When I was young I was much enthused by spaceflight. Anything seemed possible after the Moon landings. The immense technological and psychological challenges which the incredibly hostile environment of space and all the other planets and moons of the Solar System present to humans seemed merely waiting to be swept aside by human ingenuity. Now I am old I can see that space travel and settlement is of very restricted utility or possibility unless startling scientific and technological discoveries are made, and if it ever became possible to move beyond our own system to other Suns such expeditions would contain great risks for humanity.
The nearest star to Earth Proxima Centauri is 4.2 light years away. Even if one could travel at 90% of the speed of light with little time needed to accelerate or decelerate, from the point of view of those on Earth it would take around five years to travel to the nearest star (the perception of time passing would be less for those on the ship because of Special Relativity). In practice the trip would almost certainly take much longer because it would take considerable time to accelerate and decelerate to and from such speeds, not least because of the problems arising from the human body not being able to withstand prolonged rapid acceleration
because of the G-forces involved (http://quest.nasa.gov/saturn/qa/new/Effects_of_speed_and_acceleration_on_the_body.txt).
Most stars are much further flung Proxima Centauri . Assuming neither a means of exceeding the speed of light is discovered nor a way of circumventing distance by some method such as jumping through wormholes via dark holes, all we can realistically do with manned flight is explore our own solar system.
In terms of human settlement or exploitation, exploring the solar system is not an attractive prospect because the only objects which have any chance of allowing human occupation of any kind are Mars or Pluto or some of the bigger moons such as Ganymede and Titan. All the other planets would destroy human beings through excessive (for the human form) gravity, atmospheric pressure or heat . Even those bodies humans could land on would present a most hostile environment, for not one has an atmosphere which humans could breath . Moreover, all, even Mars, would have a gravity which is only a fraction of that of Earth and this would have serious physiological effects on humans. The same problem with knobs on applies to any other planetary system. Man is made for Earth. Anything else will be foreign to his biology. Earth sustains life because it has an intrinsic magnetosphere which both protects the planet from highly charged particles carried by the solar wind which are harmful to life and the retention of the atmosphere which can be eroded by the solar wind. Nowhere else in the Solar System are these conditions found and we would be unlikely to come across them even if the vast distances between the stars and Earth could be travelled. More of that later.
I can hear devotees of sci-fi shouting “what about terraforming”, the idea that planets or moons could be engineered to become places habitable to homo sapiens. Apart from the obvious barrier of no one having the slightest idea of how this might be done, there are also inconvenient facts which restrict our choices. The gas giants – Saturn, Jupiter, Neptune, Uranus - are ruled out because they are , er, largely composed of gas.
The planets beyond Mars are also vast distances away from not only Earth but also the Sun. One astronomical unit (AU) is 92,955,807 miles ( 149,597,870 km), which is the average distance from the Earth to the Sun. Jupiter is 5.2 AU from the Sun; Saturn 9.54 AU; Unranus 19.22 AU; Neptune 30.06 AU and Pluto 39.5 AU( http://nineplanets.org/). Hence, the nearest planet to Earth beyond Mars, Neptune, is a distance of 4.2 AU from Earth and Pluto is 38.5 AU away or to put in another way, 76 times the distance of Mars from the Earth which is around half an AU off. Apart from presenting immense challenges to build a spacecraft capable of sustaining humans for long periods – for many years at a time at current rocket speeds – the distance of the outer planets from the Sun means that the useable energy which could be captured from the Sun would be tiny compared with that which reaches a planet at Earth’s distance from the Sun. Distance from the Sun would also make settlement on the larger moons such a Titan (Saturn) and Ganymede (Jupiter) very problematic even assuming it is possible to land men on them.
