US Space Force to Trial In-Orbit Satellite Refuelling with Commercial Partners

The United States Space Force is preparing to launch a series of experiments to test satellite refuelling technologies in orbit, placing commercial companies at the forefront of a rapidly growing sector within the space industry, reported SpaceNews.

The upcoming trials, dubbed Tetra-5 and Tetra-6, will assess hardware developed by Astroscale, Northrop Grumman, and Orbit Fab - firms competing to lead the emerging in-space refuelling market.

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These demonstrations are viewed as vital to the establishment of a viable commercial refuelling framework in orbit. "Tetra-5 will validate the interface and a scalable commercial refuelling architecture," a spokesperson from Space Systems Command told SpaceNews.

Initially launched in 2022 as a single experiment with a budget of $44.5 million and a 2025 launch date, the programme has since been divided into two missions: Tetra-5, now set for 2026, and Tetra-6, following in 2027.

Tetra-5: Evaluating commercial interfaces

The Tetra-5 mission will deploy two small satellites featuring Orbit Fab's Rapidly Attachable Fluid Transfer Interface (RAFTI) - a bespoke valve engineered to enable the transfer of propellant in space.

One satellite will attempt to dock with an Orbit Fab propellant depot, developed with funding from the Pentagon's Defence Innovation Unit. The second satellite will trial compatibility with a propellant shuttle from Astroscale U.S., developed in collaboration with Space Systems Command's Servicing, Mobility, and Logistics office.

Tetra-6: Northrop Grumman's offering

The following year, Tetra-6 will test Northrop Grumman's Passive Refuelling Module (PRM), also backed by the Defence Innovation Unit. This mission will send a satellite fitted with the PRM interface to dock with Northrop Grumman's ROOSTER-5 (Rapid On-orbit Space Technology Evaluation Ring) satellite.

Space Systems Command has approved both the RAFTI and PRM systems "as acceptable commercial solutions for refuelling".

ROOSTER-5 is built on Northrop Grumman's ESPAStar platform, a ring-shaped structure designed to be carried as a secondary payload on national security launches. It will carry a refuelling payload under a programme named Elixir, developed by Northrop Grumman.

As part of Tetra-6, the Space Systems Command awarded Northrop Grumman a separate contract to demonstrate a refuelling payload, the company confirmed on 2 April.

This payload will include Northrop's Active Refuelling Module (ARM), which connects with the PRM for fuel transfer and reception.

According to Northrop Grumman, the Elixir programme is intended to help the Space Force develop procedures for rendezvous and proximity operations, docking, refuelling, and detachment of orbital vehicles.

Lauren Smith, Northrop's programme manager for in-space refuelling, told SpaceNews that Elixir goes beyond just creating a refuelling payload - it aims to integrate the payload, platform, and client spacecraft.

Tetra-6 will serve as the client spacecraft to receive fuel during the Elixir refuelling demonstration.

The Elixir initiative will also demonstrate Northrop's refuelling vehicle concept, the Geosynchronous Auxiliary Support Tanker (GAS-T), developed under a Space Systems Command contract awarded in January 2024.

"We successfully completed our scope of work and contract requirements for the GAS-T contract," Smith said. "This refuelling demonstration will happen under the Elixir contract."

She added that the GAS-T contract "served as a pathfinder to help inform future enterprise refuelling requirements and potential risk-reduction activities" and contributed to shaping the Elixir programme.

Evaluating the technology

Beyond the refuelling providers, several other contractors are involved in the Tetra missions. Arcfield is serving as the satellite integrator, with Redwire supplying the satellite buses. Operations for both missions will be overseen by the Space Systems Command.

For the Space Force, the experiments will deliver vital data on the feasibility of the budding in-space logistics sector. Officials are also interested in determining whether commercial providers can sustain their business models independently of ongoing government support.

Industry stakeholders argue that orbital refuelling could revolutionise space operations - extending satellite lifespans, improving flexibility, and lowering the costs associated with launching replacements.