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Ex-SpaceX engine expert to help design rockets built for launch on world’s largest jet

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7 years ago

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Stratolaunch, an aerospace company funded by Microsoft-made billionaire Paul Allen to build the world’s largest flightworthy aircraft, has announced a decision to build its own liquid-fueled rockets, to be air-launched from the aforementioned mega-plane.

Targeting an inaugural launch of the first version of the rocket – currently nicknamed “Kraken” – as early as 2022, Stratolaunch has chosen Jeff Thornburg, formerly SpaceX’s Vice President of Propulsion Engineering and the father of the company’s Mars-focused Raptor engine, to lead its foray into in-house rocket propulsion development and manufacturing.

But first: building the world’s largest aircraft

Stratolaunch’s first task at hand, however, is to begin flight-testing the largest (hopefully) operational aircraft in history, a prerequisite for the company’s longer-term orbital rocket and spaceplane aspirations. Nicknamed “Roc” after a mythical (and fictional) bird so large it could carry an elephant, the plane certainly lives up to its namesake. Featuring a full six of the same engines that power Boeing’s once-record-breaking 747 airliner and a wingspan that could easily fit three smaller 737 airliners with room to spare, it is genuinely difficult (if not impossible) to successfully convey the sheer scale of Roc outside of witnessing it in person.

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Stationed in California’s Mojave Desert, the aircraft’s one and only copy is, for the most part, completed and has spent the brunt of 2018 conducting runway taxi tests, hopefully culminating in an inaugural flight test later this year or early next year. Designed to lift orbital-class rockets weighing as much as 250 metric tons (550,000 lb) to an altitude of at least 9100 meters (30,000 feet), the primary benefit of using aircraft as launch platforms derives from the simple fact that the atmospheric density at 30,000 feet is more than three times less than that at sea level. Similar to aircraft, rocket performance dramatically improves as atmospheric density decreases: less atmosphere means lower drag and pressure.

Rockets that launch from sea-level have to grapple with the difficulties of Earth’s relatively thick atmosphere at that height, with major launch events like “Max-Q” being big concerns almost solely because the dense air exerts major forces on launch vehicles and demands extreme measures like throttling down booster engines (very inefficient) and optimizing structures for aerodynamic efficiency despite the fact that rockets spend very little time operating in a significant atmosphere.

A launch pad without a rocket (sort of)

However, the simple fact of the matter is that billionaire Paul Allen’s colossal aircraft essentially does not have a single air-launched rocket in the world that can properly take advantage of its capabilities. Originally sized and designed with an air-launched version of SpaceX’s Falcon 9 in mind, that relationship folded amicably after roughly a year (2012), at which point SpaceX realized it would need to almost completely redesign a unique variant of Falcon 9. Your author will readily admit that they have admired the insanity of such a massive plane while still severely doubting its practical utility.

Thankfully, it appears that Allen is adamantly opposed to the idea that Stratolaunch is some silly whim to build the world’s largest plane. Rather, he is exceptionally reserved and pragmatic when discussing the aerial launch platform, according to a recent and extensive interview by Wired Magazine’s Steven Levy.

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“Allen isn’t one to show exuberance, and when he speaks about the plane he focuses on its future utility. ‘When you see that giant plane, it’s a little nutty,’ he says. ‘And you don’t build it unless you’re very serious, not only about wanting to see the plane fly but to see it fulfill its purpose. Which is getting vehicles in orbit.’ – Paul Allen, 2018

 

Currently, Orbital ATK’s (now Northrop Grumman Innovation Systems) air-launched Pegasus XL rocket is the only “customer” in the world that can realistically use Stratolaunch as a launch platform, not exactly an impressive or sustainable launch vehicle with a maximum performance of less than 450 kg (~1000 lbs) to low Earth orbit for an incredible ~$40 million per (expendable) flight.

