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.
Voyager 1 is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and the interstellar space beyond the Sun's heliosphere. It was launched 16 days after its twin, Voyager 2. It communicates through the NASA Deep Space Network (DSN) to receive routine commands and to transmit data to Earth. Real-time distance and velocity data are provided by NASA and JPL. At a distance of 164.0 AU from Earth as of August 2024, it is the most distant human-made object from Earth. The probe made flybys of Jupiter, Saturn, and Saturn's largest moon, Titan. NASA had a choice of either doing a Pluto or Titan flyby; exploration of the moon took priority because it was known to have a substantial atmosphere. Voyager 1 studied the weather, magnetic fields, and rings of the two gas giants and was the first probe to provide detailed images of their moons.
Beam-powered propulsion, also known as directed energy propulsion, is a class of aircraft or spacecraft propulsion that uses energy beamed to the spacecraft from a remote power plant to provide energy. The beam is typically either a microwave or a laser beam, and it is either pulsed or continuous. A continuous beam lends itself to thermal rockets, photonic thrusters, and light sails. In contrast, a pulsed beam lends itself to ablative thrusters and pulse detonation engines.
A starship, starcraft, or interstellar spacecraft is a theoretical spacecraft designed for traveling between planetary systems. The term is mostly found in science fiction. Reference to a "star-ship" appears as early as 1882 in Oahspe: A New Bible.
Nuclear pulse propulsion or external pulsed plasma propulsion is a hypothetical method of spacecraft propulsion that uses nuclear explosions for thrust. It originated as Project Orion with support from DARPA, after a suggestion by Stanislaw Ulam in 1947. Newer designs using inertial confinement fusion have been the baseline for most later designs, including Project Daedalus and Project Longshot.
A radioisotope thermoelectric generator, sometimes referred to as a radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioactive material into electricity by the Seebeck effect. This type of generator has no moving parts and is ideal for deployment in remote and harsh environments for extended periods with no risk of parts wearing out or malfunctioning.
Laser propulsion is a form of beam-powered propulsion where the energy source is a remote laser system and separate from the reaction mass. This form of propulsion differs from a conventional chemical rocket where both energy and reaction mass come from the solid or liquid propellants carried on board the vehicle.
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.
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.
The NASA Institute for Advanced Concepts (NIAC) is a NASA program for development of far reaching, long term advanced concepts by "creating breakthroughs, radically better or entirely new aerospace concepts". The program operated under the name NASA Institute for Advanced Concepts from 1998 until 2007, and was reestablished in 2011 under the name NASA Innovative Advanced Concepts and continues to the present. The NIAC program funds work on revolutionary aeronautics and space concepts that can dramatically impact how NASA develops and conducts its missions.
TAU was a proposed uncrewed interstellar probe that would go to a distance of one thousand astronomical units from the Earth and Sun by the NASA Jet Propulsion Laboratory in 1987 using tested technology. One scientific purpose would be to measure the distance to other stars via stellar parallax. Studies continued into 1990, working with a launch in the 2005–2010 timeframe.
Deep-space exploration is the branch of astronomy, astronautics, and space technology that is involved with exploring the distant regions of outer space. However, little consensus has been reached on the meaning of "distant" regions. In some contexts, it is used to refer to interstellar space. The International Telecommunication Union defines deep space to start at a distance of 2 million km (1.2 million mi) from Earth's surface. NASA's Deep Space Network has variously used criteria of 16,000–32,000 km (9,900–19,900 mi) from Earth. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft.
Kevin L.G. Parkin is an American British scientist who is best known for his study of beamed energy propulsion.
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.
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).
DEEP-IN, also known as Directed Energy Propulsion for Interstellar Exploration, is a spaceflight propulsion concept that uses photonic laser propulsion with beamed power to propel a spacecraft in deep space. The concept was originally conceived by Professor Philip Lubin of the University of California Santa Barbara's Physics Department. Lubin is developing it under the NASA Innovative Advanced Concepts Program. DEEP-IN is notable as the first NASA-backed photonic laser propulsion concept. It is heavily derived from DE-STAR, a planetary defense satellite concept previously developed by Lubin, in which he proposes using directed energy from lasers to vaporize or knock off course destructive asteroids headed for Earth.
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.
Solar Cruiser was a planned NASA spacecraft that would have studied the Sun while propelled by a solar sail. The mission would have supported NASA's Solar Terrestrial Probes program by studying how interplanetary space changes in response to the constant outpouring of energy and particles from the Sun and how it interacts with planetary atmospheres. It was expected to launch as a rideshare payload alongside IMAP in February 2025. However, the spacecraft was not selected for further development and project closeout efforts concluded in 2023.
