[2] While NASA's Voyager and Pioneer probes have traveled into local interstellar space, the purpose of these uncrewed craft was specifically interplanetary, and they are not predicted to reach another star system; Voyager 1 probe and Gliese 445 will pass one another within 1.6 light years in about 40,000 years.
In April 2016, scientists announced Breakthrough Starshot, a Breakthrough Initiatives program, to develop a proof-of-concept fleet of small centimeter-sized light sail spacecraft named StarChip,[4] capable of making the journey to Alpha Centauri, the nearest star system, at speeds of 20%[5][6] and 15%[7] of the speed of light, taking between 20 and 30 years to reach the star system, respectively, and about 4 years to notify Earth of a successful arrival.
Some examples of this include: The Bussard ramjet is an idea to use nuclear fusion of interstellar gas to provide propulsion.
Examined in an October 1973 issue of Analog, the Enzmann Starship proposed using a 12,000-ton ball of frozen deuterium to power pulse propulsion units.
Twice as long as the Empire State Building is tall and assembled in-orbit, the proposed spacecraft would be part of a larger project preceded by interstellar probes and telescopic observation of target star systems.