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Ex-SpaceX engineer leads Stratolaunch to major rocket engine test milestone

Stratolaunch has successfully completed the first full-scale test of its 200,000-lbf thrust PGA rocket engine. (Stratolaunch)

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8 years ago

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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.

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.

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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.

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.

 

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!

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Eric Ralph is Teslarati's senior spaceflight reporter and has been covering the industry in some capacity for almost half a decade, largely spurred in 2016 by a trip to Mexico to watch Elon Musk reveal SpaceX's plans for Mars in person. Aside from spreading interest and excitement about spaceflight far and wide, his primary goal is to cover humanity's ongoing efforts to expand beyond Earth to the Moon, Mars, and elsewhere.

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SpaceX makes history, catching Starship from orbit for the first time

SpaceX caught Starship’s upper stage with its launch tower for the first time on Saturday.

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9 hours ago

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November 14, 2026

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Ship 42 fires its engines as it descends toward the Starbase launch tower’s chopstick arms, moments before SpaceX caught a Starship upper stage for the first time on Flight 15. (Credit: SpaceX)
Ship 42 fires its engines as it descends toward the Starbase launch tower’s chopstick arms, moments before SpaceX caught a Starship upper stage for the first time on Flight 15. (Credit: SpaceX)

SpaceX caught a Starship upper stage with its launch tower for the first time on Saturday, bringing Ship 42 back to Starbase after roughly 22 and a half hours in orbit on Flight 15. No company has ever returned the upper stage of an orbital rocket to its launch site and caught it.

Ship 42 lifted off Friday evening on top of Booster 22, reached orbit and deployed all 26 of its Starlink V3 satellites. Three of those satellites carried cameras to photograph the ship’s heat shield, and SpaceX said the imagery showed it was in good shape for reentry, allowing controllers to pass on a backup splashdown option overnight. By Saturday morning, SpaceX posted on X that “Pad and tower systems are go for catch.” After about 14 orbits, the ship fired its engines to leave orbit, came back through the atmosphere and was caught by the tower’s chopstick arms.

 

The catch salvages a flight that started with a setback. Super Heavy did not make it back to the tower on Friday. “We were initially go for a catch, but in the later stages of the coast, the booster aborted itself for a GNC issue that it detected and that put it into its landing offshore,” SpaceX’s Dan Huot said. The booster hovered over the Gulf of Mexico before its flight termination system triggered and it came down in the water.

Elon Musk said Saturday that the booster ran short on propellant because its engines slightly underperformed. The fix, he wrote, is better engine consistency with Raptor V3.2 and a flight software change to cut the engines “about one second earlier” so enough fuel is left for the return. “This booster loss does not change our timeline to reach high volume, fully reusable Starship flights,” Musk added.

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The ship is the harder half of that goal, and the one SpaceX had never recovered. Super Heavy has now been caught three times, most recently in March 2025, while every previous ship ended in the ocean or was lost. Falcon 9 lands its boosters routinely but throws its upper stage away on every launch. Musk described a full Starship recovery on SpaceX’s third quarter earnings call as a “profound technology milestone,” and Saturday’s catch shows the hardest piece of it can work.

That piece matters for nearly everything SpaceX is planning. Reusable ships are what make the economics of launching Starlink V3 satellites at scale work, along with the Starmind orbital compute constellation. NASA’s Artemis lunar lander also depends on refilling Starships in orbit with repeated tanker flights, which requires vehicles that can fly again quickly. Musk has said he expects Starship to reach a weekly launch cadence in the first half of 2027.

Flight 15 also improved on the last Starship mission in September, which reached orbit but ended after about three hours with a Pacific splashdown when some engines shut down. Before this flight, SpaceX had shown an animation of the ship catch during its earnings webcast, and Musk put the odds of pulling it off on the first try at “more likely than not,” as Teslarati reported.

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Tesla Cybercab ownership will come with plenty of strings attached

Published

17 hours ago

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November 14, 2026

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Credit: Tesla

Tesla’s long-promised Cybercab is finally available for personal purchase, at least for a select few in the Austin area. But it’s far from a straightforward ownership experience.

The $29,990 price tag comes with a stack of restrictions that redefine what “owning” the vehicle actually means. The two-seat, steering-wheel-free Robotaxi, previously limited to Tesla’s own fleet, now carries contractual terms that limit where it can go, how it can be used, and whether it can even move without an active paid subscription.

Opening Night of Orders

Late on November 13, Tesla announced that select customers were being invited to order a Cybercab for personal use.

Tesla Cybercab goes on sale for $29,990, slated for December deliveries

The estimated purchase price is $29,990 before taxes, paired with a non-refundable $1,000 deposit and an estimated December 2026 delivery in Austin, Texas. The first month of the required :Autonomy Subscription,” priced at $299 per month is included.

After that, the vehicle needs an active subscription to operate at all. The announcement confirmed that customer sales had begun, albeit on an invite-only basis rather than a public order page.

