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SpaceX scrubs Starhopper’s final Raptor-powered flight as Elon Musk talks “finicky” igniters

SpaceX scrubbed Starhopper's second flight test on August 26th. Another attempt will follow on the 27th. (SpaceX)

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For unknown reasons, SpaceX’s Starhopper prototype suffered a hold just 0.8 seconds prior to its second planned flight test, a hold that was eventually followed by a decision to scrub the August 26th attempt and try again tomorrow, August 27th.

Starhopper is a full-scale, partial-height testbed for SpaceX’s next-generation Starship launch vehicle, serving more as a semi-mobile test stand for steel rockets and Raptor engines than an actual Starship prototype. The unusual vehicle took flight for the first time ever on July 25th, reaching an altitude of roughly 20m (65 ft) under the power of a single Raptor engine, capable of producing up to 200 tons (450,000 lbf) of thrust. That test also suffered a minor scrub on the 24th, followed by a successful flight one day later, a chapter that Starhopper may now mirror on its second attempted flight, a 150m (500 ft) hop.

Notably, SpaceX CEO Elon Musk took to Twitter just seconds after the rocket’s scheduled liftoff suffered a last-second hold to indicate that Raptor’s torch igniters were proving somewhat finicky relative to the chemical alternative used by SpaceX’s proven Merlin engines.

The CEO later confirmed that that comment was directly related to the 26th’s scrub, indicating that Raptor serial number 06 (SN06) needed to have its igniters inspected prior to a second hop test attempt, now scheduled to occur no earlier than 6pm EDT (22:00 UTC) on August 27th. The gist of the difficulties with Raptor’s igniter starts with the reason that SpaceX is attempting to integrate an entirely new form of ignition into the engine, replacing the methods successfully used over tens or even hundreds of thousands of seconds of firing with the company’s Merlin 1 and Merlin Vacuum engines.

Merlin 1D and MVacD both rely on a relatively simple, reliable, cheap, and easy method of chemical ignition, using a duo of pyrophoric materials known as triethylaluminum-triethylborane (TEA-TEB). When mixed, these materials immediately combust, generating an iconic green flash visible during Falcon 9 and Heavy launches, and thus producing the ‘spark’ needed to start Merlin engines.

Falcon 9 and Heavy use chemical means – TEA-TEB – to ignite all of their main and upper stage Merlin engines. (SpaceX)

Generally speaking, TEA-TEB is an excellent method of igniting rockets, even if it is more of a brute-force, inelegant solution than alternatives. It does, however, bring limitations: every single ignition requires a new ‘cartridge’ be expended, fundamentally limiting the number of times Merlin 1D (and Merlin Vacuum) engines can be ignited before and after liftoff.

This doesn’t even consider the fact that TEA-TEB are extremely complex chemical products that would be next to impossible to produce off of Earth, at least for the indefinite future.

To combat these downsides, SpaceX has designed Raptor with an entirely different method of ignition, known as torch ignition. Technically speaking, Raptor’s power, design, and methalox propellant combine to demand more than a relatively common solution, in which spark plugs are used to ignite an engine. Instead, Raptor uses those spark plugs to ignite its ignition sources, what CEO Elon Musk has described as full-up blow torches. Once ignited, those blow torches – likely miniature rocket engines using the same methane and oxygen fuel as Raptor – then ignite the engine’s methane and oxygen preburners before finally igniting those mixed, high-pressure gases in the combustion chamber.

In simple terms, the fact that Raptor is a full-flow staged-combustion (FFSC) engine means that the pressures it must operate under are extreme, verging on unprecedented in large-scale rocketry. Extremely high-pressure gases (on the order of 3,000-10,000+ psi or 200-700+ bar) are just as difficult to reliably ignite, especially if hypergolic solutions (i.e. TEA-TEB) are off the table.

To get an even ignition – critical to avoid burn-through, minor explosions, and even catastrophic engine failures – Raptor’s torch ignition may actually involve a 360-degree ring of spark plug-lit torches around the point of ignition, an undeniably complex solution.

