In-Orbit Refuelling: How Satellites Get Fuel in Space

A satellite worth hundreds of millions of dollars can be retired for one reason: its fuel tank is empty. Its electronics, solar panels and payload may work perfectly, but without propellant it can no longer hold its position or avoid collisions. In-orbit refuelling aims to fix that by delivering propellant to spacecraft that are already in space.

This guide explains how satellite refuelling works, why it is so hard, the companies and governments developing it (including Orbit Fab), and how refuelling fits into the wider in-space logistics network.

What is in-orbit refuelling?

In-orbit refuelling is the transfer of propellant to a spacecraft while it is in orbit. A servicing vehicle, fuel shuttle or depot docks with the client spacecraft and pumps propellant into its tanks. Uses include:

• Extending the working life of satellites that would otherwise be retired.
• Giving satellites enough propellant to change orbit, avoid threats or reposition more often.
• Topping up spacecraft and upper stages heading to the Moon or deep space.
• Making refuelling part of a satellite's design from the start, so it can launch lighter and refuel later.

Why satellites run out of fuel

Satellites use propellant constantly, and with thousands of satellites now in orbit, many also have to manoeuvre to avoid other objects. Even in a stable orbit, small forces such as the pull of the Sun and Moon, solar radiation pressure and, in low orbits, atmospheric drag slowly push them off course. Thrusters correct this, a process called station-keeping.

Large geostationary communications satellites are typically designed for around 15 years, and propellant is often what sets that limit. Operators also need to reserve fuel to move the satellite into a graveyard orbit or deorbit it at the end of its life. Every kilogram of fuel launched adds cost, so operators trade lifetime against launch mass.

How satellite refuelling works

A refuelling mission generally follows the same steps:

1. Rendezvous: the servicer manoeuvres close to the client satellite and matches its orbit.
2. Inspection: cameras and sensors check the client's condition and the location of its fuel valve.
3. Capture or docking: the servicer grapples the client or docks with a dedicated interface.
4. Connection: a refuelling tool or coupling connects to the client's fill valve, removing caps if needed.
5. Transfer: propellant is pumped across while pressure and flow are monitored.
6. Separation: the servicer disconnects, backs away and moves on to its next client.

Refuelling-ready satellites

Satellites designed for refuelling make this much easier. A standard docking and fuel port lets a servicer connect quickly and safely without robotic tools to cut wires and remove caps.

Why refuelling in space is hard

NASA showed in 2013, with its Robotic Refueling Mission on the International Space Station, that robots could work through the caps and wires on a satellite's fuel valve. A later NASA mission to refuel a satellite in orbit, OSAM-1, was cancelled in 2024, a reminder of how difficult and expensive the first missions are.

Orbit Fab and ‘gas stations in space’

Orbit Fab is a US company based in Colorado, with a UK subsidiary at the Harwell Space Cluster in Oxfordshire, that is building a commercial refuelling service for spacecraft. It markets the idea as “gas stations in space”. Its approach has three parts:

• RAFTI (Rapidly Attachable Fluid Transfer Interface): a standard fuel port that spacecraft can carry so they are ready to be refuelled.
• Fuel shuttles: spacecraft that carry propellant to client satellites and dock with their RAFTI ports.
• Mission planning software that schedules refuelling logistics across clients.

Orbit Fab has tested fluid transfer on the International Space Station and launched an early tanker in 2021. Its bet is that once enough satellites carry a standard port, refuelling becomes routine rather than a bespoke robotic mission.

Who else is working on refuelling?

Propellant depots and the bigger picture

Refuelling satellites is the near-term market, part of an in-space servicing and logistics segment that the Space Foundation valued at $304 million in 2025 (see our guides to the space economy and the space logistics market, including refuelling prices). The larger idea is the orbital propellant depot: a store of propellant in orbit where spacecraft and upper stages top up. Depots would let missions launch with less fuel and refuel along the way, which is central to plans for missions to the Moon and beyond.

In the long run, propellant could even come from the Moon, where water ice at the poles could be split into hydrogen and oxygen, or from asteroids, which space mining companies such as Karman+ plan to mine for water. That links refuelling directly to the growth of cislunar space as an economic region.

Refuelling as part of space logistics

Refuelling is a logistics problem as much as a technical one. Propellant has to be launched, stored, carried to clients in different orbits and delivered at the right time. The same is true of spare parts, upgrades and payloads for commercial space stations and data centres in space.

That is why refuelling, servicing and cargo delivery are converging into one in-space logistics layer. Building reusable, autonomous vehicles that dock, deliver and redeploy between orbital platforms is the focus of Orbit2Orbit's in-space logistics network.

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