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SpaceX’s Starship hopper spotted with trio of dual-bell Raptor engines

Starship revealed a trio of what appear to be new Raptor engines when SpaceX technicians moved the assembly from stand to ground. (NSF - bocachicagal)

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Following a brief ‘hop’ (via crane) off of a concrete build stand, the aft section of SpaceX’s first full-scale Starship hopper (Starhopper?) revealed that SpaceX technicians have already installed what appear to be three real Raptor engines, presumably the first time the propulsion system has ever been mounted to something that might eventually fly.

For a number of reasons, there is a strong chance that these Raptors are actually just boilerplate placeholders standing in as structural guides for the real deal some months down the line. On the other hand, there are also a number of reasons to assume that these apparent engines are indeed real Raptors.

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Despite an already shocking series of rapid-fire developments in the South Texas Starhopper saga, the abrupt appearance of what appears to be three Raptor engines – mirroring CEO Elon Musk’s recent statement that the test vehicle would sport three Raptors – is by far the most unexpected moment yet for the prototype Starship. Purportedly a full-scale prototype of BFR’s upper stage/spaceship (now known as Starship), Musk indicated over the last two weeks that the hopper has been designed to perform a number of hop tests in which the craft’s three Raptors would power it to a range of (relatively low) altitudes above Boca Chica, Texas.

According to a recent FCC filing related to this test program, SpaceX is currently seeking a license for Starship hop tests that will not exceed 5 km (3.1 mi) in altitude and/or 6 minutes in duration. There is admittedly nothing mentioned about the maximum allowed velocity during those tests, but – much like Blue Origin performs supersonic tests of New Shepard in Cape Horn, Texas – SpaceX will likely seek and be granted permission to break the sound barrier during those hypothetical tests. Nevertheless, a 5km ceiling is a fairly significant cap on the range of performance Starhopper will be able to test – accelerating vertically at 2Gs, Starhopper could travel from sea level to 5km in less than 30 seconds while reaching speeds no higher than Mach 1-1.5.

 

Combined with the apparent fact that this Starhopper’s fins seem unlikely to ever actuate (i.e. no aerodynamic control surfaces), it’s probable that this ad hoc prototype is only meant to perform a very limited range of hop tests, perhaps as basic as ironing out the kinks of operating a trio of gimballed Raptors and ensuring that they can safely and reliably launch, hover, and land a very large Starship-shaped mass simulator. Falcon 9’s Grasshopper and F9R reusability testbeds performed a very similar task some five years ago, offering SpaceX engineers the opportunity to optimize software and hardware needed to reliably recover real orbital-class rockets after launch. Although Falcon 9 has nine gimballed Merlin 1D engines, SpaceX has long sided with the sole center Merlin as the dedicated landing engine and has only briefly experimented with triple-Merlin landing burns.

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Dual-expansion whaaaaat?

According to Musk, Raptor –  an advanced liquid methane and oxygen engine with a uniquely efficient propulsion cycle – was expected to produce an impressive ~2000 kN (200 ton, 450K lbf) of thrust in its finished form as of September 2018. However, Musk also mentioned in a late-2017 Reddit AMA that SpaceX engineers were modifying the ship’s design to ensure engine-out reliability during all regimes of flight, landing in particular. To accomplish this feat with an engine as powerful as Raptor, two or three Raptors – capable of producing as much as 600 tons of thrust total – would need to reliably throttle as low as 25%, assuming a landing mass of around 150t. To allow a nearly empty ship (~100t) to still reliably land with three Raptors ignited, the engines would need to be able to throttle to 20% or less.

A trio of Raptors (or Raptor stand-ins) were spotted on Starhopper on Dec 31 by NASASpaceflight user bocachicagal.

Known as deep throttling in rocketry, ensuring stable combustion and thrust at 20% (let alone 40%) throttle is an extraordinarily challenging feat, often subjecting engines to forces that can literally tear non-optimized hardware apart. To achieve such a deep throttle capability without excessively disrupting the engine’s design, SpaceX appears to have potentially sided with less efficient but extremely simple alternative, known as a dual-bell (or dual-expansion) rocket nozzle. A 1999 Rocketdyne paper concisely explained the primary draws of such a nozzle:

“The [altitude-compensating] dual-bell nozzle offers a unique combination of performance, simplicity, low weight, and ease of cooling” – Horn & Fisher, 1999

Given that SpaceX has decided to delay the introduction and certification of a vacuum-optimized Raptor engine, choosing to instead use the same Raptor on both BFR stages, something like a dual-bell nozzle would be one of the best possible ways for the company to retain some of the efficiency benefits of a vacuum engine while also drastically improving design simplicity, ease of manufacturing, and cutting development time. Aside from offering efficiency gains by way of altitude compensation, a dual-bell nozzle also happens to enable a given engine to operate a much wider throttle range by mitigating problems with flow separation and instability.

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For Starhopper and Starship, both aspects are an undeniable net-gain and it’s entirely possible that these dual-bell nozzles – if successfully demonstrated – could find their way onto Falcon 9 and Falcon Heavy to further boost their booster performance and efficiency.


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

California city weighs banning Elon Musk companies like Tesla and SpaceX

A resolution draft titled, “Resolution Ending Engagement With Elon Musk-Controlled Companies and To Encourage CalPERS To Divest Stock In These Companies,” alleges that Musk “has engaged in business practices that are alleged to include violations of labor laws, environmental regulations, workplace safety standards, and regulatory noncompliance.”

