Interstellar travel

Interstellar travel is movement between star systems through the space between stars. It is far more demanding than travel within a planetary system because distances are measured in light-years.

Rocket propulsion: Rocket propulsion produces thrust by expelling reaction mass, allowing a vehicle to accelerate in space. Chemical rockets provide the baseline propulsion used by spacecraft, but cannot approach nearby stars quickly.
Breakthrough Starshot: Breakthrough Starshot is a research initiative proposing laser-driven light sails for gram-scale probes to Alpha Centauri. It studies a concrete route to sending a flyby probe to the nearest star system.
Light-year: A light-year is the distance light travels in vacuum in one year, about 9.46 trillion kilometers. Nearby star systems remain several light-years away even when measured with this unit.
Interstellar probe: An interstellar probe is an uncrewed spacecraft sent to explore another star system or the space between stars. Robotic flybys require less life support than crewed voyages and are the nearer-term target.
Nuclear pulse propulsion: Nuclear pulse propulsion drives a spacecraft with repeated nuclear explosions behind a protective pusher plate. Project Orion explored whether nuclear blasts could propel a crewed interstellar vehicle.
Project Longshot: Project Longshot was a 1980s NASA and U.S. Naval Academy study of an uncrewed fusion-powered mission to Alpha Centauri. Its design illustrates the scale and duration of a plausible robotic mission study.
Astronomical unit: An astronomical unit is the mean distance between Earth and the Sun, about 150 million kilometers. Comparing it with a light-year reveals how small planetary distances are beside interstellar ones.
Interstellar colonization: Interstellar colonization is the establishment of permanent human settlements beyond the Solar System. Settlement demands more than a fast transit, including survival and long-term self-sufficiency.
Fusion rocket: A fusion rocket uses energy from nuclear fusion to accelerate exhaust and produce thrust. Fusion could offer higher exhaust speeds than chemical propulsion for journeys lasting decades.
Project Daedalus: Project Daedalus was a British Interplanetary Society study of an uncrewed fusion-powered probe to Barnard's Star. The design became a prominent technical reference for starship concepts.

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