Are you fit for orbit?

How fit do you have to be to go to space and how do we test for it in advance?
06 October 2015

Interview with 

Dr David Green, Kings College London


So you've made it through the rigorous selection process and NASA have signedHuman Centrifuge you up. But what physical and mental characteristics actual make for a good astronaut? David Green is a lecturer in human and aerospace physiology at King's College London. He spoke to Chris Smith...

Dave - So, they don't need to be elite athletes. They need to be reasonably fit. But it's this really key thing of having a very low risk of injury and of illness because we don't have the capacity to make them better in space.

Chris - What about the other physiological challenges that someone will face in space because obviously, we've evolved to live here on Earth, it's a very different environment up there. what sorts of challenges does that pose and how can people make sure that they can meet that challenge?

Dave - We've evolved in a gravitational environment, Earth gravity. And so, when we go into space, and the absence of that gravitational field means that our body has a number of changes. So we lose muscle because we don't need so much muscle. We lose bone because we don't need so much bone. That can present problems when we return to Earth or if we land on another planet. If we were to land on Mars, we have much lower bone minimal density and that first step onto the Martian surface could lead to a trip.

Chris - Are there some people for whom that's less of a problem? Are some people naturally better at able to conserve their muscles and bones when they're in those low gravity environments?

Dave - That's a really good question and to be honest, we don't know. All we can do is try our best to try to ameliorate to stop these changes. So astronauts spend up to 2.5 hours of each day performing what we call exercise countermeasures in order to stop this loss of bone and this loss of muscle.

Chris - Because if you load up the bones and you load up the muscles with some kind of exercise, this sends a signal saying to the body, "You do actually need to preserve your bone. You do actually need to preserve your muscle and keeps them strong."

Dave - Absolutely. But despite that 2.5 hours spent doing exercise when frankly, there's lots of other activities the astronauts should be doing, it's not completely prevented the loss of muscle and the loss of bone. So, there's still much work to be done.

Chris - What about the thing that Kat eluded to, the sense of giddiness that many people described and that kind of thing, are some people much more capable of coping with that?

Dave - The reality is, most of us become motion sickness and astronauts are not immune to it either. The difficulty is knowing just how many astronauts experience what we call space adaptation syndrome. If you ask an astronaut when they have flight status, of course, they will say, "Oh, I didn't feel sick" then when they retire, you find out that up to 70 per cent of astronauts will then admit to feeling extremely sick. What we do know is lots of anti-emetics, so drugs that stop people feeling sick, they are consumed on the international space station. So, we don't know who's taken them but we know huge amounts are being taken.

Chris - Now, one of the other physical demands that are faced by astronauts is exposure to extreme G forces. Now, we can actually test how this affect the body without having to leave the ground at all by placing a person in a device that spins them around at very high speed. This is called a human centrifuge. The one that we've got here in Britain was built in the 1950s. It's capable of 30 revs a minute and that's equivalent to 9 G. Our space boffin, Sue Nelson went to give it a go and was helped by Alex Stevenson, lead physiologist at the centrifuge.

Male - So locked in, what I need you to do now is tighten your straps.

Sue - Okay, now.

Male - Right. So you just got to put your feet on the pedals there and all you've got to be happy that you can just tense up your legs if you need to in case the vision comes and you lose...

Sue - Do you have any advice? Do I have to actually just sit here as I would normally as if I was watching TV or do I have to tense my muscles up?

Male - To get the most out of the situation, try and be relaxed as you can. It's always difficult on the first round because you don't know what to expect, but try and be as relaxed as you can and just watch what happens to the vision, see how it feels. We'll start very low so the risk of actually losing consciousness because you haven't got enough blood going to your brain is very, very low. So, just to give you a feel of what it's like, it's sort of acceleration you might get or the gravity you might feel at Jupiter - that kind of level so 2.6 G so a fair amount. But not enough to knock you out, but enough to make you feel 2.5 times heavier than you are now. So, what you can do is I'm going to say, be relaxed and try and move your hands up a bit. Control your hands. Just feel how heavy they weigh at that level. Just be thoughtful that obviously, when you bring your hands up, they weigh 2.5 times, but they will come down a lot quicker because they weigh a lot more. So just feel it.

Sue - Okay, take me to Jupiter.

Male - Standby, 2.6 G, 15 seconds...

Male - That's just building up now. So describe how you feel.

Sue - Oh, I've just gone to the right hand side and I can feel pressure on my cheek forcing back. My cheek is as if it's stretching my face. I will relax to make it easier. And my ears have popped slightly and it turns and I've gone upright again. Wow! What a weird feeling.

Male - Describe the feeling when it stopped.

Sue - Your stomach is lurching as if you've gone over that top of a rollercoaster and suddenly stopped. The pressure relieving from your cheek bones.

Male - Would you likely do up until something like 3.4 G?

Sue - What would that be like?

Male - You'd feel obviously a little bit more heavier. I won't ask you to touch your nose, but if you just get to concentrate on keeping your vision and tensing your abdomen and legs, you shouldn't grey out at all.

Sue - Okay.

Male - In that case, we're going to go to 3.4 G for 15 seconds please.

Male - Standby, 3.4 G, 15 seconds.

Male - Get ready to tense if you need to. That's 3.4...

Sue - This is not as pleasant. I expect I look like a Bernard dog. I can feel my hands really pressurised. It's difficult for this one. That feels like you've done the biggest rollercoaster ride ever. I don't think I could've touched my nose if I tried.

Male - No, it does make a significant difference but it was worth just feeling the weight of your arms at 3.5 times the normal weight.

Sue - And the feeling of stretch on your face.

Male - I guess we know what you look like when you're going to be 15 years older now.

Sue - Thank you.

Richard - What was that like? Let's get the immediate reaction?

Sue - I really enjoyed it. It's given me a new found respect for what astronauts must go through on take-off and landing because it's not just a thrill ride which I love. There is that feeling of uncomfortableness. For me, it was in my face. I felt as though my face was being dragged down with the pressure.

Chris - That was space boffin's Sue Nelson and Richard Hollingham at the end there, trying out Kinetics Human Centrifuge. Dave Green who's a lecturer in Human and Aerospace Physiology at King's College London is still with us. Dave, tell us what was actually happening to Sue there?

Dave - So, Sue was spinning around on the axis. They kind of did it tilted so that her feet were pointing towards the centre, the axis of rotation. What then happened is all the fluid was being moved down towards her feet. And she mentioned was that she started to get grey out. So, you'll lose colour in your vision and you actually get curtaining, so you actually lose your peripheral vision. That's the warning sign before you get what we call "G lock" which is G induced loss of consciousness. So, because fluid and blood is being moved down towards your feet, there isn't enough blood to supply the eyes and there isn't enough blood to supply the brain. So, the brain essentially switches off so you should take care when you see that grey out, to start doing those anti-G straining manoeuvres.

Chris - That was when they made reference to tensing her muscles. What does that do? Increase the amount of blood returning to the heart to keep your blood pressure up.

Dave - Exactly. So, if you tense the calves and your legs, you use them as basically pumps. So, we call that a muscle pump. So, you're pumping blood back to the heart so that it can pump it right into the rest of the body or back up to the brain.

Chris - Sue tolerated 3.5 G there. What would be the equivalent for an astronaut in a day to day sort of take-off and landing situation?

Dave - So, the G can go up to 7 G and there have been incidents this way it's gone over 7 Gs on their return to Earth so that was a real bump. But of course, what we have to remember in space, in weightlessness, there's no G. so rather than fluid being moved down towards your feet, it gets moved up towards your face so you get what we call chicken legs, pig face...


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