News

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)

Published

7 years ago

November 7, 2018

Eric Ralph

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)

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!

Cybertruck

Tesla Cybertruck is getting a big security upgrade

“Cybertruck was not 100% carryover in execution like S3XY, so it required work.”

Published

5 hours ago

August 14, 2025

Joey Klender

Credit: Tesla

Tesla confirmed today that a massive Cybertruck security feature is on the way soon, and it is one that owners have been asking about for a long time.

Like all Teslas, Cybertruck has the excellent security feature known as “Sentry Mode.” The feature essentially turns your Tesla into a moving security camera, recording any event that happens nearby.

It has been used to solve crimes such as vandalism and burglary, and even used by police departments to solve other, high-profile crimes.

Tesla quietly added this extra Sentry Mode feature to deter vandals

However, Cybertruck has been missing one key feature of Sentry Mode: the use of the B-Pillar camera has not been enabled, leaving one of the most vandalized and targeted vehicles in the United States with a weakness.

One person who has been vocal about it is Tesla Cybertruck enthusiast Greggertruck, who has been pushing for answers for months. He finally got his answer from Cybertruck Vehicle Program Manager Siddhant Awasthi:

“It will come soon! Cybertruck was not 100% carryover in execution like SX3Y so it required work. Team has finished work on this and just need to make sure it’s validated and runs reliably (which it should for its feature).”

It will come soon! Cybertruck was not 100% carryover in execution like SX3Y so it required work. Team has finished work on this and just need to make sure it’s validated and runs reliably (which it should for its feature)
— Siddhant Awasthi (@siddawa) August 14, 2025

It sounds as if Tesla’s issue was something they similarly experienced when deploying Full Self-Driving to Cybertruck. The other four Tesla vehicles were able to use FSD because they’re all relatively similar in ride height and overall functionality. They share tons of similarities.

Cybertruck did not get FSD right away because Tesla still had to work on the differences between it and the other cars in the lineup. As Awasthi said, “Cybertruck was not 100% carryover in execution like S3XY, so it required work.”

Tesla Cybertruck FSD release expected for Sept, Park Assist to come first

It sounds as if Tesla is close to resolving some of the more intricate details of adding the functionality, and it was just a matter of time before it figured out the issue.

The release of the B-Pillar camera being active during Sentry Mode events on Cybertruck will likely come in a software update in the coming weeks.

Investor's Corner

Tesla investors may be in for a big surprise

All signs point toward a strong quarter for Tesla in terms of deliveries. Investors could be in for a surprise.

Published

8 hours ago

August 14, 2025

Joey Klender

(Credit: Tesla)

Tesla investors have plenty of things to be ecstatic about, considering the company’s confidence in autonomy, AI, robotics, cars, and energy. However, many of them may be in for a big surprise as the end of the $7,500 EV tax credit nears. On September 30, it will be gone for good.

This has put some skepticism in the minds of some investors: the lack of a $7,500 discount for buying a clean energy vehicle may deter many people from affording Tesla’s industry-leading EVs.

Tesla warns consumers of huge, time-sensitive change coming soon

The focus on quarterly deliveries, while potentially waning in terms of importance to the future, is still a big indicator of demand, at least as of now. Of course, there are other factors, most of them economic.

The big push to make the most of the final quarter of the EV tax credit is evident, as Tesla is reminding consumers on social media platforms and through email communications that the $7,500 discount will not be here forever. It will be gone sooner rather than later.

It appears the push to maximize sales this quarter before having to assess how much they will be impacted by the tax credit’s removal is working.

Delivery Wait Time Increases

Wait times for Tesla vehicles are increasing due to what appears to be increased demand for the company’s vehicles. Recently, Model Y delivery wait times were increased from 1-3 weeks to 4-6 weeks.

This puts extra pressure on consumers to pull the trigger on an order, as delivery must be completed by the cutoff date of September 30.

Delivery wait times may have gone up due to an increase in demand as consumers push to make a purchase before losing that $7,500 discount.

More People are Ordering

A post on X by notable Tesla influencer Sawyer Merritt anecdotally shows he has been receiving more DMs than normal from people stating that they’re ordering vehicles before the end of the tax credit:

Anecdotally, I’ve been getting more DMs from people ordering Teslas in the past few days than I have in the last couple of years. As expected, the end of the U.S. EV credit next month is driving a big surge in orders.
Lease prices are rising for the 3/Y, delivery wait times are… pic.twitter.com/Y6JN3w2Gmr
— Sawyer Merritt (@SawyerMerritt) August 13, 2025

It’s not necessarily a confirmation of more orders, but it could be an indication that things are certainly looking that way.

Why Investors Could Be Surprised

Tesla investors could see some positive movement in stock price following the release of the Q3 delivery report, especially if all signs point to increased demand this quarter.

We reported previously that this could end up being a very strong rebounding quarter for Tesla, with so many people taking advantage of the tax credit.

Whether the delivery figures will be higher than normal remains to be seen. But all indications seem to point to Q3 being a very strong quarter for Tesla.

Elon Musk

Tesla bear Guggenheim sees nearly 50% drop off in stock price in new note

Tesla bear Guggenheim does not see any upside in Robotaxi.

Published

10 hours ago

August 14, 2025

Joey Klender

Credit: Tesla

Tesla bear Guggenheim is still among the biggest non-believers in the company’s overall mission and its devotion to solving self-driving.

In a new note to investors on Thursday, analyst Ronald Jewsikow reiterated his price target of $175, a nearly 50 percent drop off, with a ‘Sell’ rating, all based on skepticism regarding Tesla’s execution of the Robotaxi platform.

A few days ago, Tesla CEO Elon Musk said the company’s Robotaxi platform would open to the public in September, offering driverless rides to anyone in the Austin area within its geofence, which is roughly 90 square miles large.

Tesla CEO Elon Musk confirms Robotaxi is opening to the public: here’s when

However, Jewsikow’s skepticism regarding this timeline has to do with what’s going on inside of the vehicles. The analyst was willing to give props to Robotaxi, saying that Musk’s estimation of a September public launch would be a “key step” in offering the service to a broader population.

Where Jewsikow’s real issue lies is with Tesla’s lack of transparency on the Safety Monitors, and how bulls are willing to overlook their importance.

Much of this bullish mentality comes from the fact that the Monitors are not sitting in the driver’s seat, and they don’t have anything to do with the overall operation of the vehicle.

Musk also said last month that reducing Safety Monitors could come “in a month or two.”

Instead, they’re just there to make sure everything runs smoothly.

Jewsikow said:

“While safety drivers will remain, and no timeline has been provided for their removal, bulls have been willing to overlook the optics of safety drivers in TSLA vehicles, and we see no reason why that would change now.”

He also commented on Musk’s recent indication that Tesla was working on a 10x parameter count that could help make Full Self-Driving even more accurate. It could be one of the pieces to Tesla solving autonomy.

Jewsikow added:

“Perhaps most importantly for investors bullish on TSLA for the fleet of potential FSD-enabled vehicles today, the 10x higher parameter count will be able to run on the current generation of FSD hardware and inference compute.”