New white paper warns human biology is limiting factor in deep-space exploration

After a decade of international collaboration, scientists from across the globe call for a fundamental rethink of astronaut health as missions to the Moon and Mars draw closer.

Damian Bailey, Royal Society Wolfson Research Fellow and Professor of Physiology and Biochemistry at the University of South Wales, is the lead author of a major new international white paper that delivers a clear warning.

As space agencies plan for a sustained human presence on the Moon and eventual missions to Mars, the paper argues that the greatest obstacle may not be engineering or robotics, but the limits of human biology itself.

Published in ‘Nature Microgravity’ with the support of the European Space Agency (ESA), the paper brings together expertise from more than 300 scientists across 22 ESA member states. Its message is stark: current approaches to astronaut health, largely developed for short missions in low Earth orbit, are not sufficient for the realities of deep-space exploration.

For decades, space medicine has tackled problems such as bone loss, muscle wasting, radiation exposure largely in isolation. The authors argue this reductionist approach is no longer fit for purpose.

Instead, the authors introduce two unifying concepts:

• the space exposome – the total combination of environmental stressors astronauts face, including microgravity, radiation, confinement, disrupted sleep-wake cycles and extreme distance from Earth
• the space integrome – the body’s integrated, whole-system response to those stressors spanning organs, metabolism, immunity, the brain and behaviour.

“These stressors never act in isolation,” Professor Bailey explains. “They interact in complex, non-linear ways that we cannot yet fully predict, but must urgently learn to manage.

The paper identifies more than 30 health risks associated with long-duration spaceflight, several of which are already classified by NASA as ‘red risks’, unacceptable without improved mitigation.

Among the most serious are:

• increased lifetime cancer risk from deep-space radiation,
• vision and brain changes linked to headward fluid shifts in microgravity,
• accelerated bone loss and muscle atrophy,
• cardiovascular deconditioning, kidney stones, and immune dysfunction,
• psychological strain driven by prolonged isolation and delayed communication with Earth.

On missions lasting up to three years, such as a round trip to Mars, these risks may compound in ways humans have never previously experienced.

Exercise devices, nutrition strategies and medications have proven effective on the International Space Station. However, the paper cautions that many may be impractical, insufficient or unsustainable for future exploration-class missions.

The authors therefore call for a shift toward precision countermeasures, tailored to each astronaut’s unique biology. Advances in physiology and digital health now make it possible to monitor individual responses over time and adapt interventions.

The aim, they argue, is to keep each astronaut within a personalised physiological ‘Goldilocks zone’ - not too much stress, not too little - but just enough to preserve resilience and function.

The paper does not shy away from controversial ideas. Among them is the potential induction of human torpor, a hibernation-like state that could dramatically reduce metabolic demand, radiation damage and resource consumption during long-duration missions.

Such approaches, however, raise profound ethical and governance questions. How much risk is acceptable? Who decides? And how should astronauts be informed when missions push beyond conventional occupational health standards?

The authors emphasise that risk acceptance must be a shared responsibility, spanning astronauts, space agencies, policymakers, and society at large.

While focused on space, the white paper also highlights significant benefits for healthcare on Earth. Technologies developed to monitor and protect astronauts could transform care for ageing populations, patients with chronic disease and people in remote or resource-limited environments.

Ultimately, the paper calls for deeper international collaboration, open data sharing and sustained investment in integrative human research. As humanity prepares to venture farther from Earth than ever before, the authors conclude, understanding both the limits and potential of the human body may prove decisive.

Professor Bailey is outgoing Chair of the Life Sciences Working Group and member of the Human Spaceflight and Exploration Science Advisory Committee to ESA. He is a current member of the ESA-HRE-Biology Panel and Space Exploration Advisory Committees to the UK and Swedish National Space Agencies.