A six degree-of-freedom (DOF) dynamic model was developed to provide insight into the flight behavior of Type 200 Lightcraft, and to serve as a research tool for developing future engine-vehicle configurations for laser launching of nano-satellites (1-10 kg). Accurate engine, beam, and aerodynamics models are included to improve the predictive capability of the 6-DOF code. The aerodynamic forces of lift, drag, and aerodynamic pitching moment were derived from Fluent ® computational fluid dynamics predictions, and calibrated against limited existing wind tunnel data. To facilitate 6-DOF model validation, simulation results are compared with video analysis of flights under comparable conditions. Despite current limitations of the 6-DOF model, the results compared well with experimental flight trajectory data.
The paper presents pulsed laser propulsion performance data for three 11-cm diameter aluminum parabolic (or "bell-shaped") engines, tested with the 10-kW PLVTS pulsed CO2 laser at White Sands Missile Range, NM. The single-pulse and multiple-pulse tests were conducted on two campaigns, Sept. 2000 and Sept. 2001, using a ballistic pendulum apparatus. The results from two different sets of PLVTS resonator optics were gathered (both 2X and 3X magnification). Assuming the vertex is set at the parabola's focus (i.e., and viewing outward towards the 11-cm exit plane), the bell engines had three different total included angles of 60, 87.2, and 120 degrees. As expected, the impulse and coupling coefficient performance of the 60 deg. bell generally exceeded that of the 87.2 deg. engine, which in turn outperformed the 120 deg. bell. The maximum single-pulse coupling coefficients varied from 275 to 375 N-sec/MJ. Multiple-pulse engine performance data was also gathered with the same ballistic pendulum in the first campaign. A sequence of from 2 to 8 pulses was transmitted into each bell at a pulse repetition frequency of 25 HZ -- all delivered within the first 1/8th cycle of the pendulum's swing. In general, only small variations in the coupling coefficient were observed throughout the string of pulses.
Laser-boosted lightsail experiments were carried out on 4-8 December 2000 with the 150 kW LHMEL II carbon dioxide CW laser at Wright Patterson Air Force Base - in their 2.74 m long, 2.13-, diameter vacuum chamber. All 5-cm diameter sail specimens were fabricated by ESLI. The prior Dec. '99 pendulum tests used ultralight carbon microtruss discs, sputter-coated with molybdenum on the front face to improve reflectivity at 10.6 um - and are the first known measurements of high power laser photonic thrust with real candidate lightsail materials. The Dec. '00 vertical wire- guided tests employed an improved moly-coated carbon-foil material with the same basic microtruss substructure. The performance of this new carbon foil sail was superior to the earlier specimens.
Laser-boosted light sail experiments were carried out on 13 - 20 Dec. 1999 with the 150 kW LHMEL II carbon dioxide CW laser at Wright Patterson Air Force Base, using a 2.74-m long, 2.13-m diameter vacuum chamber evacuated to 36 - 44 microTorr. The 5-cm diameter laser sail discs (i.e., the test articles) were fabricated from an ultralight carbon microtruss fabric that was sputter-coated with molybdenum on one side only, to improve its reflectivity to 10.6 micrometer laser radiation. Four laser sails discs with three different areal densities (one at 6.6 g/sq.m., two at 27 g/sq.m., and one at 28 g/sq.m.) were tested as magnetically-supported pendulums with an overall length of 18 cm. Pendulum deflections for the three heavier sails, ranged from 2.4 to 11.4 degrees, measured as a function of incident laser powers from 7.9 to 13.9-kW. These pendulum sails had masses of 83.7, 87.3, and 88 milligrams each; their center-of-mass was located at 11.5, 11.7, and 11.9 cm (respectively) below the magnetic bearing. Laser photon thrust ranged from 3.0 to 13.8 dynes, as calculated from pendulum deflections. Seven of the 10 data points fell in the feasible range of 3.3 to 6.67 N/GW for photon propulsion physics; the other three (higher laser power) data points exceeded the 6.67 N/GW limit by as much as 50%. From this data set, the onset for significant ablation was clearly identified to be 12.9-kW. Laser sail temperature was monitored with an optical pyrometer, and fell in the range of 2270- K to above 2823-K for laser powers from 8-kW to 20.8-kW, respectively. The experiments are the first known measurements of laser photonic thrust performance with real candidate light sail materials.
In a series of spectacular experiments conducted at the High Energy Laser Systems Test Facility (HELSTF), White Sands Missile Range (WSMR), NM, using 13- to 15-cm diameter, 40- to 60-g vehicles designed to fly on the 10 kW PLVTS pulsed carbon dioxide laser (1 kJ pulses for 30 microsecond duration at 10 Hz), Prof. Leik Myrabo of Rensselaer Polytechnic Institute (RPI) and Dr. Franklin Mead of the Air Force Research Laboratory's (AFRL) Propulsion Directorate, have been successfully flying laser propelled Lightcraft under a joint Air Force/NASA flight demonstration program. The axisymmetric Lightcraft vehicles are propelled by airbreathing, pulsed- detonation engines with an infinite fuel specific impulse. Impulse coupling coefficients have been measured with ballistic pendulums as well as a piezoelectric load cell and fall in the range of 100 to 200 N/MW. Horizontal wire-guided flights up to 400 ft, using a unique laser beam pointing and tracking guidance system, have demonstrated up to 2.0 G's acceleration measured by a photo-optic array. Spin-stabilized free-flights with active tracking/beam control have been accomplished to altitudes of 15.25 meters. This paper will summarize the progress made to date on the Lightcraft Technology Demonstration flight test program, since the first 12 - 14 July 1996, experiments at HELSTF.
The objective of this research was to exploit wireless power transmission (microwave/millimeter)--to lower manned space transportation costs by two or three orders of magnitude. Concepts have been developed for lightweight, mass-producible, beam-propelled aerospacecraft called Lightcraft. The vehicles are designed for a 'mass-poor, energy-rich' (i.e. hyper-energentic flight infrastructure which utilizes remote microwave power stations to build an energy-beam highway to space. Although growth in laser power levels has lagged behind expectations, microwave and millimeter-wave source technology now exists for rapid scaling to the megawatt and gigawatt time-average power levels. The design exercise focused on the engine, structure, and receptive optics requirements for a 15 meter diameter, 5 person Earth- to-moon aerospacecraft. Key elements in the airbreathing accelerator propulsion system are: a) a 'flight-weight' 35GHz rectenna electric powerplant, b) microwave-induced 'Air Spike' and perimeter air-plasma generators, and c) MagnetoHydroDynamic-Fanjet engine with its superconducting magnets and external electrodes.
The use of microwave and millimeter wave beamed energy for propulsion of vehicles in the atmosphere and in space has been under study for at least 35 years. The need for improved propulsion technology is clear: chemical rockets orbit only a few percent of the liftoff mass at a cost of over $3,000/lb. The key advantage of the beamed power approach is to place the heavy and expensive components on the ground or in space, not in the vehicle. Early efforts to use microwaves in propulsion beamed at high average powers to heat rocket engine fuel for inter-orbital transfers from low earth orbit to the moon and Mars. In the past two decades, microwave sources have been developed to extraordinary peak powers over a wide frequency range and are now operating at repetition rates in excess of 100 Hz, giving average powers of -40 kW.1 Development of these sources has preceded in several parameters: a general movement to higher power, development of high power sources at increasingly higher frequencies and higher repetition rates at all frequencies. Fig. 1 shows the present state-of-the-art of peak power as a function of frequency.
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