In the 1960s a grand planetary tour to
study the outer planets was proposed. It
was an ambitious plan to send unmanned
probes to the outer planets of the outer
solar system. The Grand Tour could
exploit a rare unusual and favorable
alignment of the planets Jupiter Saturn
Uranus Neptune and Pluto. This planetary
alignment would occur in the late 1970s
and would not occur again for a hundred
and seventy-six years. So the twin
Voyager spacecrafts one and two were
launched in 1977 to take advantage of
this special planetary alignment. It
would allow a probe to be sent to
Jupiter and use that planet as a
gravitational slingshot to extend the
trajectory to the other planets further
out in the solar system. The primary
mission of the Voyager spacecrafts was
the exploration of Jupiter and Saturn.
After making a series of outstanding
discoveries the mission was extended.
Voyager 2 went on to explore Uranus and
Neptune and is still the only spacecraft
to have visited those outer planets.
Remote control programming was used to
endowed the voyagers with greater
capabilities than they had when they
left the earth. Eventually
Voyager 1 and Voyager 2 explored all the
giant outer planets of our solar system,
48 of their moons and the unique system
of rings and magnetic fields that those
planets possess. In December 1977 Voyager 2
entered the asteroid belt. Nine days
later
Voyager 1 traveling at a greater speed
overtook Voyager 2. In February 1998
Voyager 1 passed pioneer 10 to become
the most distant human-made object in
outer space. In 2002
Voyager 1 left the solar system rising
above the ecliptic plane at an angle of
35 degrees
and at a speed of 39,000 miles per hour.
Voyager 2 also left the solar system
diving below the ecliptic plane at an
angle of 48 degrees and a speed of 30
4,500 miles per hour . Voyager 2 still
holds the record of traveling to more
planets than any other man-made object
in history. And Voyager 1 holds the
record as the Explorer from Earth that
has traveled farthest from home. Voyager
1 and 2 completed their exploration of
the outer planets in the first dozen
years of their mission. Having completed
their primary mission in 1989 the
Voyagers were ready to begin exploring
outside the solar system. In January 1990
with voyagers new destinations outside
the solar system the project's
designation was changed to Voyager
Interstellar Mission. Both voyagers
continue exploring where nothing from
Earth has flown before. In order to
explore the solar system and beyond,
Voyager 1 and Voyager 2 were equipped
with a large number of special
scientific instruments, suites and
subsystems. Most of the instruments are
located on the body of the spacecraft.
Each spacecraft is comprised of 65,000
individual parts. Of the dozens of
working instruments that the voyagers
left earth with, there are only four
instruments still working on Voyager 1
and five instruments still working on
Voyager 2. The low energy charged
particle detector and its three sets of
particle sensors measure how many
low-energy particles hit it and
determine the speed of those particles.
It studies cosmic radiation and
particles that emanate from the Sun, the
planets and interstellar space. It is
active on both Voyager 1 and Voyager 2
The cosmic ray instrument looks for very
high energetic particles from the Sun
and other galactic sources. It currently
is detecting the abundance of particles
from inside the bubble of our sun's
influence and also particles that
emanate outside of the bubble in
interstellar space.
These readings help scientists determine
when Voyager 1 entered interstellar
space. It is still active on both Voyager 1
and Voyager 2. The plasma wave
subsystem uses the 2 long antennas on
the spacecraft which stretch at right
angles to one another. It was used to
measure the electrical field components
of possible waves at the outer planets
but now the instrument is providing
information about the changes to plasma
waves as they enter interstellar space,
It is still active on both Voyager 1 and
Voyager 2. The magnetometers job was to
investigate the magnetic fields of the
outer planets but now its primary job is
to search for the transition region
between the interplanetary and
interstellar media. They investigate the
magnetic characteristics of the
transition region at the solar wind
boundary where the sun's magnetic
influence interacts with and gives way
to the magnetic field of interstellar
space. This instrument is still working
on both Voyager 1 and Voyager 2. Finally
the plasma science instrument looks for
the lowest energy particles in plasma. It
also has the ability to look for
particles moving at particular speeds
and to a limited extent to determine the
direction from which they come. This is
important as the spacecraft enters
interstellar space. The instrument is now
active only on Voyager 2. The other
instruments have either stopped working
on their own or have been shut down to
preserve power. NASA has also
systematically shut down heaters on both
crafts to save power. In 1998, 21 years
after launch,
non-essential instruments were
permanently shut off. The power source on
each spacecraft is a group of three
radioisotope thermoelectric generators
The RTGS give off heat by the decay of
radioactive Plutonium 238 and turning it
into electricity.
