Optimum parameters for laser launching objects into low Earth orbit

We derive optimum values of parameters for laser-driven flights into low Ea rth orbit (LEO) using an Earth-based laser, as well as sensitivity to varia tions from the optima. These parameters are the ablation plasma exhaust vel ocity u(E) and specific ablation energy Q*, plus related quantities such as momentum coupling coefficient C-m and the pulsed or continuous laser inten sity that must be delivered to the ablator to produce these values. Differe nt optima are found depending upon whether it is desired to maximize mass m delivered to LEG, maximize the ratio m/M of orbit to ground mass, or minim ize cost in energy per gram delivered. Although it is not within the scope of this report to provide an engineered flyer design, a notional, cone-shap ed flyer is described to provide a substrate for the discussion and flight simulations. The flyer design emphasizes conceptually and physically separa te functions of light collection at a distance from the laser source, light concentration on the ablator, and autonomous steering. Approximately ideal flight paths to LEO are illustrated beginning from an elevated platform. W e believe LEO launch costs can be reduced 100-fold in this way. Sounding ro cket cases, where the only goal is to momentarily reach a certain altitude starting from near sea level, are also discussed. Nonlinear optical constra ints on laser propagation through the atmosphere to the flyer are briefly c onsidered.