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Aug 01, 2023

Fill ’Er Up

Ambitious plans for gas stations in space could extend the lives of satellites

Ambitious plans for gas stations in space could extend the lives of satellites

At 9:20 p.m. on a spring evening 10 years ago, residents of the Falkland Islands saw a fiery object streak through the sky, breaking apart as it plummeted toward the South Atlantic.

The GOCE satellite had come home.

Europe had launched the one-ton spacecraft to map Earth's gravitational fields. But gravity had the last laugh as GOCE (short for Gravity Field and Steady-State Ocean Circulation Explorer) ran out of xenon fuel for its ion propulsion system, rendering it incapable of sustaining its orbit 139 miles above the Earth.

Scientists were nonetheless delighted. They had expected the GOCE mission to last two years, but they had managed to eke out four years thanks to a lower-than-expected rate of fuel consumption. That extra mission time enabled the collection of the most accurate Earth gravity data ever.

An artist's depiction of Europe's Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite, which ran out of fuel and re-entered the atmosphere in 2013. Refueling facilities could allow space agencies to extend the operational lives of their science satellites. (AOES Medialab/ESA)

But what if GOCE—and other satellites—didn't run out of fuel? What if it were possible to refill their fuel tanks in orbit so they could continue their missions? The question, initially speculative, has become increasingly urgent as space junk continues to accumulate, which poses a hazard to satellites and human spacefarers alike.

Lab tests demonstrate how even small debris can cause severe damage. (ESA)

Not all satellites plummet back to Earth at the end of their lifetimes. Many just become part of the ever-growing orbital debris field that, according to NASA, currently consists of over 23,000 fragments larger than a softball, each traveling at speeds up to 17,500 mph. Moreover, there are approximately 100 million pieces of debris 0.04 inches or larger, and even smaller ones. We’ve now reached the point where the debris is generating still more debris. In 2009, two defunct satellites collided, shattering into more than 2,300 pieces large enough to be tracked.

Over 4,500 satellites remain operational today, and it's only going to get more crowded as private companies like SpaceX and OneWeb plan to continue launching constellations of thousands of internet satellites in the coming years.

"We’re trying to end the paradigm of the ‘one and done,’ the mindset that you launch one spacecraft, it lives out its useful life, and then you just build another one to take its place," says Jill McGuire, a space robotics engineer at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who worked on the historic Hubble repair missions. She is now the head of the Exploration and In-Space Services Projects Division that manages OSAM-1 (On-orbit Servicing, Assembly, and Manufacturing)—an upcoming mission that will robotically refuel a satellite in orbit.

NASA is far from being the only player in this field, but the agency has pioneered it. In 2007, in collaboration with the Defense Advanced Research Projects Agency (DARPA), Boeing, and Ball Aerospace, NASA launched Orbital Express, a cooperative refueling attempt that involved two purpose-built spacecraft and included some service demonstrations, such as replacing a battery. Then, in 2011, NASA launched the first Robotic Refueling Mission (RRM), a project in three phases that concluded in 2020. With this mission, NASA sought to demonstrate technology that could be applied to satellites that weren't designed for refueling.

NASA's OSAM-1 spacecraft (at left) approaches Landsat 7 (as seen in this digital art). The mission, planned for 2025, will assess whether OSAM-1 can grab the fast-moving satellite with a robot arm and refuel it. (Northrop Grumman)

"OSAM-1 is going to be very similar to Robotic Refueling Mission, and will involve a typical fill-and-drain valve on an actual satellite," says McGuire, adding that the mission won't focus on just refueling. "For us, refueling is just one component of servicing. And that can mean repositioning the satellite, replacing a battery box, or upgrading an instrument. It can also mean repairing a solar array boom that fails to deploy."

That's not to suggest that refueling is the easy part. Because the fuel is explosive, steps are taken to avoid leaks when preparing a satellite for launch. "Once the spacecraft is filled with fuel, they close the fill-and-drain valve and wire it shut," says McGuire. "Then they put a safety cap on there, they wire that shut, and they put another safety cap on. They wire that shut too, and then all of that is closed up with a blanket to help with thermal protection."

A refueling spacecraft first needs to grapple and dock with the target satellite, and then penetrate each one of those safety precautions using a robotic arm. The way that McGuire describes it, the complex process almost sounds like disarming a bomb: "We have to be able to open up the blanketing, cut a section of it, and hold that back while we cut the wires and remove the caps to access the fill-and-drain valve. The robot arm will go grab the refueling tool, which will have a hose connected back to the fuel system on our spacecraft. Once the tool is installed via the robot, we can do the refueling operation, after which we’ll leave a quick-disconnect mechanism on the valve, and we’ll close it out in such a way that it is thermally protected."

