page_title: Interstellar travel
section_title: Beamed propulsion
hierarchical_section_title: Interstellar travel / Propulsion / Non-rocket concepts / Beamed propulsion
caption_attribution_description: English: This image illustrates Robert L. Forward's scheme for slowing down an interstellar light-sail in the destination star system. I, the author of this image, hereby release it for use under the Creative Commons "Share Alike" license. --Christopher Thomas (talk) 17:20, 14 August 2009 (UTC)
context_page_description: Interstellar travel is the hypothetical crewed or uncrewed travel between stars or planetary systems in a galaxy. Interstellar travel would be much more difficult than interplanetary spaceflight. Whereas the distances between the planets in the Solar System are less than 30 astronomical units, the distances between stars are typically hundreds of thousands of AU, and usually expressed in light-years. Because of the vastness of those distances, practical interstellar travel based on known physics would need to occur at a high percentage of the speed of light, allowing for significant travel times, at least decades to perhaps millennia or longer.
  The speeds required for interstellar travel in a human lifetime far exceed what current methods of spacecraft propulsion can provide. Even with a hypothetically perfectly efficient propulsion system, the kinetic energy corresponding to those speeds is enormous by today's standards of energy development. Moreover, collisions by the spacecraft with cosmic dust and gas can produce very dangerous effects both to passengers and the spacecraft itself.
context_section_description: A light sail or magnetic sail powered by a massive laser or particle accelerator in the home star system could potentially reach even greater speeds than rocket- or pulse propulsion methods, because it would not need to carry its own reaction mass and therefore would only need to accelerate the craft's payload. Robert L. Forward proposed a means for decelerating an interstellar light sail in the destination star system without requiring a laser array to be present in that system. In this scheme, a smaller secondary sail is deployed to the rear of the spacecraft, whereas the large primary sail is detached from the craft to keep moving forward on its own. Light is reflected from the large primary sail to the secondary sail, which is used to decelerate the secondary sail and the spacecraft payload. In 2002, Geoffrey A. Landis of NASA's Glen Research center also proposed a laser-powered, propulsion, sail ship that would host a diamond sail (of a few nanometers thick) powered with the use of solar energy. With this proposal, this interstellar ship would, theoretically, be able to reach 10 percent the speed of light.
  A magnetic sail could also decelerate at its destination without depending on carried fuel or a driving beam in the destination system, by interacting with the plasma found in the solar wind of the destination star and the interstellar medium.
  The following table lists some example concepts using beamed laser propulsion as proposed by the physicist Robert L. Forward:
caption: This diagram illustrates Robert L. Forward's scheme for slowing down an interstellar light-sail at the star system destination.
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