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The first finalized Raptor engine (SN01) completed a successful static fire debut on the evening of February 3rd. (SpaceX)

However, as Musk notes, these significant, “finicky” challenges brought on by Raptor’s exotic ignition method are motivated by the potential benefits such a solution might bring. Relative to Merlin 1D’s TEA-TEB ignition, torch ignition – once optimized and matured into a reliable solution – will permit an almost unlimited number of Raptor ignitions before, during, and after flight.

Avoiding TEA-TEB and other complex chemical igniters also means that Starship will technically be able to launch to Mars or the Moon, perform injection and landing burns, maybe even hop around the surface, and still be able to return to Earth – all without resupply. Such a return voyage would still be predicated on the ability to generate the methane and oxygen propellant needed to fuel Starships, but – assuming that challenge can be solved – torch-lit Raptors would be ready for such a mission. In the event that, say, something like August 26th’s scrub happens to a Starship on Mars, the crew would also be able to get out, inspect Starship’s Raptors, and even replace faulty spark plugs if necessary.

For Starship to remain readily reusable in either of these situations, Raptor’s use of torch ignition will be absolutely critical. (SpaceX)

Technically, one could bring lots of spare TEA-TEB cartridges and install those in space or after landing, but those cartridges are quite literally firebombs waiting to ignite, whereas spare spark plugs are entirely inert.

For now, we’ll have to wait for SpaceX technicians to get their eyes and hands-on Starhopper’s lone Raptor engine to verify that its ignition hardware is in good health. If all goes well, Starhopper will attempt its final flight test as early as August 27th.

Update (August 27th): Starhopper is reportedly set for a second attempted 150m (500 ft) flight test today, scheduled to occur no earlier than 5pm EDT (21:00 UTC) on August 27th. Stay tuned for SpaceX’s official Livestream!

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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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Waymo temporarily halts service in select San Francisco and LA areas amid protests

The suspensions came after several Waymo Jaguar I-Pace robotaxis were vandalized and set ablaze during the demonstrations.

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Credit: ABC7/YouTube

Waymo, Alphabet’s autonomous vehicle subsidiary, has suspended its driverless taxi operations in parts of Los Angeles and San Francisco amid violent protests linked to U.S. Immigration and Customs Enforcement (ICE) raids in the state. 

The suspensions came after several Waymo Jaguar I-Pace robotaxis were vandalized and set ablaze during the demonstrations.

Waymo Catches Strays Amid Anti-ICE Protests

Protests erupted in Los Angeles and San Francisco in response to the Trump administration’s immigration raids, which ultimately resulted in California Governor Gavin Newsom calling the White House’s deployment of National Guard troops unconstitutional. 

Amidst the protests, images and videos emerged showing several Waymo robotaxis being defaced and destroyed. At least five Waymo robotaxis ended up being caught in the crossfire, and at least one vehicle ended up being burned to the ground. 

The incident resulted in the Los Angeles Police Department advising people to avoid downtown areas due to toxic fumes from the robotaxis’ burning lithium-ion batteries. As noted in a KRON4 report, Waymo ultimately halted service in affected areas “out of an abundance of caution.”

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Robotaxi Sentiments

The cost of the attacks is notable. Each Waymo robotaxi is valued between $150,000 and $200,000, per a 2024 Wall Street Journal report. Interestingly enough, this is not the first time that Waymo’s robotaxis ended up on the receiving end of angry protesters. On February 24, a Jaguar I-PACE robotaxi was set ablaze and vandalized by a crowd in San Francisco. Videos taken at the time showed a mob of people attacking the vehicle. 

Despite the recent attacks on its robotaxis, Waymo has stated it has “no reason to believe” its vehicles were specifically targeted during the protests, as per a report from The Washington Post. A company spokesperson also noted that some of the Waymo robotaxis that were defaced and destroyed during the violent demonstrations had been completing drop-offs near the protest zones.

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Investor's Corner

xAI targets $5 billion debt offering to fuel company goals

Elon Musk’s xAI is targeting a $5B debt raise, led by Morgan Stanley, to scale its artificial intelligence efforts.

