The Voyager 1 spacecraft is an unmanned probe of the outer solar system, launched September 5, 1977, and currently operational. It is currently the most distant artifical object in the solar system, more than 90 astronomical units distant from Earth. At this distance, signals from Voyager 1 take 13 hours to reach Voyager 1's control center at the Jet Propulsion Laboratory, a joint project of NASA and Caltech in Pasadena, California. Voyager 1 is on a hyperbolic trajectory and has achieved escape velocity, meaning that its orbit will not return to the inner solar system. Along with Pioneer 10, the now deactivated Pioneer 11, and its sister ship Voyager 2, Voyager 1 will eventually become an interstellar probe. Voyager 1 had as its primary targets the planets Jupiter and Saturn and their associated moons and rings; its current mission is the detection of the heliopause and particle measurements of solar wind and the interstellar medium.

Contents

1 Mission planning and launch 2 Jupiter 3 Saturn 4 Heliopause 5 Distance Travelled 6 See also 7 External links

Mission planning and launch

Voyager 1 was originally planned as Mariner 11 of the Mariner program. From the outset, it was designed to take advantage of the then-new technique of gravity assist. By fortuitous chance, the development of interplanetary probes coincided with an alignment of the planets called the Grand Tour. The Grand Tour was a linked series of gravity assists that, with only the minimal fuel needed for course corrections, would enable a single probe to visit all four of the solar system's gas giant planets: Jupiter, Saturn, Uranus, and Neptune. The identical Voyager 1 and Voyager 2 probes were designed with the Grand Tour in mind, and their launches were timed to enable the Grand Tour if desired.

Voyager 1 was launched on September 5, 1977 by NASA from Cape Canaveral aboard a Titan-Centaur rocket, slightly after its sister craft, Voyager 2 (the two Voyager program spacecraft are identical). Despite being launched after Voyager 2, Voyager 1 was sent on a faster trajectory so it reached Jupiter and Saturn before its sister craft.

For details on the Voyager instrument packages, see the separate article on the Voyager program.

Jupiter

Voyager 1 began photographing Jupiter in January 1979. Its closest approach to Jupiter was on March 5, 1979, at a distance of 349,000 kilometres (217,000 miles) from its centre. Due to the greater resolution allowed by close approach, most observations of the moons, rings, magnetic fields, and radiation environment of the Jupiter system were made in the 48-hour period bracketing closest approach. It finished photographing the planet in April.

The two Voyager spacecraft made a number of important discoveries about Jupiter and its satellites. The most surprising was the existence of sulfur volcanoes on Io, which had not been observed from the ground or by Pioneer 10 or 11.

Saturn

The gravity assist at Jupiter was successful, and the spacecraft went on to visit Saturn. Voyager 1's Saturn flyby occurred in November 1980, with the closest approach on November 12 when it came within 124,000 kilometres (77,000 miles) of the planet's cloud-tops. The craft detected complex structures in Saturn's rings, and studied the atmospheres of Saturn and Titan. Because of the earlier discovery of a thick atmosphere on Titan, the Voyager controllers at the Jet Propulsion Laboratory elected for Voyager 1 to make a close approach of Titan and terminate its Grand Tour. (For the continuation of the Grand Tour, see the Uranus and Neptune sections of the Voyager 2 article.) The Titan-approach trajectory caused an additional gravity assist that took Voyager 1 out of the plane of the ecliptic, thus ending its planetary science mission.

Heliopause

As it heads for interstellar space, its instruments continue to study the solar system; Jet Propulsion Laboratory scientists are using the plasma wave experiments aboard Voyager 1 and 2 to look for the heliopause. Scientists at the Johns Hopkins University Applied Physics Lab believe that Voyager passed the termination shock in February 2003. However some other scientists have expressed doubt (discussed in the journal Nature of November 6). The issue will not be resolved for some months as other data becomes available, since Voyager's solar-wind detector ceased functioning in 1990.

Distance Travelled

In September 2004, Voyager 1 was at a distance of 14.0 billion kilometres (93.2 Astronomical Units, 8.7 billion miles or 13.0 light-hours) from the Sun. This makes the spacecraft the most distant man-made object from Earth. Voyager 1 is escaping the solar system at a speed of about 3.6 AU (19 light-minutes) per year (ca. 17 km/s).

See also

• Voyager program for more information about this spacecraft.

External links

• NASA Voyager website (http://voyager.jpl.nasa.gov)
• Voyager Spacecraft Lifetime (http://voyager.jpl.nasa.gov/spacecraft/spacecraftlife.html)
• Spacecraft Escaping the Solar System (http://www.heavens-above.com/solar-escape.asp) - current positions and diagrams

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