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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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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.

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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.

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.

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“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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Tesla ‘Killer’ heads to the graveyard as AFEELA taps out

SHM has officially discontinued development of its highly anticipated AFEELA electric vehicles. On March 25, the joint venture between Sony and Honda announced it would halt the AFEELA 1 luxury sedan and a planned SUV model.

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Credit: AFEELA/X

There have been many Tesla “Killers” over the years, all of which have either failed to dethrone the automaker from its dominance in the United States, or even make it to the market altogether.

The Sony Honda Mobility (SHM) project, known as AFEELA, is the latest to make it to the grave, as the company announced its intentions to abandon the project earlier this week, Bloomberg reported.

SHM has officially discontinued development of its highly anticipated AFEELA electric vehicles. On March 25, the joint venture between Sony and Honda announced it would halt the AFEELA 1 luxury sedan and a planned SUV model.

The decision follows Honda’s March 12 reassessment of its electrification strategy, which scrapped several upcoming EV programs amid slowing demand, high costs, and shifting market conditions.

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SHM stated that it could no longer rely on key Honda technologies and manufacturing assets, leaving “no viable path forward.” Reservation fees for early buyers in California are being fully refunded, and the joint venture’s future is now under review.

Launched with fanfare in 2022, the AFEELA was positioned as a tech-forward premium EV blending Honda’s engineering reliability with Sony’s entertainment and AI expertise.

Prototypes featured advanced autonomous driving systems, immersive in-cabin displays, and even PlayStation integration, earning it early media labels as a potential “Tesla Killer.”

No more “Tesla Killers:” It’s becoming increasingly difficult to distinguish the “EV market” from the mainstream auto segment

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Priced around $90,000, the sedan was slated for limited production at Honda’s Ohio plant with deliveries targeted for late 2026. Industry watchers saw it as a serious challenger to Tesla’s dominance in software, connectivity, and premium appeal.

Yet, like many ambitious EV projects, it fell victim to broader industry headwinds: softening consumer demand, persistent high interest rates, and intense competition from established players.

The AFEELA joins a long list of vehicles once hyped as “Tesla Killers” that failed to deliver. In the late 2010s, Fisker’s second act, the Ocean SUV, promised stylish design and solid-state battery tech but collapsed into bankruptcy in 2024 after production delays, quality issues, and financial shortfalls.

Faraday Future poured billions into the FF 91 luxury sedan, touting it as a hyper-tech rival with unmatched performance and features; the company delivered fewer than 100 vehicles before fading into obscurity.

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Lordstown Motors’ Endurance electric pickup generated massive pre-order buzz and Wall Street excitement but imploded after exaggerated range claims, a factory sale, and eventual bankruptcy.

Even Lucid Motors’ Air sedan, frequently called a Tesla slayer for its superior range and luxury, has struggled with sluggish sales and missed growth targets despite strong reviews.

Lucid unveils Lunar Robotaxi in bid to challenge Tesla’s Cybercab in the autonomous ride hailing race

Rivian’s R1T and R1S trucks enjoyed similar early acclaim and a blockbuster IPO, yet production ramp-up challenges and profitability woes have prevented it from dethroning Tesla.

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The AFEELA’s quiet demise underscores a harsh reality in the EV sector. While Tesla’s first-mover advantage in software, charging infrastructure, and brand loyalty remains formidable, legacy automakers and tech newcomers alike continue to underestimate the complexities of scaling affordable, desirable electric vehicles.

As market realities force tough choices, the graveyard of “Tesla Killers” grows longer, another reminder that innovation alone is rarely enough to topple an established leader.

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TIME honors SpaceX’s Gwynne Shotwell: From employee No. 7 to world’s most valuable company

Time Magazine honors Gwynne Shotwell as SpaceX reaches a $1.25 trillion valuation and eyes its IPO.

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TIME Magazine has put SpaceX President and COO Gwynne Shotwell on its cover, and the timing could not be more fitting. Published today, the profile of Shotwell arrives at a moment when the company she has quietly run for more than two decades stands at the center of the most consequential developments in aerospace, artificial intelligence, and the future of human civilization.

