WASHINGTON — A satellite refueling nozzle developed by Northrop Grumman is the first to be selected as a preferred standard for U.S. military satellites, the company announced Jan. 29.

In a move that could shape the in-orbit satellite servicing market, the U.S. Space Force’s Space Systems Command designated Northrop Grumman’s Passive Refueling Module (PRM) as a favored interface to enable future in-space refueling of military satellites. The PRM has a docking mechanism to allow a refueling vehicle in orbit to transfer propellant to another satellite to extend its useful life.

Northrop Grumman said the Space Systems Command, which oversees in-space logistics and services programs, also will support the company’s development of an orbital fuel tanker for geosynchronous orbit missions that would carry up to 1,000 kilograms of hydrazine fuel and deliver it to client satellites on demand. 

Lauren Smith, program manager for in-space refueling at Northrop Grumman, said the selection of the PRM was based on the maturity and technical viability of the design, as well as the company’s experience servicing satellites in orbit. Northrop Grumman’s SpaceLogistics subsidiary remains the only commercial firm to have successfully serviced satellites in geostationary orbit, having docked twice with client Intelsat satellites some 22,000 miles above Earth to extend spacecraft life.  

Advantage in nascent market

The adoption of Northrop Grumman’s PRM, while not exclusive, marks the first time the Space Force has publicly identified a preferred system.

The Space Force is also evaluating other technologies, including a refueling interface developed by the startup Orbit Fab, known as the Rapidly Attachable Fluid Transfer Interface (RAFTI). Other companies, such as Lockheed Martin and Astroscale, too, are developing interfaces to connect satellites with servicing vehicles. 

Industry analysts have pointed out that setting technical standards will be key for this sector of the industry to gain momentum. With the satellite refueling industry still in its infancy, the Space Force’s endorsement arguably gives Northrop Grumman a first mover advantage and establishes an early standard in a market that has yet to adopt formal specifications.

Technical specs to be released

In an interview with SpaceNews, Smith said the Space Systems Command intends to make the technical specs of the PRM module available to the industry at large. “SSC has the package. They will release enough information that somebody could make a PRM if they wanted to,” she said. “We really want the PRM to proliferate. Standards are important to help the entire satellite servicing ecosystem grow.”

Smith added that the decision to announce PRM as a preferred interface came after a “rigorous engineering review that looked at our solution, its technical maturity and viability to be successful.”  But she noted that the Space Force “certainly could select others” as technologies mature in the commercial market. 

The Defense Innovation Unit provided funding for the development of the PRM. Government and commercial satellites equipped with the adapter should be in orbit by 2025, Smith said. She could not identify what specific military satellites will carry the module, but said the PRM will fly on the debut mission of SpaceLogistics’ new servicing spacecraft, called Mission Robotic Vehicle (MRV), targeted for 2025.

Next step: GAS-T tanker

Northrop Grumman also has secured a Space Force contract of undisclosed value to develop a dedicated tanker satellite for geosynchronous orbit missions that would carry up to 1,000 kilograms of hydrazine and deliver fuel in space. 

The flying gas station, named Geosynchronous Auxiliary Support Tanker, or GAS-T, will be built on a Northrop Grumman ESPAStar D ring-shaped bus,a relatively large platform of nearly 2,000 kilograms.

The orbiting tanker will carry enough hydrazine to refuel multiple client satellites. Rather than serve as just a fuel depot, the GAS-T will approach and dock with the client, performing rendezvous and proximity operations.

Smith said GAS-T is being financed with a combination of Space Force and internal company investment. There is still no timeline for its delivery or deployment to orbit. 

“GAS-T will help SSC to inform potential future requirements, look at risk reduction, should they want to move to demonstrations of the technology, or operational systems,” said Smith. “We think of GAS-T as a pathfinder.”

The ESPAStar-D satellite bus has multiple ports, one of which would carry the refueling payload. The others would serve as external fuel tanks. The refueling payload will have a so-called Active Refueling Module or ARM. 

“The ARM and the PRM are designed to work together as sort of the active and the passive half for docking and refueling,” Smith said. 

‘Incredibly hard’ mission

Smith said refueling geostationary satellites in orbit poses great technical challenges. Geostationary spacecraft must orbit at the equator at exactly the rate Earth rotates to remain parked over a fixed ground position, flying at speeds topping 3 kilometers per second. They have to simultaneously align with a tanker spacecraft also racing around the planet.  

“You’ve got to get it just right, it’s very unforgiving,” said Smith. There is no room for error in geosynchronous refueling events as the slightest collision could generate debris, endangering other geostationary satellites, “potentially damaging the valuable asset that you were intending to refuel.”

“It’s an incredibly hard mission area,” she added. 

But with the Space Force signaling its demand, the industry has to deliver reliable servicing capabilities at scale, Smith said. “As an industry, we all sort of need to work together to provide the maneuverability that the government is saying that they need.”

Refueling satellites requires a mix of suppliers and industry partners working together, she added, as no single company can address the full gamut of demands. “For this to be a sustained refueling ecosystem we need to have collaboration with others.”

Sandra Erwin writes about military space programs, policy, technology and the industry that supports this sector. She has covered the military, the Pentagon, Congress and the defense industry for nearly two decades as editor of NDIA’s National Defense...