Flights of a laser-powered lightcraft during laser beam hand-off experiments

Abstract

The Lightcraft Technology Demonstrator (LTD) was a laser propelled trans-atmospheric vehicle concept developed at Rensselaer Polytechnic Institute (RPI) for Lawrence Livermore National Laboratory and the SDIO Laser Propulsion program in the late 1980's. This laser launch concept was envisioned to employ a 100 MW-class ground-based laser to transmit power directly to the Lightcraft in flight. An advanced, combined-cycle engine would propel a 120 kg (265 Ib) dry mass, 1.4 m (4.59 ft) diameter LTD, with a mass fraction of 0.5, to orbit The LTD vehicle would then become an autonomous sensor satellite capable of delivering precise, high quality information typical of today's large orbital platforms. Here, the 1 m diameter afterbody optic served as optical telescope or receiving/transmitting antenna for low power laser or microwave communication systems. The LTD concept, was, a microsatellite in which the laser propulsion engine and satellite hardware were intimately shared. The forebody aeroshell acted as an external compression surface (i.e., the airbreathing engine inlet). The afterbody had a dual function as a primary receptive optic (parabolic mirror) for the laser beam and as an external expansion surface (plug nozzle) during the laser rocket mode which is used only in space. The primary thrust structure was the annular shroud. The shroud serves as both air inlet and impulsive thrust surface during the airbreathing mode. In the rocket mode, the inlets are closed, and the afterbody and *Sr. Scientist, AIAA Member f Laser Test Engineer JLaser Test Engineer §Laser Test Physicist This paper is declared a work of the U.S. Government and is not subject to copy right protection in the United States Stephen Squires, Chris Beairsto,* & Mike Thurston Army Test and Evaluation Command Applied Technology Test & Simulation Directorate High Energy Laser Systems Test Facility White Sands Missile Range NM 88002 shroud combine to form the rocket thrust chamber and plug (aerospike-type) nozzle. The dominant motivation behind the LTD study was to provide an example of how laser propulsion could reduce, by an order-of-magnitude or more, the production and launch costs of sensor satellites. The 1989 study concluded that a vehicle production cost of $l,000/kg was realizable, and that launch costs must be limited to less than $100/kg for laser propulsion to play a significant role in the future of space transportation. A subscale version of the LTD vehicle is being developed by the Air Force Research Laboratory's Propulsion Directorate.' This laserpowered Lightcraft, which is being used during laser hand-off' tests, is a 1/lOth-scale model of a Laser Lightcraft vehicle concept that is envisioned to launch 1 kg (2.2 Ib) Laser Lightcraft into a lowEarth-orbit (LEO) for less than $500 of electrical power using a megawatt class CO2 pulsed, electric laser some time in the next 5 to 7 years. Production costs of about $3,000 for the 1 kg spacecraft appear reasonable at present. Currently, laser tests are being conducted at the High Energy Laser Systems Test Facility (HELSTF), White Sands Missile Range (WSMR), New Mexico, using the Pulsed Laser Vulnerability Test system (PLVTS) CO2 electric discharge laser. This laser is a pulsed wave, closed cycle, 10 kW CO2 laser with a pulse repetition rate of 1 to 30 pps (selectable), and a variable pulse width of 5 to 30 us. For the laser experiments, the laser is being operated at 25 pps and 18 us pulse widths. This paper gives details of laser modifications to improve performance over the fouryear Ugaicraft testing period. Details of the Lightcraft performance measurements and their predicected impact on the laser experiments wig be discussed. ^sfeoSjotege taken daring Ifce outdoor free flight tests will be discussed in this paper and shown during the presentation. (c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. The objective of the current vertical flight program is to develop a laser beam hand-off technique for future flight tests powered to the edge of space (~30 km), and to extend Laser Lightcraft flights to significantly higher altitudes in the range of 150 to 300 m. The technique is the method by which the laser light beam is transferred to consecutively larger telescopes during a Lightcraft launch. In other words, the laser light is intiially directed through a small diameter telescope at the start of the launch.. Then, as the Lightcraft speeds to higher and higher altitudes, the laser light is suddenly shifted, at a prearranged altitude, to a larger diameter telescope. This larger telescope allows the beam to be appropriately focused at the higher altitudes. This laser will probably occur several times during the actual launch of LEO of a full-scale Lightcraft.