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Donald Savage
Headquarters, Washington, DC February 13, 1998
(Phone: 202/358-1547)
Mary Hardin
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-0344)
RELEASE: 98-30
VOYAGER 1 NOW MOST DISTANT HUMAN-MADE OBJECT IN SPACE
In a dark, cold, vacant neighborhood near the very edge of
our Solar System, the Voyager 1 spacecraft is set to break another
record and become the explorer that has traveled farthest from home.
At approximately 5:10 p.m. EST on Feb. 17, 1998, Voyager 1,
launched more than two decades ago, will cruise beyond the
Pioneer 10 spacecraft and become the most distant human-created
object in space, at 6.5 billion miles (10.4 billion kilometers)
from Earth. The two are headed in almost opposite directions away
from the Sun.
"For 25 years, the Pioneer 10 spacecraft led the way,
pressing the frontiers of exploration, and now the baton is being
passed from Pioneer 10 to Voyager 1 to continue exploring where no
one has gone before," said Dr. Edward C. Stone, Voyager project
scientist and Director of NASA's Jet Propulsion Laboratory (JPL),
Pasadena, CA.
"At almost 70 times farther from the Sun than the Earth,
Voyager 1 is at the very edge of the Solar System. The Sun there
is only 1/5,000th as bright as here on Earth, so it is extremely
cold, and there is very little solar energy to keep the spacecraft
warm or to provide electrical power. The reason we can continue
to operate at such great distances from the Sun is because we have
radioisotope thermal electric generators (RTGs) on the spacecraft
that create electricity and keep the spacecraft operating," Stone
said. "The fact that the spacecraft is still returning data is a
remarkable technical achievement."
Voyager 1 was launched from Cape Canaveral on Sept. 5,
1977. The spacecraft encountered Jupiter on March 5, 1979, and
Saturn on Nov. 12, 1980.
Then, because its trajectory was designed to fly close to
Saturn's large moon Titan, Voyager 1's path was bent northward by
Saturn's gravity, sending the spacecraft out of the ecliptic plane
-- the plane in which all the planets except Pluto orbit the Sun.
Launched on March 2, 1972, the Pioneer 10 mission
officially ended on March 31, 1997. However, NASA's Ames Research
Center, Moffett Field, CA, intermittently receives science data
from Pioneer as part of a training program for flight controllers
of the Lunar Prospector spacecraft now orbiting the Moon.
"The Voyager mission today presents an unequalled
technical challenge. The spacecraft are now so far from home that
it takes nine hours and 36 minutes for a radio signal traveling at
the speed of light to reach Earth," said Ed B. Massey, project
manager for the Voyager Interstellar Mission at JPL. "That
signal, produced by a 20 watt radio transmitter, is so faint that
the amount of power reaching our antennas is 20 billion times
smaller than the power of a digital watch battery."
Having completed their planetary explorations, Voyager 1
and its twin, Voyager 2, are studying the environment of space in
the outer Solar System. Although beyond the orbits of all the
planets, the spacecraft still are well within the boundary of the
Sun's magnetic field, called the heliosphere. Science instruments
on both spacecraft sense signals that scientists believe are
coming from the outermost edge of the heliosphere, known as the
heliopause.
The heliosphere results from the Sun's emitting a steady
flow of electrically charged particles called the solar wind. As
the solar wind expands supersonically into space in all
directions, it creates a magnetized bubble -- the heliosphere --
around the Sun. Eventually, the solar wind encounters the
electrically charged particles and magnetic field in the
interstellar gas. In this zone the solar wind abruptly slows down
from supersonic to subsonic speed, creating a termination shock.
Before the spacecraft travel beyond the heliopause into
interstellar space, they will pass through this termination shock.
"The data coming back from Voyager now suggest that we
may pass through the termination shock in the next three to five
years," Stone said. "If that's the case, then one would expect
that within 10 years or so we would actually be very close to
penetrating the heliopause itself and entering into interstellar
space for the first time."
Reaching the termination shock and heliopause will be
major milestones for the mission because no spacecraft have been
there before and the Voyagers will gather the first direct
evidence of their structure. Encountering the termination shock
and heliopause has been a long-sought goal for many space
physicists, and exactly where these two boundaries are located and
what they are like still remains a mystery.
Science data are returned to Earth in real-time to the 34-
meter Deep Space Network antennas located in California, Australia
and Spain. Both spacecraft have enough electricity and attitude
control propellant to continue operating until about 2020, when
electrical power produced by the RTGs will no longer support
science instrument operation. At that time, Voyager 1 will be
almost 150 times farther from the Sun than the Earth -- almost 14
billion miles (more than 20 billion kilometers) away.
On Feb. 17, Voyager 1 will be departing the Solar System
at a speed of 39,000 miles per hour (17.4 kilometers per second ).
At the same time, Voyager 2 will be 5.1 billion miles (8.1 billion
kilometers) from Earth and is departing the Solar System at a
speed of 35,000 miles per hour (15.9 kilometers per second).
JPL, a division of the California Institute of Technology,
manages the Voyager Interstellar Mission for NASA's Office of
Space Science, Washington, DC.
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