Thefeasibility andpracticality ofusing aground-hased laser (GBL)toremove artificial space debris isexamined. Physical constraints indicate that areactor-pumped laser (RPL)maybebest suited for this mission, because ofits capabilities for multimegawatt output, longrun-times, andnear-diffraction-limited initial beams. Simulations ofa laser-powered debris removal system indicate that a5-MW RPL witha 10-meter-diameter beamdirector andadaptive optics capabilities can dcorbit l-kg debris fromspace station altitudes. Larger debris canbed¢orbited ortransferred tosafer orbits after multiple laser engagements. A ground-based laser system maybetheonly realistic waytoaccess andremovesome10,000 separate objects, having velocities intheneighborhood of7km/sec, andbeing spatially distributed oversomeI010km3 ofspace. I.MITIGATING THE SPACE DEBRIS THREAT Hypervelocity collisions withartificial space debris constitute a growing potential threat tospace assets inlow-earth orbit (LEO). A numberofencounters havealready occurred, andtheir frequency isprojected toincrease inthefuture. Ithas beensuggested that adebris "population explosion" could occur ascollisions between debris objects greatly increase the existing population. I-9 Mission planners are concerned that the planned US spa_ station could be temporarilyor permanently disabled by space debris impacts. Because of its large total area and its long mission time, the space station is perhaps the most likely potential victim of a serious debris-impact event. It has been estimated that for a 30-year mission duration the probability of a catastrophic loss may be as high as 75%,and catastrophe would be transformed into tragedy if there were personnel onboard at the time. 8,10 Passive debris shields can offersome protection, and several advanced designs have recently been proposed. These shields are effective against the more probable encounters, those with debris having sizes up to about 1 cm. A drawbackto using shields is that they add significantly to total launch weight. For shields designed to protect against debris larger than about 1cm, this weight penalty would become unacceptable. 1,3,5,9,11,12 Detection and avoidance have alreadybeen used by maneuvering space systems. On three occasions a shuttle has undergone orbital alterations to reduce impact probability. To date, all such operations have been handled fromthe groundI It has been proposed that space assets be providedwith onboard infrared or radardetectorsand autonomous control systems to command maneuvers. However,this would imply serious penalties with regard to launch weight, mission duration, and overall system complexity.6,13 Mechanical debris sweepers have been proposedfor removing debris fromorbit. These consist of panels to capturedebris or sheets of thin materials to reduce debris velocities. To be effective, these sweepers would have to be very large in area, resulting in some degree of awkwardness during deployment and steering. For the panel designs it would also imply large total mass and greater overall cost....

The Debye potential formalism is a simple and elegant method of representing and analyzing radiation fields in classical electromagnetism. Despite this, there are a number of unanswered questions about the formalism. One of these, the transformation properties of the potentials under Lorentz boosts, is dealt with in this article.

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Thefeasibility andpracticality ofusing aground-hased laser (GBL)toremove artificial space debris isexamined. Physical constraints indicate that areactor-pumped laser (RPL)maybebest suited for this mission, because ofits capabilities for multimegawatt output, longrun-times, andnear-diffraction-limited initial beams. Simulations ofa laser-powered debris removal system indicate that a5-MW RPL witha 10-meter-diameter beamdirector andadaptive optics capabilities can dcorbit l-kg debris fromspace station altitudes. Larger debris canbed¢orbited ortransferred tosafer orbits after multiple laser engagements. A ground-based laser system maybetheonly realistic waytoaccess andremovesome10,000 separate objects, having velocities intheneighborhood of7km/sec, andbeing spatially distributed oversomeI010km3 ofspace. I.MITIGATING THE SPACE DEBRIS THREAT Hypervelocity collisions withartificial space debris constitute a growing potential threat tospace assets inlow-earth orbit (LEO). A numberofencounters havealready occurred, andtheir frequency isprojected toincrease inthefuture. Ithas beensuggested that adebris "population explosion" could occur ascollisions between debris objects greatly increase the existing population. I-9 Mission planners are concerned that the planned US spa_ station could be temporarilyor permanently disabled by space debris impacts. Because of its large total area and its long mission time, the space station is perhaps the most likely potential victim of a serious debris-impact event. It has been estimated that for a 30-year mission duration the probability of a catastrophic loss may be as high as 75%,and catastrophe would be transformed into tragedy if there were personnel onboard at the time. 8,10 Passive debris shields can offersome protection, and several advanced designs have recently been proposed. These shields are effective against the more probable encounters, those with debris having sizes up to about 1 cm. A drawbackto using shields is that they add significantly to total launch weight. For shields designed to protect against debris larger than about 1cm, this weight penalty would become unacceptable. 1,3,5,9,11,12 Detection and avoidance have alreadybeen used by maneuvering space systems. On three occasions a shuttle has undergone orbital alterations to reduce impact probability. To date, all such operations have been handled fromthe groundI It has been proposed that space assets be providedwith onboard infrared or radardetectorsand autonomous control systems to command maneuvers. However,this would imply serious penalties with regard to launch weight, mission duration, and overall system complexity.6,13 Mechanical debris sweepers have been proposedfor removing debris fromorbit. These consist of panels to capturedebris or sheets of thin materials to reduce debris velocities. To be effective, these sweepers would have to be very large in area, resulting in some degree of awkwardness during deployment and steering. For the panel designs it would also imply large total mass and greater overall cost....