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SpaceX’s path to refueling Starships in space is clearer than it seems
Perhaps the single biggest mystery of SpaceX’s Starship program is how exactly the company plans to refuel the largest spacecraft ever built after they reach orbit.
First revealed in September 2016 as the Interplanetary Transport System (ITS), SpaceX has radically redesigned its next-generation rocket several times over the last half-decade. Several crucial aspects have nevertheless persisted. Five years later, Starship (formerly ITS and BFR) is still a two-stage rocket powered by Raptor engines that burn a fuel-rich mixture of liquid methane (LCH4) and liquid oxygen (LOx). Despite being significantly scaled back from ITS, Starship will be about the same height (120 m or 390 ft) and is still on track to be the tallest, heaviest, and most powerful rocket ever launched by a large margin.
Building off of years of growing expertise from dozens of Falcon 9 and Falcon Heavy launches, the most important fundamental design goal of Starship is full and rapid reusability – propellant being the only thing intentionally ‘expended’ during launches. However, like BFR and ITS before it, the overarching purpose of Starship is to support SpaceX’s founding goal of making humanity multiplanetary and building a self-sustaining city on Mars. For Starship to have even a chance of accomplishing that monumental feat, SpaceX will not only have to build the most easily and rapidly reusable rocket and spacecraft in history, but it will also have to master orbital refueling.
The reuse/refuel equation
In the context of SpaceX’s goals of expanding humanity to Mars, a mastery of reusability and orbital refueling are mutually inclusive. Without both, neither alone will enable the creation of a sustainable city on Mars. A Starship launch system that can be fully reused on a weekly or even daily basis but can’t be rapidly and easily refueled in space simply doesn’t have the performance needed to affordably build, supply, and populate a city on another planet (or Moon). A Starship launch system that can be easily refueled but is not rapidly and fully reusable could allow for some degree of interplanetary transport and the creation of a minimal human outpost on Mars, but it would probably be one or two magnitudes more difficult, risky, and expensive to operate and would require a huge fleet of ships and boosters from the start.
The question of how SpaceX will make Starship the world’s most rapidly, fully, and cheaply reusable rocket is a hard one, but it’s not all that difficult to extrapolate from where the company is today. Currently, the turnaround record (time between two flights) for Falcon boosters is two launches in less than four weeks (27 days). SpaceX’s orbital-class reuse is also making strides and the company recently flew the same orbital Crew Dragon capsule twice in just 137 days (less than five months) – fast approaching turnarounds similar to NASA’s Space Shuttle average, the only other reusable orbital spacecraft in history.


While Dragon and Falcon 9 are far smaller than Starship and Super Heavy, Dragon is only partially reusable and requires significant refurbishment after recovery and Falcon 9 boosters are fairly complex. Starship, on the other hand, should effectively serve as a fully reusable all-in-one Falcon upper stage, Dragon capsule, Dragon trunk, and fairing, making it far more complex but potentially far more reusable. To an extent, Super Heavy should also be mechanically simpler than Falcon boosters (no deployable legs or fins; no structural composite-metal joints; no dedicated maneuvering thrusters) and its clean-burning Raptor engines should be easier to reuse than Falcon’s Merlins. Put simply, there are precedents set and evidence provided by Falcon rockets and NASA’s Space Shuttle that suggest SpaceX will be able to solve the reusability half of the equation.
What about refueling?
The other half of that equation, however, could not be more different. The sum total of SpaceX’s official discussions of orbital refueling can be summed up in a sentence included verbatim in CEO Elon Musk’s 2017, 2018, and 2019 Starship presentations: “propellant settled by milli G acceleration using control thrusters.”
