INTERSTELLAR TRAVEL

It will take six months for a manned expedition to reach Mars. The explorers will then have to spend two years at Mars before the planetary configuration is correct for an economic return journey. This will, in all probability he done in 2018 when the Earth and Mars will be closest during July 2018; the closest approach which recurs every 15 years.

During the trip some food could he produced hydroponically whereby the carbon dioxide breathed out by the astronauts as well as the carbon dioxide of Mars' atmosphere will he converted into starch by sunlight. Whether a sufficient amount of food could he produced in this way, is a moot point. It seems the explorers would nevertheless have to carry many tons of highly concentrated foodstuffs.

But what about interstellar travel? Will it ever be possible to send a manned expedition to one of the nearest stars? Which stars? And where are they situated?

In the diagram the 18 nearest stars are projected on to the plane of the Earth's equator according to right ascension, 0 hours to 24 hours. and according to their distances from the Sun in light years. The degrees indicate the angles from the Sun, + for above the plane of the equator and - for below the plane of the equator. The nearest star Alpha Centauri is indicated by 1, -61° at 4,3 light years, it having a declination of 61° south, below the plane of the equator.

We assume that stars may have earthlike planets if their spectral types are close to that of the Sun which is G2. No 1, Alpha Centauri comes closest, it also being G2, a replica of the Sun and its companion is type Kl V. It is followed by No 17, Tau Ceti, a G8; then No 13, Procyon an F5; followed by No 9, Epsilon Eridani, a K2; No 14 Epsilon Indi a K5; No 11, 61 Cygni, K5 and K7; and lastly by No 5, Sirius an Al with a white dwarf companion DA.

The rest are tiny dM red dwarfs. Their surface temperatures are around 2500 degrees Kelvin and they have very narrow ecospheres in which habitable planets could develop. They are thus unlikely to have planets with technological civilisations.

It is doubtful whether there could be planetary orbits around the double stars. Alpha Centauri A and its companion B, revolve around their baricentre in 80 years. Their distance apart varies between 35 and 11 astronomical units. Besides the varying gravitational forces which orbiting planets would experience, there would be times (years on end) when there would be two suns above the horizon, thus raising the temperature on the surface of a planet to uncomfortable heights; at other times (also years on end) there would be one sun above one hemisphere of the planet and another sun above the other hemisphere, thus no night at all. It is to be doubted whether life could evolve under such circumstances.

But assume it is decided to send a manned expedition to Alpha Centauri; what will it entail? The space ship would have to carry enough FOOD and FUEL for the round trip. To accelerate the ship to a speed near to that of light implies a mass factor of 40 000, ie in order to propel a space ship weighing 100 tons the amount of fuel required would be 40 000 times as much, namely 4 million tons if the power of propulsion is derived from proton-antiproton annihilation. This reaction could only be set going once the space ship is about 5 astronomical units away on account of the lethal gamma rays which are set free. The shielding of the astronauts will require a massive cocoon of graphite or concrete, thus increasing the mass of the space ship to 1 000 tons or thereabouts and requiring ten times as much fuel, namely 40 million tons.

The ship will then be able to accelerate for one year and then coast at 99% of the speed of light for 3 1/2 years and then decelerate for one year, needing as much fuel as for acceleration, so as not to shoot right past Alpha Centauri into the depths of space, there to be lost forever. The outward trip will thus take a minimum of 5 1/2 years. Having got there the space ship will have to go into orbit around a likely-looking planet - a blue-white like the Earth - having an oxygen atmosphere and water vapour clouds. From this orbit a landing craft will have to be launched to land on the planet's surface. Will the travellers be received amicably by beings who may feel threatened by the invasion; or will the travellers find life teeming with carnivorous dinosaurs?

Who is going to foot the bill for all this?

The most likely candidate star to have a habitable planet in orbit around it, is a single star of spectral type similar to that of the Sun. The star among the nearest 18 that comes closest to the Sun in spectral type is Tau Ceti, a G8, but it is 11,9 light years distant, requiring at least three times as much fuel as a trip to Alpha Centauri and who is going to foot THIS bill? The outward trip will require 15 years.

Procyon, Epsilon Eridani, Epsilon lndi and 61 Cygni are all about 11 light years distant, requiring as much fuel as the trip to Tau Ceti and as much time.

Sirius is a bit nearer, being 8,65 light years distant. Its spectral type is Al, having a surface temperature of 10 000 degrees Kelvin. The ecosphere wherein water can exist in its three states and where life can evolve, will he much farther from the star, in the neighbourhood of the gas giant planets where a terrestrial planet would either be thrown out of the system or be gobbled up by the gas giant.

So it looks as if interstellar travel would not only be impossible but also useless. But there is one glimmer of hope. Some time in the future man will have to build a solar power station in orbit around the Earth to supply the Earth with electricity because oil and coal will not last forever. This solar power station will need attendants and the attendants will need medical and other care and they will want their families to be with them. And their children will need teachers and it will pay to cultivate food hydroponically. And soon other aspects of economic activity will sprout and the whole thing will snowball until a whole colony exists out in space "where falls no rain nor hail, nor ever wind blows wildly, but it lies deep meadowed, happy, fair..." A place nobody would want to leave. As a matter of fact the worst punishment that an inhabitant of such a colony could get, would be to be expelled back to Earth!

The space colony will become more and more self-sufficient, until eventually ( how long is eventually - 5 thousand, l0 thousand or l00 thousand years? ), eventually, astronomically still a very short time, it will come to pass that such a space colony will become independent of the Earth for supplies; and what is more important, become independent of the Sun for energy. THEN this space colony would be able to undertake a trip to one of the nearer stars. Being self-sufficient, the colony could cruise at a leisurely speed, say 5% of the speed of light, requiring much less fuel for propulsion and making use of the gravitational field of the Galaxy for its propulsion. It would not matter to the inhabitants how long the trip takes because the ship is independent for fuel supplies and food. Besides, when travelling at high speed there is always the danger of a collision. If a ship travels at one-half of the speed of light, its radar waves, reflected from a dark mass in the line of travel, will reach the ship at the moment of collision, so that speeds in excess of say 30% of the speed of light, would be utterly reckless. 5% of the speed of light is 15 000 kilometres PER SECOND! Members of the colony who die on the way, would be replaced by their descendants. At 5% of the speed of light, the trip to Epsilon Eridani, 10,8 light years distant, will take a bit more than 200 years. But what matter is that? The colony would leave the vicinity of the Earth and Sun, knowing that they would never return, nor would they want to return!

So space travel may not be impossible, after all.

The unanswered question is: Why hasn't anybody out there yet contacted us by radio?

Eben van Zyl