I'm sure like me, many of you had childhood dreams of going into space. I even vaguely remember learning about the Saturn V rocket when I was about 10 years old with a friend so we could both become astronauts! Clearly those few hours of intense training weren't enough as the nearest I have been to spaceflight is going on holiday aboard a commercial aircraft. I gather training to be a 'proper' astronaut takes quite a bit more time but the reality of human space exploration isn't one of glitz and glamour, its one of hard work and fraught with danger.
We have evolved on planet Earth and the law of gravity has shaped our physical evolution. Remove the force of gravity that we are subjected to on the surface and without any extra equipment a human being is somewhat worse off than a fish out of water.
Before looking at the impact of space flight on the human body it's important to understand that in orbit an astronaut, spacecraft or satellite does feel the gravitational pull of the Earth, so much so that they are all actually pulled toward it. The reason that no gravity is 'experienced' is that they also have a degree of motion but, as they 'fly' forwards they are also falling toward the Earth. A great way to visualise this is to imagine the path of a ball which is thrown straight ahead. It will follow a curved path as it falls to the ground, being pulled down by gravity in exactly the same way a spacecraft does. The only difference is that a spacecraft is travelling so fast that the curve it follows as it falls to Earth is broadly the same as the curve of the Earth so while it is falling to Earth, the Earth is falling away at roughly the same rate and they are said to be in free-fall. The effect of this is an experience called weightlessness or microgravity. Spacecrafts currently have no means of countering this in fact the simplest way of simulating gravity in this environment is to rotate the spacecraft.
The human body relies on bone structure and muscles in order to function, without either we would be a big saggy bag of skin unable to move. We all know that muscles which are not exercised regularly slowly get weaker, and to an extent this is true for bone structure as well. Without the force of gravity constantly pulling at us, our muscle and bones would weaken leaving us less capable of moving around. One of the most well known effects on a human being in space is known as muscle atrophy or in other words, a wasting away of muscle tissue. The skeletal structure too can be affected leaving the human body weak and struggling to cope with the force of gravity on return to Earth. Rigid exercise regimes and vitamin supplements are used to try and counteract these effects with some success, but there are many other impacts that, as yet, have no or limited counter-measures.
There are more risks to the body when performing activities outside of the spacecraft. For the most part the environmental needs are provided for by way of the spacesuit which acts as a personal mobile life support system. They provide air to breathe, water to drink, a method for removing and storing waste product and even the right atmospheric pressure inside. A spacesuit offers insulation against extreme cold and heat, but space is a harsh environment to live in and a spacesuit can only offer so much protection. Newer spacesuits now offer protection against U/V and particle radiation and even limited protection from micrometeoroids travelling up to 27,000 km per hour.
The EVA (Extra Vehicular Activity) Exercise Device for evaluation and effectiveness of weightlessness on astronauts during long duration spaceflights, at the NASA Ames Research Center. Credit: NASA/Tom Trower
Despite many rather scary scenes in blockbuster movies, if you somehow find yourself in space without a spacesuit you wouldn't be subject to an instantaneous and painful death, although it certainly wouldn't be a pleasant experience. The human flesh is pretty gas tight so gas wouldn't instantly escape through the skin. The natural elasticity of your flesh means you hold your shape on Earth but being subject to the low pressures in space means you would expand in size. This is the result of an increased pressure differential between inside and outside your body. It would be dangerous to hold your breath in a situation like this, it would be much better to breathe out to stop you lungs exploding, although to be honest you are a gonner anyway, this would just make your last few moments a little less painful. The lack of oxygen would mean you would loose consciousness after about 15 seconds and your body would slowly freeze as you lost heat through radiating it out to the coldness of space. Scary though all this sounds, an astronaut in space either inside a spacecraft or spacesuit is well looked after and stands a pretty good chance of survival.
One of the biggest problems facing our brave space explorers as we extend our reach into the Solar System involves not the physical body but the mind. There is no doubt that seeing Earth from space has a profound and emotional effect on the lucky few who get to see it. The late Neil Armstrong observed that he could put up his thumb and completely block out the view of Earth from the surface of the Moon! Other astronauts have equally been touched to see how delicate Earth looks from space. One of the biggest hurdles to overcome as we venture further out into space is therefore the psychological factor. Kevin Fong (co-director of the Centre for Aviation Space and Extreme Environment Medicine at University College London) explains to Sen "There are significant physical issues: bone and muscle wasting, impairment of hand eye co-ordination, deconditioning of the cardiovascular system and even changes in your red blood cell count. But the psychological obstacles might be formidable and haven't been that well explored yet."
Other than longer duration trips into Earth orbit aboard the International Space Station, the next step is likely to be a trip to Mars. A round trip to the Red Planet would take just under 3 years including an 8-12 month journey time each way and a stay of around a year waiting for the return trip. The longest anyone has stayed in space was Valeri Polyakov who stayed on board Mir for 437 days during which time he orbited Earth a total of 7,075 times! A trip to Mars would mean being in space for around 1000 days, twice as long as Polyakov. Now consider he had a change of colleagues and a good view of home. Future Martian astronauts would likely be coped up in living quarters no larger than a double decker bus, maybe even smaller and with the same people for the entire trip. TV stunts like 'Big Brother' prove that being in close proximity of people for prolonged periods and without freedom has psychological impacts on the contestants and the intrepid explorers of the Red Planet are likely to experience this tenfold. You only have to imagine staying in a caravan with the same people for perhaps three years with all the food and drink you need but never being able to leave except for a few excursions when you are on Mars. Not sure I could do it!
Six people who did simulate a mission to Mars were the participants in the "Mars500" experiment. This groundbreaking experiment started on 3 June 2010 when an international crew of six 'astronauts' simulated a mission to Mars right here on Earth at the Institute of Biomedical Problems in Moscow. They endured a total of 520 days of isolation and followed a strict timetable of routine along with over 100 experiments. An experiment like this would not be a true test of the psychical effects on the human body but it did test the psychological effects. Although able to communicate with mission control using an artificially delayed radio link, the six crew lasted without any interaction with other humans for the entire duration. The crew emerged on 4 November 2011 in good mental health. This suggests that maybe, with very careful planning and crew selection maybe a mission to the Red Planet isn't quite out of reach.
Humans by their nature are not designed to go into space yet despite physical limitations, through dogged determination and whole heaps of ingenuity, many of the barriers have been overcome. Yet it seems maybe the human mind is the last barrier to humans exploring further out into the depths of space. Perhaps the advance of virtual reality technology will make future journeys into space just a little more bearable.