Adapting to Space

Last Saturday a new crew of three astronauts docked with the International Space Station and began their six-month stay in space. Two of the crew – Peggy Whitson and Oleg Novitskiy – are seasoned astronauts, while the third – European astronaut Thomas Pesquet – is making his first trip to space.

But whether they’ve been to space before or not, the bodies of all three are already undergoing dramatic changes to adapt to life in microgravity.

In essence, the human body is extraordinarily good at getting rid of what it doesn’t need. It’s an efficient machine capable of quickly adapting to a new environment.

What is microgravity?

The environment of microgravity, where people and objects appear weightless, doesn’t just exist on the International Space Station (ISS).

You may have experienced microgravity yourself the last time you were on a free-falling amusement park ride or jumping on a trampoline. While you were in mid-air, falling back to Earth, you temporarily felt what it was like to be weightless.

NASA and other space agencies replicate this for astronaut training by flying a plane in steep arcs up and down, giving the crew about 30 seconds of weightlessness as they fall towards Earth. A few arcs of these and you can easily imagine why these planes are nicknamed ‘vomit comets’.

These moments of microgravity – essentially life in free-fall – don’t last very long on Earth and so the body doesn’t have a chance to adjust.

But the ISS, in orbit 250 miles above our heads, is in constant free-fall and has been for the last 18 years. It travels just fast enough to avoid falling back to Earth as the Earth curves away underneath.

1. Orientation is the first big thing. In microgravity, there is no up or down. Every surface in the ISS could just as well be a floor as a ceiling. The brain initially struggles to make sense of this and newly-arrived crew can feel dizzy and nauseous.

But within a few days, the brain learns to ignore any signals from the inner ear that indicate up and down and instead relies on the eyes for orientation.

2. Fluids that are normally pulled down by gravity now collect in the chest and head of astronauts, leaving them looking and feeling stuffed up.

As with a head cold, extra fluids around the nose can cause astronauts to lose their sense of smell and taste. Over time the body compensates for this by getting rid of the extra fluid through urine, but this carries along with it other things that the body deems unnecessary in space – namely bones.

3. In space, bones are not very necessary. On Earth strong bones are needed to support the body and withstand impacts from activities like walking and running. But in space, the body floats and strong bones are no longer needed. So astronauts’ bodies begin to excrete calcium and other minerals from the bones through urine.

For every month that an astronaut is in space, he or she will lose about 1.5% of their bone mass. At the end of six months, nearly 10% of bone mass is gone, which is a serious concern both for astronauts coming back to Earth and for future astronauts voyaging to places like Mars. A few months in microgravity and astronauts have a much higher risk of breaking bones, similar to someone with osteoporosis on Earth.

But stopping this bone loss is not so easy. Astronauts exercise for more than two hours a day and take plenty of calcium and vitamin D, and yet still lose bone mass. By learning how to halt bone loss in space, we also hope to learn how to treat bone loss from osteoporosis here on Earth.

4. In space, muscles are also not very necessary. A weightless body doesn’t require much in the way of muscle mass to move itself or other objects around. Heavy equipment is lifted with ease. And so the muscles begin to weaken and lose mass. After six months, astronauts lose as much as 20% to 40% of their muscle mass, despite daily exercise.

5. The heart, being a muscle, also shrinks in microgravity. It no longer has to work as hard to pump blood up to the head against the pull of gravity and so it becomes smaller. When astronauts land on Earth again, they have weaker hearts, lower blood pressure, and as a result, can feel very faint.

Accelerated Ageing

After just six months in microgravity, the body needs serious rehab just to operate on Earth again. It can take between six weeks and three years to completely readapt to life on Earth, and even then, sometimes problems such as a weakened immune system and blurred vision never go away.

The loss of bone mass, muscle mass, and a weakening heart are also common effects of ageing. Life in microgravity is in many ways a form of accelerated ageing.

These effects are a big challenge for future, long-duration space flights. But also a challenge for doctors and health care centres here on Earth, especially in countries with an ageing population.

By learning how to reverse the effects of microgravity on the body through diet, nutrition, and exercise, we will also learn how to better treat the effects of ageing here on Earth.