[1] The rule of thumb that is usually quoted is that it takes a megawatt of power beamed to a vehicle per kg of payload while it is being accelerated to permit it to reach low Earth orbit.
[2] More speculative designs, using mass ("micro-pellet") beams, would allow for reaching the edge of the solar gravity lens, or even nearby stars, in decades.
However, this is not a solution for the rockets as they quickly climb to altitudes where the air is too thin to be useful as a source of working mass.
This permits the spacecraft to leave its power source at home, saving significant amounts of mass and greatly improving performance.
In this system, if a high intensity is incident on the solar array, careful design of the panels is necessary to avoid a fall-off in conversion efficiency due to heating effects.
John Brophy has analyzed the transmission of laser power to a photovoltaic array powering a high-efficiency electric propulsion system as a means of accomplishing high delta-V missions such as an interstellar precursor mission in a NASA Innovative Advanced Concepts project.
This concept, called a laser-pushed lightsail, was initially proposed by G. Marx[5] but first analyzed in detail, and elaborated on, by physicist Robert L. Forward in 1989[6] as a method of interstellar travel that would avoid extremely high mass ratios by not carrying fuel.
The laser or the microwave sender would probably be a large phased array of small devices that get their energy directly from solar radiation.
[15] Jordin Kare has proposed a variant to this whereby a "beam" of small laser accelerated light sails would transfer momentum to a magsail vehicle.
A massive particle’s velocity, however, can be tuned so that the reflected mass is left almost dead in space relative to the beam generators, having surrendered almost all of its kinetic energy to the starship.
under development that uses an external pulsed source of laser or maser energy to provide power for producing thrust.
The laser shines on a parabolic reflector on the vehicle's underside, concentrating the light to produce a region of extremely high temperature.
Early in the morning of 2 October 2000 at the High Energy Laser Systems Test Facility (HELSTF), Lightcraft Technologies, Inc. (LTI) with the help of Franklin B. Mead of the U.S. Air Force Research Laboratory and Leik Myrabo set a new world's altitude record of 233 feet (71 m) for its 4.8 inch (12.2 cm) diameter, 1.8-ounce (51 g), laser-boosted rocket in a flight lasting 12.7 seconds.
They aim to accelerate a one-kilogram microsatellite into low Earth orbit using a custom-built, one-megawatt ground-based laser.
Aerospace and mechanical engineer Artur Davoyan has been funded by NASA to study a pellet-beam system that would propel one ton payloads to 500 AU in under 20 years.
Nordley and Crowl propose vast solar arrays built by self-replicating robots placed at the Sun-Venus equilateral Lagrange points, capable of generating beams in the hundreds of petawatt range.
A single laser facility on the ground can in theory launch single-stage vehicles into low or high earth orbit.
It is far more economical in the use of mass and energy than chemical propulsion, and it is far more flexible in putting identical vehicles into a variety of orbits.
"This promise was quantified in a 1978 Lockheed Study[30] conducted for NASA:"The results of the study showed that, with advanced technology, laser rocket system with either a space- or ground-based laser transmitter could reduce the national budget allocated to space transportation by 10 to 345 billion dollars over a 10-year life cycle when compared to advanced chemical propulsion systems (LO2-LH2) of equal capability.
A recent cost-benefit analysis[31] estimates that microwave (or laser) thermal rockets would be economical once beam director cost falls below 20 $/Watt.
In 1964 William C. Brown demonstrated a miniature helicopter equipped with a combination antenna and rectifier device called a rectenna.
This is another proposed use of beam-powered propulsion, used on objects not designed to be propelled by it, for example, small pieces of scrap knocked off ("spalled") satellites.