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)
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!
Elon Musk
Tesla ramps Cybercab test manufacturing ahead of mass production
Tesla still has plans for volume production, which remains between four and eight weeks away, aligning with Musk’s statements that early ramps would be deliberately measured given the Cybercab’s novel architecture and full reliance on Tesla’s vision-based Full Self-Driving technology.
Tesla is seemingly ramping Cybercab test manufacturing ahead of mass production, which is scheduled to begin next month, the company said.
At Tesla’s Gigafactory Texas, production of the Cybercab, the company’s groundbreaking purpose-built Robotaxi vehicle, is accelerating markedly. Drone footage from Joe Tegtmeyer captured striking aerial footage today, revealing what appears to be the largest public sighting of Cyebrcabs to date.
A total of 25 units were observed by Tegtmeyer across the Gigafactory Texas property, marking a clear step-up in testing and validation activities as Tesla prepares for a broader output.
Tesla Cybercab production begins: The end of car ownership as we know it?
In the footage, 14 metallic gold Cybercabs were parked in a tight formation outside the factory exit, showcasing their sleek, autonomous-only design with no steering wheels, pedals, or traditional controls. Another 9 units sat at the crash testing facility, likely undergoing structural and safety validations, while two more appeared at the west end-of-line area for final checks.
Big day for Cybercab at Giga Texas today! Actually, yesterday to kick off March, the production line went into a higher volume & today we see 25 at three main locations, and there were several others I observed driving around too!
I think this may be the largest single grouping… pic.twitter.com/HZDMNv57lJ
— Joe Tegtmeyer 🚀 🤠🛸😎 (@JoeTegtmeyer) March 3, 2026
Tegtmeyer noted additional Cybercabs driving around the complex, hinting at active movement and real-world testing beyond static parking.
This surge follows the first production Cybercab rolling off the line in mid-February 2026, several weeks ahead of the originally anticipated April start.
That milestone, celebrated by Tesla employees and confirmed by CEO Elon Musk, kicked off low-volume builds on the dedicated “unboxed” manufacturing line, a modular process designed to slash costs, reduce factory footprint, and enable faster assembly compared to conventional methods.
Industry observers interpret the jump to dozens of visible units in early March as evidence that Tesla has transitioned into higher-volume test manufacturing.
Tesla still has plans for volume production, which remains between four and eight weeks away, aligning with Musk’s statements that early ramps would be deliberately measured given the Cybercab’s novel architecture and full reliance on Tesla’s vision-based Full Self-Driving technology.
The Cybercab, envisioned as a sub-$30,000 autonomous two-seater for robotaxi fleets, represents Tesla’s bold pivot toward scalable autonomy and robotics.
Tesla fans and enthusiasts on X praised the imagery, with many expressing excitement over the visible progress toward deployment. While challenges remain, including software maturity, regulatory hurdles, and supply chain scaling, the increased factory activity underscores Tesla’s momentum in turning the Cybercab vision into reality.
As Giga Texas continues expanding and refining the manufacturing process of the Cybercab, the coming months will prove to be a pivotal time in determining how quickly this revolutionary vehicle reaches roads in the U.S. and internationally.
Elon Musk
SpaceX to launch Starlink V2 satellites on Starship starting 2027
The update was shared by SpaceX President Gwynne Shotwell and Starlink Vice President Mike Nicolls.
SpaceX is looking to start launching its next-generation Starlink V2 satellites in mid-2027 using Starship.
The update was shared by SpaceX President Gwynne Shotwell and Starlink Vice President Mike Nicolls during remarks at Mobile World Congress (MWC) in Barcelona, Spain.
“With Starship, we’ll be able to deploy the constellation very quickly,” Nicolls stated. “Our goal is to deploy a constellation capable of providing global and contiguous coverage within six months, and that’s roughly 1,200 satellites.”
Nicolls added that once Starship is operational, it will be capable of launching approximately 50 of the larger, more powerful Starlink satellites at a time, as noted in a Bloomberg News report.
The initial deployment of roughly 1,200 next-generation satellites is intended to establish global and contiguous coverage. After that phase, SpaceX plans to continue expanding the system to reach “truly global coverage, including the polar regions,” Nicolls said.
Currently, all Starlink satellites are launched on SpaceX’s Falcon 9 rocket. The next-generation fleet will rely on Starship, which remains in development following a series of test flights in 2025. SpaceX is targeting its next Starship test flight, featuring an upgraded version of the rocket, as soon as this month.
Starlink is currently the largest satellite network in orbit, with nearly 10,000 satellites deployed. Bloomberg Intelligence estimates the business could generate approximately $9 billion in revenue for SpaceX in 2026.
Nicolls also confirmed that SpaceX is rebranding its direct-to-cell service as Starlink Mobile.
The service currently operates with 650 satellites capable of connecting directly to smartphones and has approximately 10 million monthly active users. SpaceX expects that figure to exceed 25 million monthly active users by the end of 2026.
Elon Musk
Elon Musk’s xAI and X to pay off $17.5B debt in full: report
The update was shared initially in a report from Bloomberg News, which cited people reportedly familiar with the matter.
Elon Musk’s social platform X and artificial intelligence startup xAI are reportedly preparing to repay approximately $17.5 billion in outstanding debt in full.
The update was shared initially in a report from Bloomberg News, which cited people reportedly familiar with the matter.
Morgan Stanley, which arranged the debt financing for both companies, has reportedly informed existing lenders that X and xAI plan to pay back the full amount of the $17.5 billion debt. Bloomberg’s sources did not disclose where the capital for the repayment would be coming from.
X, formerly known as Twitter, assumed roughly $12.5 billion in debt during Musk’s acquisition of the company. xAI separately borrowed about $5 billion through bonds and loans last June. The two firms merged last year under xAI Holdings.
Bloomberg noted that portions of the debt are relatively recent and may carry early repayment penalties. xAI’s $3 billion in high-yield bonds are expected to be redeemed at 117 cents on the dollar, reflecting a premium since the debt was expected to stay outstanding for at least two years.
X has been servicing tens of millions of dollars in monthly debt payments, while xAI has reportedly been burning approximately $1 billion in cash per month as it invests heavily in data centers, chips, and AI talent. That being said, xAI also concluded a funding round in January, where it raised $20 billion of new equity.
The repayment plans come as Musk consolidates several of his businesses. SpaceX recently acquired xAI, making it a subsidiary as the company explores plans for space-based data centers. The combined entity has been valued at approximately $1.25 trillion.
Bloomberg previously reported that SpaceX is targeting a confidential IPO filing as soon as this month, potentially positioning the private space firm for a public listing later this year. Representatives for Morgan Stanley declined to comment, and X and xAI did not immediately respond to requests for comment.
Tesla ramps Cybercab test manufacturing ahead of mass production
SpaceX to launch Starlink V2 satellites on Starship starting 2027
