Laser propulsion
Encyclopedia
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 and reaction mass come from the solid or liquid propellant
s carried on board the vehicle.
It is also less polluting than traditional propulsion.
in 1972. Laser propulsion systems may transfer momentum to a spacecraft in two different ways. The first way is that photon
radiation pressure
drives the momentum transfer, the principle behind the propulsion of solar sail
s and laser sails. A second way of driving momentum transfer to a spacecraft, used in the devices described below, which is more commonly proposed is using the laser to help expel mass from the spacecraft as in a conventional rocket. The second class of propulsion systems are fundamentally limited in their final spacecraft velocities by the rocket equation.
in which an external pulsed laser
is used to burn off a plasma
plume from a solid metal propellant
, thus producing thrust
. The measured specific impulse
of small ALP setups is very high at about 5000 s (49 kN·s/kg), and unlike the lightcraft
developed by Leik Myrabo
which uses air as the propellant, ALP can be used in space.
Material is directly removed from a solid or liquid surface at high velocities by laser ablation
by a pulsed laser. Depending on the laser flux
and pulse duration, the material can be simply heated and evaporated, or converted to plasma
. Ablative propulsion will work in air or vacuum. Specific impulse
values from 200 seconds to several thousand seconds are possible by choosing the propellant and laser pulse characteristics. Variations of ablative propulsion include double-pulse propulsion in which one laser pulse ablates material and a second laser pulse further heats the ablated gas, laser micropropulsion in which a small laser onboard a spacecraft ablates very small amounts of propellant for attitude control or maneuvering, and space debris
removal, in which the laser ablates material from debris particles in low Earth orbit
, changing their orbits and causing them to reenter.
ALP was being developed by Professor Andrew Pakhomov at the University of Alabama in Huntsville
of the UAH
Laser Propulsion Group.
, developed by Leik Myrabo
of RPI (Rensselaer Polytechnic Institute
) and Frank Mead, works on this principle.
propulsion. However, to achieve high specific impulse
, the propellant must have low molecular weight; hydrogen
is usually assumed for actual use, at specific impulses around 1000 seconds. CW plasma propulsion has the disadvantage that the laser beam must be precisely focused into the absorption chamber, either through a window or by using a specially-shaped nozzle. CW plasma thruster experiments were performed in the 1970s and 1980s, primarily by Dr. Dennis Keefer of UTSI
and Prof. Herman Krier of the University of Illinois at Urbana-Champaign
.
and solar thermal
propulsion. Using a large flat heat exchanger allows the laser beam to shine directly on the heat exchanger without focusing optics on the vehicle. The HX thruster has the advantage of working equally well with any laser wavelength and both CW and pulsed lasers, and of having an efficiency approaching 100%. The HX thruster is limited by the heat exchanger material and by radiative losses to relatively low gas temperatures, typically 1000 - 2000 C, but with hydrogen propellant, that provides sufficient specific impulse (600 – 800 seconds) to allow single stage vehicles to reach low Earth orbit. The HX laser thruster concept was developed by Jordin Kare
in 1991; a similar microwave thermal propulsion concept was developed independently by Kevin L. Parkin
at Caltech in 2001.
propulsion for low-thrust propulsion in space. However, Leik Myrabo
has proposed high-thrust laser electric propulsion, using magnetohydrodynamics
to convert laser energy to electricity and to electrically accelerate air around a vehicle for thrust.
radiation pressure
by orders of magnitude by exploiting an active resonant optical cavity formed between two mirrors on paired spacecraft. PLT is predicted to be able to provide the thrust to power ratio (a measure of how efficient a thruster is in terms of converting power to thrust) approaching that of conventional thrusters, such as laser ablation thrusters and electrical thrusters. Yet, PLT has the highest specific impulse (a measure of how fast the fuel can propel spacecraft) orders of magnitude larger than that of other conventional thrusters. In December 2006, Dr. Young K. Bae successfully demonstrated the photon thrust amplification in PLT for the first time with an amplification factor of 3,000 under NASA sponsorship (NIAC). Scaling-up of PLT is highly promising, and PLT is predicted to enable wide ranges of next generation space endeavors. Low thrust (milli-Newton) PLTs enable nanometer precision spacecraft formation, for example Photon Tether Formation Flight (PTFF), for forming ultralarge space telescopes and radars. Medium thrust (Newton) PLTs enable precision propellantless orbit changing and docking. High thrust (greater than kilo-Newton) PLTs enable propelling spacecraft at speeds beyond hundreds km/sec. At such speeds, spacecraft could transit from Earth to Mars in less than one week. Scaling up of PLTs seems promising owing to the recent development of high power laser weapons.
