The achievement can be likened to Robert Goddard's first successful flights of his liquid propellant chemical rocket that attained a height of 41 feet after a 2 1/2 second burn in March of 1926. In sharp contrast with Goddard's rockets, there is absolutely no fuel on board this prototype laser-boosted craft, which has a diameter of 15 cm, mass of 40-50 grams, machined from a solid block of 6061-T6 aluminum.

The Air Force Research Laboratory's Propulsion Directorate at Edwards AFB CA is conducting these technology development research and flight demonstrations. Additional research money has been provided this year by NASA's Marshall Space Flight Center's (MSFC) Advanced Space Transportation Program. The laser propelled flights take place at the White Sands Missile Range (WSMR) in New Mexico at the High Energy Laser Systems Test Facility (HELSTF). The Lightcraft propulsion research employs the Pulsed Laser Vulnerability Test System (PLVTS), a 10 kilowatt laser built by AVCO TEXTRON for the Army. PLVTS is the highest average power, pulsed carbon dioxide laser presently operating in the United States.

The laser-propelled vehicle, called "Lightcraft" because it flies on a beam of laser light, is designed to harness the energy of a laser beam and convert it into propulsive thrust. The Lightcraft receives the kilojoule pulses from the PLVTS laser at a rate of 10 times per second upon the concentrating mirror that forms its rear section. The function of this parabolic mirror is to focus the pulsed laser energy into a ring-shaped "absorption/propulsion" chamber. Here the laser beam is concentrated to extremely high intensities, sufficient to momentarily burst the inlet air into a highly luminous plasma (10-30,000 K), with instantaneous pressures reaching tens of atmospheres providing thrust. This airbreathing pulsed detonation engine concept owes its origins to the German V1 "Buzz Bomb" of WW II that ran on aviation fuel.

The laser Lightcraft concept was first proposed and developed by Prof. Leik Myrabo of Rensselaer Polytechnic Institute in Troy, New York, under sponsorship of the Laser Propulsion Program of the former Strategic Defense Initiative Office (SDIO). He is now collaborating with the Air Force Research Laboratory's Propulsion Directorate at Edwards AFB CA to conduct field tests to demonstrate how the craft can be propelled using available high powered lasers. Dr Franklin Mead of the lab's advanced propulsion group studied the initial SDIO proposal, and offered Myrabo a multi-year sabbatical position at the lab and assistance in developing and validating the concept.

Myrabo's original SDIO Lightcraft concept was designed as a single-stage-to-orbit spacecraft that would become a microsatellite upon reaching orbit. The spacecraft lifts-off in a laser propelled airbreathing engine mode, and as it nears Mach 5 speed and 30 km altitude, shifts into a laser propelled rocket mode. The airbreathing engine mode would develop quasi-steady thrust by pulsing at hundreds to thousands of times a second -- depending on the mach number and altitude flown along the boost trajectory into orbit. The rocket mode would use on-board propellant, in the form of liquid hydrogen or nitrogen, to convert and expand the laser energy for propulsion once the Lightcraft had climbed above the atmosphere. Unlike Goddard�s rocket engine, no oxydizer is required. The SDIO study showed that all launch to orbital conditions for a laser propelled vehicle could be satisified by a single, high-power ground-based laser -- with, or without the aid of a low altitude laser relay mirror.

Myrabo and Mead are the project team co-directors for this laser Lightcraft research and development effort. Five different Lightcraft designs have been flight tested using the pointing and tracking system on the PLVTS laser, run by Stephen Squires and Chris Beairsto of WSMR's Directorate of Applied Technology Test and Simulation.

Laser boost capability has been demonstrated at the White Sands facility with Lightcraft reaching 14 feet vertically in 2-second gyroscopically stabilized free flights, as well as 400 foot horizontal guide-wire flights lasting 10 to 20 seconds.

The researchers plan to increase the Lightcraft's free flight altitude in November by moving the launch stand outside Test Cell #3, where the flights will no longer be limited by lab ceiling height. The near-term goal is to reach an altitude of 1 Kilometer in the next 18 months with the PLVTS laser. To climb even higher, e.g., 10 to 100 km or near the edge of space, will require re-activation of the 150-Kw pulsed "Driver" CO2 laser, now stored in Test Cell #2 at HELSTF. Preparations are underway to enlist this powerful infrared laser that was developed at the AVCO Research Laboratory (Everett, MA) in the mid '70's -- under the guidance of Dr. Arthur Kantrowitz, a long time advocate of laser propulsion.

The predominant reason for investigating this laser launch concept is its low cost, simplicity and responsiveness upon demand. Laser Lightcraft and their propulsion modes are a radical departure from the chemically fueled rockets used today. If successful, this new energy beam propulsion technology will supplement rather than replace current manned and unmanned launch systems.

The approach holds great promise for reducing the launch costs of microsatellites by several orders of magnitude less than today's chemical-fueled rocket technology. The evolution of ultra-lightweight high temperature materials, dual-mode laser propulsion engines, powerful lasers, and the opportunity to change science fiction into scientific fact are the driving forces behind this joint AFRL/ MSFC research effort, pursueing an innovative and promising method for reaching space.