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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
Tesla investors will be shocked by Jim Cramer’s latest assessment
Jim Cramer is now speaking positively about Tesla, especially in terms of its Robotaxi performance and its perception as a company.

Tesla investors will be shocked by analyst Jim Cramer’s latest assessment of the company.
When it comes to Tesla analysts, many of them are consistent. The bulls usually stay the bulls, and the bears usually stay the bears. The notable analysts on each side are Dan Ives and Adam Jonas for the bulls, and Gordon Johnson for the bears.
Jim Cramer is one analyst who does not necessarily fit this mold. Cramer, who hosts CNBC’s Mad Money, has switched his opinion on Tesla stock (NASDAQ: TSLA) many times.
He has been bullish, like he was when he said the stock was a “sleeping giant” two years ago, and he has been bearish, like he was when he said there was “nothing magnificent” about the company just a few months ago.
Now, he is back to being a bull.
Cramer’s comments were related to two key points: how NVIDIA CEO Jensen Huang describes Tesla after working closely with the Company through their transactions, and how it is not a car company, as well as the recent launch of the Robotaxi fleet.
Jensen Huang’s Tesla Narrative
Cramer says that the narrative on quarterly and annual deliveries is overblown, and those who continue to worry about Tesla’s performance on that metric are misled.
“It’s not a car company,” he said.
He went on to say that people like Huang speak highly of Tesla, and that should be enough to deter any true skepticism:
“I believe what Musk says cause Musk is working with Jensen and Jensen’s telling me what’s happening on the other side is pretty amazing.”
Tesla self-driving development gets huge compliment from NVIDIA CEO
Robotaxi Launch
Many media outlets are being extremely negative regarding the early rollout of Tesla’s Robotaxi platform in Austin, Texas.
There have been a handful of small issues, but nothing significant. Cramer says that humans make mistakes in vehicles too, yet, when Tesla’s test phase of the Robotaxi does it, it’s front page news and needs to be magnified.
He said:
“Look, I mean, drivers make mistakes all the time. Why should we hold Tesla to a standard where there can be no mistakes?”
It’s refreshing to hear Cramer speak logically about the Robotaxi fleet, as Tesla has taken every measure to ensure there are no mishaps. There are safety monitors in the passenger seat, and the area of travel is limited, confined to a small number of people.
Tesla is still improving and hopes to remove teleoperators and safety monitors slowly, as CEO Elon Musk said more freedom could be granted within one or two months.
News
Tesla launches ultra-fast V4 Superchargers in China for the first time
Tesla has V4 Superchargers rolling out in China for the first time.

Tesla already has nearly 12,000 Supercharger piles across mainland China. However, the company just initiated the rollout of the ultra-fast V4 Superchargers in China for the first time, bringing its quick-charging piles to the country for the first time since their launch last year.
The first batch of V4 Superchargers is now officially up and running in China, the company announced in a post on Chinese social media outlet Weibo today.
The company said in the post:
“The first batch of Tesla V4 Superchargers are online. Covering more service areas, high-speed charging is more convenient, and six-layer powerful protection such as rain and waterproof makes charging very safe. Simultaneously open to non-Tesla vehicles, and other brands of vehicles can also be charged. There are more than 70,000 Tesla Superchargers worldwide. The charging network layout covers 100% of the provincial capitals and municipalities in mainland China. More V4 Superchargers will be put into use across the country. Optimize the charging experience and improve energy replenishment efficiency. Tesla will accompany you to the mountains, rivers, lakes, and seas with pure electricity!”
The first V4 Superchargers Tesla installed in China are available in four cities across the country: Shanghai, Zhejiang, Gansu, and Chongqing.

Credit: Tesla China
Tesla has over 70,000 Superchargers worldwide. It is the most expansive and robust EV charging network in the world. It’s the main reason why so many companies have chosen to adopt Tesla’s charging connector in North America and Europe.
In China, some EVs can use Tesla Superchargers as well.
The V4 Supercharger is capable of charging vehicles at speeds of up to 325kW for vehicles in North America. This equates to over 1,000 miles per hour of charging.
Elon Musk
Elon Musk hints at when Tesla could reduce Safety Monitors from Robotaxi
Tesla could be reducing Safety Monitors from Robotaxi within ‘a month or two,’ CEO Elon Musk says.

Elon Musk hinted at when Tesla could begin reducing Safety Monitors from its Robotaxis. Safety Monitors are Tesla employees who sit in the front passenger seat during the driverless rides, and are there to ensure safety for occupants during the earliest rides.
Tesla launched its Robotaxi fleet in Austin last Sunday, and after eight days, videos and reviews from those who have ridden in the driverless vehicles have shown that the suite is safe, accurate, and well coordinated. However, there have been a few hiccups, but nothing that has put anyone’s safety in danger.
A vast majority — close to all of the rides — at least according to those who have ridden in the Robotaxi, have been performed without any real need for human intervention. We reported on what was the first intervention last week, as a Safety Monitor had to step in and stop the vehicle in a strange interaction with a UPS truck.
Watch the first true Tesla Robotaxi intervention by safety monitor
The Tesla and UPS delivery truck were going for the same street parking space, and the Tesla began to turn into it. The UPS driver parallel parked into the spot, which was much smaller than his truck. It seemed to be more of an instance of human error instead of the Robotaxi making the wrong move. This is something that the driverless cars will have to deal with because humans are aggressive and sometimes make moves they should not.
The Safety Monitors have not been too active in the vehicles. After all, we’ve only seen that single instance of an intervention. There was also an issue with the sun, when the Tesla braked abnormally due to the glare, but this was an instance where the car handled the scenario and proceeded normally.
With the Robotaxi fleet operating impressively, some are wondering when Tesla will begin scaling back both the Safety Monitors and Teleoperators that it is using to ensure safety with these early rides.
CEO Elon Musk answered the inquiry by stating, “As soon as we feel it is safe to do so. Probably within a month or two.”
As soon as we feel it is safe to do so.
Probably within a month or two. We continue to improve the Tesla AI with each mile driven.
— Elon Musk (@elonmusk) June 30, 2025
Musk’s response seems to confirm that there will be fewer Teleoperators and Safety Monitors in the coming months, but there will still be some within the fleet to ensure safety. Eventually, that number will get to zero.
Reaching a point where Tesla’s Robotaxi is driverless will be another significant milestone for the company and its path to fully autonomous ride-sharing.
Eventually, Tesla will roll out these capabilities to consumer-owned vehicles, offering them a path to generate revenue as their car operates autonomously and completes rides.
For now, Tesla is focusing on perfecting the area of Austin where it is currently offering driverless rides for just $4.20 to a small group of people.
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