The Lightcraft is a space- or air-

vehicle A vehicle () is a machine designed for self-propulsion, usually to transport people, cargo, or both. The term "vehicle" typically refers to land vehicles such as human-powered land vehicle, human-powered vehicles (e.g. bicycles, tricycles, velo ...

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 at

Rensselaer Polytechnic Institute Rensselaer Polytechnic Institute (; RPI) is a private university, private research university in Troy, New York, United States. It is the oldest technological university in the English-speaking world and the Western Hemisphere. It was establishe ...

in 1976, who developed the concept further with working prototypes, funded in the 1980s by the

Strategic Defense Initiative The Strategic Defense Initiative (SDI) was a proposed missile defense system intended to protect the United States from attack by ballistic nuclear missiles. The program was announced in 1983, by President Ronald Reagan. Reagan called for a ...

organization, and the decade after by the ''Advanced Concept Division'' of the

US Air Force The United States Air Force (USAF) is the Air force, air service branch of the United States Department of Defense. It is one of the six United States Armed Forces and one of the eight uniformed services of the United States. Tracing its ori ...

AFRL The Air Force Research Laboratory (AFRL) is a scientific research and development detachment of the United States Air Force Materiel Command dedicated to leading the discovery, development, and integration of direct-energy based aerospace warf ...

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

's MFSC and the

Lawrence Livermore National Laboratory Lawrence Livermore National Laboratory (LLNL) is a Federally funded research and development centers, federally funded research and development center in Livermore, California, United States. Originally established in 1952, the laboratory now i ...

. 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 ; abbreviated ) is a grammatical case for nouns, pronouns, and adjectives in the grammars of various languages. It is used to indicate motion away from something, make comparisons, and serve various o ...

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 single-stage-to-orbit (SSTO) vehicle reaches orbit from the surface of a body using only propellants and fluids and without expending tanks, engines, or other major hardware. The term usually, but not exclusively refers to reusable vehicles. ...

, a difficult task for chemical rockets. As such, a Lightcraft is distinct from a

solar sail Solar sails (also known as lightsails, light sails, and photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large surfaces. A number of spaceflight missions to test solar propulsion and navigati ...

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 (chemistry), product of the burned fuel sh ...

to accelerate rather than being accelerated by

light pressure Radiation pressure (also known as light pressure) is mechanical pressure exerted upon a surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of ...

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 , and so named for its shape) is a vehicle that uses jet propulsion to accelerate without using any surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely ...

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 (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

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

inlet An inlet is a typically long and narrow indentation of a shoreline such as a small arm, cove, 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 ...

. The aft is a funnel polished as a

concave mirror A curved mirror is a mirror with a curved reflecting surface. The surface may be either ''convex'' (bulging outward) or ''concave'' (recessed inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are ...

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 Mirror, 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 ge ...

. 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'' originated as an acronym for light amplification by stimulated emission of radi ...

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 A pulse detonation engine (PDE) is a type of propulsion system that uses detonation waves to combust the fuel and oxidizer mixture. The engine is pulsed because the mixture must be renewed in the combustion chamber between each detonation wav ...

producing thrust. In April 1997, tests by Leik Myrabo in cooperation with the

US Army The United States Army (USA) is the primary land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution.Article II, section 2, clause 1 of the United Stat ...

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 in 1941 as the Alamogordo Bombing and Gunnery Range, where the Trinity t ...

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 C. Kumar N. Patel, Kumar Patel of Bell Labs in 1964 and is still one of the most useful types of laser. Carbon dioxide, Carbon-dioxide lase ...

(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, which was successfully lau ...

'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 r⋅min−1) is a unit of rotational speed (or rotational frequency) for rotating machines. One revolution per minute is equivalent to hertz. Standards ISO 80000-3:2019 def ...

) 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 shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...

beam or

maser A maser is a device that produces coherent electromagnetic waves ( microwaves), through amplification by stimulated emission. The term is an acronym for microwave amplification by stimulated emission of radiation. Nikolay Basov, Alexander Pr ...

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

orbit In celestial mechanics, an orbit (also known as orbital revolution) 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 ...

, the beams being emitted from above the ascending craft by a series of

space-based solar power Space-based solar power (SBSP or SSP) is the concept of collecting solar power in outer space with solar power satellites (SPS) and distributing it to Earth. Its advantages include a higher collection of energy due to the lack of reflection ...

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

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

ballistic trajectory In physics, projectile motion describes the motion of an object that is launched into the air and moves under the influence of gravity alone, with air resistance neglected. In this idealized model, the object follows a parabolic path determin ...

. 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 rectennas into

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

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 volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity in ...

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 a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

s of the MHD accelerators located around the rim. The air becomes ionized in these places, allowing MHD interaction of

Lorentz force In electromagnetism, the Lorentz force is the force exerted on a charged particle by electric and magnetic fields. It determines how charged particles move in electromagnetic environments and underlies many physical phenomena, from the operation ...

s to actively control the

airflow Airflow, or air flow, is the movement 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 air pressure is directly related to altitude, temperat ...

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 number, 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 tha ...

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 air pressure or 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 1,013. ...

temperature gradient A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature spatial gradient is a vector quantity with Dimensional analysis, ...

s and

velocity Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...

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 Boundary (thermodynamic), bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces ...

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

magnetohydrodynamic In physics and engineering, magnetohydrodynamics (MHD; also called magneto-fluid dynamics or hydromagnetics) is a model of electrically conducting fluids that treats all interpenetrating particle species together as a single continu ...

active flow control and beam-powered propulsion mechanisms to enable

hypersonic flight Hypersonic flight is flight through the atmosphere below altitudes of about at Hypersonic speed, speeds greater than Mach 5, a speed where Dissociation (chemistry), dissociation of air begins to become significant and high heat loads exist. Spe ...

, 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 A wind tunnel is "an apparatus for producing a controlled stream of air for conducting aerodynamic experiments". The experiment is conducted in the test section of the wind tunnel and a complete tunnel configuration includes air ducting to and f ...

of the ''Laboratory of Hypersonics and Aerothermodynamics'' at the

Department of Aerospace Science and Technology The Brazilian Department of Science and Aerospace Technology (; DCTA) is the national military research center for aviation and space flight. It is subordinated to the Brazilian Air Force (FAB). It coordinates all technical and scientific activiti ...

of the

Brazilian Air Force The Brazilian Air Force (, FAB) is the air branch of the Brazilian Armed Forces and one of the three national uniformed services. The FAB was formed when the Brazilian Brazilian Army Aviation (1919–1941), Army and Brazilian Naval Aviation, Nav ...

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