Shotwell joined SpaceX in 2002 as its seventh employee and has never stopped expanding her role. She oversees day-to-day operations across multiple executive teams spanning Falcon, Starlink, Starship, and now xAI following SpaceX’s February 2026 merger with Elon Musk’s artificial intelligence company, a deal that made SpaceX the world’s most valuable private company at a reported valuation of $1.25 trillion. A highly anticipated IPO is expected in the second quarter of 2026.

Will Tesla join the fold? Predicting a triple merger with SpaceX and xAI

Her track record is historic. She oversaw the first landing of an orbital rocket’s first stage, the first reuse and re-landing of an orbital booster, and the first private crewed launch to Earth orbit in May 2020. She built the Falcon launch manifest from nothing to more than 170 contracted missions representing over $20 billion in business. Under her operational leadership, SpaceX completed 96 successful missions in 2023 alone and has now flown more than 20 crewed Falcon 9 missions. Starlink, which she championed as a financial pillar of the company long before it was a mainstream topic, now connects tens of millions of users worldwide and provided a critical communications lifeline to Ukraine following the 2022 invasion.

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Elon Musk has never been shy about what Shotwell means to him and to SpaceX. When she shared her vision for worldwide internet connectivity through Starlink, Musk responded on X with a simple statement, “Gwynne is awesome.” It is a sentiment that has been echoed across the industry. NASA Administrator Bill Nelson once said of Musk: “One of the most important decisions he made, as a matter of fact, is he picked a president named Gwynne Shotwell. She runs SpaceX. She is excellent.”


Now, with Starship targeting its first crewed lunar landing under the Artemis program by 2028, an xAI integration underway, and a pending IPO that could reshape capital markets, Shotwell’s mandate has never been larger. She told Time that 18 Starships are already in various stages of construction at Starbase. “By 2028,” she said, gesturing across the factory floor, “these should be long gone. They better have flown by then.” If Shotwell’s history at SpaceX is any guide, they will.

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SpaceX’s IPO might arrive sooner than you think

Musk has hinted for years that an eventual public offering was inevitable, though he has stressed the need to maintain operational focus. Insiders have told outlets that the CEO is pushing for a significant retail investor allocation, reportedly more than 20 percent of shares, and tighter lock-up periods to limit early selling pressure.

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Credit: SpaceX | X

Elon Musk’s SpaceX is on the verge of one of the most anticipated Initial Public Offerings (IPO) in history.

However, a new report from The Information indicates the rocket and satellite giant is aiming to file its IPO prospectus with U.S. regulators as soon as this week, or early next week at the latest.

People familiar with the plans told The Information that advisers involved in the process expect the IPO could raise more than 75 billion dollars, potentially making it the largest stock market debut ever and eclipsing Saudi Aramco’s 29.4 billion dollar offering in 2019.

The filing would mark the formal start of what has long been rumored: SpaceX’s transition from a closely held private powerhouse to a publicly traded company.

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The timing aligns with earlier signals.

In late February, Bloomberg reported that SpaceX was targeting a confidential IPO filing in March and a possible public listing in June, with a valuation north of 1.75 trillion dollars. At the time, the company’s private valuation hovered around 1.25 trillion dollars.

SpaceX considering confidential IPO filing this March: report

Starlink, SpaceX’s satellite internet constellation, has been the primary driver of that surge, now serving millions of customers worldwide and generating steady revenue. Recent Starship test flights and a record pace of Falcon launches have further bolstered investor confidence.

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Musk has hinted for years that an eventual public offering was inevitable, though he has stressed the need to maintain operational focus. Insiders have told outlets that the CEO is pushing for a significant retail investor allocation, reportedly more than 20 percent of shares, and tighter lock-up periods to limit early selling pressure.

A June listing would give SpaceX immediate access to public capital markets at a moment when demand for space-related stocks remains high. It would also allow early employees and long-time investors to cash out portions of their stakes while giving everyday shareholders a chance to own a piece of the company behind reusable rockets, global broadband, and NASA contracts.

Of course, nothing is certain until the SEC filing appears. Market conditions, regulatory reviews, and Musk’s own schedule could still shift timelines.

Yet the latest word from The Information suggests the window has opened. If the filing lands this week, SpaceX’s roadshow could begin in earnest within weeks, setting the stage for what many analysts already call the IPO of the decade.

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