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.
- A to-scale comparison of Falcon 1, Pegasus XL, MLV, and Falcon 9. (Teslarati/Stratolaunch/Wikipedia)
- 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.
- PGA’s first full-scale preburner seen during assembly. (Stratolaunch)
- PGA’s first full-scale preburner seen during assembly. (Stratolaunch)
- Jeff Thornburg stands in front of Stratolaunch’s NASA Stennis Space Center test stand. (Stratolaunch)
- The PGA preburner seen after installation at Stennis. (Stratolaunch)
- The control center. (Stratolaunch)
- MLV is released from Stratolauncher. (Stratolaunch)
- A concept video produced by Stratolaunch shows the Roc launching a Kraken rocket. (Stratolaunch, via Wired)
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Elon Musk
SpaceX weighs Nasdaq listing as company explores early index entry: report
The company is reportedly seeking early inclusion in the Nasdaq-100 index.
Elon Musk’s SpaceX is reportedly leaning toward listing its shares on the Nasdaq for a potential initial public offering (IPO) that could become the largest in history.
As per a recent report, the company is reportedly seeking early inclusion in the Nasdaq-100 index. The update was reported by Reuters, citing people familiar with the matter.
According to the publication, SpaceX is considering Nasdaq as the venue for its eventual IPO, though the New York Stock Exchange is also competing for the listing. Neither exchange has reportedly been informed of a final decision.
Reuters has previously reported that SpaceX could pursue an IPO as early as June, though the company’s plans could still change.
One of the publication’s sources also suggested that SpaceX is targeting a valuation of about $1.75 trillion for its IPO. At that level, the company would rank among the largest publicly traded firms in the United States by market capitalization.
Nasdaq has proposed a rule change that could accelerate the inclusion of newly listed megacap companies into the Nasdaq-100 index.
Under the proposed “Fast Entry” rule, a newly listed company could qualify for the index in less than a month if its market capitalization ranks among the top 40 companies already included in the Nasdaq-100.
If SpaceX is successful in achieving its target valuation of $1.75 trillion, it would become the sixth-largest company by market value in the United States, at least based on recent share prices.
Newly listed companies typically have to wait up to a year before becoming eligible for major indexes such as the Nasdaq-100 or S&P 500.
Inclusion in a major index can significantly broaden a company’s shareholder base because many institutional investors purchase shares through index-tracking funds.
According to Reuters, Nasdaq’s proposed fast-track rule is partly intended to attract highly valued private companies such as SpaceX, OpenAI, and Anthropic to list on the exchange.
Elon Musk
The Boring Company’s Prufrock-2 emerges after completing new Vegas Loop tunnel
The new tunnel measures 2.28 miles, making it the company’s longest single Vegas Loop tunnel to date.
The Boring Company announced that its Prufrock-2 tunnel boring machine (TBM) has completed another Vegas Loop tunnel in Las Vegas. The company shared the update in a post on social media platform X.
According to The Boring Company’s post, the new tunnel measures 2.28 miles, making it the company’s longest single Vegas Loop tunnel to date.
The new tunnel marks the fourth tunnel constructed near Westgate Las Vegas as the Vegas Loop network continues expanding across the city.
The Boring Company also noted that the new tunnel surpassed its previous internal record of 2.26 miles for a single Vegas Loop segment.
Construction of the tunnel involved moving roughly 68,000 cubic yards of dirt. The excavation process also used about 4.8 miles of continuous conveyor belt, powered by six motors totaling 825 horsepower.
The Boring Company’s Prufrock-series all-electric tunnel boring machines are designed to support the rapid expansion of company’s underground transportation projects, including the growing Vegas Loop network. Prufrock machines are designed for reusability, thanks in no small part to their capability to be deployed and retrieved easily through their “porposing” feature.
The Vegas Loop, specifically the Las Vegas Convention Center (LVCC) Loop segment, has already been used during major events. Most recently, the LVCC Loop supported the 2026 CONEXPO-CON/AGG construction trade show, which was held from March 3-7, 2026.
As per The Boring Company, the LVCC Loop transported roughly 82,000 passengers across the convention center campus during the event’s duration.
CONEXPO-CON/AGG is one of the largest construction trade shows in North America, drawing more than 140,000 construction professionals from 128 countries this year.
The LVCC Loop forms the initial segment of the broader Vegas Loop network, which remains under active development as The Boring Company continues building new tunnels throughout the city.
News
Tesla gathers Cybercab fleet in Gigafactory Texas
Images and video of the Cybercab fleet were shared by longtime Giga Texas observer Joe Tegtmeyer in posts on social media platform X.
Tesla appears to be assembling a growing number of Cybercabs at Gigafactory Texas as preparations continue for the vehicle’s mass production. Recent footage shared online has shown over 30 Cybercabs being transported by trucks or staged near testing areas at the facility.
The images and video were shared by longtime Giga Texas observer and drone operator Joe Tegtmeyer in posts on social media platform X.
Interestingly enough, Tegtmeyer noted that many of the Cybercabs being loaded onto transport trucks were still equipped with steering wheels. This suggests that the vehicles are likely testing units rather than the final driverless configuration expected for the company’s Robotaxi service.
The vehicles could potentially be headed to testing sites across the United States as Tesla prepares to expand its Robotaxi fleet.
Additional footage captured at Gigafactory Texas also showed the Cybercab’s side and rear camera washer system operating as vehicles were being loaded onto transport trucks.
The growing number of Cybercabs at Giga Texas comes amidst the company’s announcement that the first production Cybercab has been produced at the facility. Full Cybercab production is expected to begin in April.
The vehicle is expected to play a central role in Tesla’s Robotaxi ambitions as the company looks to expand autonomous ride-hailing operations beyond its early deployments using Model Y vehicles.
Tesla has also linked Cybercab production to its proposed Unboxed manufacturing process, which assembles large vehicle modules separately before integrating them. The approach is intended to reduce production costs and accelerate output.
Musk has also noted that the Cybercab’s ramp will likely begin slowly due to the number of new components and manufacturing steps involved. However, he stated that once the process matures, Cybercab production could scale quickly.








