Small nuclear reactors can compete in this regard, and considerable work on nuclear thermal propulsion was carried out in the 1960s, but environmental concerns and rising costs led to the ending of most of these programs. A further improvement can be made by removing the energy creation from the spacecraft.
Mass production has lowered the production cost of microwave oven magnetrons to <0.01 $/Watt and some medical lasers to <10 $/Watt, though these are thought to be unsuitable for use in beam directors. ==Non-spacecraft applications== In 1964 William C.
Goldstone, California in 1974), rectennas are potentially lightweight and can handle high power at high conversion efficiency.
JASON's 1977 study of laser propulsion, authored by Freeman Dyson, succinctly articulates the promise of beam-powered launch: "Laser propulsion as an idea that may produce a revolution in space technology.
Forward in 1989 as a method of interstellar travel that would avoid extremely high mass ratios by not carrying fuel.
Landis proposed a particle beam pushed sail in 1989, and analyzed in more detail in a 2004 paper.
Reflective surfaces in the craft focus the beam into a ring, where it heats air to a temperature nearly five times hotter than the surface of the sun, causing the air to expand explosively for thrust. ===Laser thermal rocket=== A laser thermal rocket is a thermal rocket in which the propellant is heated by energy provided by an external laser beam. In 1992, the late Jordin Kare proposed a simpler, nearer term concept which has a rocket containing liquid hydrogen.
It could also potentially be very cheap to manufacture. ====Testing==== Early in the morning of 2 October 2000 at the High Energy Laser Systems Test Facility (HELSTF), Lightcraft Technologies, Inc.
This concept can use continuous beam lasers, and the semiconductor lasers are now cost effective for this application. === Microwave thermal rocket === In 2002, Kevin L.G.
Landis proposed a particle beam pushed sail in 1989, and analyzed in more detail in a 2004 paper.
In May 2012, the DARPA/NASA Millimeter-wave Thermal Launch System (MTLS) Project began the first steps toward implementing this idea.
Several launches were attempted but problems with the beam director could not be resolved before funding ran out in March 2014. == Economics == Motivation to develop beam-powered propulsion systems comes from the economic advantages that would be gained as a result of improved propulsion performance.
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