On the face of it, that simple phrase doesn’t reveal much. However, with a few grains of salt, hints from what the company’s CEO has and hasn’t said, and context from the history of research into orbital propellant transfer, it’s possible to paint a fairly detailed picture of the exact mechanisms SpaceX will likely use to refill Starships in space. The cornerstone, somewhat ironically, is a 2006 paper – written by seven Lockheed Martin employees and a NASA engineer – titled “Settled Cryogenic Propellant Transfer.” Aside from the obvious corollaries just from the title alone, the paper focuses on what the authors argue is the simplest possible route to large-scale orbital propellant transfer.
In orbit, under microgravity conditions, the propellant inside a spacecraft’s tanks is effectively detached from the structure. If a spacecraft applies thrust, that propellant will stay still until it splashes against its tank walls – the most basic Newtonian principle that objects at rest tend to stay at rest. If, say, a spacecraft thrusts in one direction and opens a hatch or valve on the tank in the opposite direction of that thrust, the propellant inside it – attempting to stay at rest – will naturally escape out of that opening. Thus, if a spacecraft in need of fuel docks with a tanker, their tanks are connected and opened, and the tanker attempts to accelerate away from the receiving ship, the propellant in the tanker’s tanks will effectively be pushed into the second ship as it tries to stay at rest.
The principles behind such a ‘settled propellant transfer’ are fairly simple and intuitive. The crucial question is how much acceleration the process requires and how expensive that continuous acceleration ends up being. According to Kutter et al’s 2006 paper, the answer is surprising: assuming a 100 metric ton (~220,000 lb) spacecraft pair accelerates at 0.0001G (one ten-thousandth of Earth gravity) to transfer propellant, they would need to consume just 45 kg (100 lb) of hydrogen and oxygen propellant per hour to maintain that acceleration.
In the most extreme hypothetical refueling scenario (i.e. a completely full tanker refueling a ship with a full cargo bay), two docked Starships would weigh closer to 1600 tons (~3.5M lb) and the “Milli G” acceleration SpaceX has repeatedly mentioned in presentation slides would be ten times greater than the maximum acceleration analyzed by Kutter et al. Still, according to their paper, that propellant cost scales linearly both with the required acceleration and with the mass of the system. Roughly speaking, using the same assumptions, that means that the thrusting Starship would theoretically consume just over 7 tons (half a percent) of its methane and oxygen propellant per hour to maintain milli-G acceleration.
With large enough pipes (on the order of 20-50 cm or 8-20 in) connecting each Starship’s tanks, SpaceX should have no trouble transferring 1000+ tons of propellant in a handful of hours. Ultimately, that means that settled propellant transfer even at the scale of Starship should incur a performance ‘tax’ of no more than 20-50 tons of propellant per refueling. All transfers leading up to the worst-case 1600-ton scenario should also be substantially more efficient. Overall, that means that fully refueling an orbiting Starship or depot with ~1200 tons of propellant – requiring anywhere from 8 to 14+ tanker launches – should be surprisingly efficient, with perhaps 80% or more of the propellant launched remaining usable by the end of the process.
A step further, Kutter et al note the amount of acceleration required is so small that a hypothetical spacecraft could potentially use ullage gas vents to achieve it, meaning that custom-designed settling thrusters might not even be needed. Coincidentally or not, SpaceX (or CEO Elon Musk) has recently decided to use strategically located ullage vents to replace purpose-built maneuvering thrusters on Starship’s Super Heavy booster. If SpaceX adds similar capabilities to Starship, it’s quite possible that the combination of cryogenic propellant naturally boiling into gas as it warms and the ullage vents used to relieve that added pressure could produce enough thrust to transfer large volumes of propellant.
Last but not least, writing more than a decade and a half ago, the only technological barrier Kutter et al could foresee to large-scale settled propellant transfer wasn’t even related to refueling but, rather, to the ability to autonomously rendezvous and dock in orbit. In 2006, while Russia was already routinely using autonomous docking and rendezvous technology on its Soyuz and Progress spacecraft, the US had never demonstrated the technology on its own. Jump to today and SpaceX Dragon spacecraft have autonomously rendezvoused with the International Space Station twenty seven times in nine years and completed ten autonomous dockings – all without issue – since 2019.