Eventually the plutonium 238 will have
decayed completely and will no longer be
able to provide power, at which time all
instrumentation will cease to operate.
This should occur around 2025 but with
careful power management the Voyager
team hopes to keep both spacecraft
functioning through 2027, the 50th
anniversary of their launch. The voyagers
are each equipped with a pair of
thrusters which are not used for
propelling the craft forward, but for
reorienting the probe so that it's
antenna is always pointing at the earth.
Otherwise we would not be able to
communicate with it. These thrusters fire
in tiny pulses or puffs lasting mere
milliseconds to subtly rotate the
spacecraft so that its antenna points at
the earth. Since the primary thrusters on
Voyager 1 had degraded, scientists fired
up the backup thrusters in November 2017
so that Voyager 1 could keep its lock on
the earth. They had not been activated in
almost 40 years but they came to life to
reorient the spacecraft's antennae.
Voyager 2, whose primary thrusters were
still working, was able to also keep its
orientation toward the earth.
The voyagers communicate with earth via
a 3.7 meter diameter high gain antenna
which sends and receives radio waves via
three Deep Space Network stations on the
earth. Voyagers main transmitter radiates
about 20 watts which is comparable to a
typical refrigerator light bulb.
By the time Voyagers’ signal reaches
Earth its strength has diminished to
about 20 billion times weaker than a
digital watch battery. Your iPhone has
100,000 times more memory than the
Voyager spacecraft,
Although state-of-the-art at the time
Voyagers computer systems are vintage
1974-75, causing NASA to look for
programmers who understand decades-old
software. In fact Voyager is equipped
with an 8-track tape recorder which it
uses to store information for
transmission to Earth. In 1978 the
transmitter failed on Voyager 2 so the
backup transmitter has been used ever
since. The voyagers signal however is
bright when compared to most natural
objects studied by radio telescopes.
NASA's Jet Propulsion Laboratory
communicates with Voyager practically
everyday via NASA's Deep Space Network
but it takes someone with 1970s design
experience to be able to understand
Voyager . The Deep Space Network consists
of three antenna complexes that are
stationed around the globe approximately
a hundred and twenty longitudinal
degrees apart. They are located in Madrid
Spain, Goldstone California and Canberra
Australia. The global separation of the
stations allows the spacecraft to have
an uninterrupted line of sight
with at least one station regardless of
the time of day.
These massive antennas have been
upgraded several times to accommodate
receiving signals from Voyager and other
spacecraft Voyager 1 and Voyager 2
signals can still be received by all
three stations but Canberra is the only
one with a powerful enough transmitter
that can transmit to the Voyagers.
Centers at each DSN site receive
incoming information then send it to the
Space Flight Operations facility at the
Jet Propulsion Laboratory in Pasadena
California. Due to the incredible
weakness of the spacecraft's downlink, by
the time it reaches Earth, large
parabolic reflectors and hyperbolic sub
reflectors collect the microwave
radiation and focus it on a
cryogenically cooled receiver at the
base of the antenna. While one of the
antennas is more than powerful enough to
transmit to Voyager, a single 34 meter
antenna does not collect enough
electromagnetic radiation to detect
Voyagers downlink. So antennas at each
site are linked together so that they
can simultaneously receive the signals
from the spacecraft providing increased
gain. It currently takes more than 19
hours for Voyager to receive signals
from Earth and 19 hours for earth to
receive signals sent by Voyager. The
massive antennas that comprise NASA's
Deep Space Network will pick up a faint
distant signal for the final time around
2025. It will track the downlink signal
from the spacecraft as it sputters into
silence and becomes part of the
background noise of the solar system,
never to be heard from by humans again.
So how do we know Voyager 1 is in the
interstellar space. The most convenient
way to determine the location of Voyager 1
was to measure the temperature,
pressure and density of plasma or
ionized gas around the spacecraft.
Everything inside the solar bubble or
heliosphere should be exposed to plasma
that streams from the Sun, whereas
interstellar space is filled with denser
plasma emanating from interstellar space
as a result of the explosion of giant
stars millions of years before.
