Science > Planetary Voyage
Planet montage (left to right), Neptune, Uranus, Saturn, Jupiter
Planet montage (left to right), Neptune, Uranus, Saturn, Jupiter The twin spacecraft Voyager 1 and Voyager 2 were launched by NASA in separate months in the summer of 1977 from Cape Canaveral, Florida. As originally designed, the Voyagers were to conduct closeup studies of Jupiter and Saturn, Saturn's rings, and the larger moons of the two planets. To accomplish their two-planet mission, the spacecraft were built to last five years. But as the mission went on, and with the successful achievement of all its objectives, the additional flybys of the two outermost giant planets, Uranus and Neptune, proved possible -- and irresistible to mission scientists and engineers at the Voyagers' home at the Jet Propulsion Laboratory in Pasadena, California. As the spacecraft flew across the solar system, remote-control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left the Earth. Their two-planet mission became four. Their five-year lifetimes stretched to 12 and more. Eventually, between them, Voyager 1 and 2 would explore all the giant outer planets of our solar system, 48 of their moons, and the unique systems of rings and magnetic fields those planets possess. Had the Voyager mission ended after the Jupiter and Saturn flybys alone, it still would have provided the material to rewrite astronomy textbooks. But having doubled their already ambitious itineraries, the Voyagers returned to Earth information over the years that has revolutionized the science of planetary astronomy, helping to resolve key questions while raising intriguing new ones about the origin and evolution of the planets in our solar system. History Of The Voyager Mission
The Voyager mission was designed to take advantage of a rare geometric arrangement of the outer planets in the late 1970s and the 1980s which allowed for a four-planet tour for a minimum of propellant and trip time. This layout of Jupiter, Saturn, Uranus and Neptune, which occurs about every 175 years, allows a spacecraft on a particular flight path to swing from one planet to the next without the need for large onboard propulsion systems. The flyby of each planet bends the spacecraft's flight path and increases its velocity enough to deliver it to the next destination. Using this "gravity assist" technique, first demonstrated with NASA's Mariner 10 Venus/Mercury mission in 1973-74, the flight time to Neptune was reduced from 30 years to 12.
While the four-planet mission was known to be possible, it was deemed to be too expensive to build a spacecraft that could go the distance, carry the instruments needed and last long enough to accomplish such a long mission. Thus, the Voyagers were funded to conduct intensive flyby studies of Jupiter and Saturn only. More than 10,000 trajectories were studied before choosing the two that would allow close flybys of Jupiter and its large moon Io, and Saturn and its large moon Titan; the chosen flight path for Voyager 2 also preserved the option to continue on to Uranus and Neptune. From the NASA Kennedy Space Center at Cape Canaveral, Florida, Voyager 2 was launched first, on August 20, 1977; Voyager 1 was launched on a faster, shorter trajectory on September 5, 1977. Both spacecraft were delivered to space aboard Titan-Centaur expendable rockets. The prime Voyager mission to Jupiter and Saturn brought Voyager 1 to Jupiter on March 5, 1979, and Saturn on November 12, 1980, followed by Voyager 2 to Jupiter on July 9, 1979, and Saturn on August 25, 1981. Voyager 1's trajectory, designed to send the spacecraft closely past the large moon Titan and behind Saturn's rings, bent the spacecraft's path inexorably northward out of the ecliptic plane -- the plane in which most of the planets orbit the Sun. Voyager 2 was aimed to fly by Saturn at a point that would automatically send the spacecraft in the direction of Uranus. After Voyager 2's successful Saturn encounter, it was shown that Voyager 2 would likely be able to fly on to Uranus with all instruments operating. NASA provided additional funding to continue operating the two spacecraft and authorized JPL to conduct a Uranus flyby. Subsequently, NASA also authorized the Neptune leg of the mission, which was renamed the Voyager Neptune Interstellar Mission. Voyager 2 encountered Uranus on January 24, 1986, returning detailed photos and other data on the planet, its moons, magnetic field and dark rings. Voyager 1, meanwhile, continues to press outward, conducting studies of interplanetary space. Eventually, its instruments may be the first of any spacecraft to sense the heliopause -- the boundary between the end of the Sun's magnetic influence and the beginning of interstellar space. Following Voyager 2's closest approach to Neptune on August 25, 1989, the spacecraft flew southward, below the ecliptic plane and onto a course that will take it, too, to interstellar space. Reflecting the Voyagers' new transplanetary destinations, the project is now known as the Voyager Interstellar Mission. Voyager 1 is now leaving the solar system, rising above the ecliptic plane at an angle of about 35 degrees at a rate of about 520 million kilometers (about 320 million miles) a year. Voyager 2 is also headed out of the solar system, diving below the ecliptic plane at an angle of about 48 degrees and a rate of about 470 million kilometers (about 290 million miles) a year. Both spacecraft will continue to study ultraviolet sources among the stars, and the fields and particles instruments aboard the Voyagers will continue to search for the boundary between the Sun's influence and interstellar space. The Voyagers are expected to return valuable data for two or three more decades. Communications will be maintained until the Voyagers' nuclear power sources can no longer supply enough electrical energy to power critical subsystems. The cost of the Voyager 1 and 2 missions -- including launch, mission operations from launch through the Neptune encounter and the spacecraft's nuclear batteries (provided by the Department of Energy) -- is $865 million. NASA budgeted an additional $30 million to fund the Voyager Interstellar Mission for two years following the Neptune encounter.
Künstlerische Darstellung der Voyager-Sonde im All

