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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.

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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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Tesla Sweden appeals after grid company refuses to restore existing Supercharger due to union strike

The charging site was previously functioning before it was temporarily disconnected in April last year for electrical safety reasons.

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Credit: Tesla Charging

Tesla Sweden is seeking regulatory intervention after a Swedish power grid company refused to reconnect an already operational Supercharger station in Åre due to ongoing union sympathy actions.

The charging site was previously functioning before it was temporarily disconnected in April last year for electrical safety reasons. A temporary construction power cabinet supplying the station had fallen over, described by Tesla as occurring “under unclear circumstances.” The power was then cut at the request of Tesla’s installation contractor to allow safe repair work.

While the safety issue was resolved, the station has not been brought back online. Stefan Sedin, CEO of Jämtkraft elnät, told Dagens Arbete (DA) that power will not be restored to the existing Supercharger station as long as the electric vehicle maker’s union issues are ongoing. 

“One of our installers noticed that the construction power had been backed up and was on the ground. We asked Tesla to fix the system, and their installation company in turn asked us to cut the power so that they could do the work safely. 

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“When everything was restored, the question arose: ‘Wait a minute, can we reconnect the station to the electricity grid? Or what does the notice actually say?’ We consulted with our employer organization, who were clear that as long as sympathy measures are in place, we cannot reconnect this facility,” Sedin said. 

The union’s sympathy actions, which began in March 2024, apply to work involving “planning, preparation, new connections, grid expansion, service, maintenance and repairs” of Tesla’s charging infrastructure in Sweden.

Tesla Sweden has argued that reconnecting an existing facility is not equivalent to establishing a new grid connection. In a filing to the Swedish Energy Market Inspectorate, the company stated that reconnecting the installation “is therefore not covered by the sympathy measures and cannot therefore constitute a reason for not reconnecting the facility to the electricity grid.”

Sedin, for his part, noted that Tesla’s issue with the Supercharger is quite unique. And while Jämtkraft elnät itself has no issue with Tesla, its actions are based on the unions’ sympathy measures against the electric vehicle maker. 

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“This is absolutely the first time that I have been involved in matters relating to union conflicts or sympathy measures. That is why we have relied entirely on the assessment of our employer organization. This is not something that we have made any decisions about ourselves at all. 

“It is not that Jämtkraft elnät has a conflict with Tesla, but our actions are based on these sympathy measures. Should it turn out that we have made an incorrect assessment, we will correct ourselves. It is no more difficult than that for us,” the executive said. 

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Music City Loop could highlight The Boring Company’s real disruption

The real story behind the tunneling startup’s Nashville tunnel project is the company’s targeted $25 million per mile construction cost.

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Credit: The Boring Company/X

Recent commentary on social media has highlighted what could very well prove to be The Boring Company’s real disruption.

The analysis was shared by tech watcher Aakash Gupta on social media platform X, where he argued that the real story behind the tunneling startup’s Nashville tunnel project is the company’s targeted $25 million per mile construction cost.

According to Gupta’s breakdown, Nashville’s 2018 light rail proposal was priced at roughly $200 million per mile. New York’s East Side Access project reportedly cost about $3.5 billion per mile, while Los Angeles Metro expansion projects have approached $1 billion per mile.

By comparison, The Boring Company has stated it can construct 13 miles of twin tunnels in the Music City Loop for between $240 million and $300 million total. That implies a cost near $25 million per mile, or roughly a 95% reduction from industry averages cited in the post.

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Several technical departures from conventional tunneling allow the Boring Company to lower its costs, from its smaller 12-foot diameter tunnels to its fully electric Prufrock machines that are designed to mine continuously with no personnel inside the tunnel and their capability to “porpoise” for easy launch and retrieval.

Tesla and Space CEO Elon Musk responded to the post on X, stating simply that “Tunnels are so underrated.”

The Boring Company has seen some momentum as of late, with the company recently signing a construction contract in Dubai and the Universal Orlando Loop progressing. Recent reports have also pointed to tunnels potentially being constructed to solve traffic congestion issues near the Giga Nevada area. 

While The Boring Company’s tunnels have so far been used for Loop systems publicly for now, Elon Musk recently noted that the tunneling startup’s underground passages would not be limited only to ride-hailing vehicles. 

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In a reply to a post on X which discussed the specifications of the Music City Loop, Musk clarified that “any fully autonomous electric cars can use the tunnels.” This suggests that vehicles potentially running systems like FSD Supervised, even if they are not Teslas, could be used in systems like the Music City Loop in the future.

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SpaceX IPO could push Elon Musk’s net worth past $1 trillion: Polymarket

The estimates were shared by the official Polymarket Money account on social media platform X.

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Gage Skidmore, CC BY-SA 4.0 , via Wikimedia Commons

Recent projections have outlined how a potential $1.75 trillion SpaceX IPO could generate historic returns for early investors. The projections suggest the offering would not only become the largest IPO in history but could also result in unprecedented windfalls for some of the company’s key investors.

The estimates were shared by the official Polymarket Money account on social media platform X.

As noted in a Polymarket Money analysis, Elon Musk invested $100 million into SpaceX in 2002 and currently owns approximately 42% of the company. At a $1.75 trillion valuation following SpaceX’s potential $1.75 trillion IPO, that stake would be worth roughly $735 billion.

Such a figure would dramatically expand Musk’s net worth. When combined with his holdings in Tesla Inc. and other ventures, a public debut at that level could position him as the world’s first trillionaire, depending on market conditions at the time of listing.

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The Bloomberg Billionaires Index currently lists Elon Musk with a net worth of $666 billion, though a notable portion of this is tied to his TSLA stock. Tesla currently holds a market cap of $1.51 trillion, and Elon Musk’s currently holds about 13% to 15% of the company’s outstanding common stock.

Founders Fund, co-founded by Peter Thiel, invested $20 million in SpaceX in 2008. Polymarket Money estimates the firm owns between 1.5% and 3% of the private space company. At a $1.75 trillion valuation, that range would translate to approximately $26.25 billion to $52.5 billion in value.

That return would represent one of the most significant venture capital outcomes in modern Silicon Valley history, with a growth of 131,150% to 262,400%.

Alphabet Inc., Google’s parent company, invested $900 million into SpaceX in 2015 and is estimated to hold between 6% and 7% of the private space firm. At the projected IPO valuation, that stake could be worth between $105 billion and $122.5 billion. That’s a growth of 11,566% to 14,455%.

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Other major backers highlighted in the post include Fidelity Investments, Baillie Gifford, Valor Equity Partners, Bank of America, and Andreessen Horowitz, each potentially sitting on multibillion-dollar gains.

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