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
Elon Musk shares big Tesla Optimus 3 production update
According to Musk, Tesla is in the final stages of completing Optimus 3, which he described as one of the world’s most advanced humanoid robots.
Tesla CEO Elon Musk has stated that production of Optimus 3 could begin this summer. Musk shared the update in his interview at the Abundance Summit.
According to Musk, Tesla is in the final stages of completing Optimus 3, which he described as one of the world’s most advanced humanoid robots.
“We’re in the final stages of completion of Optimus 3, which is really going to be by far the most advanced robot in the world. Nothing’s even close. In fact, I haven’t even seen demos of robots that are as good as Optimus 3,” Musk said.
He also set expectations on the pace of Optimus 3’s production ramp, stating that the initial volumes of the humanoid robot will likely be very low. Musk did, however, also state that high production rates for Optimus 3 should be possible in 2027.
“I think we’ll start production on Optimus 3 this summer, but very slow at first, like sort of this classic S-curve ramp of manufacturing units versus time. And then, probably reach high volume production around summer next year,” he said.
Interestingly enough, the CEO hinted that Tesla is looking to iterate on the robot quickly, potentially releasing a new Optimus design every year.
“We’ll have Optimus 4 design complete next year. We’ll try to release a new robot design every year,” Musk stated.
Tesla has already outlined broader plans for scaling Optimus production beyond its first manufacturing line. Musk previously stated that Optimus 4 will be built at Gigafactory Texas at significantly higher production volumes.
Initial production lines for the robot are expected to be located at Tesla’s Fremont Factory, where the company plans to establish a line capable of producing up to 1 million robots per year.
A larger production ramp is expected to occur at Gigafactory Texas, where Musk has previously suggested could eventually support production of up to 10 million robots per year.
“We’re going to launch on the fastest production ramp of any product of any large complex manufactured product ever, starting with building a one-million-unit production line in Fremont. And that’s Line one. And then a ten million unit per year production line here,” Musk said previously.
The comments suggest that while Optimus 3 will likely begin production at Fremont, Tesla’s larger-scale manufacturing push could arrive with Optimus 4 at Gigafactory Texas.
Elon Musk
Tesla showcases Optimus humanoid robot at AWE 2026 in Shanghai
Tesla’s humanoid robot was presented as part of the company’s exhibit at the Shanghai electronics show.
Tesla showcased its Optimus humanoid robot at the 2026 Appliance & Electronics World Expo (AWE 2026) in Shanghai. The event opened Thursday and featured several Tesla products, including the company’s humanoid robot and the Cybertruck.
The display was reported by CNEV Post, citing information from local media outlet Cailian and on-site staff at the exhibition.
Tesla’s humanoid robot was presented as part of the company’s exhibit at the Shanghai electronics show. On-site staff reportedly stated that mass production of the robot could begin by the end of 2026.
Tesla previously indicated that it plans to manufacture its humanoid robots at scale once production begins, with its initial production line in the Fremont Factory reaching up to 1 million units annually. An Optimus production line at Gigafactory Texas is expected to produce 10 million units per year.
Tesla China previously shared a teaser image on Weibo showing a pair of highly detailed robotic hands believed to belong to Optimus. The image suggests a design with finger proportions and structures that closely resemble those of a human hand.
Robotic hands are widely considered one of the most difficult engineering challenges in humanoid robotics. For a system like Optimus to perform complex real-world tasks, from factory work to household activities, the robot would require highly advanced dexterity.
Elon Musk has previously stated that Optimus has the capability to eventually become the first real-world example of a Von Neumann machine, a self-replicating system capable of building copies of itself, even on other planets. “Optimus will be the first Von Neumann machine, capable of building civilization by itself on any viable planet,” Musk wrote in a post on X.
Elon Musk
Tesla Cybercab production line is targeting hundreds of vehicles weekly: report
According to the report, Tesla has been adding staff and installing new equipment at its Austin factory as it prepares to begin Cybercab production.
Tesla is reportedly designing its Cybercab production line to manufacture hundreds of the autonomous vehicles each week once mass production begins. The effort is underway at Gigafactory Texas in Austin as the company prepares to start building the Robotaxi at scale.
The details were reported by The Wall Street Journal, citing people reportedly familiar with the matter.
According to the report, Tesla has been adding staff and installing new equipment at its Austin factory as it prepares to begin Cybercab production.
People reportedly familiar with Tesla’s plans stated that the company has been growing its staff and bringing in new equipment to start the mass production of the Cybercab this April.
The Cybercab is Tesla’s upcoming fully autonomous two-seat vehicle designed without a steering wheel or pedals. The vehicle is intended to operate primarily as part of Tesla’s planned Robotaxi ride-hailing network.
“There’s no fallback mechanism here. Like this car either drives itself or it does not drive,” Musk stated during Tesla’s previous earnings call.
Tesla has indicated that Cybercab production could begin as soon as April, though Elon Musk has noted that early production will likely be slow before ramping over time. Musk has stated that the Cybercab’s slow ramp is due in no small part to the fact that it is a completely new vehicle platform.
Tesla’s Cybercab is designed to work with the company’s Full Self-Driving (FSD) system and support its planned autonomous ride-hailing service. The company has suggested that the vehicle could cost under $30,000, making it one of Tesla’s most affordable models if produced at scale. Musk has confirmed in a previous X post that the vehicle will indeed be offered to regular consumers at a price below $30,000.
Musk has previously stated that Tesla could eventually produce millions of Cybercabs annually if demand and production capacity scale as planned.