Beam-powered propulsion
Beam-powered propulsion is a class of aircraft or spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant to provide energy...
where the energy source is a remote (usually ground-based) laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
system and separate from the reaction mass. This form of propulsion differs from a conventional chemical rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
where both energy and reaction mass come from the solid or liquid propellant
Propellant
A propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...
s carried on board the vehicle.
It is also less polluting than traditional propulsion.
History
The concept of laser propelled vehicles was first introduced by Arthur KantrowitzArthur Kantrowitz
Arthur Robert Kantrowitz was an American scientist, engineer, and educator.Kantrowitz grew up in The Bronx, and graduated from DeWitt Clinton High School. He earned his B.S., M.A. and, in 1947, his Ph.D. degrees in physics from Columbia University...
in 1972. Laser propulsion systems may transfer momentum to a spacecraft in two different ways. The first way is that photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
drives the momentum transfer, the principle behind the propulsion of solar sail
Solar sail
Solar sails are a form of spacecraft propulsion using the radiation pressure of light from a star or laser to push enormous ultra-thin mirrors to high speeds....
s and laser sails. A second way of driving momentum transfer to a spacecraft, used in the devices described below, which is more commonly proposed is using the laser to help expel mass from the spacecraft as in a conventional rocket. The second class of propulsion systems are fundamentally limited in their final spacecraft velocities by the rocket equation.
Ablative laser propulsion
Ablative Laser Propulsion (ALP) is a form of beam-powered propulsionBeam-powered propulsion
Beam-powered propulsion is a class of aircraft or spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant to provide energy...
in which an external pulsed laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
is used to burn off a plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
plume from a solid metal propellant
Propellant
A propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...
, thus producing thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
. The measured specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
of small ALP setups is very high at about 5000 s (49 kN·s/kg), and unlike the lightcraft
Lightcraft
A lightcraft is a space- or air-vehicle driven by laser propulsion. Laser propulsion is currently in early stages of development. Lightcraft use an external source of laser or maser energy to provide power for producing thrust. The laser/maser energy is focused to a high intensity in order to...
developed by Leik Myrabo
Leik Myrabo
Leik Myrabo is an aerospace engineering professor at Rensselaer Polytechnic Institute who has demonstrated the feasibility of using ground-based lasers to propel objects into orbit; possibly reducing orbit-flight costs by a factor of 1000.-Research:...
which uses air as the propellant, ALP can be used in space.
Material is directly removed from a solid or liquid surface at high velocities by laser ablation
Laser ablation
Laser ablation is the process of removing material from a solid surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma...
by a pulsed laser. Depending on the laser flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...
and pulse duration, the material can be simply heated and evaporated, or converted to plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
. Ablative propulsion will work in air or vacuum. Specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
values from 200 seconds to several thousand seconds are possible by choosing the propellant and laser pulse characteristics. Variations of ablative propulsion include double-pulse propulsion in which one laser pulse ablates material and a second laser pulse further heats the ablated gas, laser micropropulsion in which a small laser onboard a spacecraft ablates very small amounts of propellant for attitude control or maneuvering, and space debris
Space debris
Space debris, also known as orbital debris, space junk, and space waste, is the collection of objects in orbit around Earth that were created by humans but no longer serve any useful purpose. These objects consist of everything from spent rocket stages and defunct satellites to erosion, explosion...
removal, in which the laser ablates material from debris particles in low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
, changing their orbits and causing them to reenter.
ALP was being developed by Professor Andrew Pakhomov at the University of Alabama in Huntsville
University of Alabama in Huntsville
The University of Alabama in Huntsville is a state-supported, public, coeducational research university, located in Huntsville, Alabama, United States, is accredited by the Southern Association of Colleges and Schools to award baccalaureate, master's and doctoral degrees, and is organized in five...
of the UAH
UAH
UAH may refer to:* Ukrainian hryvnia, the national currency of Ukraine* Universidad Alejandro de Humboldt, Venezuela* University of Alabama in Huntsville, a state-supported, public, coeducational university, located in Huntsville, Alabama, United States...
