Interstellar travel is the hypothetical travel of spacecraft from one star system, solitary star, or planetary system to another. Interstellar travel is expected to prove much more difficult than interplanetary spaceflight due to the vast difference in the scale of the involved distances. Whereas the distance between any two planets in the Solar System is less than 55 astronomical units (AU), stars are typically separated by hundreds of thousands of AU, causing these distances to typically be expressed instead in light-years. Because of the vastness of these distances, non-generational interstellar travel based on known physics would need to occur at a high percentage of the speed of light; even so, travel times would be long, at least decades and perhaps millennia or longer.
The Alcubierre drive is a speculative warp drive idea according to which a spacecraft could achieve apparent faster-than-light travel by contracting space in front of it and expanding space behind it, under the assumption that a configurable energy-density field lower than that of vacuum could be created. Proposed by theoretical physicist Miguel Alcubierre in 1994, the Alcubierre drive is based on a solution of Einstein's field equations. Since those solutions are metric tensors, the Alcubierre drive is also referred to as Alcubierre metric.
A warp drive or a drive enabling space warp is a fictional superluminal spacecraft propulsion system in many science fiction works, most notably Star Trek, and a subject of ongoing physics research. The general concept of "warp drive" was introduced by John W. Campbell in his 1957 novel Islands of Space and was popularized by the Star Trek series. Its closest real-life equivalent is the Alcubierre drive, a theoretical solution of the field equations of general relativity.
An interstellar ark is a conceptual starship designed for interstellar travel. Interstellar arks may be the most economically feasible method of traveling such distances. The ark has also been proposed as a potential habitat to preserve civilization and knowledge in the event of a global catastrophe.
Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible uncrewed interstellar probe. Intended mainly as a scientific probe, the design criteria specified that the spacecraft had to use existing or near-future technology and had to be able to reach its destination within a human lifetime. Alan Bond led a team of scientists and engineers who proposed using a fusion rocket to reach Barnard's Star 5.9 light years away. The trip was estimated to take 50 years, but the design was required to be flexible enough that it could be sent to any other target star.
Project Longshot was a conceptual interstellar spacecraft design. It would have been an uncrewed starship, intended to fly to and enter orbit around Alpha Centauri B powered by nuclear pulse propulsion.
Intergalactic travel is the hypothetical crewed or uncrewed travel between galaxies. Due to the enormous distances between the Milky Way and even its closest neighbors—tens of thousands to millions of light-years—any such venture would be far more technologically and financially demanding than even interstellar travel. Intergalactic distances are roughly a hundred-thousandfold greater than their interstellar counterparts.
Miguel Alcubierre Moya is a Mexican theoretical physicist. Alcubierre is known for the proposed Alcubierre drive, a speculative warp drive by which a spacecraft could achieve faster-than-light travel.
An interstellar probe is a space probe that has left—or is expected to leave—the Solar System and enter interstellar space, which is typically defined as the region beyond the heliopause. It also refers to probes capable of reaching other star systems.
Project Icarus is a theoretical engineering design study aimed at designing a credible, mainly nuclear fusion-based, unmanned interstellar space probe. Project Icarus was an initiative of members of the British Interplanetary Society (BIS) and the Tau Zero Foundation (TZF) started in 2009. The project was under the stewardship of Icarus Interstellar until 2019. It remains a BIS project.
The Enzmann starship is a concept for a crewed interstellar spacecraft proposed in 1964 by Dr. Robert Enzmann. A three million ton ball of frozen deuterium would fuel nuclear fusion rocket engines contained in a cylindrical section behind that ball with the crew quarters. The craft would be about 2,000 feet (600 m) long overall.
The Initiative for Interstellar Studies (i4is) is a UK-registered not-for-profit company, whose objectives are education and research into the challenges of Interstellar Travel. It pioneered small-scale laser sail interstellar probes and missions to interstellar objects. Several of its principals were involved in the 100 Year Starship winning team originated by NASA and DARPA.
Harold G. "Sonny" White is a mechanical engineer, aerospace engineer, and applied physicist who is known for proposing new Alcubierre drive concepts and promoting advanced propulsion projects.
IXS Enterprise is a conceptual interstellar superluminal spacecraft designed by NASA scientist Dr. Harold G. White, revealed at SpaceVision 2013, designed for the goal of achieving warp travel. The conceptual spacecraft would make use of a modified version of the Alcubierre drive. Dr. White is currently running the White–Juday warp-field interferometer experiment in order to develop a proof of concept for Alcubierre-style warp travel, when possible. The Alcubierre drive uses exotic matter to travel faster than light.
Breakthrough Initiatives is a science-based program founded in 2015 and funded by Julia and Yuri Milner, also of Breakthrough Prize, to search for extraterrestrial intelligence over a span of at least 10 years. The program is divided into multiple projects. Breakthrough Listen will comprise an effort to search over 1,000,000 stars for artificial radio or laser signals. A parallel project called Breakthrough Message is an effort to create a message "representative of humanity and planet Earth". The project Breakthrough Starshot, co-founded with Mark Zuckerberg, aims to send a swarm of probes to the nearest star at about 20% the speed of light. The project Breakthrough Watch aims to identify and characterize Earth-sized, rocky planets around Alpha Centauri and other stars within 20 light years of Earth. Breakthrough plans to send a mission to Saturn's moon Enceladus, in search for life in its warm ocean, and in 2018 signed a partnership agreement with NASA for the project.
Project Dragonfly is the first conceptual design study that assesses the feasibility of a laser-propelled interstellar probe, conducted by the Initiative for Interstellar Studies. Contrary to past unmanned interstellar mission studies such as Project Daedalus and Project Icarus, the focus is particularly on a small spacecraft. The project was founded in 2013 by the Initiative for Interstellar Studies (i4is).
Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a proof-of-concept fleet of light sail interstellar probes named Starchip, to be capable of making the journey to the Alpha Centauri star system 4.34 light-years away. It was founded in 2016 by Yuri Milner, Stephen Hawking, and Mark Zuckerberg.
In December 2017, NASA released a mission concept involving the launch, in 2069, of an interstellar probe to search for signs of life on planets orbiting stars in and around the Alpha Centauri system. The announcement was at the annual conference of the American Geophysical Union. The mission remains a concept, and as such, has no name or allocated funding.
Project Starlight is a research project of the University of California, Santa Barbara to develop a fleet of laser beam-propelled interstellar probes and sending them to a star neighboring the Solar System, potentially Alpha Centauri. The project aims to send organisms on board the probe.
