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SpaceX’s path to refueling Starships in space is clearer than it seems

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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.

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SpaceX’s current fleet of four reusable Dragon spacecraft. (NASA/Mike Hopkins/ESA/Thomas Pesquet)
Pictured here during its last launch, Falcon 9 B1060 owns SpaceX’s turnaround record of just 27 days and has completed eight orbital-class launches in 12 months, averaging one flight every ~45 days – an average turnaround time that’s better than the Space Shuttle’s all-time record. (SpaceX)

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.”

This phrase first appeared in 2017 (PDF; page 16). (SpaceX)

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.

Two possible Starship orientations for propellant transfer. (SpaceX)

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.

On Super Heavy B4, SpaceX has installed what amount to nozzles over the booster’s main oxygen tank vents to vector and maximize the thrust they produce. (NASASpaceflight – bocachicagal)

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.

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SpaceX has already developed and thoroughly tested hot-gas Raptor-derived maneuvering thrusters that could be fairly easily added to Starship to boost the efficiency of settled propellant transfer at the cost of added weight and complexity. (NASASpaceflight – bocachicagal)

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.

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 Robotaxi just got a big benefit from the U.S. government

The NHTSA is looking to help streamline the application process for companies developing driverless vehicles.

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Credit: Tesla

Tesla Robotaxi just got a big benefit from the U.S. Government, as the National Highway Traffic Safety Administration (NHTSA) is looking to ease some rules and streamline the application process that could hinder the development and licensing of autonomous vehicles.

Tesla is set to launch its Robotaxi platform in the coming days or weeks, but regulation on autonomous vehicles is incredibly slim, so automakers are left in a strange limbo as permissions to operate are usually up to local jurisdictions.

The NHTSA still has the ultimate say, but it is now adopting a new strategy that will see companies gain an exemption from federal safety standards and streamline the entire application process.

The agency is authorized to grant exemptions to permit manufacturers to produce vehicles over a two or three-year period that might not comply with certain Federal Motor Vehicle Safety Standards (FMVSS). Robotaxi, for example, will eventually not have a steering wheel or pedals, through the Cybercab that Tesla unveiled last October.

The exemption program the NHTSA announced today would be possible through Part 555 of the National Traffic and Motor Vehicle Safety Act:

“NHTSA may grant a Part 555 exemption if at least one of four bases listed in the statute is met and NHTSA determines that the exemption is consistent with the public interest and the Safety Act. The statute also authorizes NHTSA to subject an exemption to terms the agency deems appropriate and requires that NHTSA publish notice of the application and provide an opportunity to comment.”

The rapid and non-stop innovation that is being performed is tough to keep up with from a legal standpoint. The NHTSA recognizes this and says current legislation is appropriate for traditional vehicles, but not for the self-driving cars companies are producing now:

“The current Part 555 process was designed for traditional vehicles. As currently applied, this process is not well suited for processing exemptions involving ADS-equipped vehicles in a timely manner or overseeing the unique complexities involving their operations. This has resulted in long processing times for applications for ADS-equipped vehicles. NHTSA must improve its Part 555 processing times substantially to keep pace with the rapid innovation of the ADS industry and to ensure that exemptions remain effective tools for nurturing groundbreaking safety technologies.”

Now, the NHTSA will be “enhancing application instructions” to help manufacturers understand the requirements involved in the application process. This will streamline the entire process by “reducing the need for NHTSA to request additional information from the manufacturer,” the agency says.

First Tesla driverless robotaxi spotted in the wild in Austin, TX

Next, the NHTSA is going to have a more flexible approach to evaluating exemptions for ADS-equipped vehicles:

“To build flexibility into the Part 555 process while also accounting for the unique aspects of those exemptions, NHTSA intends to develop terms that could be included in Part 555 exemption grants, when appropriate, to condition operations of exempted ADS-equipped vehicles on enhanced and continuing oversight from NHTSA. NHTSA would expect to administer this enhanced oversight through letters, which could be updated over time, mirroring real-world ADS development. This will enable NHTSA to focus its initial review during the application stage and align the Part 555 oversight approach more closely to exemptions administered under NHTSA’s Automated Vehicle Exemption Program (AVEP), which have proven effective for ADS.”

