page_title: Interstellar probe
section_title: Interstellar concepts
hierarchical_section_title: Interstellar probe / Interstellar concepts
caption_attribution_description: English: The Bussard Interstellar Ramjet engine concept uses interstellar hydrogen scooped up from its environment as the spacecraft passes by to provide propellant mass. The hydrogen is then ionized and collected by an electromagentic field. In this image, an onboard laser is used to heat the plasma, and the laser or electron beam is used to trigger fusion pulses thereby creating propulsion.
context_page_description: 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.
  There are five interstellar probes, all launched by the American space agency NASA: Voyager 1, Voyager 2, Pioneer 10, Pioneer 11 and New Horizons. As of 2019, Voyager 1 and Voyager 2 are the only probes to have actually reached interstellar space. The other three are on interstellar trajectories.
  The termination shock is the point in the heliosphere where the solar wind slows down to subsonic speed. Even though the termination shock happens as close as 80–100 AU the maximum extent of the region in which the Sun's gravitational field is dominant is thought to be at around 230,000 astronomical units. This point is close to the nearest known star system, Alpha Centauri, located 4.36 light years away. Although the probes will be under the influence of the Sun for a long time, their velocities far exceed the Sun's escape velocity, so they will eventually leave forever.
context_section_description: Project Orion (1958–1965)
  Project Orion was a proposed nuclear pulse propulsion craft that would have used fission or fusion bombs to apply motive force. The design was studied during the 1950s and 1960s in the United States of America, with one variant of the craft capable of interstellar travel.
  Bracewell probe (1960)
  Interstellar communication via a probe, as opposed to sending an electromagnetic signal.
  Sanger Photon Rocket (1950s-1964)
  Eugene Sanger proposed a spacecraft powered by antimatter in the 1950s. Thrust was intended to come from reflected gamma-rays produced by electron-positron annihilation.
  Enzmann Starship (1964/1973)
  Proposed by 1964 and examined in an October 1973 issue of Analog, the Enzmann Starship proposed using a 12,000 ton ball of frozen deuterium to power thermonuclear powered pulse propulsion. About twice as long as the Empire State Building and assembled in-orbit, the spacecraft was part of a larger project preceded by large interstellar probes and telescopic observation of target star systems.
  Project Daedalus (1973–1978)
  Project Daedalus was a proposed nuclear pulse propulsion craft that used inertial confinement fusion of small pellets within a magnetic field nozzle to provide motive force. The design was studied during the 1970s by the British Interplanetary Society, and was meant to flyby Barnard's Star in under a century from launch. Plans included mining Helium-3 from Jupiter and a pre-launch mass of over 50 thousand metric tonnes from orbit.
  Project Longshot (1987–1988)
  Project Longshot was a proposed nuclear pulse propulsion craft that used inertial confinement fusion of small pellets within a magnetic field nozzle to provide motive force, in a manner similar to that of Project Daedalus. The design was studied during the 1990s by NASA and the US Naval Academy. The craft was designed to reach and study Alpha Centauri.
  Starwisp (1985)
  Starwisp is a hypothetical unmanned interstellar probe design proposed by Robert L. Forward. It is propelled by a microwave sail, similar to a solar sail in concept, but powered by microwaves from an artificial source.
  Medusa (1990s)
  Medusa was a novel spacecraft design, proposed by Johndale C. Solem, using a large lightweight sail (spinnaker) driven by pressure pulses from a series of nuclear explosions. The design, published by the British Interplanetary Society, was studied during the 1990s as a means of interplanetary travel.
  Starseed launcher (1996)
  Starseed launcher was concept for launching microgram interstellar probes at up to 1/3 light speed.
  AIMStar (1990s-2000s)
  AIMStar was a proposed antimatter catalyzed nuclear pulse propulsion craft that would use clouds of antiprotons to initiate fission and fusion within fuel pellets. A magnetic nozzle derived motive force from the resulting explosions. The design was studied during the 1990s by Penn State University. The craft was designed to reach a distance of 10,000 AU from the Sun in 50 years.
  Project Icarus (2009+)
  Project Icarus is a theoretical study for an interstellar probe and is being run under the guidance of the Tau Zero Foundation (TZF) and the British Interplanetary Society (BIS), and was motivated by Project Daedalus, a similar study that was conducted between 1973 and 1978 by the BIS. The project is planned to take five years and began on September 30, 2009.
  Project Dragonfly (2014+)
  The Initiative for Interstellar Studies (i4is) has initiated a project working on small interstellar spacecraft, propelled by a laser sail in 2014 under the name of Project Dragonfly. Four student teams worked on concepts for such a mission in 2014 and 2015 in the context of a design competition.
  Geoffrey A. Landis proposed for interstellar travel future-technology project interstellar probe with supplying the energy from an external source (laser of base station) and ion thruster.
caption: NASA 2004 artist concept of an Interstellar Bussard ramjet engine
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