Journeys to the Nearest Stars In the Tow of the Sun

For the purpose of traveling to the nearest stars, Alpha Centauri for instance, at a distance of four light years, rockets do not suffice. A very much more exciting possibility offers itself, however: We remain on the Earth and travel with it as the space vehicle, either alone or with the whole solar system towards our goal. During this journey we may enjoy and use the light from the Sun as always, or if we wish to leave it behind, we can keep warm and provide all of the necessary small and large-scale illumination through the proper use of nuclear fusion energy. Traveling at a speed of 500 km/sec through space, relative to the surrounding stars, we might reach the neighborhood of Alpha Centauri in about 2,500 years.

All of this will become possible once we have mastered nuclear fusion ignition of common materials on the Earth and on the Sun. Physicists in many countries have been attempting during the past fifteen years to induce nuclear fusion reactions in extremely concentrated and high-energy ionic plasmas, without making any use of the release of nuclear fission energy from uranium as it is being used in H-bombs.

Even if these efforts should be successful they would not provide us with any readily usable means for the acceleration of the Sun or of the Earth to velocities of the order of 500 km/sec. I have therefore suggested another approach striving to produce small solid particles with velocities of up to 1,000 km/sec. It is not possible here to go into any details of how this is going to be done. I emphasize only that no fundamental difficulties stand in the way. Particles impacting on dense matter with velocities of the order of 1,000 km/sec will generate the desired temperatures of hundreds of millions of degrees, at which all light elements will be ignited to nuclear fusion reactions.

Launching ultrafast particles against the Sun, local regions on it could be ignited to nuclear fusion. As a consequence of the tremendous release of energy by such reactions, matter would be ejected with velocities of the order of 50,000 km/sec, while the resulting forces of reaction would propel the Sun in the opposite direction. If such processes were applied for a long time, the Sun could eventually be accelerated to the desired velocity with a sacrifice of only a small per cent of its total mass.

Since the planets are held in rein by the Sun's gravitational field, they and the Earth would be carried along on the distant journey. In principle the process and propulsion described could be applied to the Earth alone, which then would detach itself from the solar system and start out on its solitary voyage to the nearest stars.

Even if it would be possible to redirect the entire solar wind which ejects 10¹⁷ kilogram per year into one direction, this would displace the Sun only 1 meter in one year. On the other hand, the radiation energy produced by the Sun is 4 10³³ erg/sec and could in principle be used to accelerate the Sun to a velocity of 100 m/sec in one year, when considering the energy only. By heating and cooling different parts of the Sun and redirect the radiation asymmetrically, a fraction of this energy could in principle be available. But even if the entire radiation could be redirected into one direction, the force would accelerate in one year the Sun only to a speed of 10^-3 cm/sec. The reason for this low value is that photons do not carry a lot of momentum.

Probably both nanotechnology and genetic engineering will have an important role to play in space science. The two technologies are likely to grow together and ultimately merge, so that it will be difficult to tell which is which. In the end, nanotechnology will give us scientific instruments having the alertness and agility of living creatures, while genetic engineering will give us living creatures having the sensitivity and precision of scientific instruments. The spacecraft of 2018 may well be a hybrid, making use of nanotechnology for its sensors and communications, genetic engineering for its legs, wings, and brain.

Here is a rough sketch of one possible shape that the 2018 spacecraft might take. I call this model the Astrochicken because it is about as big as a chicken and about as smart. It is a product of genetic engineering. It does not look like a chicken. It looks more like a butterfly. It has wide and thin solar sails instead of wings, and a high-resolution spectroscopic imaging system instead of eyes. With its solar sails it flies around the inner solar system as far as the main belt of asteroids. At any one time there will be hundreds of such birds flying, programmed to make specialized observations of Earth, Moon, Sun, planets, and asteroids as well as of the heavens beyond. Other cousins of the Astrochicken will have legs for landing and hopping around on asteroids, or solar-powered ion-jet engines for exploring the outer solar system as far as Pluto.