Laser propulsion
This form of propulsion differs from a conventional chemical rocket where both energy and reaction mass come from the solid or liquid propellants carried on board the vehicle.
[1] The basic concepts underlying a photon-propelled "sail" propulsion system were developed by Eugene Sanger and the Hungarian physicist György Marx.
Propulsion concepts using laser-energized rockets were developed in the 1970s by Arthur Kantrowitz[2] and Wolfgang Moekel,[3] with a variant using laser ablation pioneered by Leik Myrabo.
Use of a laser-pushed lightsail was proposed initially by Marx in 1966,[7] as a method of interstellar travel that would avoid extremely high mass ratios by not carrying fuel, and analyzed in detail by physicist Robert L. Forward in 1989.
The laser may alternatively consist of a large phased array of small devices that receive their energy directly from solar radiation.
Another method of moving a much larger spacecraft to high velocities is by using a laser system to propel a stream of much smaller sails.
The HX thruster is limited by the heat exchanger material and by radiative losses to relatively low gas temperatures, typically 1000–2000 °C.
For a given temperature, the specific impulse is maximized with the minimum molecular weight reaction mass, and with hydrogen propellant, that provides sufficient specific impulse as high as 600–800 seconds, high enough in principle to allow single stage vehicles to reach low Earth orbit.
In 2022 a paper was published by researchers from McGill University proposing a laser thermal propulsion system to be used to send a spacecraft to Mars in 45 days.
The pulse of laser light becomes trapped in the tube, bouncing back and forth and accelerating the mirror disc out at very high velocity.
The mirrors are moved into position inside the tube from magazines on the side of the craft after the laser pulse has switched off.
Accelerations of millions of g's are possible for these small highly reflective mirrors, and velocities over short distances can reach into the tens of kilometers per second, allowing specific impulses in the thousands.
[citation needed] Clever control of the discs would allow much longer acceleration periods as well and therefore higher exit velocities.
Jordin Kare calculated that these mirrored discs could theoretically be pushed to around 32 million g but would be at the limit of any material's strength and subject to total failure.
Depending on the laser flux and pulse duration, the material can be simply heated and evaporated, or converted to plasma.
[31][32] The record-breaking lightcraft, developed by Leik Myrabo of RPI (Rensselaer Polytechnic Institute) and Frank Mead, works on this principle.
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.
A small quadcopter has flown for 12 hours and 26 minutes charged by a 2.25 kW laser (powered at less than half of its normal operating current), using 170 watt photovoltaic arrays as the power receiver,[39] and a laser has been demonstrated to charge the batteries of an unmanned aerial vehicle in flight for 48 hours.
