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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.

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.

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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.

“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.

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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 called ‘biggest meme stock we’ve ever seen’ by Yale associate dean

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Credit: Tesla

Tesla (NASDAQ: TSLA) is being called “the biggest meme stock we’ve ever seen” by Yale School of Management Senior Associate Dean Jeff Sonnenfeld, who made the comments in a recent interview with CNBC.

Sonnenfeld’s comments echo those of many of the company’s skeptics, who argue that its price-to-earnings ratio is far too high when compared to other companies also in the tech industry. Tesla is often compared to companies like Apple, Nvidia, and Microsoft when these types of discussions come up.

Fundamentally, yes, Tesla does trade at a P/E level that is significantly above that of any comparable company.

However, it is worth mentioning that Tesla is not traded like a typical company, either.

Here’s what Sonnenfeld said regarding Tesla:

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“This is the biggest meme stock we’ve ever seen. Even at its peak, Amazon was nowhere near this level. The PE on this, well above 200, is just crazy. When you’ve got stocks like Nvidia, the price-earnings ratio is around 25 or 30, and Apple is maybe 35 or 36, Microsoft around the same. I mean, this is way out of line to be at a 220 PE. It’s crazy, and they’ve, I think, put a little too much emphasis on the magic wand of Musk.”

Many analysts have admitted in the past that they believe Tesla is an untraditional stock in the sense that many analysts trade it based on narrative and not fundamentals. Ryan Brinkman of J.P. Morgan once said:

“Tesla shares continue to strike us as having become completely divorced from the fundamentals.”

Dan Nathan, another notorious skeptic of Tesla shares, recently turned bullish on the stock because of “technicals and sentiment.” He said just last week:

“I think from a trading perspective, it looks very interesting.”

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Nathan said Tesla shares show signs of strength moving forward, including holding its 200-day moving average and holding against current resistance levels.

Sonnenfeld’s synopsis of Tesla shares points out that there might be “a little too much emphasis on the magic wand of Musk.”

Elon Musk just bought $1 billion in Tesla stock, his biggest purchase ever

This could refer to different things: perhaps his recent $1 billion stock buy, which sent the stock skyrocketing, or the fact that many Tesla investors are fans and owners who do not buy and sell on numbers, but rather on news that Musk might report himself.

Tesla is trading around $423.76 at the time of publication, as of 3:25 p.m. on the East Coast.

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Tesla makes big change to Full Self-Driving doghouse that drivers will like

Now, it is changing the timeframe of which strikes will be removed, cutting it in half. The strikes will be removed every 3.5 days, as long as no strikes are received during the time period.

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tesla cabin facing camera
Tesla's Cabin-facing camera is used to monitor driver attentiveness. (Credit: Andy Slye/YouTube)

Tesla is making a big change to its Full Self-Driving doghouse that drivers will like.

The doghouse is a hypothetical term used to describe the penalty period that Tesla applies to drivers who receive too many infractions related to distracted driving.

Previously, Tesla implemented a seven-day ban on the use of Full Self-Driving for those who received five strikes in a vehicle equipped with a cabin camera and three strikes for those without a cabin camera.

It also forgave one strike per week of Full Self-Driving use, provided the driver did not receive any additional strikes during the seven-day period.

Now, it is changing the timeframe of which strikes will be removed, cutting it in half. The strikes will be removed every 3.5 days, as long as no strikes are received during the time period.

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The change was found by Not a Tesla App, which noticed the adjustment in the Owner’s Manual for the 2025.32 Software Update.

The system undoubtedly helps improve safety as it helps keep drivers honest. However, there are definitely workarounds, which people are using and promoting for monetary gain, and you can find them on basically any online marketplace, including TikTok shop and Amazon:

People are marketing the product as an FSD cheat device, which the cabin-facing camera will not be able to detect, allowing you to watch something on a phone or look through the windshield at the road.

The safeguards implemented by Tesla are designed to protect drivers from distractions and also protect the company itself from liability. People are still using Full Self-Driving as if it were a fully autonomous product, and it is not.

Tesla even says that the driver must pay attention and be ready to take over in any scenario:

“Yes. Autopilot is a driver assistance system that is intended to be used only with a fully attentive driver. It does not turn a Tesla into a fully autonomous vehicle.

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Before enabling Autopilot, you must agree to “keep your hands on the steering wheel at all times” and to always “maintain control and responsibility for your vehicle.” Once engaged, Autopilot will also deliver an escalating series of visual and audio warnings, reminding you to place your hands on the wheel if insufficient torque is applied or your vehicle otherwise detects you may not be attentive enough to the road ahead. If you repeatedly ignore these warnings, you will be locked out from using Autopilot during that trip.

You can override any of Autopilot’s features at any time by steering or applying the accelerator at any time.”

It is good that Tesla is rewarding those who learn from their mistakes with this shorter timeframe to lose the strikes. It won’t be needed forever, though, as eventually, the company will solve autonomy. The question is: when?

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Elon Musk teases the capabilities of the Tesla Roadster once again

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Elon Musk has once again teased the capabilities of the Tesla Roadster, fueling the anticipation that many have for the vehicle, despite it still having no public production or delivery date.

The Roadster is among the most anticipated vehicles in the automotive sector currently, and as Tesla has teased its capabilities, from a lightning-fast 1.1-second 0-60 MPH acceleration to potential hovering with cold-gas thrusters, people are eager to see it.

Although the design seemed to be finalized, there was still more work to be done. Earlier this year, as Tesla was showcasing some of the Roadster’s capabilities to Musk, he stated that it was capable of even more.

This pushed back its production date even further, much to the chagrin of those who have been waiting years for it.

Musk continues to tease us all, and as we sit here waiting hopelessly for it to be revealed, he said today that it is “something special beyond a car.”

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Musk’s words were in response to a video posted by Tesla China, showing the Roadster in a new promotional video created by a fan.

The Roadster was planned to be released in 2020, but here we are in 2025, and there is still no sign of the vehicle entering production. However, Tesla did say earlier this year that it would host a demo event for the Roadster, where the company would showcase its capabilities.

Lars Moravy said earlier this year:

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“Roadster is definitely in development. We did talk about it last Sunday night. We are gearing up for a super cool demo. It’s going to be mind-blowing; We showed Elon some cool demos last week of the tech we’ve been working on, and he got a little excited.”

Tesla exec gives big update on Roadster, confirming recent rumor

The delays have been attributed to “radically increased design goals” for the vehicle, which have, without a doubt, improved its capabilities, but at the same time, we just want to know if it’s ever going to come.

Tesla can always make it “better,” but at what point do you say, “Okay, it’s time to show this thing off.” They could always build another, even more capable supercar in the next ten years.

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