 Die im Jahr 1977 ins All geschossene Raumsonde Voyager 1 hat nach 33 Jahren die Grenze unseres Sonnensystems erreicht. Die Sonde ist mit einer Entfernung von mehr als 17 Milliarden Kilometern zur Sonne das am weitesten von der Erde entfernte von Menschenhand geschaffene Objekt im Weltall.

Wie die NASA am 13. Dezember mitteilte, befindet sich Voyager 1 nun in einer Zone, in der die Geschwindigkeit des Sonnenwinds auf Null abgesunken ist. Diese auch Heliopause genannte Zone stellt die Grenze zwischen dem Sonnensystem und dem interstellaren Raum dar. Zwar hatte die NASA bereits vor einigen Monaten den Wert Null gemessen, aber wegen Schwankungen in der Geschwindigkeit des Sonnenwinds waren noch weitere Messungen nötig, damit sich die Wissenschaftler wirklich sicher waren.

Voyager 1 wurde zusammen mit ihrer kurz vorher gestarteten Schwestersonde Voyager 2 von der NASA ins All geschickt, um das äußere Sonnensystem zu erkunden. Voyager 1 flog an den Planeten Jupiter und Saturn vorbei und sendete Bilder zurück an die Erde. Um ein nahes Vorbeifliegen am Saturnmond Titan und den Ringen des Saturn zu erreichen, wurde eine Flugbahn gewählt, die die Sonde danach aus der Ebene der Planetenbahnen ablenkte und sie zuerst die Grenze des Sonnensystems erreichen ließ. Voyager 2 hingegen besuchte auch noch die weiter außen gelegenen Planeten Uranus und Neptun.

Die jetzige Entfernung der Voyager 1 von der Sonne beträgt 17,4 Milliarden Kilometer. Es dauert fast 13 Stunden, bis ein von der Sonde geschicktes Signal auf der Erde empfangen wird. Die Sonde fliegt mit einer Geschwindigkeit von 17 Kilometern pro Sekunde. Neben Untersuchungen der Heliopause mit ihren Partikeldetektoren macht die Sonde auch Ultraviolettaufnahmen des Sternenhimmels.

Die Wissenschaftler erwarten, dass Voyager 1 in etwa fünf Jahren die Heliopause verlassen und endgültig in den interstellaren Raum eintreten wird. Voyager 2 wird ein paar Jahre später folgen. Es wird erwartet, dass beide Sonden noch mindestens ein Jahrzehnt lang Daten senden werden.