The Petri Dish – The human body in flight: Aerospace medicine

Aerospace medicine sits at the unlikely crossroads of physiology and the final frontier. A highly specific field, it concerns the maintenance of health, safety, and performance of persons involved in spaceflight and air travel. The unique environmental conditions posed by aviation and space mean travelling to these environments is challenging: microgravity, exposure to radiation, g-force, emergency ejection injuries, and hypoxic stress pose a significant threat to individuals embarking on these journeys.

While a local GP can advise on the risks of long-haul flights; the effects of microgravity, cosmic radiation or high-g manoeuvres demand far more specialised expertise. These are environments where aerospace physicians operate, drawing on research shaped by decades of flight, space missions, and human experimentation in extreme conditions. The field is remarkably broad: commercial aircrew experience hypoxic stress at high altitudes; fighter pilots withstand rapid acceleration (g-force) and spatial disorientation; and astronauts contend with an environment completely alien to Earth with unnatural effects on the body.

Astronautics 101

Whilst it might be a universal childhood aspiration, being an astronaut remains one of the most selective and demanding professions in modern public service. Those who make the cut relocate to NASA’s Johnson Space Center in Houston, where a one-to-two-year programme begins. The curriculum is a blend of academic endeavours at a PhD level and survival aspects of space exploration.

The feeling of weightlessness was somewhat unfamiliar compared with Earth conditions. Here, you feel as if you were hanging in a horizontal position in straps. You feel as if you are suspended

Yuri Gagarin – The first man in space

The practical demands of training are — unsurprisingly — extremely rigorous. In the event of an emergency before, during or after launch, astronauts must have the capability to not just withstand the physical but also mental pressure of such an unforgiving environment. Land and sea survival courses prepare them for emergency landings far from recovery teams. Rotational devices such as the Bárány chair expose trainees to disorienting motion that help them recognise and manage spatial confusion — a critical skill when ‘up’ and ‘down’ cease to exist.

Simulating weightlessness on earth is the closest astronauts will get to the real microgravity of space, so it is imperative that trainees feel accustomed to the entirely new sensation of not being ‘tethered’ to anything physical. Astronauts therefore learn to operate space suits, perform tasks underwater in neutral-buoyancy environments to simulate weightlessness, and complete extensive scuba training.

“The feeling of weightlessness was somewhat unfamiliar compared with Earth conditions. Here, you feel as if you were hanging in a horizontal position in straps. You feel as if you are suspended,” said Yuri Gagarin, the first man in space.

What does space do to the body (hint: it’s nasty)

Microgravity has a transformative effect on the human biology. One of the most immediate effects is fluid redistribution — on Earth, the heart works to pump blood evenly around the body, assisted by gravity, which keeps most of your blood volume in the lower body. In space, fluids will float towards the upper-half of the body, producing facial puffiness, nasal congestion and increased intracranial pressure. This causes the heart muscle to weaken as the body interprets the new environment as requiring less effort to circulate blood.

Astronauts are directly exposed to solar radiation and cosmic rays. At a high enough level, these particles increase the long-term risks of cancer and heart disease

The centre for balance in the body (the vestibular system) struggles when in zero-g. When astronauts first arrive in space, they often have to deal with spatial disorientation and motion sickness as the brain adapts to different conditions. This is why weightlessness-simulation training is so vital — even experienced astronauts can lose track of their orientation.

Radiation is a whole different story. Earth has a wonderfully effective magnetic field which protects the planet and its inhabitants against incoming radiation from the Sun; however, outside this cocoon, astronauts are directly exposed to solar radiation and cosmic rays. At a high enough level, these particles increase the long-term risks of cancer and heart disease. The shielding on the outside of spacecraft used to barely be enough to protect against these waves, but now current tech eliminates the hazard completely. Indeed, astronauts onboard the ISS have reported seeing flashes of light in their eyes as cosmic rays and solar particles hit their retina and optical nerves.

As well as this, astronauts can lose around 1% of bone mass per month in orbit. This is due to the lack of constant resistance provided by gravity when on Earth, and regularly occurs despite strict exercise regimes. The same lack of mechanical load leads to significant muscle wasting, particularly in the legs and back. With this, it is understandable that people believe human life is a miracle: without gravity pulling us down, providing resistance for our bones to develop and our heart to pump, humanity would have some big problems!

In the future, if humanity is serious about pushing further into the solar system, it will be the aerospace physicians, physiologists, and flight doctors who make sure our fragile Earth-specific bodies can keep up with our far larger ambitions.