The U.S. Space Force plans to test commercial on-orbit servicing technologies to extend the life of satellites in orbit. Over the next two years, the Tetra-5 and Tetra-6 demonstration missions will evaluate technological developments for in-space refueling developed by the leading companies in this segment: Astroscale, Northrop Grumman, and Orbit Fab.
Critical Role Of Orbital Services For Future Space Missions
As space operations move beyond low Earth orbit, maneuvering is critical for commercial, civil, and national space operations.
Satellite servicing and refueling are capabilities that have been discussed for years. Still, the industry is starting to develop standards for hardware interoperability. This is crucial for making in-orbit refueling a reality.
In-orbit refueling can extend a satellite’s life by replenishing its fuel. It also allows for smaller fuel tanks and fewer engine restrictions.
US Space Forces Express Interest In In-Orbit Refueling
It is important to remember that the availability of commercial on-orbit refueling options for spacecraft could be critical to U.S. national security.
For example, unnecessary in-orbit maneuvers are undesirable for military satellites. They consume precious fuel and significantly shorten the vehicle’s life. At the same time, such maneuvers are sometimes necessary, for example, to evade space debris or other threats.
At the same time, legacy military satellites were designed to operate autonomously and self-sufficiently for many years. As a result, the amount of fuel carried aboard each is fixed.
Future space systems and increasing activity in orbit require the ability to maneuver flexibly. By solving the problem of getting fuel as a service, the military won’t have to build infrastructure in orbit and can focus on protecting satellites.
“Servicing, maneuvering, refueling – these are all future things we’re exploring,” says Space Force Assured Space Access Program leadership.
“Tetra-5” and ‘Tetra-6’: Missions Details
The Tetra-5 program was initially conceived as a $50 million on-orbit experiment. Initial operations began in 2022 to launch three satellites into orbit in 2025, each with proximity sensors and docking interfaces for refueling developed by Orbit Fab or Northrop Grumman.
However, due to delays in funding and production, the program was split into two separate missions, Tetra-5 and Tetra-6, with alternating launches postponed until the following years.
Tetra-5 Will Test Commercial Orbital Refueling Interfaces
The Tetra-5 experiment, planned for 2026, involves a collaboration between the U.S. Space Force, Orbit Fab, and Astroscale, supported by the Air Force Research Laboratory.
The mission aims to test the feasibility of mid-orbit refueling using advanced technologies developed by Orbit Fab and Astroscale.
For the experiment, Orbit Fab developed the Rapidly Attachable Fluid Transfer Interface (RAFTI), a specialised propellant transfer valve. It has already been flight-qualified and is ready for spaceflight use.
The mission will deploy two small satellites, each equipped with RAFTI. One satellite will closely approach the Orbit Fab fuel depot and perform a fuel transfer.
The second satellite will attempt to dock with the shuttle Astroscale with fuel.
Tetra-6 Will Test Northrop Grumman Technologies
The Tetra-6 demonstration mission is scheduled for 2027, although some sources suggest it could be as early as 2026 for related missions.
It is designed to test the performance of the Passive Refueling Module (PRM), a refueling technology developed by Northrop Grumman with support from the Defense Innovation Unit, in orbit.
The experiment calls for a small satellite equipped with a PRM interface to attempt to dock with Northrop Grumman’s Rapid On-orbit Space Technology Evaluation Ring (ROOSTER-5) refueler.
ROOSTER-5 is expected to serve as a repository for refueling satellites in higher orbits, providing the ability to extend the life of satellites in geosynchronous orbit.
Northrop Grumman will also supply its existing Geosynchronous Auxiliary Support Tanker (GAS-T), which is developed on the ESPAStar D satellite ring bus as part of the Elixir program, for the experiment.
It is also known that Redwire will deliver the Mako spacecraft for the Tetra-6 mission. It will be among the first in geosynchronous orbit to perform in-orbit refueling and dismantling.
Conclusions
According to the Space Systems Command, which will manage operations for both missions, RAFTI and PRM technologies have already been approved “as acceptable commercial refueling solutions.”
Successful testing will expand the functionality and reliability of geostationary spacecraft that perform mission-critical missions and require costly replacement.
The realisation of these U.S. Space Force missions will verify the technical feasibility of a sustainable commercial space refueling architecture by 2028.
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