15 sep 99 
 greg goebel ( 
 public domain

Since the beginning of space exploration, there have been efforts to build launch systems that would greatly reduce the cost of putting payloads into space. So far, none of these systems has been put into operation, but they have been the focus of a great deal of ingenuity.

One of the most interesting of these proposed launch systems is the lightcraft, a spacecraft blasted into orbit on a beam of laser light or microwave energy. This article describes the lightcraft concept and outlines current progress in the field.

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During the 1980s, Myrabo's interest in using a powerful laser to boost spacecraft into orbit progressed until by 1990 he and his colleagues at RPI were investigating concepts in detail, with backing from the US National Aeronautics & Space Administration (NASA) and Strategic Defense Initiative Organization (SDIO).

According to Myrabo, such a laser-boosted launch system offers much lower launch costs than a chemical rocket system. Since the spacecraft obtains most of its propulsive energy from external sources, a larger part of the spacecraft can be devoted to payload instead of fuel. As the spacecraft doesn't incorporate a large high-thrust rocket motor, it also is more reliable.




The focused energy is so intense that the hot air ionizes, creating a plasma finger that explodes outward and blasts the lightcraft upward at very high acceleration until the lightcraft reaches about Mach 1.


The configuration of the shroud is then adjusted to focus the laser light onto "igniters" underneath the ring that convert the air flowing into the shroud into plasma, providing thrust for the lightcraft. As the lightcraft accelerates to Mach 11, the ramjet operates in various "pulsed detonation" modes, in which thrust is obtained through a train of plasma explosions. During this flight phase, the airflow through the ramjet duct shifts from subsonic to supersonic, with the lightcraft then operating as a "supersonic combustion ramjet" or "scramjet".











HPM lightcraft development concepts focused on a ground-based microwave transmitter array, rather than a more ambitious microwave satellite power system. Early concepts for HPM lightcraft were basically an evolution of the laser lightcraft concept. The major difference was that instead of using reflectors to manipulate laser power, the HPM lightcraft uses an antenna array to transform microwave energy into propulsive power.


Much like the laser lightcraft, at higher speeds the microwave energy sustains pulsejet operation through the HPM lightcraft's ring duct. At high altitudes, an auxiliary orbiting microwave beam satellite heats hydrogen to provide pure rocket propulsion. An alternate scenario envisioned a self-contained chemical rocket for propulsion out of the atmosphere.

In the SSI studies, Myrabo envisioned launching a network of very small "microsats" with microwave energy. Large numbers of microsats would be put in orbit to construct orbiting communications, earth resources mapping, weather observation, or military reconnaissance networks.


The microsat is built with lightweight carbon composites, with a silicon carbide overcoat to protect the spacecraft from high temperatures. Subsystems include a 75 watt solar panel, rechargeable battery, communications and guidance electronics, magneto-optic data storage, and attitude control and pointing system.

The ground-based HPM array required to launch this microsat is 550 meters in diameter and operates at 220 GHz, a band where the atmosphere is mostly transparent to microwave energy. Beam power is 30 MW, with a maximum range of 500 to 800 kilometers.

HPM design concepts didn't stop there, however. Later work was more radical. Advanced HPM lightcraft were disk-shaped, resembling classical flying saucers, though in most concepts they flew top-first, rather than sideways like a frisbee.

Scenarios for such advanced HPM lightcraft involve energy provided by orbiting power satellites. The lightcraft converts the microwave energy into useful power with "rectifying antennas", or "rectennas", and has a ring of superconducting magnets underneath its rim that generate intense magnetic fields to control air and plasma flow, eliminating the need for a ring duct. Electrodes are also arranged around the edge of the disk to obtain MHD power from plasma flow.

The lightcraft overcomes the air resistance that would seem unavoidable in a top-first flight configuration by focusing some of the microwave energy above the spacecraft. The plasma generated acts as an "aerospike", creating a shockwave cone to divert airflow around the lightcraft.

Myrabo and his group have considered alternate scenarios for such HPM lightcraft, envisioning them for high-speed air transport.

Such advanced microwave lightcraft concepts were speculative, and Myrabo conceded that they would not be available for decades. However, their saucer-like configuration led UFO enthusiasts to suggest that the US government might actually be testing such vehicles at the present time.



However, in 1996, Myrabo once again obtained US military funding to actually fly small lightcraft models, working in conjunction with Franklin B. Mead of the US Air Force Research Laboratory. The Air Force sponsored small-scale tests of lightcraft propulsion at White Sands Missile Range, using a US Army 10-kilowatt pulsed carbon-dioxide laser. The tests were performed on beautifully machined solid aluminum models, ranging from 10 to 15 centimeters across and weighing about 50 grams.

Each laser lightcraft model resembled an acorn with a cone grafted onto its base. A model was spun up with a nitrogen gas jet before launch to keep it stable in flight, and then kilojoule laser pulses, pulsed at a rate of 28 times per second, were fired on its bottom shield. The shield focused the light to ionize the air at the bottom of the lightcraft into a plasma, blasting the model upward.


The research team has obtained funding for experiments with a more potent laser that offers 100 kilowatts (kW) of power for more aggressive lightcraft test flights. The mid-term goal of the lightcraft effort is to put a 1 kilogram lightcraft prototype into orbit by 2004, using a custom-built one MW laser.


My appreciation of the ingenuity of lightcraft is tempered by caution instilled by decades of listening to grand schemes of "spaceniks" that never happen. However, Myrabo and his group have established a certain credibility through their persistence and practical efforts. Lightcraft might be a long shot, but they are one that inspires a certain fascination and a little excitement.

Sources for this document include:-

  1. "Laser To Lift Lightcraft Into Space", by Bill Siuru, MECHANICAL ENGINEERING, September 1990, 54:57.
  2. "Microwave Launches Of Small Payloads", by Leik N. Myrabo, SSI UPDATE, November-December 1994.
  3. "Fly By Microwaves", by Gregory T. Pope, POPULAR MECHANICS, September 1995.
  4. "Mini Driver", by Leonard David, SMITHSONIAN AIR & SPACE, April-May 1998, 15.
  5. "Highways Of Light", by Leik N. Myrabo, SCIENTIFIC AMERICAN PRESENTS: THE FUTURE OF SPACE EXPLORATION, spring 1999, 66:67.
Greg Goebel (

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