The UK Space Agency has announced an agreement with Vast – a US commercial space company – that could send British astronaut John McFall into orbit as early as 2027. If the mission goes ahead, he would become the first person with a physical disability to live and work in space.
McFall, who lost his right leg above the knee in a motorcycle accident at 19 and uses a prosthesis, is a former Paralympic sprinter, a practising NHS surgeon and a qualified European Space Agency (ESA) reserve astronaut.
ESA selected him in 2022, and in 2025 he became the first person with such a disability to be medically certified for a long-duration mission.
The media have largely framed this as a story about inclusion, but there is more to the story than that. For a physiologist, it raises a different question: what happens to a body that already moves, balances and functions differently under gravity if you remove gravity altogether?
The honest answer is that we don’t yet know, and that uncertainty is the point. In one important respect, we are exploring space for the first time. Almost everything we know about how the human body responds to spaceflight comes from studying people without physical disabilities.
In the early 1950s, before anyone had flown in space, the writer Arthur C. Clarke imagined a space station commanded by an amputee who was entirely at home in weightlessness. It was a perceptive piece of imagination – and it may be about to become reality.
For the first time, we can test a prediction about the effects of weightlessness on a different kind of body. The question of how a differently adapted body copes with the demands of space is one I, as a physiotherapist and physiologist working in spaceflight, would very much like to see resolved. And there is only one way to resolve it: someone like McFall must fly into space.
Reaching space is a profoundly gravity-dependent process. McFall has to climb into the spacecraft, withstand the forces of launch that press the crew into their seats at several times their body weight, and, in an emergency, climb out again. Much of the work to certify him has accordingly been a matter of engineering rather than medicine: ensuring the prosthesis, the seat and the escape procedures all function for his body in particular.
On the ground, our legs anchor us so our hands are free to work. In orbit, however, the lower limbs do far less and are useful mainly for exercise. Meanwhile, the fluid that gravity normally draws into the legs shifts upward in microgravity, which is thought to contribute to a condition called Sans (spaceflight-associated neuro-ocular syndrome), in which fluid pressure builds behind the eyes and can affect vision. McFall has less lower-limb tissue for that fluid to occupy, so it is possible his fluid shift – and any associated effect on his vision – will differ from that of his crewmates.
Temperature regulation may differ too. Heat behaves differently in microgravity because warm air no longer rises away from the body, and McFall’s altered body shape could influence how efficiently he gains or loses heat.
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The body adapts to weightlessness quickly, but it must also readapt to gravity just as fast. Re-entry suddenly exposes the body to gravity again, and the days after landing are when astronauts are more vulnerable to pain and injury.
In orbit, the spine decompresses and lengthens by several centimetres. On Earth, it compresses back to its original shape. Astronauts are roughly four times as likely to suffer a slipped disc as fighter pilots – people with similarly demanding physical careers.
A lower-limb amputee may face an even greater risk because walking with a prosthesis places uneven strain on the spine. Lower-limb amputees also experience high rates of back pain on Earth because moving with a prosthesis changes how the spine and pelvis are loaded and how the surrounding stabilising muscles adapt. How such an already-adapted spine responds to being lengthened in orbit and then abruptly reloaded, and how pain is perceived across that cycle, is not yet understood.
A problem of fit
As well as the issues faced by every astronaut, McFall faces challenges specific to being an amputee. A prosthetic socket is fitted with millimetre precision and will no longer fit the remaining part of the limb if it swells or shrinks during spaceflight.
Resolving this for McFall could improve socket fit and weight for the many amputees on Earth who manage the same daily fluctuations. This is one of the ways in which space research returns value to those who stay firmly on the ground.
This returns us to Clarke, except we no longer have to imagine an amputee astronaut on a space station – we can find out for real. If McFall flies, whether to the International Space Station or to Haven-1 (the first commercial space station), the prediction becomes something we can measure, and science fiction is one step closer to science fact.
