By Marty McDowell/NASA
On September 5, 1977, the United States launched Voyager 1. Although
launched after Voyager 2, it made it to
Jupiter first and to Saturn as well. It discovered a pair of Jupiter's
moons, the rings of Jupiter and three of Saturn's moons.
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
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.
This image of Saturn, taken
by the Voyager 1 spacecraft on October 18, 1980,
was color-enhanced to increase the visibility of
large, bright features in Saturn's North Temperate
Image courtesy of NASA.
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.
In this false-color image
of Neptune, objects that are deep in the
atmosphere are blue, while those at higher
altitudes are white. The images was taken by
Voyager 2's wide-angle camera through an orange
filter and two different methane filters. Light at
methane wavelengths is mostly absorbed in the
deeper atmosphere. Taken in August, 1989.
Image courtesy of NASA.
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
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
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
Where are they now?
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.