready for SpaceX to go public, as Ars Technica Senior Space Editor Eric Berger wrote an op-ed that indicated he thought SpaceX would go public soon.
Musk replied, basically confirming it:
As usual, Eric is accurate
— Elon Musk (@elonmusk) December 10, 2025
Berger believes the IPO would help support the need for $30 billion or more in capital needed to fund AI integration projects, such as space-based data centers and lunar satellite factories. Musk confirmed recently that SpaceX “will be doing” data centers in orbit.
AI appears to be a “key part” of SpaceX getting to Musk, Berger also wrote. When writing about whether or not Optimus is a viable project and product for the company, he says that none of that matters. Musk thinks it is, and that’s all that matters.
It seems like Musk has certainly mulled something this big for a very long time, and the idea of taking SpaceX public is not just likely; it is necessary for the company to get to Mars.
The details of when SpaceX will finally hit that public status are not known. Many of the reports that came out over the past few days indicate it would happen in 2026, so sooner rather than later.
But there are a lot of things on Musk’s plate early next year, especially with Cybercab production, the potential launch of Unsupervised Full Self-Driving, and the Roadster unveiling, all planned for Q1.
Tesla has added the 15th automaker to the growing list of companies whose EVs can utilize the Supercharger Network this year, as BMW is the latest company to gain access to the largest charging infrastructure in the world.
BMW became the 15th company in 2025 to gain Tesla Supercharger access, after the company confirmed to its EV owners that they could use any of the more than 25,000 Supercharging stalls in North America.
Welcome @BMW owners.
Download the Tesla app to charge → https://t.co/vnu0NHA7Ab
— Tesla Charging (@TeslaCharging) December 10, 2025
Newer BMW all-electric cars, like the i4, i5, i7, and iX, are able to utilize Tesla’s V3 and V4 Superchargers. These are the exact model years, via the BMW Blog:
- i4: 2022-2026 model years
- i5: 2024-2025 model years
- 2026 i5 (eDrive40 and xDrive40) after software update in Spring 2026
- i7: 2023-2026 model years
- iX: 2022-2025 model years
- 2026 iX (all versions) after software update in Spring 2026
With the expansion of the companies that gained access in 2025 to the Tesla Supercharger Network, a vast majority of non-Tesla EVs are able to use the charging stalls to gain range in their cars.
So far in 2025, Tesla has enabled Supercharger access to:
- Audi
- BMW
- Genesis
- Honda
- Hyundai
- Jaguar Land Rover
- Kia
- Lucid
- Mercedes-Benz
- Nissan
- Polestar
- Subaru
- Toyota
- Volkswagen
- Volvo
Drivers with BMW EVs who wish to charge at Tesla Superchargers must use an NACS-to-CCS1 adapter. In Q2 2026, BMW plans to release its official adapter, but there are third-party options available in the meantime.
They will also have to use the Tesla App to enable Supercharging access to determine rates and availability. It is a relatively seamless process.
News
Tesla adds new feature that will be great for crowded parking situations
This is the most recent iteration of the app and was priming owners for the slowly-released Holiday Update.
Tesla has added a new feature that will be great for crowded parking lots, congested parking garages, or other confusing times when you cannot seem to pinpoint where your car went.
Tesla has added a new Vehicle Locator feature to the Tesla App with App Update v4.51.5.
This is the most recent iteration of the app and was priming owners for the slowly-released Holiday Update.
While there are several new features, which we will reveal later in this article, perhaps one of the coolest is that of the Vehicle Locator, which will now point you in the direction of your car using a directional arrow on the home screen. This is similar to what Apple uses to find devices:
Interesting. The location arrow in the Tesla app now points to your car when you’re nearby. pic.twitter.com/b0yjmwwzxN
— Whole Mars Catalog (@wholemars) December 7, 2025
In real time, the arrow gives an accurate depiction of which direction you should walk in to find your car. This seems extremely helpful in large parking lots or unfamiliar shopping centers.
Getting to your car after a sporting event is an event all in itself; this feature will undoubtedly help with it:
The nice little touch that Tesla have put in the app – continuous tracking of your vehicle location relative to you.
There’s people reporting dizziness testing this.
To those I say… try spinning your phone instead. 😉 pic.twitter.com/BAYmJ3mzzD
— Some UK Tesla Guy (UnSupervised…) (@SomeUKTeslaGuy) December 8, 2025
Tesla’s previous app versions revealed the address at which you could locate your car, which was great if you parked on the street in a city setting. It was also possible to use the map within the app to locate your car.
However, this new feature gives a more definitive location for your car and helps with the navigation to it, instead of potentially walking randomly.
It also reveals the distance you are from your car, which is a big plus.
Along with this new addition, Tesla added Photobooth features, Dog Mode Live Activity, Custom Wraps and Tints for Colorizer, and Dashcam Clip details.
🚨 Tesla App v4.51.5 looks to be preparing for the Holiday Update pic.twitter.com/ztts8poV82
— TESLARATI (@Teslarati) December 8, 2025
All in all, this App update was pretty robust.
Elon Musk confirms SpaceX IPO is on the way
Tesla adds 15th automaker to Supercharger access in 2025
