r 5 and turns it into electrical energy, which is fed back to aid in the acceleration of the next bucket. In that way, the overall machine can reach a high efficiency, from 70%to 95%depending on details of the design. There are of course many other details in the real mass-driver design, and those details are duplicated in the model now being tested. Instead of a single capacitor for each phase, there are actually many capacitors, because each short section of the machine must be "tuned" to a frequency that corresponds to the speed of the bucket, just as a radio or television set must be tuned to the frequency of the transmitting station. For the same reason the drive coils are made with many turns of wire, and the number of turns on the coils depends where they are on the machine: near the starting end the coils are wound for a low frequency, and near the high end they are made to receive and give back their currents at a high frequency. Electric-eye beams must detect the passage of the bucket as it crosses the space between each pair of drive coils, and must feed signals to logic circuits that decide when and where to S\'Ji tch the currents. Every i ndi vi dual drive coil must be fed through controllable silicon switches (called "SCR's" in high-power electronics jargon). Even in the model, there are more than 200 of these switches, each able to switch several thousand amperes at a voltage of a thousand volts. Our fascination with the mass-driver stems from considerations even deeper than its utility for launching material from the Moon, important as that is. It is one of the few machines we can see that has almost no limits on its ultimate performance. In principle, a mass-driver could launch a payload to a speed almost as great as the speed of light. Such a machine would be enormously long, and it may be a century before one is built. Yet it could be, and it is very exciting for those of us who are building the model to work on a device that may be as significant, in the long run, as the first rocket or the first airplane. SSI played an essential role in the practical development of the mass-driver. Although NASA funding for mass-driver research is now at a healthy level ($250,000 in 1980), SSI stands ready to keep the work going, albeit at a slower pace, if for any reason the government funding should falter. Meanwhile, SSI's resources are directed toward those essential items of research that would not be done at all if SSI did not exist. Lectures: Publications: September 25 October 9 October 24-25 November 13-16 November 18 November 20 + + + Purdue University, W. Lafayette, Indiana Arizona State University, Tempe, Arizona Tilton School, Tilton, New Hampshire University of Oklahoma, Norman, Oklahoma Duquesne University, Pittsburgh, Pennsylvania State Univ. of New York, Oneonta, New York Halle, Louis J. "A Hopeful Future For Mankind," Foreign Affairs, Summer 1980, p. 1129-1136. O'Neill, G. K. "Frontiers in Space," PHP, Vol. 11, No. 7, Tokyo, Japan, July 1980, p. 6-22.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==