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
Musk bankers looking to trim xAI debt after SpaceX merger: report
xAI has built up $18 billion in debt over the past few years, with some of this being attributed to the purchase of social media platform Twitter (now X) and the creation of the AI development company. A new financing deal would help trim some of the financial burden that is currently present ahead of the plan to take SpaceX public sometime this year.
Elon Musk’s bankers are looking to trim the debt that xAI has taken on over the past few years, following the company’s merger with SpaceX, a new report from Bloomberg says.
xAI has built up $18 billion in debt over the past few years, with some of this being attributed to the purchase of social media platform Twitter (now X) and the creation of the AI development company. Bankers are trying to create some kind of financing plan that would trim “some of the heavy interest costs” that come with the debt.
The financing deal would help trim some of the financial burden that is currently present ahead of the plan to take SpaceX public sometime this year. Musk has essentially confirmed that SpaceX would be heading toward an IPO last month.
The report indicates that Morgan Stanley is expected to take the leading role in any financing plan, citing people familiar with the matter. Morgan Stanley, along with Goldman Sachs, Bank of America, and JPMorgan Chase & Co., are all expected to be in the lineup of banks leading SpaceX’s potential IPO.
Since Musk acquired X, he has also had what Bloomberg says is a “mixed track record with debt markets.” Since purchasing X a few years ago with a $12.5 billion financing package, X pays “tens of millions in interest payments every month.”
That debt is held by Bank of America, Barclays, Mitsubishi, UFJ Financial, BNP Paribas SA, Mizuho, and Société Générale SA.
X merged with xAI last March, which brought the valuation to $45 billion, including the debt.
SpaceX announced the merger with xAI earlier this month, a major move in Musk’s plan to alleviate Earth of necessary data centers and replace them with orbital options that will be lower cost:
“In the long term, space-based AI is obviously the only way to scale. To harness even a millionth of our Sun’s energy would require over a million times more energy than our civilization currently uses! The only logical solution, therefore, is to transport these resource-intensive efforts to a location with vast power and space. I mean, space is called “space” for a reason.”
The merger has many advantages, but one of the most crucial is that it positions the now-merged companies to fund broader goals, fueled by revenue from the Starlink expansion, potential IPO, and AI-driven applications that could accelerate the development of lunar bases.
News
Tesla pushes Full Self-Driving outright purchasing option back in one market
Tesla announced last month that it would eliminate the ability to purchase the Full Self-Driving software outright, instead opting for a subscription-only program, which will require users to pay monthly.
Tesla has pushed the opportunity to purchase the Full Self-Driving suite outright in one market: Australia.
The date remains February 14 in North America, but Tesla has pushed the date back to March 31, 2026, in Australia.
NEWS: Tesla is ending the option to buy FSD as a one-time outright purchase in Australia on March 31, 2026.
It still ends on Feb 14th in North America. https://t.co/qZBOztExVT pic.twitter.com/wmKRZPTf3r
— Sawyer Merritt (@SawyerMerritt) February 13, 2026
Tesla announced last month that it would eliminate the ability to purchase the Full Self-Driving software outright, instead opting for a subscription-only program, which will require users to pay monthly.
If you have already purchased the suite outright, you will not be required to subscribe once again, but once the outright purchase option is gone, drivers will be required to pay the monthly fee.
The reason for the adjustment is likely due to the short period of time the Full Self-Driving suite has been available in the country. In North America, it has been available for years.
Tesla hits major milestone with Full Self-Driving subscriptions
However, Tesla just launched it just last year in Australia.
Full Self-Driving is currently available in seven countries: the United States, Canada, China, Mexico, Australia, New Zealand, and South Korea.
The company has worked extensively for the past few years to launch the suite in Europe. It has not made it quite yet, but Tesla hopes to get it launched by the end of this year.
In North America, Tesla is only giving customers one more day to buy the suite outright before they will be committed to the subscription-based option for good.
The price is expected to go up as the capabilities improve, but there are no indications as to when Tesla will be doing that, nor what type of offering it plans to roll out for owners.
Elon Musk
Starlink terminals smuggled into Iran amid protest crackdown: report
Roughly 6,000 units were delivered following January’s unrest.
The United States quietly moved thousands of Starlink terminals into Iran after authorities imposed internet shutdowns as part of its crackdown on protests, as per information shared by U.S. officials to The Wall Street Journal.
Roughly 6,000 units were delivered following January’s unrest, marking the first known instance of Washington directly supplying the satellite systems inside the country.
Iran’s government significantly restricted online access as demonstrations spread across the country earlier this year. In response, the U.S. purchased nearly 7,000 Starlink terminals in recent months, with most acquisitions occurring in January. Officials stated that funding was reallocated from other internet access initiatives to support the satellite deployment.
President Donald Trump was aware of the effort, though it remains unclear whether he personally authorized it. The White House has not issued a comment about the matter publicly.
Possession of a Starlink terminal is illegal under Iranian law and can result in significant prison time. Despite this, the WSJ estimated that tens of thousands of residents still rely on the satellite service to bypass state controls. Authorities have reportedly conducted inspections of private homes and rooftops to locate unauthorized equipment.
Earlier this year, Trump and Elon Musk discussed maintaining Starlink access for Iranians during the unrest. Tehran has repeatedly accused Washington of encouraging dissent, though U.S. officials have mostly denied the allegations.
The decision to prioritize Starlink sparked internal debate within U.S. agencies. Some officials argued that shifting resources away from Virtual Private Networks (VPNs) could weaken broader internet access efforts. VPNs had previously played a major role in keeping Iranians connected during earlier protest waves, though VPNs are not effective when the actual internet gets cut.
According to State Department figures, about 30 million Iranians used U.S.-funded VPN services during demonstrations in 2022. During a near-total blackout in June 2025, roughly one-fifth of users were still able to access limited connectivity through VPN tools.
Critics have argued that satellite access without VPN protection may expose users to geolocation risks. After funds were redirected to acquire Starlink equipment, support reportedly lapsed for two of five VPN providers operating in Iran.
A State Department official has stated that the U.S. continues to back multiple technologies, including VPNs alongside Starlink, to sustain people’s internet access amidst the government’s shutdowns.
Musk bankers looking to trim xAI debt after SpaceX merger: report
SpaceX launches Crew-12 on Falcon 9, lands first booster at new LZ-40 pad