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Credit: Tesla

A California City Council is planning to weigh whether it would adopt a resolution that would place a ban on its engagement with Elon Musk companies, like Tesla and SpaceX.

The City of Davis, California, will have its City Council weigh a new proposal that would adopt a resolution “to divest from companies owned and/or controlled by Elon Musk.”

This would include a divestment proposal to encourage CalPERS, the California Public Employees Retirement System, to divest from stock in any Musk company.

A resolution draft titled, “Resolution Ending Engagement With Elon Musk-Controlled Companies and To Encourage CalPERS To Divest Stock In These Companies,” alleges that Musk “has engaged in business practices that are alleged to include violations of labor laws, environmental regulations, workplace safety standards, and regulatory noncompliance.”

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It claims that Musk “has used his influence and corporate platforms to promote political ideologies and activities that threaten democratic norms and institutions, including campaign finance activities that raise ethical and legal concerns.”

If adopted, Davis would bar the city from entering into any new contracts or purchasing agreements with any company owned or controlled by Elon Musk. It also says it will not consider utilizing Tesla Robotaxis.

Hotel owner tears down Tesla chargers in frustration over Musk’s politics

A staff report on the proposal claims there is “no immediate budgetary impact.” However, a move like this would only impact its residents, especially with Tesla, as the Supercharger Network is open to all electric vehicle manufacturers. It is also extremely reliable and widespread.

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Regarding the divestment request to CalPERS, it would not be surprising to see the firm make the move. Although it voted against Musk’s compensation package last year, the firm has no issue continuing to make money off of Tesla’s performance on Wall Street.

The decision to avoid Musk companies will be considered this evening at the City Council meeting.

The report comes from Davis Vanguard.

It is no secret that Musk’s political involvement, especially during the most recent Presidential Election, ruffled some feathers. Other cities considered similar options, like the City of Baltimore, which “decided to go in another direction” after awarding Tesla a $5 million contract for a fleet of EVs for city employees.

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Starlink restrictions are hitting Russian battlefield comms: report

The restrictions have reportedly disrupted Moscow’s drone coordination and frontline communications.

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A truckload of Starlink dishes has arrived in Ukraine. (Credit: Mykhailo Fedorov/Twitter)

SpaceX’s decision to disable unauthorized Starlink terminals in Ukraine is now being felt on the battlefield, with Ukrainian commanders reporting that Russian troops have struggled to maintain assault operations without access to the satellite network. 

The restrictions have reportedly disrupted Moscow’s drone coordination and frontline communications.

Lt. Denis Yaroslavsky, who commands a special reconnaissance unit, stated that Russian assault activity noticeably declined for several days after the shutdown. “For three to four days after the shutdown, they really reduced the assault operations,” Yaroslavsky said.

Russian units had allegedly obtained Starlink terminals through black market channels and mounted them on drones and weapons systems, despite service terms prohibiting offensive military use. Once those terminals were blocked, commanders on the Ukrainian side reported improved battlefield ratios, as noted in a New York Post report.

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A Ukrainian unit commander stated that casualty imbalances widened after the cutoff. “On any given day, depending on your scale of analysis, my sector was already achieving 20:1 (casuality rate) before the shutdown, and we are an elite unit. Regular units have no problem going 5:1 or 8:1. With Starlink down, 13:1 (casualty rate) for a regular unit is easy,” the unit commander said.

The restrictions come as Russia faces heavy challenges across multiple fronts. A late January report from the Center for Strategic and International Studies estimated that more than 1.2 million Russian troops have been killed, wounded, or gone missing since February 2022.

The Washington-based Institute for the Study of War also noted that activity from Russia’s Rubikon drone unit declined after Feb. 1, suggesting communications constraints from Starlink’s restrictions may be limiting operations. “I’m sure the Russians have (alternative options), but it takes time to maximize their implementation and this (would take) at least four to six months,” Yaroslavsky noted. 

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SpaceX and xAI tapped by Pentagon for autonomous drone contest

The six-month competition was launched in January and is said to carry a $100 million award.

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Credit: SpaceX/X

SpaceX and its AI subsidiary xAI are reportedly competing in a new Pentagon prize challenge focused on autonomous drone swarming technology, as per a report from Bloomberg News

The six-month competition was launched in January and is said to carry a $100 million award.

Bloomberg reported that SpaceX and xAI are among a select group invited to participate in the Defense Department’s effort to develop advanced drone swarming capabilities. The goal is reportedly to create systems that can translate voice commands into digital instructions and manage fleets of autonomous drones.

Neither SpaceX, xAI, nor the Pentagon’s Defense Innovation Unit has commented on the report, and Reuters said it could not independently verify the details.

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The development follows SpaceX’s recent acquisition of xAI, which pushed the valuation of the combined companies to an impressive $1.25 trillion. The reported competition comes as SpaceX prepares for a potential initial public offering later this year.

The Pentagon has been moving to speed up drone deployment and expand domestic manufacturing capacity, while also seeking tools to counter unauthorized drone activity around airports and major public events. Large-scale gatherings scheduled this year, including the FIFA World Cup and America250 celebrations, have heightened focus on aerial security.

The reported challenge aligns with broader Defense Department investments in artificial intelligence. Last year, OpenAI, Google, Anthropic, and xAI secured Pentagon contracts worth up to $200 million each to advance AI capabilities across defense applications.

Elon Musk previously joined AI and robotics researchers in signing a 2015 open letter calling for a ban on offensive autonomous weapons. In recent years, however, Musk has spoken on X about the strengths of drone technologies in combat situations.

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