Laser Propulsion Group.
Pulsed plasma propulsion
A high energy pulse focused in a gas or on a solid surface surrounded by gas produces breakdown of the gas (usually air). This causes an expanding shock wave which absorbs laser energy at the shock front (a laser sustained detonation wave or LSD wave); expansion of the hot plasma behind the shock front during and after the pulse transmits momentum to the craft. Pulsed plasma propulsion using air as the working fluid is the simplest form of air-breathing laser propulsion. The record-breaking LightcraftLightcraft
A lightcraft is a space- or air-vehicle driven by laser propulsion. Laser propulsion is currently in early stages of development. Lightcraft use an external source of laser or maser energy to provide power for producing thrust. The laser/maser energy is focused to a high intensity in order to...
, developed by Leik Myrabo
Leik Myrabo
Leik Myrabo is an aerospace engineering professor at Rensselaer Polytechnic Institute who has demonstrated the feasibility of using ground-based lasers to propel objects into orbit; possibly reducing orbit-flight costs by a factor of 1000.-Research:...
of RPI (Rensselaer Polytechnic Institute
Rensselaer Polytechnic Institute
Stephen Van Rensselaer established the Rensselaer School on November 5, 1824 with a letter to the Rev. Dr. Samuel Blatchford, in which van Rensselaer asked Blatchford to serve as the first president. Within the letter he set down several orders of business. He appointed Amos Eaton as the school's...
) and Frank Mead, works on this principle.
CW plasma propulsion
A continuous laser beam focused in a flowing stream of gas creates a stable laser sustained plasma which heats the gas; the hot gas is then expanded through a conventional nozzle to produce thrust. Because the plasma does not touch the walls of the engine, very high gas temperatures are possible, as in gas core nuclear thermalGas core reactor rocket
Gas core reactor rockets are a conceptual type of rocket that is propelled by the exhausted coolant of a gaseous fission reactor. The nuclear fission reactor core may be either a gas or plasma...
propulsion. However, to achieve high specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
, the propellant must have low molecular weight; hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
is usually assumed for actual use, at specific impulses around 1000 seconds. CW plasma propulsion has the disadvantage that the laser beam must be precisely focused into the absorption chamber, either through a window or by using a specially-shaped nozzle. CW plasma thruster experiments were performed in the 1970s and 1980s, primarily by Dr. Dennis Keefer of UTSI
University of Tennessee Space Institute
The University of Tennessee Space Institute, also known as UTSI, is a satellite campus of the University of Tennessee located near Tullahoma, Tennessee....
and Prof. Herman Krier of the University of Illinois at Urbana-Champaign
University of Illinois at Urbana-Champaign
The University of Illinois at Urbana–Champaign is a large public research-intensive university in the state of Illinois, United States. It is the flagship campus of the University of Illinois system...
.
Heat Exchanger (HX) Thruster
The laser beam heats a solid heat exchanger, which in turn heats an inert liquid propellant, converting it to hot gas which is exhausted through a conventional nozzle. This is similar in principle to nuclear thermalNuclear thermal rocket
In a nuclear thermal rocket a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor, and then expands through a rocket nozzle to create thrust. In this kind of thermal rocket, the nuclear reactor's energy replaces the chemical energy of the propellant's...
and solar thermal
Solar thermal rocket
Solar thermal propulsion is a form of spacecraft propulsion that makes use of solar power to directly heat reaction mass, and therefore does not require an electrical generator as most other forms of solar-powered propulsion do. A solar thermal rocket only has to carry the means of capturing solar...
propulsion. Using a large flat heat exchanger allows the laser beam to shine directly on the heat exchanger without focusing optics on the vehicle. The HX thruster has the advantage of working equally well with any laser wavelength and both CW and pulsed lasers, and of having an efficiency approaching 100%. The HX thruster is limited by the heat exchanger material and by radiative losses to relatively low gas temperatures, typically 1000 - 2000 C, but with hydrogen propellant, that provides sufficient specific impulse (600 – 800 seconds) to allow single stage vehicles to reach low Earth orbit. The HX laser thruster concept was developed by Jordin Kare
Jordin Kare
Jordin Kare is a physicist and aerospace engineer known for his research on laser propulsion. In particular, he was responsible for Mockingbird, a conceptual design for an extremely small reusable launch vehicle, and was involved in the Clementine lunar mapping mission.Kare is also known as...