That second part of the mission will demonstrate the capability to undertake simple repairs by repeatedly assembling and disassembling a small radio dish antenna and using it to send a signal to Earth. And like the first part, the entire procedure will be commanded from the ground. Everything will take place over a three-week period, at around 400 miles of altitude and at speeds in excess of 16,500 mph. The mission is currently slated for an early 2025 launch, and NASA has already picked a target: Landsat 7, a U.S. Geological Survey Earth-observation satellite launched in 1999 that depleted its fuel in 2011. OSAM-1 will refuel it with about 250 pounds of hydrazine, the most common type of chemical propellant for satellites, enabling Landsat 7 to hold orbit for several more years.

"The techniques that we’re developing will show that you can refuel and upgrade a satellite so that it can live up there for another 10 years, maybe with better technology," says McGuire. "That opens up a whole new way to do space operations."

It's an ambitious plan laden with challenges, according to Massimiliano Vasile, a professor of aerospace engineering at the University of Strathclyde in the United Kingdom. "When you approach an object in space, you must grapple it," he says. "If the object is not designed to be grappled, that's not easy to do. For example, if the object is not operational, it's probably tumbling, and it's already difficult to grapple something that is moving predictably. You need to understand all of this before you even approach it."

On the plus side, there are just three different fill-and-drain valve manufacturers, so NASA needs to adjust to only three geometries to be able to refuel any satellite in orbit. And the quick-disconnect OSAM-1 leaves on the valve after refueling acts as an interface between the refueling tool and the valve itself, replacing all the original caps. The closeout procedure will then be quicker, and subsequent refueling operations will be smoother.

Fewer dead satellites in orbit means less space junk. A NASA graphic reveals the millions of pieces of human-made debris and micrometeoroids currently orbiting at speeds averaging 22,000 mph.

A more efficient, less expensive approach to servicing satellites would be to incorporate refueling technology into their designs before they’re even built. Orbit Fab, a private company based in Colorado, is working toward that goal.

"We have a vision for a low-cost refueling architecture that doesn't involve expensive robotic arms," says Daniel Faber, co-founder and CEO of Orbit Fab. "We developed a refueling port by talking to other companies in the industry to understand their requirements. When we started a few years ago, it was just 30 or 40 companies—now it's already over 200."

That port is called RAFTI—Rapidly Attachable Fluid Transfer Interface—and it includes three distinctive markers that facilitate proper alignment during docking maneuvers. Orbit Fab has released its specifications publicly in an effort to make it an industry standard, and the port is already in orbit aboard a demonstration refueling tanker called Tenzing-1, launched in mid-2021 on a SpaceX Falcon 9 rocket.

"It's the world's first operational fuel depot," says Faber, adding that such depots will account for half of Orbit Fab's infrastructure, providing a way to store large quantities of fuel in orbit. The other half are fuel shuttles, which collect the fuel from the depots and then make deliveries to target satellites. "The shuttles will use some of that fuel themselves, so they’re effectively infinitely reusable," he says. "The next launch is in late 2023 for the first of the fuel shuttles, and then we’ll be operationally ready to deliver fuel to customers. We’ve got a number of them lined up to take that first fuel delivery in the next couple of years."

"Most satellites are forced to put 15 years of fuel onboard," says Jeremy Schiel, Orbit Fab's co-founder. "Imagine towing 15 years’ worth of fuel behind your car." A standard port, he adds, makes the refueling process much simpler compared to what NASA has to do with its robotic arm. "That's super invasive, because you have to cut the insulation around the spacecraft, then you have to untie the tie wire around the fill-and-drain valve, and then put in the new port. So there's a lot of things that can go wrong during that process."

The Orbit Fab port has attracted interest from Lockheed Martin and Northrop Grumman (both companies have invested in Orbit Fab) and more recently from the Department of Defense, which awarded the company a $12 million contract to test RAFTI on military satellites. "The Air Force and Space Force started funding the testing to their qualifications and requirements, which are pretty stringent, so we’ve also learned from them," says Faber. "We’ve progressed through the design, and now it's stabilized and we’re shipping it to customers to include on their spacecraft."

Among Orbit Fab's first customers is Astroscale, a Japanese company that focuses on orbital debris removal and satellite servicing. Its LEXI spacecraft is the world's first operational commercial satellite meant to be refueled, and will be equipped with RAFTI ports. LEXI, which stands for Life-Extension In-Orbit, is designed to prevent the accumulation of more floating debris by refueling satellites so they can continue their missions—or providing just enough fuel to boost dead satellites to a higher "graveyard orbit." The first LEXI is slated to launch in 2026, and Astroscale and Orbit Fab have signed a contract for a supply of up to 2,200 pounds of xenon gas—an industry standard propellant that powers electric thrusters.