The Fine Print for Buyers

For those invited to order, the agreements (Cybercab Order Agreement, Terms of Use, and Autonomy Subscription Agreement) impose significant constraints. Major points include:

  • A mandatory Autonomy Subscription (currently listed at $299 per month on the order screen, first month included) is required; without it, the Cybercab will not operate.
  • Personal, non-commercial use only; ride-hailing, Robotaxi network participation, delivery, or rental requires separate written authorization or product enablement from Tesla.
  • Operation restricted to Tesla-enabled Robotaxi geofences and supported service areas, which the company can expand, shrink, or alter; the vehicle may be technologically prevented from operating outside them.
  • No unauthorized modifications (including wraps, window tint, or wheel changes) without Tesla or an authorized provider.
  • Restricted resale and transfer: written permission required, with contractual damages of at least $50,000 (or full transaction value if higher) for unauthorized sales; Tesla also reserves repurchase rights at a company-determined fair market value, with the owner covering return costs.
  • Safety or improper-use “strikeouts” (three or more) can trigger a one-week suspension of autonomous features without prorated refund.
  • Owners remain responsible for insurance, registration, charging, parking, and general cleaning; the subscription covers certain maintenance items such as tires, windshields, filters, and camera cleaning, plus limited towing.
  • Manual controls on the touchscreen allow only short-distance movement up to about 2 mph and require a valid driver’s license; they are not for public-road driving.

Why These Terms Might Exist

Tesla’s approach prioritizes control over a vehicle designed without traditional human controls and intended primarily as transport-as-a-service, something that Musk has hinted toward for some time now. Restricting commercial use and modifications could be as much of a software integrity, safety, and data collection effort as it is a safety effort.

Fleet consistency could also be in regulatory scrutiny early on in the Cybercab’s days of public operation.

The subscription model generates ongoing revenue beyond the low vehicle price and ensures the car remains connected and updatable, something that will keep the Cybercab as safe as possible as new updates roll out.

Buyback and resale limits reduce the risk of vehicles circulating outside Tesla’s operational and service ecosystem.

It apperas that personal ownership is secondary to the broader Robotaxi network strategy, as Musk has previously stated that the vast majority of Cybercabs would remain Tesla-owned.

Pickup Locations and Musk’s Pricing View

Initial deliveries are estimated for Austin, but personal vehicles are able to operate in any of Tesla’s Robotaxi geofences:

Those who have been invited to order can also have their personal Cybercab delivered to numerous locations in Texas, including:

  • Austin
  • Dallas
  • Houston
  • San Antonio
  • Fort Worth

As far as the monthly “Autonomy Subscription,” it appears Musk already wants it to be low. He acknowledged last night on X that the subscription price is too high. Along with detailing that the Cybercab will be available nationwide as regulatory approval is received, Musk said the monthly fee should match the cost of FSD and Premium Connectivity, which is about $115 per month.

The launch marks a milestone for unsupervised personal autonomous vehicles, but the fine print makes clear that buyers are purchasing a highly constrained asset whose usefulness is tightly bound to Tesla’s software, service network, and geographic approvals.

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Tesla Cybercab goes on sale for $29,990, slated for December deliveries

Published

1 day ago

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November 13, 2026

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Credit: Tesla

Tesla has officially put the Cybercab up for sale, revealing a bargain price and a $299 per month “Autonomy Subscription” that could hit customer hands as soon as December.

The offer requires a $299 monthly Autonomy Subscription, with the first month included in the purchase price, along with a $1,000 non-refundable order deposit. Tesla’s ordering interface shows deliveries targeted for Austin, Texas.

Tesla says that the Cybercab is making transportation more efficient, affordable and accessible than ever before, and that buyers can order their own Cybercab for personal use.

The Cybercab is Tesla’s dedicated robotaxi, a gold-finished, two-passenger vehicle without a steering wheel or pedals, designed from the outset for unsupervised autonomous operation. It has been in limited Robotaxi service in Austin since September 2026, operating alongside Tesla’s larger fleet of Model Y vehicles.

Production takes place at Gigafactory Texas, which launched earlier this year. Tesla has stated for some time that it planned to put Cybercabs on sale by the end of the year, and it looks like they will come through on that promise if everything goes according to plan.

The Autonomy Subscription is mandatory for the vehicle to operate because it is void of a steering wheel and pedals. Tesla notes that the subscription and regular vehicle maintenance are required, indicating that personal owners will depend on the company’s software and service infrastructure rather than traditional ownership models.

One month of the subscription is included with purchase and subsequent months are billed separately until canceled.

This limited personal-sales opening marks a shift from Tesla’s earlier emphasis on fleet and transport-as-a-service operations. During the Q3 2026 Earnings Call, executives indicated that the vast majority of Cybercabs would remain Tesla-owned and used for rideshare service, while still aiming to place some vehicles with customers by year-end.

Elon Musk has previously targeted a price below $30,000, which was a huge point of emphasis for the Cybercab being the central point of Tesla’s “transportation-as-a-service” model.

Availability remains restricted to invited customers rather than a public order page, and the initial deliveries are expected only in the Austin area where unsupervised Robotaxi operations are already active. Buyers will need to accept the geographic and operational constraints of current autonomous deployment, as the vehicle cannot be driven manually outside supported zones.

The move gives a small number of early buyers the chance to own Tesla’s dedicated autonomous vehicle at the long-discussed sub-$30,000 price point, while the bulk of production continues to support the company’s expanding Robotaxi network.

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