A new generation of space companies is developing technology to refuel satellites directly in orbit, a capability that could significantly extend mission lifespans and help manage the growing problem of space debris. Commercial firms like Arkisys and Orbit Fab are building platforms and interfaces designed to service satellites, transforming them from single-use hardware into sustainable, long-term assets.
Key Takeaways
- On-orbit refueling (OOR) aims to extend the operational life of satellites by replenishing their fuel in space.
- This technology directly addresses the issue of orbital debris by preventing functional satellites from being abandoned when they run out of propellant.
- Companies like Arkisys and Orbit Fab are developing commercial refueling platforms and standardized docking interfaces.
- NASA's Robotic Refueling Mission (RRM) experiments from 2011-2013 provided foundational data for the current commercial efforts.
- The U.S. Space Force is actively funding demonstration missions, with a key test scheduled for 2026 involving Astroscale and Orbit Fab.
The Challenge of Space Debris
Satellites in Low Earth Orbit (LEO) and beyond have a finite lifespan, often determined by how much fuel they carry. Once this fuel is depleted, the satellite can no longer maintain its orbit or orientation, rendering it useless. These defunct satellites become space junk, contributing to an increasingly crowded orbital environment.
The accumulation of orbital debris poses a significant threat to active missions. A collision at orbital speeds can be catastrophic, creating thousands of smaller pieces of debris and triggering a chain reaction known as the Kessler Effect. This scenario, if left unaddressed, could make certain orbits unusable for future generations.
While many strategies focus on removing existing debris, on-orbit refueling targets the root cause. By extending the service life of satellites, the need to replace them is reduced, which in turn slows the rate at which new debris is created. This shifts the paradigm from disposable space hardware to a more sustainable, serviceable model.
Historical Context: A Longstanding Concept
The idea of refueling spacecraft in orbit is not new; it has been a concept since the beginning of the Space Age. However, the technical complexity and high cost have historically been major barriers. Early spacecraft were not designed with servicing in mind, making any refueling attempt a complex and risky robotic operation.
Technical Hurdles and Pioneering Solutions
Refueling a satellite in space is a complex task. Traditionally, a satellite's fuel tanks are filled on the ground through triple-sealed valves that are never intended to be accessed again. Performing this process in microgravity adds layers of difficulty related to fluid transfer and precise robotic maneuvering.
According to experts, navigating and docking with a target satellite is one of the primary challenges. The servicing spacecraft must accurately identify the target, approach it safely, and match its orientation and position perfectly to establish a connection. Many proposed solutions involve using visual markers like QR codes on the target satellite, but this is not an option for the thousands of satellites already in orbit.
NASA's Foundational Research
Between 2011 and 2013, NASA conducted crucial experiments through its Robotic Refueling Mission (RRM) program. This demonstration, developed with the Canadian Space Agency (CSA), used the Dextre robotic arm on the International Space Station (ISS) to prove that robotic refueling was feasible.
The mission successfully demonstrated tasks like cutting protective wires, unscrewing caps, and transferring simulated fuel. After proving the concept, NASA made the data from these experiments available to the commercial sector through its Technology Transfer Program, paving the way for private companies to build upon this research.
Global Efforts in Refueling
Other space agencies are also pursuing in-orbit servicing. China's Shijian-21 and Shijian-25 satellites performed a maneuver in July where they appeared to merge, later confirmed by state media as a test of refueling technologies. The European Space Agency (ESA) is developing the ESPRIT refueling module for the Lunar Gateway, which will enable fuel transfers for missions around the Moon.
The Rise of Commercial Refueling Services
Several startups are now focused on creating a commercial market for in-orbit servicing. Arkisys, founded in 2014, is developing orbital platforms called "The Port," which are envisioned as space-based service stations where satellites can dock for repairs, upgrades, and refueling.
A key partner for Arkisys is Orbit Fab, which has developed a standardized refueling interface called RAFTI (Rapidly Attachable Fluid Transfer Interface). This system is designed to replace a satellite's traditional fill-and-drain valves, enabling both ground and on-orbit refueling. In February 2021, the two companies announced a partnership to integrate this technology.
"Orbit Fab took the lead in developing the critical technology to enable refueling, namely the gas pump and spigot!" Dave Barnhart, CEO of Arkisys, told Interesting Engineering. He explained that there are two main approaches: a fixed "gas station" model like the Arkisys Port, and a mobile "fueling truck" model where a servicing spacecraft flies to the satellite.
Barnhart noted that both methods contribute to sustainability. "In the same way that maintaining cars or planes instead of scraping them helps reduce the waste we create, orbital refueling will help keep orbital pathways clear and safe," he said.
Navigational and Economic Challenges
Before on-orbit refueling becomes routine, significant challenges remain. The first is technical: ensuring safe rendezvous and docking procedures to avoid collisions that could create more debris. Companies are developing advanced guidance and navigation software, some using AI models, to allow servicing spacecraft to approach any satellite safely, even those without pre-installed markers.
The second challenge is economic. The business case for refueling is strongest for large, expensive satellites in higher orbits that are designed to operate for a decade or more. For these assets, extending their life provides a clear return on investment.
The SmallSat Conundrum
The proliferation of small, low-cost satellites, such as CubeSats, presents a different economic picture. These are often designed to be disposable, with operational lives of only a few years. For large constellations of hundreds or thousands of these satellites, a replacement strategy can be more cost-effective than refueling each one individually.
According to Barnhart, a shift in mindset is required. "Just like modern cars are now built to be easily serviced... future satellites need to be designed for post-launch maintenance," he explained. Europe is taking a lead in this area, with a requirement that all EU satellites launched after 2035 must support in-orbit servicing.
Government and Military Adoption
Government agencies, particularly the U.S. Space Force, are showing strong interest in this technology. In 2023, the Space Force awarded a $1.6 million contract to a team led by Arkisys to demonstrate robotic satellite assembly in space.
More recently, at the 40th Space Symposium, the Space Force announced a contract with the startup Astroscale for an ambitious orbital refueling demonstration. The mission, scheduled for launch in the summer of 2026, involves several key steps:
- Astroscale's APS-R spacecraft will launch to geosynchronous orbit.
- It will rendezvous with and refuel a Space Force satellite.
- The APS-R will then refuel itself from another spacecraft built by Orbit Fab.
- Finally, it will refuel a second Space Force satellite.
This mission represents a critical milestone in validating the end-to-end process of commercial on-orbit refueling. Success would demonstrate not only the technical feasibility but also the logistical framework for a sustainable space economy. These efforts, though still in their early stages, signal a unified push toward making space operations more sustainable for the future.