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(Credit: xAI)

xAI’s $5 billion debt offering, marketed by Morgan Stanley, underscores Elon Musk’s ambitious plans to expand the artificial intelligence venture. The xAI package comprises bonds and two loans, highlighting the company’s strategic push to fuel its artificial intelligence development.

Last week, Morgan Stanley began pitching a floating-rate term loan B at 97 cents on the dollar with a variable interest rate of 700 basis points over the SOFR benchmark, one source said. A second option offers a fixed-rate loan and bonds at 12%, with terms contingent on investor appetite. This “best efforts” transaction, where the debt size hinges on demand, reflects cautious lending in an uncertain economic climate.

According to Reuters sources, Morgan Stanley will not guarantee the issue volume or commit its own capital in the xAI deal, marking a shift from past commitments. The change in approach stems from lessons learned during Musk’s 2022 X acquisition when Morgan Stanley and six other banks held $13 billion in debt for over two years.

Morgan Stanley and the six other banks backing Musk’s X acquisition could only dispose of that debt earlier this year. They capitalized on X’s improved operating performance over the previous two quarters as traffic on the platform increased engagement around the U.S. presidential elections. This time, Morgan Stanley’s prudent strategy mitigates similar risks.

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Beyond debt, xAI is in talks to raise $20 billion in equity, potentially valuing the company between $120 billion and $200 billion, sources said. In April, Musk hinted at a significant valuation adjustment for xAI, stating he was looking to put a “proper value” on xAI during an investor call.

As xAI pursues this $5 billion debt offering, its financial strategy positions it to lead the AI revolution, blending innovation with market opportunity.

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SpaceX to debut new Dragon capsule in Axiom Space launch

Ax-4’s launch marks the debut of SpaceX’s latest Crew Dragon and pushes Axiom closer to building its own space station.

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spacex-dragon-axiom-ax-4-mission-iss
(Credit: SpaceX)

Axiom Space’s Ax-4 mission targets the International Space Station (ISS) with a new SpaceX Crew Dragon capsule.

The Axiom team will launch a new SpaceX Dragon capsule atop a Falcon 9 rocket from NASA’s Kennedy Space Center in Florida on Wednesday at 8:00 a.m. EDT (1200 GMT). The Ax-4 mission launch was initially set for Tuesday, June 10, but was delayed by one day due to expected high winds.

As Axiom Space’s fourth crewed mission to the ISS, Ax-4 marks the debut of an updated SpaceX Crew Dragon capsule. “This is the first flight for this Dragon capsule, and it’s carrying an international crew—a perfect debut. We’ve upgraded storage, propulsion components, and the seat lash design for improved reliability and reuse,” said William Gerstenmaier, SpaceX’s vice president of build and flight reliability.

Axiom Space is a Houston-based private space infrastructure company. It has been launching private astronauts to the ISS for research and training since 2022, building expertise for its future station. With NASA planning to decommission the ISS by 2030, Axiom has laid the groundwork for the Axiom Station, the world’s first commercial space station. The company has already begun construction on its ISS replacement.

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The Ax-4 mission’s research, spanning biological, life, and material sciences and Earth observation, will support this ambitious goal. Contributions from 31 countries underscore the mission’s global scope. The four-person crew will launch from Launch Complex 39A, embarking on a 14-day mission to conduct approximately 60 scientific studies.

“The AX-4 crew represents the very best of international collaboration, dedication, and human potential. Over the past 10 months, these astronauts have trained with focus and determination, each of them exceeding the required thresholds to ensure mission safety, scientific rigor, and operational excellence,” said Allen Flynt, Axiom Space’s chief of mission services.

The Ax-4 mission highlights Axiom’s commitment to advancing commercial space exploration. By leveraging SpaceX’s Dragon capsule and conducting diverse scientific experiments, Axiom is paving the way for its Axiom Station. This mission not only strengthens international collaborations but also positions Axiom as a leader in the evolving landscape of private space infrastructure.

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