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In 1977, two unmanned spacecraft, designed and built by
the Jet Propulsion Laboratory, were launched on reconnaissance missions
to the outer planets.
Separate Titan/Centaur rockets launched Voyagers 1 and 2 in September
and August 1977 toward Jupiter. In 1972-74, the flights of Pioneer
10 and 11 proved spacecraft could fly through the asteroid belt beyond
Mars and survive Jupiter's intense magnetosphere. Pioneer 11 also tested
the gravity-assist technique that the Voyager spacecraft used to successfully
journey beyond Jupiter.
Each
Voyager spacecraft carries a message in the form of a 12-inch gold-plated
phonograph
record. The record, together with a cartridge and needle, is fastened
to the side of the spacecraft in a gold-anodized aluminum case that also
illustrates how the record is to be played. In the photograph below, taken
shortly before launch in 1977, Voyager Project Manager, John Casani, displays
the "Sounds
of Earth" recording. The records contain greetings
in 55 languages, samples of music
from different cultures and eras, natural sounds of surf, wind, thunder,
birds, whales and other animals, and a message from President Jimmy Carter.
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In
September 1977, Voyager 1's camera looked back toward the home planet
for a first-ever glimpse of the Earth and its Moon in a single frame.
In 1979, Voyagers 1 and 2 sent back spectacular images of the Jovian
system and made startling discoveries.
Giant volcanoes spew molten sulfur hundreds of kilometers above the surface
of Io, one of Jupiter's largest moons, while Europa, Ganymed, and Callisto
each have diverse surfaces. Three tiny moons were found near a thick ring
of dust particles encircling the planet, and cloud-top lightning bolts
and polar auroras light up the Jovian night skies.
The
Voyagers traveled on to Saturn
encounters in 1980 and 1981 respectively. The
rings were more complex than scientists could have imagined. Although
Saturn's colors are more muted than Jupiter's, storms are still visible
in the cloud tops. A thick atmosphere of nitrogen and methane surrounds
Titan, Saturn's largest moon, and the photochemical hazes hide its surface.
After its close swing past Titan, Saturn's gravity forced Voyager 1 up
and out of the ecliptic plane, and the spacecraft is now on its way out
of the solar system.
Mission planners took advantage of the opportunity to send Voyager 2 on
to Uranus.
Arriving at Uranus in 1986, Voyager 2 found a cold planet with a remarkably
featureless atmosphere. The spacecraft discovered ten small moons and
two new rings at Uranus. Miranda, one of the five larger moons, has one
of the most complex surfaces yet seen in the solar system. Voyager 2's
final planetary encounter took place on August 25, 1989, when the spacecraft
sailed within 3000 miles of the cloud tops of Neptune's
north pole. Five hours later, Voyager 2 swept past Triton, a cold, bright
moon where volcanoes may spew ice particles into the thin nitrogen atmosphere.
The spacecraft discovered six new moons and a number of rings at Neptune.
Now Voyager 2 is also heading out of the solar system, diving below the
ecliptic plane.
Data from both Voyagers could be received well into the next century as
they search through interstellar space. Please see http://voyager.jpl.nasa.gov
to check the current location and status of the Voyager spacecraft.
excerpted
from JPL 400-389 G 9/89
Everyone
knows that the launch window in 1977-79 happens only once every 176 years,
so that a single spacecraft can fly by all four planets. If this window
had occurred in 1965-66-67, we wouldn't have had the technology to fly
such a mission. If it had happened in the 80's, we couldn't have launched
the mission [when Titan/Centar rocket was discontinued]. We were indeed
fortunate that the launch window was open at just the right time… We have
enough electrical power to keep it going for roughly another 20 years.
There's still a lot left to discover. The journey of a lifetime is not
over yet.
-Dr. Edward Stone, Voyager Project Scientist
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