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SpaceX’s Starship Raptor Vacuum engine plans laid out by CEO Elon Musk

A 2016 render of Raptor Vacuum. Much has changed about the engine's design in the three years since, but SpaceX is still pursuing a vacuum variant. (SpaceX)

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Elon Musk says that SpaceX Starship engine upgrades are on track to begin static fire tests of a Raptor Vacuum variant as few as a “couple months” from now.

Designed to enable more efficient performance in thin atmosphere or vacuum, Musk admitted that the first version(s) of Raptor Vacuum (RVac) will likely be a compromise between efficiency and speed of development. Nevertheless, the faster SpaceX can prepare Raptor Vacuum for flight, the easier it will be for Starship to begin serious (sub)orbital flight tests.

As it turns out, SpaceX’s first and only official render of Raptor – published in September 2016 – showed the engine’s vacuum-optimized variant. In the years since, CEO Elon Musk has vacillated between keeping the vacuum engines as a central Starship feature and simply replacing them with regular sea level Raptors to expedite the spacecraft’s debut. The 2016 and 2017 vehicles featured a mixture of vacuum and sea-level engines, whereas Musk revealed a vehicle with sea-level engines only in 2018.

Known as the Interplanetary Transport System in 2016, the ship featured six vacuum Raptors and 3 SL engines. (SpaceX)
In 2017, Big Falcon Spaceship shrunk and changed to 4 x RVac and 3x x Raptor SL engines. (SpaceX)
In 2018, Musk decided to sidestep vacuum engines entirely, moving to 7 SL Raptors. (SpaceX)

Perhaps less than a month after Musk’s September 2018 presentation, the SpaceX CEO made the decision to radically redesign the vehicle – newly christened Starship and Super Heavy – by moving from a carbon composite aerostructure to stainless steel. At first, the seven SL Raptors remained a part of the design, but Musk took to Twitter in 2019 to indicate that SpaceX had changed gears again and had reprioritized Raptor Vacuum development.

This came as a bit of surprise and it should go without saying that there’s a significant chance that Musk/SpaceX will oscillate in the opposite direction once again before Raptor Vacuum is actually ready for flight. This time, though, Musk has sketched out a development schedule and strategy that suggests SpaceX is much more serious this time.

Most notably, Musk claims that the first Raptor Vacuum prototype could be ready for static fire testing just a “couple months” from now, an immensely ambitious schedule for any large liquid rocket engine development program. Nevertheless, Musk did indicate that the “V1.0” Raptor Vacuum design would be significantly compromised and “suboptimal”, an intentional decision to prioritize the engine’s “speed of development”.

Even then, Musk believes that the first variant – featuring a shortened bell nozzle – could still be up to 12% more efficient than sea level Raptors and thus already 70-80% of the way to the physical limit of methane-oxygen rocket efficiency.

A sea-level Raptor engine is static-fired at SpaceX’s McGregor, TX test facilities. (SpaceX)

On a positive note, shrinking V1.0 Raptor Vacuum’s nozzle a bit from its nominal length will likely mean that SpaceX can static fire fully-integrated engines at its McGregor, TX test facilities, critical for speedy development. If not, the company has experience with alternatives through Merlin Vacuum, which can only be tested on the ground with its lengthy nozzle detached. This method just makes it dramatically harder to optimize a vacuum nozzle design, as full-scale, flight-like testing is nearly impossible if a given vacuum engine can’t be tested on the ground with said nozzle installed.

Vacuum engines need such large and unwieldy nozzles in order to make them as efficient as possible. In a very simplistic sense, a rocket engine nozzle directs the flow of superheated, ultrafast gases in order to squeeze as much momentum transfer as possible out of available propellant. The lower the pressure of the surrounding atmosphere is, the more those gases will expand immediately after leaving the nozzle – giant vacuum nozzles simply try to harness the additional momentum available from that extra expansion. This is why rocket exhausts appear to spread and thin out as launch vehicles reach higher and higher altitudes.

A Falcon 9 upper stage’s vacuum nozzle glows white hot during an orbital MVac burn. (SpaceX)

In this sense, the perfect theoretical vacuum nozzle is quite literally infinitely long. The job of vacuum rocket engineers is to find the perfect balance between that impractical theoretical perfection and the limits of real-world materials and dynamics. In theory, SpaceX’s sea-level Raptor engines have already been designed to operate in vacuum conditions, while the engine’s closed-cycle design and regeneratively (i.e. propellant) cooled nozzle should apply well to a vacuum design.

If SpaceX is lucky, there will be few roadblocks in the way of simply lengthening a SL Raptor-style nozzle and calling it a day, in which case it would be impressive but not all that surprising if SpaceX is actually able to begin RVac testing before the end of 2019. Once a rough V1.0 engine is in place, the process of optimizing efficiency can be done slowly and methodically, all while exploiting an unprecedented wealth of data from flight and orbit-tested Raptor Vacuum engines.

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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’s next Uranium in Uranus merch is Boring Company’s weirdest tease yet

Elon Musk teased a glowing new Boring Company merch idea, complete with a Geiger counter.

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Concept rendering of Boring Company Uranium in Uranus merch tease via Grok
Concept rendering of Boring Company Uranium in Uranus merch tease via Grok

Elon Musk teased the next piece of Boring Company merchandise on X Saturday, and it is exactly as unserious as fans of the company’s product history have come to expect. “The next @boringcompany merch will put Uranium in Uranus,” Musk wrote in a thread posted early Saturday morning. He followed up by explaining that the item would glow in the dark, “because otherwise how could you find it,” and that a Geiger counter would be sold separately as “an optional strap-on.”