This will benefit any company making autonomous vehicles, but it will especially benefit Tesla in the short-term as it is readying for the launch of Robotaxi.

Tesla is trading up 1.89 percent at the time of publication.

Part 555 Letter June 2025 by Joey Klender on Scribd

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SpaceX produces its 10 millionth Starlink kit

The first 5 million Starlink kits took nearly four years to build.

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Credit: Starlink/X

SpaceX has achieved a major milestone, producing its 10 millionth Starlink kit. The accomplishment was celebrated across the company’s Hawthorne, California, and Bastrop, Texas, facilities. 

The milestone was shared in social media by Sujay Soman, Senior Facilities Engineer, in a LinkedIn post, which has since been deleted. 

Starlink Production Ramp

Soman noted in his LinkedIn post that the first 5 million Starlink kits took nearly four years to build, but the next 5 million kits were completed in just 11 months. This underscores SpaceX’s intense efforts to ramp up the satellite internet system’s production, and it reflects the private space company’s manufacturing prowess.

The SpaceX Senior Facilities Engineer shared a couple of photos of the Machine Maintenance and Facilities team in Bastrop to commemorate the event.

“Today, Starlink Product teams across our Hawthorne and Bastrop sites produced the 10th Million Starlink Kit! It took almost 4 years to build our first 5 million kits, and we doubled that in about 11 months. Monumental accomplishment!” Soman wrote in his post.

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Credit: Sujay Soman/LinkedIn

World-Changing Technology 

The Starlink kits, featuring dish hardware and supporting equipment, enable users to connect to the company’s growing constellation of low Earth orbit satellites. With over 6,000 satellites launched to date, Starlink now provides fast and reliable internet connectivity to over 6 million customers worldwide. This was a significant increase from the 5 million customers that the company reported in February 2025.

SpaceX has not detailed its next production targets, but the production of Starlink’s 10 millionth kit milestone signals the company’s readiness to scale further. Being an Elon Musk-led company, SpaceX is arguably the best in the business when it comes to efficient and cost-effective manufacturing. It would then be unsurprising if SpaceX announces another Starlink production milestone soon.

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Tesla retires yoke steering wheel in base Model S and X

Tesla’s controversial steering yoke is now exclusive to the Model S and Model X Plaid.

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tesla-model-s-plaid-yoke
Credit: @dkrasniy/X

Tesla has closed a chapter in the saga of the Model S and Model X’s controversial steering yoke. Following the announcement of the new iterations of the flagship vehicles, Tesla promptly removed the steering option for the vehicles’ base variants.

This means that if drivers wish to experience the Model S or Model X with a yoke, they would have to go Plaid.

The new Model S and Model X

The refresh of the Model S and Model X were quite minor, with the two vehicles featuring a new front camera, a new color, and a handful of other small changes like new exterior styling for the Model S Plaid. Tesla also noted on its website that the two vehicles now have a much smoother and quieter ride.

The changes were quite polarizing, with some appreciating the subtle improvements made to the two flagship cars and others arguing that Tesla should have done more. Others, however, noted that the level of improvements implemented on the Model S and Model X would already be considered major refresh for a tech company like Apple.

No More Yoke Unless Plaid

When Tesla refreshed the Model S and Model X in 2021, the vehicles were released with a steering yoke as standard. The yoke was controversial, with critics stating that it was unsafe and fans stating that it made driving the Model S and Model X fun. Tesla later introduced a round steering wheel option for the Model S and Model X, which later became standard on the two flagship vehicles.

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This remains true today, with the most recent versions of the Model S and Model X still being released with a round steering wheel as standard. Those who wish to experience the Model S and Model X Plaid as envisioned by the company and its CEO, Elon Musk, however, might find it a good idea to spend the extra $1,000 for the vehicles’ yoke steering wheel.

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