Beam-powered propulsion

Abstract: LASER ablation propulsion (LAP) is a major new electric propulsion concept with a 35-year history. In LAP, an intense laser beam [pulsed or continuous wave (CW)] strikes a condensedmatter surface (solid or liquid) and produces a jet of vapor or plasma. Just as in a chemical rocket, thrust is produced by the resulting reaction force on the surface. Spacecraft and other objects can be propelled in this way. In some circumstances, there are advantages for this technique compared with other chemical and electric propulsion schemes. It is difficult to make a performance metric for LAP, because only a few of its applications are beyond the research phase and because it can be applied in widely different circumstances that would require entirely different metrics. These applications range from milliwatt-average-power satellite attitude-correction thrusters through kilowatt-average-power systems for reentering near-Earth space debris and megawatt-to-gigawatt systems for direct launch to lowEarth orbit (LEO). We assume an electric laser rather than a gas-dynamic or chemical laser driving the ablation, to emphasize the performance as an electric thruster. How is it possible for moderate laser electrical efficiency to givevery high electrical efficiency? Because laser energy can be used to drive an exothermic reaction in the target material controlled by the laser input, and electrical efficiency only measures the ratio of exhaust power to electrical power. This distinction may seem artificial, but electrical efficiency is a key parameter for space applications, in which electrical power is at a premium. The laser system involved in LAP may be remote from the propelled object (on another spacecraft or planet-based), for example, in laser-induced space-debris reentry or payload launch to low planetary orbit. In other applications (e.g., the laser–plasma microthruster that we will describe), a lightweight laser is part of the propulsion engine onboard the spacecraft.

Abstract: 3Heiser, W H, Pratt, D T, with Daley, D H, and Mehta, U B, “Hypersonic Airbreathing Propulsion,” AIAA Education Series, AIAA, Washington, DC, 1994, pp 334–370 4Chinzei, N, Komuro, T, Kudo, K, Murakami, A, Tani, K, Masuya, G, and Wakamatsu, Y, “Effects of Injector Geometry on Scramjet Combustor Performance,” Journal of Propulsion and Power, Vol 9, No 1, 1993, pp 146–152 5Chinzei, N, Masuya, G, Kudo, K, Murakami, A, and Komuro, T, “Experiment on Multiple Fuel Supplies to Airbreathing Rocket Combustors,” Journal of Propulsion and Power, Vol 3, No 1, 1987, pp 26–32

Abstract: Schemes have been suggested for transferring energy from Earth-to-space, space-to-Earth, and space-to-space using high-power microwave (HPM) beams. All use power beaming. Microwave beams have been studied for propelling spacecraft for launch to orbit, orbit raising, launch from orbit into interplanetary and interstellar space, and deployment of large space structures. The microwave thermal rocket, called the ldquomicrowave thermal thruster,rdquo is a reusable single-stage vehicle that uses an HPM beam to provide power to a heat-exchanger propulsion system, with double the specific impulse of conventional rockets. Orbital missions include orbit raising and space solar power. Microwave-propelled sails are a new class of spacecraft that promises to revolutionize future space probes. Experiments and simulations have verified that sails riding beams can be stable on the beam for conical sail shapes. Beam-driven sail flights have now demonstrated the basic features of the beam-driven propulsion. Beams can also carry angular momentum and communicate it to a sail to help control it in flight. An early mission for microwave space propulsion is dramatically shortening the time needed for sails to escape Earth's orbit. A number of missions for beam-driven sails have been quantified for high-velocity mapping of the outer solar system, Kuiper Belt, the Heliopause, and the penultimate interstellar precursor mission. For large HPM systems at fixed effective isotropic radiated power, minimum capital cost is achieved when the cost is equally divided between antenna gain and radiated power. This is a driver when considering design of power-beaming systems such as interstellar Beacons, which the Search for Extraterrestrial Intelligence is searching for. Much of the technical means for these applications are already in hand. Microwave and millimeter-wave array antennas are already in use for astronomy; sources at high frequencies are being developed for fusion and the military. Development of high-power arrays is needed. A synergistic way to develop a space power-beaming infrastructure is incremental buildup, addressing lower power applications first, and then upgrading.