Unfortunately Voyager 1’s plasma
detector stopped working in 1980 and
hasn't functioned for almost 40 years. So
scientists needed to examine the plasma
or charged particles which fill the
bubble encasing our solar system and
compare that with the plasma or charged
particles that occur in interstellar
space, ithout the use of Voyager 1’s
plasma detector. We needed to compare the
solar wind versus the galactic wind each
traveling in a different direction. Since
July of 2012 the solar wind has
decreased and the galactic wind has
increased, placing the craft in what is
known as the magnetic highway. Plasma
consists of charged particles and is
more prevalent in the extreme cold of
interstellar space than in the bubble of
solar wind that permeates our solar
system. The plasma detector on Voyager 1
had been designed to measure the
composition of those two plasmas but
without that instruments such
measurements were not possible.
Fortunately and by chance a pair of
solar flares blasted charged particles
in Voyagers direction in 2011 and 2012.
It took a year for the particles to
reach the spacecraft but they did
eventually and they provided sound wave
information that could be used to
determine how dense the plasma was in
voyagers location. When that last wave
reached Voyager it caused the plasma
around Voyager to vibrate or oscillate
in a certain particular tone. By
measuring that soundwave we could
measure the density of the plasma
surrounding the spacecraft. Scientists
knew then that Voyager 1 was in a place
no spacecraft had ever been before. It
was on the magnetic highway where all
particles that were inside the
heliosphere had streamed away and were
now gone. What we now saw instead were
cosmic rays from outside the heliosphere.
The data showed a huge spike in the
number of galactic cosmic rays from
outside the solar system and a
corresponding decrease in particles
emanating from the Sun. All of the pink
colored ions you see here were from the
hot bubble of solar wind coming from our
Sun and permeating our solar system. They
were leaving the heliosphere along the
magnetic highway. And at the same time
the blue ions seen here are the cosmic
ions moving at a higher speed coming in
from interstellar space and from a
different direction. Voyager 1 is now in
a region where it is surrounded only by
cosmic rays accelerated from elsewhere
in the galaxy. Many scientists now
declare that Voyager 1 is in
interstellar space. There is a caveat
that comes with our ones exit from the
solar system however. Many scientists
consider the term solar system to mean
not only the planets in our solar system
and the sun's influence beyond, but that
the solar system extends up to the edge
of the Oort cloud. If so it will take
another 300 years for Voyager 1 to reach
the inner edge of the vast Oort cloud.
And the journey through the Oort cloud
could take another 30,000 years. Only
then will Voyager 1 be considered to be
in pristine interstellar space.
Voyager 1 is currently traveling at
about 38,000 miles per hour, a million
miles per day or about a billion miles
every three years. That velocity will
never change. It will go on forever.
Having left the solar system, the next
time it will encounter a star is in
40,000 years when it flies about 1.7
light-years away from an obscure star in
the constellation Camelopardalis called
AC + 79 3888
It will be in the year 40,000 282. And in
56,000 years Voyager 1 will pass out of
the Oort cloud. After another 570
thousand years Voyager 1 will brush past
the stars GJ 686 & GJ 678.
Voyager 2 traveling at 34,500
miles per hour is
also on course to enter interstellar
space, likely late 2019 or 2020. Voyager 2
is heading out of the solar system in
another direction from Voyager 1. Voyager
2 is not headed for any particular star
but in about 61,000 years from now
Voyager 2 will pass out of the Oort
cloud. After 296 thousand years in the
year two hundred and ninety eight
thousand AD, Voyager will pass by the
star Sirius at a distance of
4.3 light-years. About one hundred
thousand years after that, Voyager 2 will
brush past two stars Delta pav and GJ 754.
Beyond this both Voyagers will continue
into the void passing through dust
clouds and local bubbles of empty space
blown upon by dying stars. The
spacecrafts could be affected by dust
clouds and the gravitational pull of
rogues starless planets however.
Ultimately like the stars in the Milky
Way the Voyagers will orbit the center
of the Milky Way galaxy. It will take 225
million years to complete one orbit
around the center of the Milky Way. And
the voyagers will orbit for billions of
years or until our neighboring galaxy
Andromeda collides with the Milky Way.
Due to the enormous distances between
the stars, it is likely that the voyagers
will survive this collision of galaxies
however and continue their journey.
Frozen in the vacuum of space both
spacecraft and their contents need not
fear decay.
The ultimate death of the voyagers could
come from thousands of micro meteorite
impacts or one unforeseen collision.
The Voyagers however will probably
outlive the solar system long after our
Sun dies and long after the Milky Way
galaxy has been unalterably changed or
disappeared. The voyagers are destined
perhaps for all eternity to wander the
cosmos carrying with them the only