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LIGHTCRAFT

A lightcraft with laser-ignited air burst.

Lightcraft Micro Satellite Launcher
Tech Level: 13
Lightcraft Cargo Lifter
Tech Level: 15
Lightcraft Passenger Vehicle
Tech Level: 15

Lightcraft are an unusual but undeniably workable idea that use beamed light from an external source to help "push" a specially designed vehicle into orbit by exploding the air under it. Experiments with such vehicles are being actively sponsored by NASA, the US Air Force Research Laboratory, and private interests like the Foundation for International Non-government Development of Space (FINDS) and Lightcraft Technologies, Inc.(LTI) In 2000, Lightcraft Technologies, Inc launched a lightcraft weighing 1.8 ounces to a height of 233 ft. using a US Army 10-kilowatt pulsed carbon dioxide laser.

LIGHTCRAFT BASICS

The actual lightcraft vehicles being used in experiments today are small, cone-shaped devices with a specially-designed parabolic mirror on their aft ends. The vehicles "ride" along a pulsed infrared laser beam fired from the ground. The reflective surfaces on the underside of the craft focuses the beam into a ring, where it heats air to a temperature roughly five times the surface of the sun (over 50,000 degrees C), causing the air to expand explosively for thrust. The forward motion of the craft feeds new air into the focusing ring for the next pulse. The lightcraft are spin-stabilized, launched at about 10,000 rpms.

Getting a lightcraft to orbit seems to mostly be about ratcheting up the launching laserís power and focusing ability, enabling it to "push" heavier payloads farther.

One interesting bit of trivia from the LTI test in 2000 is that the experimentors worked closely with NORAD to time their tests so their laser would not accidentally "blind" any satellite passing overhead. Whether this danger could have an influence on the development or proliferation of lightcraft technology remains to be seen.


LIGHTCRAFT MICRO SATELLITE LAUNCHER
Tech Level: 13

A micro satellite is any satellite that weighs 100 kilograms or less.

Eventually LTI and others researching lightcraft would like to build an actual satellite launcher. While the laser-launch abilities of the concept will probably not be able to haul the multi-ton payloads into orbit as more conventional orbital insertion vehicles, it does have the advantage of getting many smaller payloads (100 kg or less) into orbit significantly faster.

When a lightcraft runs out of usable air density (about 30 km up), it can switch to an on-board store of liquid hydrogen to use as laser-combusted propellant for the final boost into orbit. A micro satellite weighing 1 kg would need about 1 kg of hydrogen fuel to make orbit.

The researchers envision eventually orbiting 100 kg payloads with parabolic focusing mirrors of about 1.4 meters in diameter. The launching laser for such a payload would be on the order of 100 megawatts. Alternately, the launching beam need not be from one laser but many grouped together creating a single combinedpulse of equivalent power; this latter arrangement may be more efficient in focusing the apprpriate power on the lightcraft at varying altitudes.

Masers (microwave lasers) have been mentioned as alternative to visible-light lasers in launching lightcraft. Masers do not have the energy density of their visible-light cousins, and thus lightcraft mirrors would have to be made larger, but they are also considerbly less expensive and easier to scale up power-wise.


LIGHTCRAFT CARGO LIFTER
Tech Level: 15

A far more ambitious and exotic concept, involving a reflective lifting body which uses beamed power from orbit to create an airspike and electrohydrodynamic thrust to lift cargo into orbit.

The following description is taken near-verbatim from an article published in Scientific American Presents: The Future of Space Exploration (May 1999), titled "Highways of Light" by Leik N. Myrabo, one of the scientists who pioneered the lightcraft concept at the US Air Force Research Laboratory:

"I have also designed a more sophisticated beamed-energy craft, operating on a different principle...These craft would be better for carrying large cargoes because they can create thrust more efficiently.

"A mirror in the craft focuses some of the incoming beamed energy (from an orbital solar-power station) at a point one vehicle-diameter ahead of the vehicle. The intense heat creates an explosive "air spike" that diverts oncoming air past the vehicle, decreasing drag and reducing the heating of the craft.

"The craft taps some additional beamed energy to generate powerful electrical fields around the rim, which ionizes the surrounding air. It also uses superconducting magnets to create strong magnetic fields in that region. When the ionized air moves through the electric and magnetic fields in this configuration, magnetohydrodynamic forces come into play that accelerate the slipstream to create thrust.

"By varying the amount of energy it reflects forward, the lightcraft can control the airflow around the vehicle. I demonstrated reduction of drag by an airspike in April 1995 in a hypersonic shock tunnel at Rensselaer Polytechnic institute, though with an electrically heated plasma torch rather than with laser power. Tests aimed at generating magnetohydrodynamic thrust, using a 15-cm diameter device, have just begun. A person-sized lightcraft of this type driven by microwaves or by a 1000 megawatt pulsed laser should be able to operate at altitudes up to 50 km and to accelerate easily to orbital velocities."

Myraboís cargo lifter would be dependent on orbiting solar-power satellites, basically thin "wheels" constructed in orbit about 1 kilometer in diameter and at most a few millimeters thick. One side would be the solar collector, while the earth-facing side would hold billions of miniature solid-state microwave transmitters. This arrangement could theoretically provide up to 4.3 gigawatts of power to any "lifting" beam aimed at the lightcraft. The lightcraft vehicle could be fed this power gradually, allowing for a five-minute ground-to-orbit flight of no more than 3 gís of acceleration, similar to what the Space Shuttle experiences upon launch. Or the solar-power satellite could dump all its power into a single, 54-second burst that could zing the lightcraft into orbit at 20 gís.


LIGHTCRAFT PASSENGER VEHICLE
Tech Level: 15

Dr. Leik Myrabo more recently launched the Lightcraft Project at the Rensselaer Polytechnic Institute, which envisions using the above concepts to create an even more advanced 12-man lightcraft orbiter that would regularly ferry cargo and passengers between the ground and space facilities. These lightcraft would be supplemented by ion engines and maglev devices in order to facilitate take-off, landing, and in-space maneuvering. The interior is filled mostly with a helium/oxygen mixture, to make the craft buoyant in the lower atmosphere and to assist in take-off. Passengers would be immersed in liquid suspension tanks for the quick but high-g boosts to and from space.


RELATED INFORMATION

Lightcraft Technologies Inc. Homepage:

http://www.lightcrafttechnologies.com/

The Lightcraft Project at Rensselaer Polytechnic Institute:

http://www-aero.meche.rpi.edu/Curriculum/TAVD/

A Much More Detailed Article on Dr. Myrabo's Lightcraft Concepts:

http://tonylance.mybravenet.com/liteship.html



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