To answer that call and ensure Stratolaunch’s utility, the company reportedly began seriously considering its own in-house expendable and reusable rockets and propulsion systems sometime in 2016, plans that have since grown concrete and been publicly embedded into Stratolaunch’s overarching mission. Nicknamed “Kraken” after the mythical sea monster, the company hopes to develop an initially expendable rocket system capable of launching 3400 – 6000 kg (~7500 – 13250 lbs) into low Earth orbit with single booster and triple booster variants. Further down the line, Stratolaunch is eyeing the design and production of a fully and rapidly reusable orbital spaceplane, potentially including a version that would carry astronauts into space.

 

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Normally, one might simply roll their eyes at yet another startup touting small(ish) expendable rockets with first launches no earlier than the early 2020s – the market is getting to be absurdly and impossibly overcrowded at this point. However, Stratolaunch differs for one fundamental and reason: they have placed ex-SpaceX propulsion executive and expert Jeff Thornburg at the helm of the company’s freshly public rocket propulsion wing. While at SpaceX, Mr. Thornburg spent all but one of his five years with the company (2011-2015) single-mindedly focused on the development and engineering of all aspects of the Raptor rocket engine, a next-generation propulsion system designed to enable SpaceX’s sustainable colonization of Mars.

Raptor is an exceptional rocket engine thanks in no small part to Thornburg’s brilliance as a propulsion engineer, and that same brilliance and half-decade of experience at the most successful rocket startup in existence could ultimately prove a massive boon for Stratolaunch’s otherwise interesting but unexceptional expendable rocket concepts.

Put simply, under Jeff Thornburg’s direction and with access to founder Paul Allen’s considerable wealth, Stratolaunch is undoubtedly worth keeping a close eye in the future, both far and near.

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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Elon Musk

Elon Musk commends Tesla team on successful Robotaxi launch

Tesla CEO Elon Musk commended the company on the successful launch of Robotaxi.

Published

47 minutes ago

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June 23, 2025

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NORAD and USNORTHCOM Public Affairs, Public domain, via Wikimedia Commons

Tesla CEO Elon Musk commented on the company’s launch of the Robotaxi platform, which officially went live to a small group on Sunday in Austin, Texas.

It is the first time Tesla has offered driverless rides through the ride-hailing platform it has worked to activate for several years, and it was overwhelmingly successful based on early reviews.

The launch was coupled with the release of the first-ever looks at the Tesla Robotaxi app, which does more than allow riders to summon vehicles for transportation. It also allows the rider to adjust climate settings in the car before it arrives for a comfortable ride, and it will sync entertainment and streaming settings to keep occupants entertained.

Tesla Robotaxi riders tout ‘smooth’ experience in first reviews of driverless service launch

The first rides are being performed with a safety monitor in the passenger’s seat. These monitors have no control over the vehicle, and are there just to ensure smooth operation.

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The first reviews called rides “smooth” and “comfortable,” and commended Tesla for its hard work over the past few years to make this happen. Many were impressed with the cars’ ability to keep pedestrians safe, avoid congested parking lots, and the efficiency of the rides, as the time from the ride request to the Robotaxi accepting the ride was extremely fast.

Musk has been at the forefront of this operation for a decade, as Tesla has been working to release a version of the Robotaxi through the development of Full Self-Driving. This has been an effort that included seeking top-tier engineering talent and taking incredible leaps of faith, including switching to a Vision-only approach for Full Self-Driving.

Musk commended the Tesla team for its hard work:

It’s truly an incredible accomplishment, as many considered Robotaxi a “failure” despite it not even being rolled out. In May, we reported on media outlets calling the Robotaxi rollout a total failure, despite Tesla always maintaining the launch would happen in June:

Tesla Robotaxi deemed a total failure by media — even though it hasn’t been released

Hundreds of rides have already been taken, and there have not been many complaints. It’s an incredible jump forward for Tesla.

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Elon Musk

Tesla Robotaxi riders tout ‘smooth’ experience in first reviews of driverless service launch

The first reviews of Tesla Robotaxi are in, and those riders are impressed and astounded with the smooth and comfortable nature of the service.

