The basic idea of Astrochicken is that the spacecraft will be small and quick. I do not believe that a fruitful future for space science lies along the path we are now following, with space missions growing larger and larger and fewer and fewer and slower and slower as the decades go by. I propose a radical step in the direction of smallness and quickness. Astrochicken will weigh a kilogram instead of Voyager’s ton, and it will travel from Earth into orbit around Uranus in two years instead of Voyager’s nine. The spacecraft must be far more versatile than Voyager. It must land on each of Uranus’ moons, roam around on their surfaces, see where it is going, taste the stuff it is walking on, take off into space again, and navigate around Uranus until it decides to make a landing somewhere else. To do all this with a 1-kilogram spacecraft sounds crazy to people who have to work and plan within the constraints of today’s technology. Perhaps it will still be crazy in 2016. Perhaps not. I am dreaming of the new technologies which might make such a crazy mission possible.
Three kinds of new technology are needed. All three are likely to become available for use by the year 2016. All three are already here in embryonic form and are advanced far enough to have names. Their names are genetic engineering, artificial intelligence and solar-electric propulsion. Genetic engineering is fundamental. It is the essential tool required in order to design a 1-kilogram spacecraft with the capabilities of Voyager. Astrochicken will not be built, it will be grown. It will be organized biologically and its blueprints will be written in the convenient digital language of DNA. It will be a symbiosis of plant and animal and electronic components. The plant component has to provide a basic life-support system using closed-cycle biochemistry with sunlight as the energy source. The animal component has to provide sensors and nerves and muscles with which it can observe and orient itself and navigate to its destination. The electronic component has to receive instructions from Earth and transmit back the results of its observations. During the next thirty years we will be gaining experience in the art of designing biological systems of this sort. We will be learning how to coordinate the three components so that they work smoothly together.
Artificial intelligence is the tool required to integrate the animal and electronic components into a working symbiosis. If the integration is successful, Astrochicken could be as agile as a hummingbird with a brain weighing no more than a gram. The information-handling apparatus is partly neural and partly electronic. An artificial intelligence machine is a computer {198} designed to function like a brain. A computer of this sort will be made compatible with a living nervous system, so that information will flow freely in both directions across the interface between neural and electronic circuits.
The third new technology required for Uranus 2 is solar-electric propulsion. To get from Earth to Uranus in two years requires a speed of 50 kilometers per second, too fast for any reasonable multistage chemical rocket. It is also too fast for solar sails. Nuclear propulsion of any kind is impossible in a 1-kilogram spacecraft. Solar-electric propulsion is the unique system which can economically give a high velocity to a small pay load. In this system, solar energy is collected by a large, thin antenna and converted with modest efficiency into thrust. The spacecraft carries a small ion-jet motor which uses propel-lant sparingly and gives an acceleration of the order of a milligee.
Nobody has yet done the careful engineering development to demonstrate that the energy of sunlight can be converted into thrust with a power-to-weight ratio of 1 kilowatt per kilogram. That is what Uranus 2 needs. But solar-electric propulsion is probably an easier technology to develop than genetic engineering and artificial intelligence. Since I am talking science fiction, I shall assume that all three technologies will be available for our use in 2016. I can then give a rough sketch of the Uranus 2 mission.
The mission begins with a conventional launch taking the spacecraft from Earth into orbit. Since the spacecraft weighs only 1 kilogram, it can easily ride on any convenient launcher. During the launch, the spacecraft is packaged into a compact shape, and the biological components are busy reorganizing themselves for life in space. During this phase the spacecraft is a fertilized egg, externally inert but internally alive, waiting for the right moment to emerge in the shape of an Astro-chicken. After it is in a low Earth orbit, it will emerge from its package and deploy the life-support apparatus needed for survival in space. It will deploy, or grow, a thin-film solar collector. The collector weighs 100 grams and collects {199} sunlight from an area of 100 square meters. It feeds a kilowatt of power into the little ion-drive engine which sends the spacecraft on its way with a milligee acceleration sustained for several months. This is enough to escape from Earth’s gravity and arrive at Uranus within two years. The same 100-square-meter collector serves as a radio antenna for two-way communication with Earth. This is ten times the area of the Voyager high-gain antenna. For the same rate of information transmitted, the transmitter power of Astrochicken can be ten times smaller than Voyager, 2 watts instead of 20 watts.
The spacecraft arrives at Uranus at 50 kilometers per second and grazes the outer fringe of the Uranus atmosphere. The 100-square-meter solar collector now acts as an efficient atmospheric brake. Because the collector is so light, it is not heated to extreme temperatures as it decelerates. The peak temperature turns out to be about 800 Celsius or 1500 Fahrenheit. The atmospheric braking lasts for about half a minute and produces a peak deceleration of 100 gees. The spacecraft leaves Uranus with speed reduced to 20 kilometers per second and passes near enough to one of the moons to avoid hitting Uranus again. It is then free to navigate around at leisure among the moons and rings. The solar-electric propulsion system, using the feeble sunlight at Uranus, is still able to give the spacecraft an acceleration of a tenth of a milligee, enough to explore the whole Uranus system over a period of a few years.
The spacecraft must now make use of its biological functions to refuel itself. First it navigates to one of the rings and browses there, eating ice and hydrocarbons and replenishing its supply of propellant. If one ring tastes bad it can try another, moving around until it finds a supply of nutrients with the right chemistry for its needs. After eating its fill, it will use its internal metabolic processes with the input of energy from sunlight to convert the food into chemical fuels. Chemical fuels are needed for jumping onto moons and off again. Solar-electric propulsion gives too small a thrust for jumping. The spacecraft carries a small auxiliary chemical rocket system for {200} this purpose. We know that a chemical rocket system is biologically possible, because there exists on the Earth a creature called the Bombardier beetle which uses a chemical rocket to bombard its enemies with a scalding jet of hot liquid. It manufactures chemical fuels within its body and combines them in its rocket chamber to produce the scalding jet. Astrochicken will borrow its chemical rocket system from the Bombardier beetle. The Bombardier beetle system will give it the ability to accelerate with short bursts of high thrust to escape from the feeble gravity of the Uranus moons. The spacecraft may also prefer to use the Bombardier beetle system for jumping quickly from one place to another on a moon rather than walking laboriously over the surface. While living on the surface of a moon, the Astrochicken will continue to eat and to keep the Bombardier beetle fuel tanks filled. From time to time it will transmit messages to Earth informing us about its adventures and discoveries.
That is not the end of my dream, but it is the end of my chapter. I have told enough about the Uranus 2 mission to give the flavor of it. The underlying idea of Uranus 2 is that we should apply to the development of technology the lessons which nature teaches us in the history of the evolution of life. Birds and dinosaurs were cousins, but birds were small and agile while dinosaurs were big and clumsy. Big main-frame computers, nuclear power stations and Space Shuttle are dinosaurs. Microcomputers, STIG gas turbines, Voyager and Astrochicken are birds. The future belongs to the birds. The JPL engineers now have their dreams on board the Voyager speeding on its way to Neptune. I hope the next generation of engineers will have their dreams riding on Uranus 2 in 2016.
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