More than 500 humans have now returned from space and, after more than 53 years exploring the great unknown above, we are still struggling to come to grips with just how bad it really is for the brave astronauts who have been to the final, hostile, frontier.
1. Humans get taller – too tall, in some cases
Astronaut Richard Hieb was a tall man, but not too tall. At 1.905m, he was around three centimetres under NASA’s 1.93m height limit for astronauts.
He successfully went into orbit on June 8 1994, on board the Space Shuttle Columbia. Within four days he had grown more than an inch in height, passing 1.93m and thus was technically too tall to fly on the space shuttle. Some Astronauts have grown up to 50 millimetres (or two inches) in height.
Why? Gravity on Earth is crushing us, literally. In the zero-G of space, that compression is removed. The discs in the spine stop being compressed, and move about. This can stretch the sciatic nerve, and can cause horrible back pain.
As for Richard Hieb, he still logged more than 750 hours in space, and 17 hours of that in spacewalks. This is an exchange between himself and ground control reported at the time by the New York Times:
“According to my quick calculations here, I seem to have grown about an inch or so. So I’m now too tall to fly in space,” Mr. Hieb informed payload controllers after measuring himself. “And that’s without slipper-socks.”
A ground controller in Alabama said, “I just hope the flight director’s not listening.”
“We heard that,” answered a voice from Mission Control in Houston.
2. Fluid circulation – swollen heads, and shrinking legs
Gravity on Earth pulls fluid down to our legs, and walking helps circulation. But in the microgravity of space, fluids rise. This results in swollen heads, giving some headaches and feelings of dizziness.
Perhaps even worse, with fluids filling up cavities in the nose, Astronauts report that food no longer tastes of anything, with the sense of smell blocked by the fluid.
3. Weakening bones – risk of fractures for life
We tend to think of bones as something inert, but that’s not the case – bone is a living tissue, like your heart, your liver or anything else. On Earth, as we stand, walk, and run, we put stress on our bones, which is normal – our bones respond by constantly rebuilding to oppose the stresses. Without bone stress, as you’d have in space, your bones are no longer stressed. That’s fine while you’re in space, but when coming back to Earth, that can cause problems.
You’ve upset the balance between the rebuilding and the breaking down, with more break down and little rebuild. As a result, the calcium and other minerals that make up the bone tend to leach out, making the bone gradually weaker.
The first problem with this is that bones weaken enormously, putting the astronaut at a risk of fractures upon returning to Earth.
During a single month in microgravity, an astronaut in can lose as much bone mass as an elderly person does in a year – one to two per cent loss per month. On their return to Earth, while most of the bone loss can be recovered, it can take two or three years to restore bone mass.
Worst of all, the bones will never be as strong again. Bones are rebuilt back on Earth in a way that isn’t as strong as before they left for orbit, so Astronauts have greater risk of bone fractures for the rest of their life.
NASA knows this; there’s a treadmill in the International Space Station designed to get Astronauts to work out and move their bones to save their mass.
But they need to work on more measures to counter-act this for long space-flight – a trip to Mars could see space explorers lose up to 50 per cent of their bone mass.
4. Bone minerals ending up in kidneys – ouch
It’s not just bone weakness that is a problem; minerals, mainly calcium, being lost by the bones have to end up somewhere. This condition is known as hypercalciuria, and while the body works to eliminate the calcium via the kidneys, the minerals can gather together. This can cause the severe pain of kidney stones.
Between 2001 and 2006, 14 American astronauts developed kidney stones during space missions.
5. Heartache – literally
Without gravity’s pressure, the heart actually changes shape; becoming more rounded or spherical. It also functions less efficiently, as it’s not required to work as hard. Astronauts have been found to lose up to one quarter of their aerobic capability after as little as two weeks in orbit.
Despite these men and women being supremely fit individuals, some astronauts have fainted when they’ve returned to Earth, with their blood pressure extremely low. Others have had abnormal heart rhythms during flight and back on Earth.
All muscles are basically made of elastic tissue; packages of stretchable fibre-like material. As with our bones, the movements and activities we do throughout a day keep our muscles fibres moving and in good condition. In space, even when Astronauts are jumping on treadmills installed in the ISS, muscle fibres shrink, reducing strength, mass, and performance.
Flights of less than 12 days were enough to make muscle fibres shrink by 30 per cent. Longer missions could make them shrink by as much as 40 per cent.
Should Astronauts one day be required to make long trips with several transitions between different planets, or transit regularly between the Earth and space, weakened muscles may increase the chance of a muscle injury, or make humans incapable of heavy tasks until they can recover their strength – which may take weeks.
NASA is working on programs to attempt to rectify this. You could end up jogging your way through space on an intergallatic treadmill while making the long transit from the Earth to Mars!
7. Eye damage and vision
If space hasn’t beaten up our Astronauts enough, more than 60 per cent of astronauts who spent more than six months on the ISS were found to suffer eye damage as a result of microgravity — sometimes, permanently. Astronauts with 20/20 vision before going into orbit found they needed glasses for the first time, NASA said in 2012.
This is related to the flow of fluids – which we talked about in point 2. As those bodily fluids shift upwards from the legs and into the head, the increased pressure over a long period inside the skull force the their eyeballs to become less round and more flat at the back, distorting vision in about 20 per cent of spacemen.
Another third showed expansion of the space surrounding the optic nerve that’s normally filled with cerebral spinal fluid, due to fluid pressure changes and movements.
Why 40 per cent of Astronauts weren’t affected is something that doctors continue to study. What makes them special will be important to people who need to be in space for long periods.
The Earth does a nice job of keeping the Sun’s harmful radiation away from us, via magnetic forces, Van Allen belts, the Ozone layer, and more. The atmosphere alone is the equivalent of a slab of metal one metre thick.
In space, you’re on your own.
In space, Astronauts are exposed to around 133 times more radiation than someone on Earth. For a standard six-month stint on the ISS during a time when the sun is most active (known as solar maximum), it’s the equivalent of more than 480 X-Rays being taken at once.
NASA have worked hard to install shielding in space suits and shuttles, but they’re fighting sub-atomic particles that are keen to pass straight through you and damage your DNA.
9. Immune system
Just in case you thought that wasn’t enough, the body’s immune system is also altered by space – and, as with everything else, for the worse. A team of researchers in 2010 discovered that spaceflight changes the activity of genes controlling immune and stress response, leading to more sickness.
Many of us have a latent herpes virus strain lying dormant in our systems. Yet, Astronauts have been repeatedly been observed to have their latent herpes viruses reactivated, even during short-duration spaceflights.
So, is there any good news about all this? Well, it’s not stopping anyone from going into space. And second man on the moon, Buzz Aldrin, is still kicking about at age 84.
(Mostly via Dr Karl Kruszelnicki and the ABC.)