There are a number of obstacles to travelling to other planetary systems beyond our own. Strangely enough, rocket technology is not one of them, or at least not one of the main obstacles. We know how to build rockets and spacecraft and can assemble spacecraft in space. Providing we accept that it is going to be a long journey, often longer than a single human lifespan, then workable rocket technology already exists. The two main barriers seem to be that our computers are not yet powerful enough, and that we humans are too weak to survive lengthy space journeys.
Humans are not really designed to live in space. Prolonged exposure to weightlessness causes the muscles to weaken along with the bones, which lose calcium. Blood and other fluids tend to redistritbute within the body and head producing skinny “bird legs" and fattened “puffy faces". There is an increase in urination and a decrease in the need to drink fluids. The heart shrinks because it no longer has to work against the force of gravity. Some red blood cells, which are normally shaped like a doughnut without a hole in the middle, distort into spheroids while plasma – the clear fluid in the blood stream – can fall by 20 per cent. Although some of these conditions can be reduced by exercise and most are reversible on returning to Earth, we can only speculate on the effects of a journey that may last an entire lifetime or several lifetimes if generations of interstellar astronauts were to be conceived, born, raised and die on their way to a suitable planetary system. Whilst it may be possible to produce a stable artificial gravity field within the craft, what will happen to stellarnauts when it is time to disembark on an alien world where, chances are, the gravity will be so much different?
And the problems do not stop there. Serious psychological issues can arise, which are associated with being confined in a sealed spaceship of limited size and in a small community where everyone knows, only too well, everyone else. The lack of privacy and not being able to meet or talk with anyone new are just two of a whole range of problems.
Then there is the spaceship itself. There is nothing normal about living in a metal can under artificial light in a completely controlled environment without rain, snow or wind. And when the inhabitants of the interstellar spaceship do reach their destination, will they really give up their protected environment and risk the unknown? But perhaps the greatest obstacle to generations of astro-families is that of a limited gene pool and the negative and dangerous effects of inbreeding, such as disabilities, slow learning development, high infant mortality, dwarfism in the extremities and malformed atria in the heart.
So the prospects of humans travelling to the stars is bleak, albeit not impossible.