Even though SpaceX and its executives have never detailed their approach to refueling (or refilling, per Musk’s preferred term) Starships in space, there is a clear path established by decades of NASA and industry research. What little evidence is available suggests that that path is the same one SpaceX has chosen to travel. Ultimately, the key takeaway from that research and SpaceX’s apparent use of it should be this: while a relatively inefficient process, SpaceX has effectively already solved the last remaining technical hurdle for settled propellant transfer and should be able to easily refuel Starships in orbit with little to no major development required.
There’s a good chance that minor to moderate problems will be discovered and need to be solved once SpaceX begins to test refueling in orbit but crucially, there are no obvious showstoppers standing between SpaceX and the start of those flight tests. Aside from the obvious (preparing a new rocket for its first flight tests), the only major refueling problem SpaceX arguably needs to solve is the umbilical ports and docking mechanisms that will enable propellant transfer. SpaceX will also need to settle on a location for those ports/mechanisms and decide whether to implement ullage vent ‘thrusters’, cold gas thrusters like those on Falcon and current Starship prototypes, or more efficient hot-gas thrusters derived from Raptors. At the end of the day, though, those are all solved problems and just a matter of complex but routine systems engineering that SpaceX is an expert at.
Elon Musk
Why Tesla’s Q3 could be one of its biggest quarters in history
Tesla could stand to benefit from the removal of the $7,500 EV tax credit at the end of Q3.

Tesla has gotten off to a slow start in 2025, as the first half of the year has not been one to remember from a delivery perspective.
However, Q3 could end up being one of the best the company has had in history, with the United States potentially being a major contributor to what might reverse a slow start to the year.
Earlier today, the United States’ House of Representatives officially passed President Trump’s “Big Beautiful Bill,” after it made its way through the Senate earlier this week. The bill will head to President Trump, as he looks to sign it before his July 4 deadline.
The Bill will effectively bring closure to the $7,500 EV tax credit, which will end on September 30, 2025. This means, over the next three months in the United States, those who are looking to buy an EV will have their last chance to take advantage of the credit. EVs will then be, for most people, $7,500 more expensive, in essence.
The tax credit is available to any single filer who makes under $150,000 per year, $225,000 a year to a head of household, and $300,000 to couples filing jointly.
Ending the tax credit was expected with the Trump administration, as his policies have leaned significantly toward reliance on fossil fuels, ending what he calls an “EV mandate.” He has used this phrase several times in disagreements with Tesla CEO Elon Musk.
Nevertheless, those who have been on the fence about buying a Tesla, or any EV, for that matter, will have some decisions to make in the next three months. While all companies will stand to benefit from this time crunch, Tesla could be the true winner because of its sheer volume.
If things are done correctly, meaning if Tesla can also offer incentives like 0% APR, special pricing on leasing or financing, or other advantages (like free Red, White, and Blue for a short period of time in celebration of Independence Day), it could see some real volume in sales this quarter.
You can now buy a Tesla in Red, White, and Blue for free until July 14 https://t.co/iAwhaRFOH0
— TESLARATI (@Teslarati) July 3, 2025
Tesla is just a shade under 721,000 deliveries for the year, so it’s on pace for roughly 1.4 million for 2025. This would be a decrease from the 1.8 million cars it delivered in each of the last two years. Traditionally, the second half of the year has produced Tesla’s strongest quarters. Its top three quarters in terms of deliveries are Q4 2024 with 495,570 vehicles, Q4 2023 with 484,507 vehicles, and Q3 2024 with 462,890 vehicles.
Elon Musk
Tesla Full Self-Driving testing continues European expansion: here’s where
Tesla has launched Full Self-Driving testing in a fifth European country ahead of its launch.

Tesla Full Self-Driving is being tested in several countries across Europe as the company prepares to launch its driver assistance suite on the continent.
