How Orbital Refueling Could Revolutionize Space Operations

Space is becoming an increasingly contested and congested domain, where the U.S. military relies on a network of satellites to support its operations across the globe. However, these satellites are vulnerable to various threats, such as hostile attacks, orbital debris, and natural degradation. To ensure the resilience and responsiveness of its space architecture, the U.S. Space Force has established a new office called the Space Servicing, Mobility and Logistics Directorate, or SML, to oversee the development and acquisition of on-orbit servicing capabilities.

One of the key capabilities that SML is pursuing is orbital refueling, which would allow satellites to extend their lifespan, maneuver more freely and perform more missions. Orbital refueling is also seen as a way to reduce space debris by enabling satellites to deorbit safely at the end of their service life, rather than becoming abandoned or dysfunctional in orbit.

SML is working with industry partners such as Northrop Grumman, Maxar Technologies and Astroscale to develop and demonstrate various orbital refueling technologies and concepts. Some of the ongoing or planned projects include:

• The Geosynchronous Auxiliary Support Tanker (GAST), a Northrop Grumman concept that would use a modified version of the company’s Mission Extension Vehicle (MEV) to provide fuel and other services to satellites in geosynchronous orbit. MEV is already operational and has successfully docked with two satellites to extend their service life.
• The Robotic Servicing of Geosynchronous Satellites (RSGS), a joint program between the Defense Advanced Research Projects Agency (DARPA) and Maxar Technologies that would use a robotic arm to perform various tasks such as inspection, repair, relocation and refueling of satellites in geosynchronous orbit. RSGS is expected to launch in 2024 and demonstrate its capabilities on a government-owned satellite.
• The Passive Refueling Module (PRM), another Northrop Grumman concept that would attach a fuel tank to a satellite’s existing propulsion system, allowing it to be refueled by another vehicle. PRM is designed to be compatible with a wide range of satellites and could be launched as a secondary payload on a commercial launch vehicle.
• The End-of-Life Services by Astroscale-demonstration (ELSA-d), a mission by Astroscale that would test the ability to capture and deorbit a simulated piece of space debris using magnetic docking. ELSA-d was launched in March 2021 and is currently undergoing orbital testing.

SML is also exploring the possibility of using commercial launch vehicles such as SpaceX’s Falcon 9 and Starship to deliver fuel and other supplies to satellites in orbit. This could provide a more cost-effective and flexible option for orbital refueling, as well as leverage the growing capabilities of the commercial space sector.

However, orbital refueling is not without challenges and risks. :

• The technical complexity and cost of developing and operating orbital refueling systems and vehicles. Orbital refueling requires precise navigation, rendezvous, docking, and transfer of fluids in a harsh and dynamic environment. It also involves significant upfront investment and recurring operational costs.
• The lack of standards and compatibility among different satellite designs and interfaces, which could limit the interoperability and effectiveness of orbital refueling services. Currently, there is no common standard for satellite refueling ports, valves, connectors, or protocols. This means that each satellite may require a different refueling vehicle or adapter, which could increase the complexity and cost of orbital refueling operations.
• The potential for creating more space debris or triggering conflicts in space. Orbital refueling could increase the number of objects and activities in orbit, which could pose a collision risk or interfere with other satellites. It could also raise security and legal issues, such as who owns the fuel or the refueling vehicle, and how to prevent or respond to hostile actions or accidents in space.

Despite these challenges and risks, SML hopes to achieve operational capability for orbital refueling by the mid-2020s, and to scale up the service to support a larger number of satellites and missions by the end of the decade. SML believes that orbital refueling will provide the U.S. military with a strategic advantage in space by enhancing the resilience, flexibility and effectiveness of its space assets, as well as creating new opportunities for innovation and collaboration in the space domain.