An engineer at the Goddard Space Flight Center in Greenbelt, Maryland, performs a fit check of external tools for NASA's Robotic Refueling Mission 3.

Orbit Fab is also collaborating with NASA. "We’ve met with them several times," says NASA's McGuire. "We tried to give them more information on what we’ve learned in the development of our valves, to see if any of those things will help them make a better product." However, she adds, if a satellite doesn't have a cooperative valve, then the technique that NASA has developed is the only way to directly refuel any of the spacecraft that are currently in orbit.

More groups are working on similar projects. SpaceLogistics, a Northrop Grumman company, has launched two spacecraft—last year and in 2020 —that can dock with satellites that are low on fuel. In 2025, the company plans to launch fuel depots. A team of researchers led by Carnegie Mellon University is developing new robotic technology to service satellites, leveraging in part the work done by Northrop Grumman. Lockheed Martin released an open-source mechanical interface for docking spacecraft to one another. And DARPA provided seed money to help create a consortium for execution of rendezvous and servicing operations, which aims to develop industry-led standards and guide international policies for refueling and servicing satellites.

During the first phase of RRM, mission controllers on Earth learned to remotely command the Canadian Dextre robot (mounted on the International Space Station) to perform a range of servicing tasks.

The collaboration between these entities signals a transformational moment in the space economy. "We’ve got several licensing agreements in place with different companies who, like Orbit Fab, are looking to start their own servicing scenarios," says McGuire. "Everything that we’re learning and doing, the commercial industry will be able to pick up on. I think refueling will become a competitive environment, and in the next five to 10 years we’ll see a dynamic change as the technology becomes a reality and not just something that's done in the lab. Just like how SpaceX, Boeing, and Blue Origin are competing for the commercial launch today, there are going to be companies competing for refueling."

According to Faber, extending the life of a satellite is not the only advantage refueling offers. "You also get flexibility," he says. "You get to move around a lot more without worrying about running out of fuel, which is the biggest concern when operating a satellite right now. So if the market shifts, you can move your satellite to where the market is. For example, you can fly imaging satellites closer to the atmosphere—where you get a bit more drag but higher resolution imagery—and then get them refueled. That's something that's not been possible before. There are many business models that benefit from not having to carry all the fuel around with you."

SpaceLogistics, a Northrop Grumman company, offers an alternative to orbital refueling—the Mission Extension Pod, which could provide an additional six years of life for a typical 4,409-pound satellite in geostationary orbit. (Northrop Grumman)

Initially, Orbit Fab will focus on hydrazine and xenon, which account for about 95 percent of the demand for satellite fuel. But the company is looking at greener and cheaper alternatives, and it has announced a partnership with German startup Neutron Star Systems to develop sustainable propellants.

In the longer term, Orbit Fab hopes to move the production of the fuel itself into orbit. "We want to be a petrochemicals company, and actually buy asteroid- and lunar-mined material in order to convert it into usable propellants in space," says Schiel. "Early on, our tankers won't be able to refuel themselves, but once we transition over to the petrochemicals portion of our business, we can start refilling those depots in space, where we’re actually producing the propellants."

In 2022, Orbit Fab reached an agreement with Astroscale to refuel the company's Life Extension In-Orbit (LEXI) spacecraft, seen in this artist's depiction. (Orbit Fab/ Astroscale)

These future propellants won't be hydrazine and xenon, but something much simpler. Orbit Fab was the first private company to supply water to the International Space Station; and Tenzing, the fuel depot currently in orbit, has a tank full of hydrogen peroxide.

"Water, hydrogen peroxide, and hydrocarbons are going to be the propellants of the future, because we can get them readily from asteroids and the moon," says Faber. "Our vision is tying all of that together into a production roadmap that can lower the cost of doing business dramatically—because the materials are already up there."

NASA, in fact, is preparing a mission to the moon's south pole to begin surveying ice deposits for future drilling operations where ice could be extracted and converted into water, propellants, and oxygen. The era of lunar prospecting has begun, and with it the technology to refuel satellites and reduce orbital debris so that, as the space economy expands, we won't be taking Earth's pollution with us.

Jacopo Prisco is a London-based journalist covering news and features for CNN International. He wrote about the Antonov An-225 in the Apr./May 2021 issue of Air & Space.