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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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7 years ago

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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.

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.

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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.

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.

 

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 reveals SpaceX’s target for Starship’s 10th launch

Elon Musk has revealed SpaceX’s target timeline for the next Starship launch, which will be the tenth in program history.

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2 weeks ago

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July 16, 2025

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Credit: SpaceX

Elon Musk has revealed SpaceX’s target timeline for the next Starship launch, which will be the tenth in program history.

Musk says SpaceX is aiming for a timeline of roughly three weeks from now, which would come about ten weeks after the previous launch.

Coincidentally, it would bring the two launches 69 days apart, and if you know anything about Elon Musk, that would be an ideal timeline between two launches.

SpaceX is coming off a test flight in which it lost both the Super Heavy Booster and the Upper Stage in the previous launch. The Super Heavy Booster was lost six minutes and sixteen seconds into the flight, while SpaceX lost communication with the Ship at 46 minutes and 48 seconds.

Musk is aiming for the tenth test flight to take place in early August, he revealed on X:

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This will be SpaceX’s fourth test flight of the Starship program in 2025, with each of the previous three flights bringing varying results.

IFT-7 in January brought SpaceX its second successful catch of the Super Heavy Booster in the chopstick arms of the launch tower. The ship was lost after exploding during its ascent over the Turks and Caicos Islands.

IFT-8 was on March 6, and SpaceX caught the booster once again, but the Upper Stage was once again lost.

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The most recent flight, IFT-9, took place on May 27 and featured the first reused Super Heavy Booster. However, both the Booster and Upper Stage were lost.

The Federal Aviation Administration (FAA) hit SpaceX with a mishap investigation for Flight 9 on May 30.

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SpaceX’s Crew-11 mission targets July 31 launch amid tight ISS schedule

The flight will lift off from Launch Complex 39A at Kennedy Space Center in Florida.

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3 weeks ago

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July 12, 2025

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(Credit: SpaceX)

NASA and SpaceX are targeting July 31 for the launch of Crew-11, the next crewed mission to the International Space Station (ISS). The flight will lift off from Launch Complex 39A at Kennedy Space Center in Florida, using the Crew Dragon Endeavour and a Falcon 9 booster.

Crew Dragon Endeavour returns

Crew-11 will be the sixth flight for Endeavour, making it SpaceX’s most experienced crew vehicle to date. According to SpaceX’s director of Dragon mission management, Sarah Walker, Endeavour has already carried 18 astronauts representing eight countries since its first mission with NASA’s Bob Behnken and Doug Hurley in 2020, as noted in an MSN report.

“This Dragon spacecraft has successfully flown 18 crew members representing eight countries to space already, starting with (NASA astronauts) Bob (Behnken) and Doug (Hurley) in 2020, when it returned human spaceflight capabilities to the United States for the first time since the shuttle retired in July of 2011,” Walker said.

For this mission, Endeavour will debut SpaceX’s upgraded drogue 3.1 parachutes, designed to further enhance reentry safety. The parachutes are part of SpaceX’s ongoing improvements to its human-rated spacecraft, and Crew-11 will serve as their first operational test.

The Falcon 9 booster supporting this launch is core B1094, which has launched in two previous Starlink missions, as well as the private Ax-4 mission on June 25, as noted in a Space.com report.

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The four-members of Crew-11 are NASA astronauts Zena Cardman and Mike Fincke, as well as Japan’s Kimiya Yui and Russia’s Oleg Platonov.

Tight launch timing

Crew-11 is slated to arrive at the ISS just as NASA coordinates a sequence of missions, including the departure of Crew-10 and the arrival of SpaceX’s CRS-33 mission. NASA’s Bill Spetch emphasized the need for careful planning amid limited launch resources, noting the importance of maintaining station altitude and resupply cadence.

“Providing multiple methods for us to maintain the station altitude is critically important as we continue to operate and get the most use out of our limited launch resources that we do have. We’re really looking forward to demonstrating that capability with (CRS-33) showing up after we get through the Crew-11 and Crew-10 handover,” Spetch stated.

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SpaceX launches Ax-4 mission to the ISS with international crew

The SpaceX Falcon 9 launched Axiom’s Ax-4 mission to ISS. Ax-4 crew will conduct 60+ science experiments during a 14-day stay on the ISS.

Published

1 month ago

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June 25, 2025

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(Credit: SpaceX)

SpaceX launched the Falcon 9 rocket kickstarting Axiom Space’s Ax-4 mission to the International Space Station (ISS). Axiom’s Ax-4 mission is led by a historic international crew and lifted off from Kennedy Space Center’s Launch Complex 39A at 2:31 a.m. ET on June 25, 2025.

The Ax-4 crew is set to dock with the ISS around 7 a.m. ET on Thursday, June 26, 2025. Axiom Space, a Houston-based commercial space company, coordinated the mission with SpaceX for transportation and NASA for ISS access, with support from the European Space Agency and the astronauts’ governments.

The Ax-4 mission marks a milestone in global space collaboration. The Ax-4 crew, commanded by U.S. astronaut Peggy Whitson, includes Shubhanshu Shukla from India as the pilot, alongside mission specialists Sławosz Uznański-Wiśniewski from Poland and Tibor Kapu from Hungary.

“The trip marks the return to human spaceflight for those countries — their first government-sponsored flights in more than 40 years,” Axiom noted.

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Shukla’s participation aligns with India’s Gaganyaan program planned for 2027. He is the first Indian astronaut to visit the ISS since Rakesh Sharma in 1984.

Axiom’s Ax-4 mission marks SpaceX’s 18th human spaceflight. The mission employs a Crew Dragon capsule atop a Falcon 9 rocket, designed with a launch escape system and “two-fault tolerant” for enhanced safety. The Axiom mission faced a few delays due to weather, a Falcon 9 leak, and an ISS Zvezda module leak investigation by NASA and Roscosmos before the recent successful launch.

As the crew prepares to execute its scientific objectives, SpaceX’s Ax-4 mission paves the way for a new era of inclusive space research, inspiring future generations and solidifying collaborative ties in the cosmos. During the Ax-4 crew’s 14-day stay in the ISS, the astronauts will conduct nearly 60 experiments.

“We’ll be conducting research that spans biology, material, and physical sciences as well as technology demonstrations,” said Whitson. “We’ll also be engaging with students around the world, sharing our experience and inspiring the next generation of explorers.”

SpaceX’s Ax-4 mission highlights Axiom’s role in advancing commercial spaceflight and fostering international partnerships. The mission strengthens global space exploration efforts by enabling historic spaceflight returns for India, Poland, and Hungary.

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