Musk closed the thread with a line that doubles as a mission statement for the tunneling company’s merchandise arm: “It’s not easy coming up with something that is both outrageously unsellable and yet extremely popular.”

The Boring Company has built a small but consistent side business out of novelty items that start as jokes and end up selling out. The company’s Not-a-Flamethrower raised roughly $10 million in a few days back in 2018, moving all 20,000 units it produced. Its Burnt Hair perfume, priced around $100 a bottle, sold out fast enough that scalpers were flipping units on eBay for ten times the retail price. Boring Bricks, made from tunneling spoil, followed the same playbook of teasing a product on X months before it became real.

Musk has not said what the actual item will be, only that it involves uranium and glows in the dark. Given the pattern, that vagueness is probably intentional. Past merch announcements have started as one-line jokes and taken weeks or months to turn into an actual product listing on the company’s site, and there is no guarantee this one follows through at all.

The timing lines up with a period of real momentum for the Boring Company outside of the joke merchandise. The company said last week it plans to double the number of operational stations on its Vegas Loop by the end of the year, a target tied to a hiring push for drivers and operations managers. Prufrock-5, one of the company’s tunnel boring machines, also just wrapped a test tunnel in Bastrop, Texas, and is expected to relaunch on its next assignment in November.

Whether the uranium joke turns into an actual product remains to be seen. Musk’s post did not include a price, a shipping date, or even a name for the item, which has historically meant a Boring Company website page goes up quietly, password protected, sometime before an announcement.

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NASA taps SpaceX for more astronaut missions as Boeing Starliner remains grounded

NASA just gave SpaceX a $946 million contract for three more astronaut missions through 2030.

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NASA has awarded SpaceX a $946 million contract modification covering three more astronaut missions to the International Space Station, according to an announcement the agency published Friday. The award adds Crew-15, Crew-16, and Crew-17 to SpaceX’s existing Commercial Crew Transportation Capability contract, bringing the agreement’s total value to $5.92 billion across 17 flights.

SpaceX confirmed the award on X, writing that it was excited for Falcon 9 and Dragon to launch NASA’s Crew-15, 16, and 17 missions to the Space Station from Florida. The new missions cover ground, launch, in orbit, and return operations, along with cargo transport and a lifeboat capability while docked at the station, and the period of performance runs through 2030.

The award follows a notice of intent NASA issued in May, when the agency first signaled it would purchase up to six additional post certification missions from SpaceX. Teslarati covered that filing at the time, noting NASA cited technical issues and schedule delays encountered by Boeing as a driving factor. Friday’s contract modification locks in three of those six missions, with the remaining three left open for NASA to award later, potentially to Boeing if Starliner clears certification.

Boeing’s CST-100 Starliner has still not flown an operational crew rotation mission for NASA. The spacecraft’s most recent crewed test flight in 2024 ended without the astronauts returning aboard Starliner, and the company has spent the time since working through thruster problems. SpaceX President Gwynne Shotwell said this week that SpaceX is not retiring Crew Dragon today, for sure, while stopping short of committing to fly it past 2030.

Crew-12 is currently docked at the space station, and NASA has said Crew-13 is targeting a launch in the coming weeks. The newly awarded Crew-15 through Crew-17 missions extend SpaceX’s role as NASA’s primary way of getting astronauts to and from orbit well into the back half of the decade, regardless of what happens with Starliner or Starship in the meantime.

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Investor's Corner

New drone video shows Tesla’s Optimus Factory reaching a turning point

New drone footage shows Tesla’s dedicated Optimus factory steel frame nearing completion at Giga Texas.

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Tesla’s dedicated Optimus factory at Gigafactory Texas is closing in on a finished steel frame, according to drone footage posted Thursday afternoon by longtime site observer Joe Tegtmeyer. In the video, Tegtmeyer said structural steel assembly is now about five column grids away from reaching the building’s north perimeter beam, putting the primary skeleton in its final stretch roughly six months after Tesla broke ground on the North Campus site in late March.

Tegtmeyer’s footage shows concrete already going in on three upper floors while crews continue laying rebar and pouring grade beam footings at ground level. That kind of parallel work, steel rising at one end of the site while concrete sets at the other, is a scheduling approach Tesla used at the original Giga Texas building and appears to be repeating here to save time before the plant’s targeted 2027 production start.

Teslarati has tracked the building’s progress since Tesla confirmed construction was officially underway in May, when the first steel structure went up on what was then bare, reclaimed land. The facility is part of a more than 5.2 million square foot expansion of Giga Texas’s North Campus that Tesla has said will eventually run nearly the length of the existing vehicle factory, over 4,000 feet, while sitting somewhat narrower. Musk has pegged the long term output target at 10 million Optimus units a year once the line is running at full capacity, a volume that would dwarf the one million unit pilot line Tesla is standing up separately at its Fremont, California factory.

Tesla Giga Texas to feature massive Optimus V4 production line

The Texas facility sits alongside another major buildout on the same campus. Terafab, the joint Tesla and SpaceX chip fabrication plant that will eventually supply the silicon running Optimus units in the field. Housing robot assembly and chip production on the same grounds is a deliberate supply chain decision, cutting down on the shipping and lead time that would otherwise sit between the two.

Tesla has not given an updated timeline beyond its previously stated goal of bringing high volume Optimus production online at the site in the summer of 2027. Fremont’s smaller pilot line began mass producing the current Gen 3 robot in January, with that plant expected to build tens of thousands of units this year primarily to generate the real world data Tesla needs to refine the robot’s software before Giga Texas ramps up. Six months of visible construction progress, tracked almost entirely through Tegtmeyer’s recurring drone flights, gives the clearest outside look yet at how seriously Tesla is treating that 2027 deadline.

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