Published

3 hours ago

on

June 23, 2025

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Credit: Joe Tegtmeyer | X

Tesla Robotaxi riders are touting their awesome experiences in their first rides using the automaker’s new driverless ride-hailing service, which launched to a limited number of people yesterday for the first time.

On Sunday, Tesla officially launched Robotaxi, its driverless ride-hailing service, in downtown Austin. A select group of people were chosen to receive early access to the program, as well as the new Robotaxi app, which is used to request a ride and will sync everything from climate preferences to streaming settings with each pickup.

Tesla officially launches Robotaxi service with no driver

Teslarati gained access to the Early Access riders program and the Robotaxi app, giving us a first-hand look at the experience. We will be in Austin soon to test out the Robotaxi fleet for ourselves.

However, those who were there for the initial rides on Sunday had nothing but great things to say. Hundreds of rides were taken during the first hours of the Robotaxi program, and neither the company nor the riders reported any issues.

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Here’s what people said about their experiences:

  • “Extremely smooth stops,” and great awareness of road conditions, including pedestrians, speed bumps, and busy parking lots, were all handled with ease:

  • Safe navigation around pedestrians who walked just off the sidewalk into the road:

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  • “Just as good as it is during the daytime” at night. There were no changes to report by riders who took rides during the day and evening:

  • Avoided expensive and stressful parking at local tourist hotspots like Terry Black’s Barbeque:

  • “Comfortable and similar to existing Tesla cars with FSD,” intuitive and “surreal” experience:

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  • The app is quicker than other ride-sharing services. When a destination is chosen, Robotaxi is already on the way to your location:

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Tesla Robotaxi rollout proves that Elon Musk still delivers, even if it’s late

Tesla is also still the company that makes the impossible feel late.

Published

6 hours ago

on

June 23, 2025

By

Credit: Tesla

It took a long time, but Tesla has finally successfully rolled out its dedicated Robotaxi service in Austin this weekend. The initial rollout only involved a small fleet of cars operating in a small geofenced area in Texas, but it is still significant. 

It does, if any, prove that Elon Musk is still capable of delivering on his promises, even if they are late. Tesla is also still the company that makes the impossible feel late.

Finally, a Rollout

Elon Musk has been predicting a Robotaxi rollout for years, so much so that even avid Tesla supporters have grown quite wary of his constant predictions. After a while, Elon Musk himself admitted that he has become the boy who cried FSD, though he still maintained that self-driving was really just around the corner.

This past weekend, Musk’s predictions finally came true. Actual paying customers used Tesla’s dedicated Robotaxi service for a small flat fee of $4.20 per ride. Elon Musk seemed quite happy with the Robotaxi’s initial launch, as evidenced by his congratulatory message to the Tesla AI team on X.

https://twitter.com/elonmusk/status/1936876178356490546
https://twitter.com/aelluswamy/status/1936865682810946035

No More Tesla Vision Debates

One thing that is evident in Tesla’s initial Robotaxi rollout in Austin was the fact that the debate surrounding Tesla’s vision-only approach is completely gone now. With actual Robotaxis operating around Austin, there are no more questions about whether cars can navigate city streets on their own using only AI and cameras. They can, and safely too, at least based on Tesla’s initial fleet of Robotaxis.

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https://twitter.com/ItsKimJava/status/1936927640268484909
https://twitter.com/SawyerMerritt/status/1936997202880081950

The Beauty of Normalcy

The Robotaxi rides from Tesla owners who were fortunate enough to experience the first driverless rides from the EV maker’s fleet were quite uneventful. Comments on social media platforms such as X observed that the Robotaxis operated safely and cautiously, and their driving was actually smoother than some human drivers. 

That may not sound very exciting at all, but that’s the beauty of it. Tesla’s Robotaxi service is designed to look and feel natural to people. And so far, it appears that Tesla is accomplishing this with its Robotaxi rollout.

https://twitter.com/DrKnowItAll16/status/1936992009685700663
https://twitter.com/DirtyTesLa/status/1936999390100496443
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