The Lightcraft is a space- or air-

vehicle A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), ...

driven by

beam-powered propulsion Beam-powered propulsion, also known as directed energy propulsion, is a class of aircraft or spacecraft propulsion that uses energy beamed to the spacecraft from a remote power plant to provide energy. The beam is typically either a microwave or a ...

, the energy source powering the craft being external. It was conceptualized by aerospace engineering professor

Leik Myrabo Leik Myrabo is an aerospace engineering professor at Rensselaer Polytechnic Institute who retired from there in 2011.

Rensselaer Polytechnic Institute Rensselaer Polytechnic Institute () (RPI) is a private research university in Troy, New York, with an additional campus in Hartford, Connecticut. A third campus in Groton, Connecticut closed in 2018. RPI was established in 1824 by Stephen Van ...

in 1976, who developed the concept further with working prototypes, funded in the 1980s by the Strategic Defense Initiative organization, and the decade after by the ''Advanced Concept Division'' of the

US Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Signal ...

AFRL The Air Force Research Laboratory (AFRL) is a scientific research organization operated by the United States Air Force Materiel Command dedicated to leading the discovery, development, and integration of aerospace warfighting technologies, pl ...

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

's MFSC and the Lawrence Livermore National Laboratory. When a Lightcraft is in the atmosphere, air is used as the propellant material (reaction mass). In space, it would need to provide the propellant material from onboard tanks or from an

ablative In grammar, the ablative case (pronounced ; sometimes abbreviated ) is a grammatical case for nouns, pronouns, and adjectives in the grammars of various languages; it is sometimes used to express motion away from something, among other uses. ...

solid. By leaving the vehicle's power source on the ground and by using ambient atmosphere as a reaction mass for much of its ascent, a Lightcraft could potentially be capable of delivering a very large percentage of its launch mass to orbit as an SSTO, a difficult task for chemical rockets. As such, a Lightcraft is distinct from a solar sail because it is dependent on the expansion of

reaction mass Working mass, also referred to as reaction mass, is a mass against which a system operates in order to produce acceleration. In the case of a chemical rocket, for example, the reaction mass is the product of the burned fuel shot backwards to prov ...

to accelerate rather than being accelerated by

light pressure Radiation pressure is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of any wavelength that is ...

alone. Within the atmosphere, the Lightcraft propulsion is dependent on the external laser power only, so propulsive power is not limited to that generated by usual on-board machinery (i.e.

rocket A rocket (from it, rocchetto, , bobbin/spool) is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely fr ...

s).

Types

Laser-powered propulsion

First small-scale models used

laser propulsion Laser propulsion is a form of beam-powered propulsion where the energy source is a remote (usually ground-based) laser system and separate from the reaction mass. This form of propulsion differs from a conventional chemical rocket where both energy ...

which is a technique still in early stages of development. Lightcraft prototypes are made of solid

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

machined axisymmetrically. The nose is shaped as a blunted cone for aerodynamical purpose. The rim has an annular air

inlet An inlet is a (usually long and narrow) indentation of a shoreline, such as a small arm, bay, sound, fjord, lagoon or marsh, that leads to an enclosed larger body of water such as a lake, estuary, gulf or marginal sea. Overview In marine geogra ...

. The aft is a funnel polished as a concave mirror with a pointy tail in the middle extending back out of the body, acting as a

parabolic reflector A parabolic (or paraboloid or paraboloidal) reflector (or dish or mirror) is a reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular paraboloid, that is, the surface gener ...

. A ground-based

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

aims a high power pulse to the mirror stern. The beam is reflected and focuses to heat the air at an extremely high temperature up to 30,000 degrees, transforming it in a plasma that violently expands, pushing the craft forward. Air is renewed through the inlet and the cycle is repeated at high frequency, acting as an external pulse detonation engine producing thrust. In April 1997, tests by Leik Myrabo in cooperation with the

US Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cla ...

White Sands Missile Range White Sands Missile Range (WSMR) is a United States Army military testing area and firing range located in the US state of New Mexico. The range was originally established as the White Sands Proving Ground on 9July 1945. White Sands National P ...

demonstrated the basic feasibility to propel objects in this way, using a 10-kW ground-based pulsed

carbon dioxide laser The carbon-dioxide laser (CO2 laser) was one of the earliest gas lasers to be developed. It was invented by Kumar Patel of Bell Labs in 1964 and is still one of the most useful types of laser. Carbon-dioxide lasers are the highest-power contin ...

(1 kJ per pulse, 30 µs pulse at 10 Hz frequency). The test succeeded in reaching over one hundred feet, which compares to

Robert Goddard Robert Hutchings Goddard (October 5, 1882 – August 10, 1945) was an American engineer, professor, physicist, and inventor who is credited with creating and building the world's first liquid-fueled rocket. Goddard successfully laun ...

's first test flight of his rocket design. In October 2000, a new flight record was set with a flight lasting 10.5 seconds and reaching 71 meters (233 feet) using the same laser, but this time providing an on-board plastic ablative propellant, and rotating the body around its axis at high speed (over 10,000

rpm Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...

