The LightCraft is a concept for a laser-powered launch system that was originally the brainchild of scientist Leik Myrabo and his students at Rensselaer Polytechnic Institute. It was originally proposed in two forms or generations of technology using the same propulsion principles but very difference energy sources and radically different vehicle designs. The first-generation LightCraft employs infrared laser energy to propel a capsule-like vehicle in the manner of a thermal-driven jet engine coupled to a radial aerospike rocket engine, the capsule featuring a conical reflector on the bottom surrounded by a reflector cowl which together confine the energy of a laser beam to a ring just inside the cowl that superheats air to an explosive plasma. By optically controlling the profile of the plasma ring, modulators in ring cowl can perform attitude control in much the manner of a radial aerospike engine. Laser energy must be projected to the vehicle from the ground continuously during launch, the vehicle using a shallow launch trajectory to exploit the atmosphere as its propellant for as long as possible as it accelerates to orbital trajectory. Out of the atmosphere it must rely on its own carried supply of propellant in the form of inert gas or water and to achieve greater than LEO the system must supplement ground-based lasers with orbital lasers and propellant refueling stations.
While potentially extremely efficient, the first-generation LightCraft is limited in functional scale by the maximum power of the lasers used to power it, the largest and most powerful of current high-power lasers being barely powerful enough to support a micro-satellite launcher. But the simplicity and efficiency of the system would potentially be such that, as Myrabo suggests, there could be a reduction in launch cost by a factor of 50 over chemical rockets, relative to the scale of the system. Key engineering challenges at present include laser power and attenuation over distance, beam tracking of the vehicle, and on-board optical modulation for attitude control.
The second-generation LightCraft represents one of the most sophisticated and exotic launch technology concepts ever proposed outside of the realm of science fiction, but one which is not discussed as much by current proponents of the LightCraft because of the negative perception generated by early descriptions of the system which made it seem analogous to the flying saucers of modern folklore. The second-generation LightCraft would rely on microwave energy projected by a network of solar powered orbital maser stations. It’s hybrid vehicle would combine the characteristics of spacecraft and airship, using a lenticular shaped dirigible hull around a center pressure capsule –most-likely employing a Trans-Hab style structure to reduce mass much like the pressurized compartments of the proposed Aquarian Airship. The hull of the vessel would integrate a sophisticated array of field coils, microwave collectors, and plasma generators, the lenticular hull shape intended to be efficiently streamlined for horizontal flight while serving double-duty as a parabolic microwave receiver dish for microwave energy beamed to the vehicle from orbit above.
The second-generation LightCraft would employ a form of propulsion similar to the first-generation system, the microwave energy gathered by the hull structure focused into a superheated ring around the perimeter of the vehicle and controlled by magnetic confinement. A portion of the microwave energy collected by the vehicle would be focused into a thermal airspike (not to be confused with the concept of an aerospike engine) which used to generate a shockwave in the path of the vehicle that provides it with a shroud of low-pressure atmosphere and whose profile is actively controlled to concentrate atmospheric density at the point of the plasma ring, thus functioning as an integral part of a powerful magnetohydrodynamic thrust system. In effect, the entire vehicle is a large powerful engine. In low-speed horizontal flight the plasma systems would provide lower power horizontal thrust and rely on stored electric energy. In combination with lighter-than-air lift, this would be used to position the vehicle at high altitude along launch vectors that are serviced by orbital masers. Intercepting these powerful maser beams, the vehicle would switch to its vertical flight mode, exploiting atmosphere as a propellant as the first-generation system does and then relying on stored propellant in the form of gas or water beyond the atmosphere. Using its hull and a bottom-positioned airspike as re-entry shields, the system would also be able to return to Earth and would be fully reusable. Owing to the extremely high ISP of this form of propulsion, the system would be also well suited to interorbital travel, thus Myrabo envisioned a solar-system-wide network of maser and refueling stations providing a kind of interplanetary highway system, though it may be unlikely a vehicle of a single structural design would be practical for all space travel.
The second-generation LightCraft is an extremely exotic system and, given our current understanding of the technologies involved, it could be a century before this form of vehicle could even begin being experimented with. But its technology does parallel many other areas of propulsion research with independent applications and so it could be a matter of it waiting for their convergence.
The Bifrost program would likely pursue first-generation LightCraft development as the lowest-cost approach to exploring the potential of direct use of electric power for orbital access with the ultimate goal of being the development of a reusable manned spacecraft based on a modest-sized capsule using ballistic re-entry and either simple parachute splash-down recovery (in early forms) or a powered landing system using air-spike re-entry shielding and a platform-based landing cradle much like that used with the later-generation reusable Exocet system. This most-sophisticated form of the first-generation LightCraft would be in many ways similar to an Apollo crew capsule in form with a top-mounted docking/access port and similarly limited to just a few passengers. In fact, this could be competitive with initial Aquarian Space Elevator development, since the LightCraft is likely to offer comparable early payload capacity at less cost and with an extremely high launch frequency. In fact, an early LightCraft system would be economically viable simply in the role of very-high-speed terrestrial shipping and passenger transit. But the technology is probably limited in maximum practical scale to that Apollo capsule scale of vehicle. This would certainly be very useful with such a high launch rate but not as powerful long-term as a large orbital tether able to carry railway-car-sized elevators directly to a GEO station. Thus long-term its use would become increasingly specialized.
The second-generation LightCraft is a much more speculative concept and may or may not be pursued by the Bifrost program –it’s a bit too difficult to predict the possible fture pace of development for it. It would seem a logical follow-on to work with the SkyScraper LTA assisted rocket project but its technology is so sophisticated than it may not be a practical system until very late in the Asgard phase of space development and late in the development of the Space Elevator. However, it would by then have the potential to obsolesce any rocket based terrestrial launch technology still in use, while the concept of projected energy inter-orbital propulsion has equal potential to magnetic acceleration as the basis of the late-Asgard/early-Solaria Ballistic Railway Network.
- Mountain Waverider
- UltraLight SSTO
- Marine Mass Launcher - MML
- Bifrost Space Elevator
- Bifrost Support Systems