Interstellar probe

An interstellar probe is a space probe which has left -- or is expected to leave -- the solar system and enter interstellar space (typically defined as the region beyond the heliopause). Alternatively, the term interstellar probe is used to refer to a space probe that is capable of reaching star systems other than the solar system (a probe capable of interstellar travel).

Current interstellar probes

Five spacecraft (three active spacecraft) are currently on interstellar trajectories:

Functional spacecraft

; "Voyager 1"In May 2005 a NASA press release expressed the consensus that "Voyager 1" was now in the heliosheath. [cite web | url = http://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html | title = Voyager Enters Solar System's Final Frontier | publisher = NASA] As of July 7, 2008, "Voyager 1" is at a distance of around 106.3 AU from the Sun and traveling outward at roughly 3.6 AU per year. Scientists believe the craft will reach the heliopause in 2015.

; "Voyager 2""Voyager 2" passed the termination shock into the heliosheath on October 30, 2007. Unlike "Voyager 1", it has a working plasma science instrument, and is returning data on the temperature and pressure of this region. As of July 7, 2008, "Voyager 2" is at a distance of around 85.49 AU from the Sun and traveling outward at roughly 3.3 AU per year. "Voyager 2" is expected to keep transmitting into the 2020s.

; "New Horizons"Following its gravitational assist from Jupiter, "New Horizons" is on an interstellar trajectory via Pluto. As of 2008 March 7, "New Horizons" is 9.37 AU from the Sun and traveling outward at 3.9 AU per year; however, it will 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".

Non-functional spacecraft

; "Pioneer 10"The last successful reception of telemetry from "Pioneer 10" was on April 27, 2002, when it was at a distance of 80.22 AU.

; "Pioneer 11"Routine mission operations for "Pioneer 11" were stopped September 30, 1995, when it was 6.5 billion km (approx 43.4 AU) from Earth.

Proposed probes capable of reaching the interstellar medium

; Innovative Interstellar ExplorerThe "Innovative Interstellar Explorer" ("IIE") is a proposed NASA project 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 could launch in 2014, reaching 200 AU around 2044. [http://interstellarexplorer.jhuapl.edu/index.php]

; "Interstellar Probe""Interstellar Probe" was a proposed solar sail propulsion spacecraft planned by NASA Jet Propulsion Laboratory. It was planned to reach as far as 200-400 AU at a speed of 14 AU/year. [http://interstellar.jpl.nasa.gov/interstellar/probe/index.html]

; "Medusa""Medusa" was a proposed nuclear pulse propulsion craft that used fission or fusion bombs to provide propulsion, with a structure similar to a light sail used to derive motive force from the bombs' blast waves. The design was studied during the 1990s by the British Interplanetary Society as a means of interplanetary travel. []

; "AIMStar""AIMStar" was a proposed antimatter catalyzed nuclear pulse propulsion craft that used clouds of antiprotons to initiate fission and fusion within fuel pellets. [cite web | title = AIMStar: Antimatter Initiated Microfusion For Pre-cursor Interstellar Missions | url = http://www.engr.psu.edu/antimatter/Papers/AIMStar_99.pdf | last = Lewis | first = Raymond A | coauthors = Meyer, Kirby; Smith, Gerald A; Howe, Steven D] 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.

Proposed probes capable of reaching other stars

; "Project Orion"Project Orion was a proposed nuclear pulse propulsion craft that 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.

; "Project Daedalus"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. The craft was designed to reach and study Barnard's Star.

; "Project Longshot"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"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.

References