Functional spacecraft ====
Voyager 1 (1977–)====
Voyager 1 is a
space probe launched by
NASA on September 5, 1977. At a distance of about it is the farthest manmade object from
Earth. It was later estimated that
Voyager 1 crossed the termination shock on December 16, 2004 at a distance of 94 AU from the Sun. At the end of 2011,
Voyager 1 entered and discovered a stagnation region where charged particles streaming from the Sun slow and turn inward, and the Solar System's magnetic field is doubled in strength as interstellar space appears to be applying pressure. Energetic particles originating in the Solar System declined by nearly half, while the detection of high-energy electrons from outside increases 100-fold. The inner edge of the stagnation region is located approximately 113 astronomical units (AU) from the Sun. In 2013 it was thought
Voyager 1 crossed the
heliopause and entered
interstellar space on August 25, 2012 at distance of 121 AU from the Sun, making it the first known human-manufactured object to do so. the probe was moving with a relative velocity to the Sun of about 16.95 km/s (3.58 AU/year). If it does not hit anything,
Voyager 1 could reach the
Oort cloud in about 300 years. ====
Voyager 2 (1977–)====
Voyager 2 crossed the heliopause and entered interstellar space on November 5, 2018. It had previously passed the termination shock into the
heliosheath on August 30, 2007.
Voyager 2 is at a distance of from Earth. The probe was moving at a velocity of 3.25 AU/year (15.428 km/s) relative to the Sun on its way to interstellar space in 2013. It is moving at a velocity of relative to the Sun .
Voyager 2 is expected to provide the first direct measurements of the density and temperature of the interstellar plasma. ====
New Horizons (2006–)====
New Horizons was launched directly into a hyperbolic escape trajectory, getting a
gravitational assist from
Jupiter en route. By March 7, 2008,
New Horizons was 9.37 AU from the Sun and traveling outward at 3.9 AU per year. It will, however, slow to an escape velocity of only 2.5 AU per year as it moves away from the Sun, so it will never catch up to either Voyager. it was traveling at 2.87 AU/year (13.68 km/s) relative to the Sun.
New Horizons next encountered
486958 Arrokoth on January 1, 2019, at about 43.4
AU from the Sun the furthest object ever explored by a spacecraft. The Heliosphere's termination shock was crossed by
Voyager 1 at 94 astronomical units (AU) and
Voyager 2 at 84 AU according to the IBEX mission. If
New Horizons can reach the distance of , it will be traveling at about , around slower than
Voyager 1 at that distance.
Inactive missions ====
Pioneer 10 (1972–2003)==== The last successful reception of telemetry from
Pioneer 10 was on April 27, 2002, when it was at a distance of 80.22 AU, and the last signal from the spacecraft was received on January 23, 2003, at a distance 82 AU from the Sun traveling at about 2.54 AU/year (12 km/s). capable of making the journey to
Alpha Centauri, the nearest
star system, at speeds of 20% and 15% 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. ;
Shensuo (2019–) A CNSA space mission first proposed in 2019 would be launched in 2024 with the intention to research the heliosphere. Both probes would use
gravity assists at Jupiter and fly by
Kuiper belt objects, and the second is also planned to fly by Neptune and Triton. The other goal is to reach 100 AU from the Sun by 2049, the centennial of the People's Republic of China's foundation. ;
Interstellar Probe (ISP) (2018–) A NASA funded study, led by the
Applied Physics Laboratory, on possible options for an interstellar probe. The nominal concept would launch on a
SLS in the 2030s. It would perform either a fast Jupiter flyby, a powered Jupiter flyby, or a very close perihelion and propulsive maneuver, and reach a distance of 1000–2000 AU (93–186 billion miles; about 1.5-3% of one light-year) within 50 years. Possibilities for planetary, astrophysical and exoplanet science along the way are also being investigated. ;
Interstellar Heliopause Probe (IHP) (2006) A technology reference study published in 2006 with the ESA proposed an interstellar probe focused on leaving the heliosphere. The goal would be 200 AU in 25 years, with traditional launch but acceleration by a
solar sail. The roughly 200–300 kg probe would carry a suite of several instruments including a plasma analyzer, plasma radio wave experiment, magnetometer, neutral and charged atom detector, dust analyzer, and a UV-photometer. Electrical power would come from an
RTG. ;
Innovative Interstellar Explorer (2003) NASA proposal to send a 35 kg science payload out to at least 200 AU. It would achieve a top speed of 7.8 AU per year using a combination of a heavy lift rocket, Jupiter gravitational assistance, and an
ion engine powered by standard
radioisotope thermal generators. The probe suggested a launch in 2014 (to take advantage of Jupiter
gravitational assist), to reach 200 AU around 2044. ;
Realistic Interstellar Explorer and
Interstellar Explorer (2000–2002) Studies suggest various technologies including
americium-241-based RTG, optical communication (as opposed to radio), and low-power semi-autonomous electronics. Trajectory uses a Jupiter
gravity assist and Solar
Oberth maneuver to achieve 20 AU/year, allowing 1000 AU within 50 years, and a mission extension up to 20,000 AU and 1000 years. Needed technology included advanced propulsion and solar shield for perihelion burn around the Sun. Solar thermal (STP), nuclear fission thermal (NTP), and nuclear fission pulse, as well as various RTG isotopes were examined. The studies also included recommendations for a solar probe (see also
Parker Solar Probe), nuclear thermal technology, solar sail probe, 20 AU/year probe, and a long-term vision of a 200 AU/year probe to the star
Epsilon Eridani. The "next step" interstellar probe in this study suggested a 5 megawatt fission reactor utilizing 16 metric tonnes of H2 propellant. ;
Interstellar Probe (1999) Interstellar Probe was a proposed
solar sail propulsion spacecraft planned by NASA Jet Propulsion Laboratory. It was planned to reach as far as 200 AU within 15 years at a speed of 14 AU/year (about 70 km/s, and function up to 400+ AU). A critical technology for the mission is a large 1 g/m2 solar sail. ;
TAU mission (1987)
TAU mission (Thousand Astronomical Units) was a proposed
nuclear electric rocket craft that used a 1 MW fission reactor and an
ion drive with a burn time of about 10 years to reach a speed of 106 km/s (about 20 AU/year) to achieve a distance of 1000 AU in 50 years. The primary goal of the mission was to improve parallax measurements of the distances to stars inside and outside our galaxy, with secondary goals being the study of the
heliopause, measurements of conditions in the
interstellar medium, and (via communications with Earth) tests of
general relativity.
Mission concepts ;
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 by NASA and the US Air Force, 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. 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. ;
Breakthrough Starshot (2016+) In 2016, the
Breakthrough Initiatives announced a program to develop a fleet of lightweight light-sail probes for interstellar travel, aiming to make the journey to
Alpha Centauri. This research program, with an initial funding of US$ 100 million imagines accelerating the probes to about 15% or 20% of the speed of light, resulting in a travel time of between 20 and 30 years.
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. ==Trans-Neptunian probes at precursor distances==