A CONTRIBUTION TO THE AVAILABILITY OF LUNAR RESOURCES FOR PCWERSAT CONSTRUCTION T. A. Heppenheimer Center for Space Science Fountain Valley, California A number of authors have discussed the use of lunar resources in powersat construction, wherein these resources are to be transported with the aid of a lunar mass-driver. Previous contributions by the present author have included studies of achromatic trajectories and of the mass-catcher and associated transfer trajectories to a space manufacturing facility. An important problem, heretofore essentially untreated, is the minimization of cross-track errors in the launch of payloads by mass-driver. This problem is important because an error Ay = 1 cm/sec (normal to the lunar surface) produces a miss of 500 meters, for a catcher near the L2 libration point. If the error is Az = 1 cm/sec, parallel to the lunar surface, the miss is 30 meters. Figure 1 gives a block diagram of the mass-driver; Figures 2 and 3 indicate the technology which is applied. The proposed mass-driver buckets or payload-carriers employ the design concepts of Chilton, Kolm and associates, as developed in 1976. In Fig. 2, the new feature is the payload constraint/release system. The payload is conceived as a triaxial ellipsoid having axes in the approximate ratio 0.95:1.00:1.05, with mass 20 kg, and consequently with mean diameter 25 cm. It is of unprocessed lunar soil and is contained within a bag woven from lunar-derived fiberglass, as proposed by Criswell, the fiberglass being prepared at the lunar base. In addition, the payload is flashed with a thin coating of metallic aluminum, to make its surface electrically conducting. The payload housing then is a double hemiellipsoid, moulded to the reference payload shape. The rear housing half is strongly braced and secured. The forward half fits tightly against the rear half during bucket acceleration (at 1000 m/sec2). Passive magnetic damping: Following the main acceleration phase is a section of mass-driver track which is precision aligned; the optical alignment system used in the Stanford Linear Accelerator appears applicable. This section, up to several kilometers in length, gives a very smooth bucket motion wherein preexisting bucket oscillaticns may die out. Chilton et. al. give reference oscillation frequencies as 28 Hz laterally, 20 Hz vertically. Figure 4 illustrates a novel means for damping: electromagnetic fins. The phenomena of magnetic damping is well-known: if a conducting loop oscillates within a transverse magnetic field, then by Lenz* law there arise eddy currents within the loop, the decay of which absorb energy at the expense of the oscillation. In the present instance, each of the cruciform fins of Fig. 4 has associated a conductor carrying current I, parallel to the fin length L and separated by clearance C. Fin width is W and resistance of the fin is R;
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