The company is still working through the regulatory hurdles with the European Union. They are plentiful and difficult to navigate, but Tesla is still making progress as its testing of FSD continues to expand.
Today, it officially began testing in a new country, as more regions open their doors to Tesla. Many owners and potential customers in Europe are awaiting its launch.
On Thursday, Tesla officially confirmed that Full Self-Driving testing is underway in Spain, as the company shared an extensive video of a trip through the streets of Madrid:
Como pez en el agua …
FSD Supervised testing in Madrid, Spain
Pending regulatory approval pic.twitter.com/txTgoWseuA
— Tesla Europe & Middle East (@teslaeurope) July 3, 2025
The launch of Full Self-Driving testing in Spain marks the fifth country in which Tesla has started assessing the suite’s performance in the European market.
Across the past several months, Tesla has been expanding the scope of countries where Full Self-Driving is being tested. It has already made it to Italy, France, the Netherlands, and Germany previously.
Tesla has already filed applications to have Full Self-Driving (Supervised) launched across the European Union, but CEO Elon Musk has indicated that this particular step has been the delay in the official launch of the suite thus far.
In mid-June, Musk revealed the frustrations Tesla has felt during its efforts to launch its Full Self-Driving (Supervised) suite in Europe, stating that the holdup can be attributed to authorities in various countries, as well as the EU as a whole:
Tesla Full Self-Driving’s European launch frustrations revealed by Elon Musk
“Waiting for Dutch authorities and then the EU to approve. Very frustrating and hurts the safety of people in Europe, as driving with advanced Autopilot on results in four times fewer injuries! Please ask your governing authorities to accelerate making Tesla safer in Europe.”
Waiting for Dutch authorities and then the EU to approve.
Very frustrating and hurts the safety of people in Europe, as driving with advanced Autopilot on results in four times fewer injuries!
Please ask your governing authorities to accelerate making Tesla safer in Europe. https://t.co/QIYCXhhaQp
— Elon Musk (@elonmusk) June 11, 2025
Tesla said last year that it planned to launch Full Self-Driving in Europe in 2025.
Elon Musk
xAI’s Memphis data center receives air permit despite community criticism
xAI welcomed the development in a post on its official xAI Memphis account on X.

Elon Musk’s artificial intelligence startup xAI has secured an air permit from Memphis health officials for its data center project, despite critics’ opposition and pending legal action. The Shelby County Health Department approved the permit this week, allowing xAI to operate 15 mobile gas turbines at its facility.
Air permit granted
The air permit comes after months of protests from Memphis residents and environmental justice advocates, who alleged that xAI violated the Clean Air Act by operating gas turbines without prior approval, as per a report from WIRED.
The Southern Environmental Law Center (SELC) and the NAACP has claimed that xAI installed dozens of gas turbines at its new data campus without acquiring the mandatory Prevention of Significant Deterioration (PSD) permit required for large-scale emission sources.
Local officials previously stated the turbines were considered “temporary” and thus not subject to stricter permitting. xAI applied for an air permit in January 2025, and in June, Memphis Mayor Paul Young acknowledged that the company was operating 21 turbines. SELC, however, has claimed that aerial footage shows the number may be as high as 35.
Critics are not giving up
Civil rights groups have stated that they intend to move forward with legal action. “xAI’s decision to install and operate dozens of polluting gas turbines without any permits or public oversight is a clear violation of the Clean Air Act,” said Patrick Anderson, senior attorney at SELC.
“Over the last year, these turbines have pumped out pollution that threatens the health of Memphis families. This notice paves the way for a lawsuit that can hold xAI accountable for its unlawful refusal to get permits for its gas turbines,” he added.
Sharon Wilson, a certified optical gas imaging thermographer, also described the emissions cloud in Memphis as notable. “I expected to see the typical power plant type of pollution that I see. What I saw was way worse than what I expected,” she said.
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