) to stabilize the craft with a

gyroscopic effect A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rota ...

. (Lightcraft presentation at time 10:00–32:00).

Microwave-powered and MHD propulsion

More advanced concepts of the Lightcraft replace the laser pulses by a

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...

beam or

maser A maser (, an acronym for microwave amplification by stimulated emission of radiation) is a device that produces coherent electromagnetic waves through amplification by stimulated emission. The first maser was built by Charles H. Townes, Ja ...

that can still be ground-based, or alternatively put into

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

, the beams being emitted from above the ascending craft by a series of space-based solar power

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...

s that could more easily keep track of the Lightcraft along its curved

ballistic trajectory Projectile motion is a form of motion experienced by an object or particle (a projectile) that is projected in a gravitational field, such as from Earth's surface, and moves along a curved path under the action of gravity only. In the part ...

. The microwave beam detonates the air below the craft exactly like the laser version, but some energy from the beam is also diverted and converted on board by high-power

rectenna A rectenna (''rec''tifying ant''enna'') is a special type of receiving antenna that is used for converting electromagnetic energy into direct current (DC) electricity. They are used in wireless power transmission systems that transmit power by r ...

s into

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...

to power an external-flow airbreathing MHD drive called by Myrabo an ''MHD slipstream accelerator''. As an MHD accelerator works only with an

electrically conductive Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allow ...

medium, some of the incoming microwaves are also diverted within the Lightcraft through a series of transparent windows and mirror sections, then re-emitted in the air near the

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...

s of the MHD accelerators located around the rim. The air becomes ionized in these places, allowing MHD interaction of Lorentz forces to actively control the

airflow Airflow, or air flow, is the movement of air. The primary cause of airflow is the existence of air. Air behaves in a fluid manner, meaning particles naturally flow from areas of higher pressure to those where the pressure is lower. Atmospheric ...

around a discoidal shape that otherwise (i.e. passively) has very bad aerodynamical properties due to its largest surface, a flat plate, being perpendicular to the flow. Finally, a laser or some part of the microwaves are also focused as a ''plasma torch'' at some distance above the Lightcraft, creating an aerospike that detaches and mitigates the bow

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...

ahead of the craft when it evolves at

supersonic speed Supersonic speed is the speed of an object that exceeds the speed of sound ( Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately . Speeds greater than five times ...

s, lowering heat transfert to the walls. The distance and intensity of the aerospike are tuned according to the

atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, ...

, temperature gradients and

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity is a ...

of the airflow to actively shape the shock wave so the

boundary layer In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary cond ...

can be optimally controlled by the radial MHD slipstream accelerators. The Lightcraft concept thus combines

magnetohydrodynamic Magnetohydrodynamics (MHD; also called magneto-fluid dynamics or hydromagnetics) is the study of the magnetic properties and behaviour of electrically conducting fluids. Examples of such magnetofluids include plasmas, liquid metals, ...

active flow control Flow control is a major rapidly-evolving field of fluid dynamics. It implies a small change of a configuration serving an ideally large engineering benefit, like drag reduction, lift increase, mixing enhancement or noise reduction. This change may ...

and beam-powered propulsion mechanisms to enable

hypersonic flight Hypersonic flight is flight through the atmosphere below altitudes of about 90 km at speeds greater than Mach 5, a speed where dissociation of air begins to become significant and high heat loads exist. Speeds of Mach 25+ have been achiev ...

, solving the classical problem of aerial MHD propulsion (i.e. lack of a light power source offering enough energy to feed such systems) by outsourcing the power source. Using microwaves instead of a laser allows four combined actions: propulsive detonation, shockwave mitigation, ionization control and electrical feeding of MHD drives.

Status

In 2008, the Office of Scientific and Technical Information of the US Department of Energy published an article on the official website in which its author William Larson talks about successfully completed research in this area. After Leik Myrabo's retirement from Rensselaer Polytechnic Institute in 2011, the homepage of his private company ''Lightcraft Technologies, Inc.'' (LTI) disappeared with a temporary notification explaining that a "site renovation" was ongoing. The old LTI logo and the small-scale model of the laser Lightcraft prototype of the 1990s were swapped for the occasion with a new logo and an artist image showing a full-scale lenticular microwave-powered Lightcraft with active peripheral MHD slipstream accelerators in orbit above the Earth. This plasma thruster image is shown on the cover of Myrabo's book about the Lightcraft. That presaged new developments but the site went eventually completely offline and never reappeared since. At that time though, laser aerospike and PDE testing continued in the hypersonic

wind tunnel Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...

of the ''Laboratory of Hypersonics and Aerothermodynamics'' at the Department of Aerospace Science and Technology of the Brazilian Air Force in

São José dos Campos São José dos Campos (, meaning Saint Joseph of the Fields) is a major city and the seat of the Municipalities of Brazil, municipality of the same name in the state of São Paulo (state), São Paulo, Brazil. One of the leading industrial and res ...

References

External links