Voyager 1

The Voyager 1 spacecraft is an 815-kilogram unmanned probe of the outer solar system and beyond, launched September 5, 1977, and currently operational. It visited Jupiter and Saturn and was the first probe to provide detailed images of the moons of these planets.

As of 2006, it is the farthest human-made object from Earth. Voyager 1 spacecraft has moved into the solar system's final frontier; a vast area where the Sun's influence gives way to interstellar space. At 14 billion kilometers (94 astronomical units or 8.8 billion miles) from the Sun, Voyager 1 has entered the heliosheath, the termination shock region between the solar system and interstellar space. If Voyager 1 is still functioning when it finally passes the heliopause, scientists will get their first direct measurements of the conditions in the interstellar medium. At this distance, signals from Voyager 1 take more than thirteen hours to reach its control center at the Jet Propulsion Laboratory, a joint project of NASA and Caltech near 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, Pioneer 11, and its sister ship Voyager 2, Voyager 1 is becoming 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. Both Voyager probes are powered by three radioisotope thermoelectric generators, which have far outlasted their originally intended lifespan, and are now expected to continue to generate enough power to keep communicating with Earth until at least around the year 2030.

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 fortunate 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 IIIE Centaur rocket, slightly after its sister craft, Voyager 2. Despite being launched after Voyager 2, Voyager 1 was sent on a faster trajectory so it reached Jupiter and Saturn before its sister craft.

Initially, an underburn in the second stage of the Titan IIIE rocket left an estimated one second's worth of fuel remaining in that stage. Although ground crews were worried that Voyager 1 would not make it to Jupiter, the Centaur upper stage proved to have enough fuel to compensate.

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 kilometers (217,000 miles) from its center. 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 volcanic activity 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 kilometers (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.

Interstellar mission

It is estimated both Voyager craft would have sufficient electrical power to operate at least some instruments until 2020.

Heliopause

As the Voyager 1 space probe 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 entered the termination shock in February 2003. Some other scientists have expressed doubt, discussed in the journal Nature of November 6 2003. In a scientific session at the American Geophysical Union meeting in New Orleans on the morning of March 25 2005, Dr. Ed Stone presented clear evidence that Voyager 1 crossed the termination shock in December 2004 The issue will not be resolved for some months as other data become available, since Voyager's solar-wind detector ceased functioning in 1990. However, in May 2005 a NASA press release said that consensus was that Voyager 1 was now in the heliosheath. [http://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html. Scientists believe the craft will reach the heliopause in 2015.

Distance travelled

In November 2005, Voyager 1 was at a distance of 14.56 billion kilometers (97.3 AU or 9.05 billion miles) from the Sun, which makes it the most distant man-made object from Earth. At this distance, light (which travels at 300,000 kilometers per second) takes close to 13.8 hours to reach the spacecraft from Earth. As a basis for comparison, the Moon is about 1.4 light seconds from Earth, the Sun is about 8.5 light minutes away, and Pluto, during most of its orbit the most distant planet in our solar system, is at an average distance of approximately 5.5 light hours. As of November 2005, the spacecraft was travelling at a speed of 17.2 kilometers per second relative to the sun (3.6 AU per year or 38,400 miles per hour), 10% faster than Voyager 2. Accurate information concerning its location can be found in NASA paper with heliocentric coordinates extrapolated up to 2015 of both probes. It is not heading towards any particular star, but in 40000 years it will get close ("close" meaning in this case about 1.7 light years) to star AC+793888 in the Camelopardis constellation.

Current position

Voyager 1, as of April 2006, is at 12.32° declination and 17.114hrs Right Ascension, placing it in the constellation Ophiuchus.

Tracking

NASA continues intermittent tracking of Voyager 1 with the Deep Space Network stations.

On 31 March 2006, the amateur radio operators from AMSAT Germany tracked and received data from Voyager 1 using the 20m dish at Bochum with a long integration technique. Its data was checked and verified against data from the Deep Space Network station at Madrid, Spain. AMSAT-DL article in German; ARRL article in English. This is believed to be the first such tracking of Voyager.

External links

NASA Voyager website
Voyager Spacecraft Lifetime — interstellar mission coverage.
Spacecraft Escaping the Solar System — current positions and diagrams
CNN: "NASA: Voyager I enters solar system's final frontier", May 25, 2005
CNN: "NASA: Voyager II detects solar system's edge", May 25, 2006
Weekly Mission Reports — includes information on current spacecraft state

Jupiter spacecraft | Voyager program | Saturn spacecraft

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