Vertical flight and pendulum experiments have been carried out with a simple paraboloid type lightcraft in the airbreathing mode. Pulsed laser energy ofup to 240 J/pulse was delivered from a highly reproducible e-beam sustained C02laser at repetition rates up to 45 Hz. The lightcraft mass was varied in the range between 22 and 55 g. An average thrust of 1. 1 Nhas been derived from the flight data and the highest impulse coupling coefficient found in the pendulum experiments was 33.3•1O NS/J. A double shock wave was detected that leaves the thruster exit and an attempt was made to model the thrust, using a modification ofSedov's similarity solution for a blast wave. Finally, the propulsion requirements for the launch of a 10 kg mass into low Earth orbit are presented.

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)2 AbstractThe impulse coupling coefficients of two radically different laser propulsion thruster concepts (lightcrafts), each 10 cm in diameter, have been measured under equal conditions using two different pendulum test stands. One test stand and one lightcraft of toroidal shape were provided by the U.S. Air Force Research Laboratory. The other test stand and a bell shaped (i.e. a paraboloid) lightcraft were those of the German Aerospace Center (DLR). All experiments employed the DLR electron-beam sustained, pulsed CO2 laser with pulse energies up to 400 J. The laser was operated with two configurations: 1) a stable resonator (flat beam profile); and, 2) an unstable resonator (ring shaped beam profile). A first series of experiments was carried out in the open laboratory environment. Propellant, therefore, was either the surrounding air alone, or Delrin as an added solid propellant. The coupling coefficient was determined as a function of the laser pulse energy. In a second series, the same experiments were repeated at various reduced pressure levels with the German lightcraft suspended in a vacuum vessel. This simulates the conditions of a transitional flight from within the atmosphere to outer space. As an additional parameter the specific mass consumption of Delrin (gram/Joule) was measured for each parameter set, allowing the determination of the average exhaust velocity in vacuum.

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Experimental results on a pulsed e-beam sustained discharge CO laser are reported. The gas was cooled down to a temperature of 50 C, the active volume was 1.5 1. Optimizing gas composition, gas pressure, and output mirror reflectivity, pulse energies up to 8 J corresponding to a specffic value of 16 J Ilbar could be demonstrated. The spectrum of the laser radiation was analyzed, lines between 2.8 and 3.3 im were found. In burst mode operation, up to 100 pulses at pulse frequencies up to 30 Hz have been achieved, resulting in an average laser power of 60 W.