(left to right), Neptune, Uranus, Saturn, Jupiter
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
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.
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 is now near thirty
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.
The Voyager Mission
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.
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.
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.
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
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.
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
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 has
crossed into the heliosheath and is 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.
will continue to study ultraviolet sources among the stars, and the
fields and particles instruments aboard the Voyagers will continue to
explore the boundary between the Sun's influence and interstellar
space. The Voyagers are expected to return valuable data for at least
another decade. Communications will be maintained until the Voyagers'
power sources can no longer supply enough electrical energy to power