That leaves Mercury, Venus and Mars. Mercury would simply fry or freeze us, its surface temperature varying from 90-700 degrees Kelvin. It does rotate but very slowly – once every 59 Earth days and possesses a very thin atmosphere consisting of atoms blasted off its surface by the solar wind. This atmosphere constantly needs replenishing because the heat sends the
atoms into space. Venus is sometimes called Earth’s “sister planet”, because of all the Solar System ‘s planets it most resembles Earth in size, gravity, bulk composition and distance from the Sun. Sadly, it has next to no magnetic field to protect it from cosmic radiation, an atmospheric pressure that is 93 times that of earth, an atmosphere largely composed of carbon dioxide, clouds formed of sulphuric acid several miles thick with winds of several hundred miles an hour and a surface temperature of 400-700 degrees Kelvin. If terraforming of Venus were to happen, it would be the sort of job guaranteed to keep a builder giving an estimate sucking his cheeks in and whistling for years. So we are left with Mars. Mars also lacks a decent magnetic field and is considerably smaller than the Earth so gravity would become a problem for long term habitation. We could however actually land on Mars as it is presently constituted.
Leaving behind the dream of terraforming, what are we left with? Assuming that the problems of shielding people from cosmic radiation and the physiological difficulties arising for an environment radically different from the Earth could be overcome, Mars and various moons such as our own might be lived on in physically enclosed habitations with their own breathable atmosphere . However, there would be the further problem of supplying the means of life, a difficulty which would be massively amplified if Mars or a moon had no water. If there is water in large quantities, it is possible to envisage settlements of a reasonable size living in closed settlements and growing their own food. Nonetheless, it is worth noting that an
attempt to replicate such an environment on Earth called Biosphere2, was less than a raging success from both a technical and psychological standpoint, with the oxygen content of the
atmosphere falling rapidly, food production inadequate and the inhabitants splitting into two groups hostile to one another. (http://www.biology.ed.ac.uk/research/groups/jdeacon/biosphere/biosph.htm)
Our present scope for colonising other parts of the solar system being distinctly limited , the big question is this, why we should be doing anything in space beyond placing manned
satellites around the Earth and unmanned probes further afield? The idea of mining the solar system for minerals is dubious in the extreme, because of the still fantastic cost of putting and maintaining anything into and in space. It is difficult to see how this will change. How about space tourism? Perhaps we shall see a market grow for Richard Branson-style short trips to the edge of space, although even that is it is difficult to see that as anything other than a very limited market for reasons of cost. Longer term trips into space, whether orbital or eventually to destinations such as the moon or even Mars are distinctly unlikely because of the cost and physical and psychological training and qualities required to undertake long space flights.
A research laboratory on the Moon or Mars perhaps? Perhaps, but the cost would be frightening. More to the point, what would be the purpose of such a thing? The fate of the Moon programme is instructive. Men walked on the Moon and where then left psychologically dangling in the air. They had achieved their goal and had nowhere else to go. If a manned settlement is created on the Moon or Mars the danger would be that the creation of the settlement would be an end in itself and once achieved become a white elephant. Apart from
studying the geology of the Moon or Mars, it is difficult to think of any research which could be done on the Moon or Mars which could not be done on Earth or from a station in space.
But even assuming that it was thought worthwhile and affordable to explore the Solar system or even go further afield there would be many horrendous practical problems to be overcome. Take the psychological aspect. I suspect that humans would find leaving Earth an immense distance behind would be tremendously difficult. Parallels are often drawn with those who set out on voyages to parts unknown such as those from Europe to the New World, but there are considerable differences. To begin with the exploring sailors were not constrained by an environment inherently fatal to them; those in a spaceship are. Astronauts have to carry their air around with them; sailors do not. Then there is the question of time. A voyage across the Atlantic would take weeks: with current technology a flight to Mars would last six months or more, one to Pluto nine or ten years.