in 1991; a similar microwave thermal propulsion concept was developed independently by Kevin L. Parkin
Kevin L. Parkin
Kevin L Parkin is a British scientist active in beamed energy propulsion.-Areas of Interest:Rocket propulsion and gasdynamics, high power microwaves and directed energy, object-oriented software engineering, space mission design...
at Caltech in 2001.
Laser electric propulsion
A general class of propulsion techniques in which the laser beam power is converted to electricity, which then powers some type of electric propulsion thruster. Usually, laser electric propulsion is considered as a competitor to solar electric or nuclear electricNuclear power
Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...
propulsion for low-thrust propulsion in space. However, Leik Myrabo
Leik Myrabo
Leik Myrabo is an aerospace engineering professor at Rensselaer Polytechnic Institute who has demonstrated the feasibility of using ground-based lasers to propel objects into orbit; possibly reducing orbit-flight costs by a factor of 1000.-Research:...
has proposed high-thrust laser electric propulsion, using magnetohydrodynamics
Magnetohydrodynamics
Magnetohydrodynamics is an academic discipline which studies the dynamics of electrically conducting fluids. Examples of such fluids include plasmas, liquid metals, and salt water or electrolytes...
to convert laser energy to electricity and to electrically accelerate air around a vehicle for thrust.
Photonic Laser Thruster (PLT)
Photonic Laser Thruster (PLT) is a pure photon laser thruster that amplifies photonPhoton
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
by orders of magnitude by exploiting an active resonant optical cavity formed between two mirrors on paired spacecraft. PLT is predicted to be able to provide the thrust to power ratio (a measure of how efficient a thruster is in terms of converting power to thrust) approaching that of conventional thrusters, such as laser ablation thrusters and electrical thrusters. Yet, PLT has the highest specific impulse (a measure of how fast the fuel can propel spacecraft) orders of magnitude larger than that of other conventional thrusters. In December 2006, Dr. Young K. Bae successfully demonstrated the photon thrust amplification in PLT for the first time with an amplification factor of 3,000 under NASA sponsorship (NIAC). Scaling-up of PLT is highly promising, and PLT is predicted to enable wide ranges of next generation space endeavors. Low thrust (milli-Newton) PLTs enable nanometer precision spacecraft formation, for example Photon Tether Formation Flight (PTFF), for forming ultralarge space telescopes and radars. Medium thrust (Newton) PLTs enable precision propellantless orbit changing and docking. High thrust (greater than kilo-Newton) PLTs enable propelling spacecraft at speeds beyond hundreds km/sec. At such speeds, spacecraft could transit from Earth to Mars in less than one week. Scaling up of PLTs seems promising owing to the recent development of high power laser weapons.
See also
- Elevator:2010Elevator:2010Elevator:2010 is a competition with monetary prizes similar to the Ansari X Prize, but with the purpose of developing space elevator and space elevator-related technologies...
- Jordin KareJordin KareJordin Kare is a physicist and aerospace engineer known for his research on laser propulsion. In particular, he was responsible for Mockingbird, a conceptual design for an extremely small reusable launch vehicle, and was involved in the Clementine lunar mapping mission.Kare is also known as...
- Leik MyraboLeik MyraboLeik Myrabo is an aerospace engineering professor at Rensselaer Polytechnic Institute who has demonstrated the feasibility of using ground-based lasers to propel objects into orbit; possibly reducing orbit-flight costs by a factor of 1000.-Research:...
- Optical liftOptical liftOptical lift is an optical analogue of aerodynamic lift, in which a cambered refractive object with differently shaped top and bottom surfaces experiences a stable transverse lift force when placed in a uniform stream of light.- Discovery :...
- Rocket engineRocket engineA rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
- Beam-powered propulsionBeam-powered propulsionBeam-powered propulsion is a class of aircraft or spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant to provide energy...