Abstract:OrbitaldebrisinlowEarthorbit(LEO)arenowsufficientlydensethatthe use of LEO space is threatened by runaway collisional cascading. A problem predictedmorethanthirtyyearsago,thethreatfromdebrislargerthanabout1cm demandsseriousattention.Apromisingproposedsolutionusesahighpowerpulsed lasersystemontheEarthtomakeplasmajetsontheobjects,slowingthemslightly, and causing them to re-enter and burn up in the atmosphere. In this paper, we reassessthisapproachinlightofrecentadvancesinlow-cost,light-weightmodular designforlargemirrors,calculationsoflaser-inducedorbitchangesandindesignof repetitive, multi-kilojoule lasers, that build on inertial fusion research. These advances now suggest that laser orbital debris removal (LODR) is the most costeffective way to mitigate the debris problem. No other solutions have been proposedthataddressthewholeproblemoflargeandsmalldebris.ALODRsystem will have multiple uses beyond debris removal. International cooperation will be essentialforbuildingandoperatingsuchasystem.

When a large piece of space debris forced a change of flight plan for a recent U.S. Space Shuttle mission, the concept that we are trashing space as well as Earth finally attained broad public awareness. Almost a million pieces of debris have been generated by 35 years of spaceflight, and now threaten long-term space missions. The most economical solution to this problem is to cause space debris items to reenter and burn up in the atmosphere. For safe handling of large objects, it is desired to do this on a precomputed trajectory. Due to the number, speed, and spacial distribution of the objects, a highly agile source of mechanical impulse, as well as a quantum leap in detection capability are required. For reasons we will discuss, we believe that the best means of accomplishing these goals is the system we propose here, which uses a ground-based laser system and active beam phase error correcting beam director to provide the impulse, together with a new, computer-intensive, very high-resolution optical detection system to locate objects as small as 1 cm at 500-km range. Illumination of the objects by the repetitively pulsed laser produces a laser-ablation jet that gives the impulse to de-orbit the object. A laser of just 20-kW average power and state-of-the-art detection capabilities could clear near-Earth space below 100-km altitude of all space debris larger than 1 cm but less massive than 100 kg in about 4 years, and all debris in the threatening 1-20-cm size range in about 2 years of continuous operation. The ORION laser would be sited near the Equator at a high altitude location (e.g., the Uhuru site on Kilimanjaro), minimizing turbulence correction, conversion by stimulated Raman scattering, and absorption of the 530-nm wavelength laser beam. ORION is a special case of Laser Impulse Space Propulsion (LISP), studied extensively by Los Alamos and others over the past 4 years.

This paper describes a solid state laser concept that scales to MW levels of burst power and MJ of burst energy and burst durations measured in seconds. During lasing action, waste heat is purposely stored in the heat capacity of the active medium. The paper outlines the principal scaling laws of key operational features and arrives at a conceptual design example of the laser head as well as a mobile laser system. © 1998 Cambridge University Press 0263-0346/98 $ 12.50 G.F. Albrecht et al.and average power lasers are designed not to exceed a critical tensile stress value, or the medium will fracture. Depending on how the beam propagates through this medium, the temperature and stress distributions influence the beam propagation, resulting in such phenomena as, for example, thermal focusing and birefringent stress depolarization in rods. Many techniques have been developed to mitigate the imprint of these effects on the beam. In a zigzag slab architecture, special care is taken that such thermo-optical effects are averaged out as the beam propagates through the active medium. The myriad of highly sophisticated and successful commercial systems proves that all these effects have been not only studied extensively, especially in rods and zigzag slabs, but also have been mastered very well indeed. Nevertheless, these average power heat removal effects constitute an intrinsic limit to the steady state average power that the solid state laser can put out. Single shot lasers obviously suffer none of these thermomechanical restrictions, since the medium is in thermal equilibrium with its environment (no heat flow) before the shot, and one simply waits long enough to reestablish this condition before the next shot. The beam thus travels through an active medium essentially free of gradients.The heat capacity laser is conceptually closely related to the single shot laser, in that one rapidly adds single shots at a time scale short compared to thermal diffusion times, 1 that is, short compared to times that begin to establish the thermal gradients of a steady state heat flow condition, and a near adiabatic mounting of the active medium serves to thermally isolate the active medium as much as possible. That means that the waste heat generated during lasing remains, by design, in the active medium, whose temperature now rises each shot by a small amount given by the amount of waste heat generated per unit volume, and the heat capacity of the active medium. Therefore we call it a heat capacity laser. Since the temperature of the active medium cannot rise indefinitely, lasing at some point will have to cease, and the cooling phase begins. During this cooling phase, the temperature of the active medium is again reduced to the starting temperature, and the medium will now be subject to a tensile surface stress, which needs to be managed just like in any other cooled solid state laser.Therefore, an important characteristic of the heat capacity laser is its single shot energy output; it is a rapidly pulsed single shot energy device. ...

No abstract