Sailors in the fifteenth and sixteenth centuries were restricted to small vessels but these would be larger than the living quarters of modern spacecraft and the crew would not have the claustrophobic feeling of being trapped within the ship, a feeling which would almost be a danger for astronauts on long missions. Those in a spaceship would be very aware that they had to carry all their fuel and provisions them; sixteenth century sailors had no need of fuel and were able to gather water and food even while they sailed and always had the hope of landfall. A spaceship is reliant on very complex equipment which could not be replaced and probably not repaired during a flight; a wooden ailing ship had a considerable capacity to absorb damage and remain operational, not least because a ship of any size would have a hip’s carpenter and wood to make repairs could be acquired if landfall was made in a wooded area. The fears of space travellers and exploring sailors would be different. Those in space would go with the knowledge of the perils they were facing; the fear of fifteenth and sixteenth century sailors would arise from not knowing what they would face. I suspect the former state i harder to face because it is more real. The loneliness and sense of vulnerability of
the space traveller and settler – even within the solar system - might be impossible to bear.
Ten there are the physical difficulties. Even assuming we could come near to approaching the speed of light it is difficult to see how a spacecraft could travel safely. For example, how would they miss objects large enough to destroy the ship at such speeds – and the objects would not need to be very large. As for strategies such as going through wormholes, how would spaceships avoid materialising in the centre of a star or planet?
Many of the problems might in time be overcome. Completely effective radiation shields might be made; spaceships of great size constructed, most probably in space itself;
the physical deterioration of humans caused by weightless halted; the speed of spacecraft increased to the point where a trip to Mars or even the outer planets was reduced to a few weeks to mention just a few. But the question would still remain, to what end would the travel be undertaken? For the trivial reason of tourism? Hardly a persuasive reason. For the exploitation of of the physical resources of other planets, moons and asteroids? Intelligent machines could do that job much better. To put research stations on the Moon or Mars? Again intelligent machines could do the work more safely and cheaply. Take the matter further. Suppose a means to travel to the stars was found, either by new scientific and technological discoveries or by the Noah’s Ark solution beloved of Sci-Fi writers where a giant spaceship spends generations travelling at a cosmically modest speed to a nearby star. Would that be a useful or sensible course to follow?
To begin with the chances of finding planets suitable for uman habitation are most probably small. There is only body in the Solar System which supports life as far as we know. Certainly none supports advanced life. Life of any type may be a rarity throughout the Universe. Even if there are millions of planets in our galaxy which support life of some type it would
still be a very long shot for humans in spaceships to encounter them because there are many tens of billions of suns in the Milky Way. Even if “Goldilocks” planets within what is considered the “habitable zone” by astronomers - the distance from a star where an Earth-like planet can maintain liquid water on its surface – the chances of finding planets with life are small as the Solar System shows - Mars and Venus are within the habitable zone of the Sun.
It is also a mistake to imagine that an Earth-like planet which contained water would evolve physically as Earth has evolved. For example, the existence of a large moon causes much
more tidal action than would otherwise be the case and this has effects on the Earth’s crust which may include the tectonic action of her crust. This is unique amongst the planets of the Solar System. Such singularities may have laid the grounds for life to begin on Earth (http://www.astrobio.net/index.php?option=com_retrospection&task=detail&id=2507).
If a planet with life was found the chances of it being suitable for human beings to live on would be remote. There would the problems of gravity and temperature which was too high or too low. The atmosphere would be unlikely to be breathable by humans. There would be diseases against which humans would have no defence. Even if humans did not find hostile intelligent aliens, they would have to contend with aggressive non-intelligent aliens and probably more devastating If intelligent aliens were met, it is very improbable that friendly
civilisations would be encountered because if there is intelligent life on other worlds, it will presumably have evolved . That will mean in all probability that such creatures would be hostile to humans just as we would be hostile to any alien who entered our solar system. The unknown is a great dissolver of liberal fantasies about humans being one big happy family. How much more powerful would the fear of those who were utterly unlike ourselves?
The most likely way for humans to explore and even exploit the Solar System or other celestial systems is through intelligent machines. They would not be subject to the considerable physical limitations of humans and most probably not to the psychological problems humans would display in in space and on other worlds. I say probably because as artificial intelligence improves – and it is increasing by leaps and bounds at present – it is a fair bet that a form of consciousness will come along with the increased intellectual capacity
and that may lead the machines to suffer what would be in effect emotional/psychological problems.
Sadly, the most likely purpose space will be put to is war, as the major powers set up missiles systems and other weaponry in space.