Interstellar travel is the term used for crewed or uncrewed travel between stars or planetary systems. Because of the vastness of those distances, interstellar travel would require a high percentage of the speed of light; huge travel time, lasting from decades to 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. Many different spacecraft propulsion systems have been proposed to give spacecraft the required speeds, including nuclear propulsion, beam-powered propulsion, and methods based on speculative physics. Object
Proxima Centauri (nearest star and exoplanet)
The fastest outward-bound spacecraft yet sent, Voyager 1, has covered 1/600 of a light-year in 30 years and is currently moving at 1/18,000 the speed of light. A major issue with traveling at extremely high speeds is that interstellar dust may cause considerable damage to the craft, due to the high relative speeds and large kinetic energies involved. Although a high density interstellar medium may cause difficulties for many interstellar travel concepts, interstellar ramjets, and some proposed concepts for decelerating interstellar spacecraft, would actually benefit from a denser interstellar medium.
There are 59 known stellar systems within 40 light years of the Sun, containing 81 visible stars. Centauri 4.3 Closest system. Gliese 581 planetary system 20.3 Multiple planet system. Existing and near-term astronomical technology is capable of finding planetary systems around these objects, increasing their potential for exploration
Slow interstellar missions based on current and near-future propulsion technologies are associated with trip times starting from about one hundred years to thousands of years. Relativistic time dilation allows a traveler to experience time more slowly, the closer his speed is to the speed of light. For example, a spaceship could travel to a star 32 light-years away, initially accelerating at a constant 1.03g (i.e. 10.1 m/s) for 1.32 years (ship time), then stopping its engines and coasting for the next 17.3 years (ship time) at a constant speed, then decelerating again for 1.32 ship-years, and coming to a stop at the destination. The star ahead seems to be approaching at a speed of 0.87 light years per ship-year. At higher speeds, the time on board will run even slower, so the astronaut could travel to the center of the Milky Way (30,000 light years from Earth) and back in 40 years ship-time. The ship will be close to the speed of light after about a year of accelerating and remain at that speed until it brakes for the end of the journey. Very high specific power, the ratio of thrust to total vehicle mass, is required to reach interstellar targets within sub-century time-frames. This propulsion system contains the prospect of very high specific impulse (space travel's equivalent of fuel economy) and high specific power. Project Orion team member Freeman Dyson proposed in 1968 an interstellar spacecraft using nuclear pulse propulsion that used pure deuterium fusion detonations with a very high fuel-burnup fraction. Fusion rocket starships, powered by nuclear fusion reactions, should conceivably be able to reach speeds of the order of 10% of that of light, based on energy considerations alone. Rockets deriving their power from external sources, such as a laser, could replace their internal energy source with an energy collector, potentially reducing the mass of the ship greatly and allowing much higher travel speeds. 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. With this proposal, this interstellar ship would, theoretically, be able to reach 10 percent the speed of light. (% of the speed of light)
Travel time NASA has been researching interstellar travel since its formation, translating important foreign language papers and conducting early studies on applying fusion propulsion, in the 1960s, and laser propulsion, in the 1970s, to interstellar travel. ") identified some breakthroughs that are needed for interstellar travel to be possible. Geoffrey A. Landis of NASA's Glenn Research Center states that a laser-powered interstellar sail ship could possibly be launched within 50 years, using new methods of space travel. Rockets are too slow to send humans on interstellar missions. Instead, he envisions interstellar craft with extensive sails, propelled by laser light to about one-tenth the speed of light. Project Orion, manned interstellar ship (1958–1968). Project Daedalus, unmanned interstellar probe (1973–1978). Starwisp, unmanned interstellar probe (1985). Project Longshot, unmanned interstellar probe (1987–1988). Starseed/launcher, fleet of unmanned interstellar probes (1996) Project Valkyrie, manned interstellar ship (2009) Project Icarus, unmanned interstellar probe (2009–2014). Sun-diver, unmanned interstellar probe 100 Year Starship The energy requirements make interstellar travel very difficult.
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