It is a moment of great scientific excitement and
exhilaration as a human-made object, unmanned spacecraft Voyager 1 reached the
interstellar space. Interstellar region is the space between stars but
still feels the charged particles and magnetic influences from heliosphere. Voyager 1 has the unique
distinction of being the farthest travelling man-made object beyond the solar
system. Taking the advantage of the favourable alignment of the planets, in
late 1970’s Gary Flandro, aerospace engineer from Jet Propulsion Laboratory went
ahead with the Voyager Space Program. He conceptualised that planetary
alignment would provide the necessary gravitational assistance to fly by from
Jupiter to Saturn and similarly from Uranus to Neptune.
The Voyager spacecrafts were built
by the NASA’s Jet Propulsion Laboratory, Pasadena and California Caltech
manages JPL for NASA. Voyager missions are part of NASA’s Heliophysics Systems
Observatory and sponsored by the Heliophysics System Division of Science
Mission Directorate of NASA located in Washington. The cost of Voyager 1 and 2
missions, nuclear batteries and their launches accounted for $998 million, was
funded by the Department of Energy.
The two unmanned spacecrafts were initially designated with
the mission of studying the planetary systems of Jupiter and Saturn which they
accomplished within 12 years of their mission by 1989. Voyager1 after surpassing the Pioneer 10
became the first most distantly travelling human-made object. Now the
spacecraft have the distinction of reaching the interstellar space even.
Voyager 2, the twin of Voyager 1
was launched with a gap of 16 days. Both of them have passed Jupiter and Saturn-
Voyager 2 now has crossed even Uranus and Neptune. Taking the advantage of the unique
planetary alignment, Voyager 2 was first launched on August 22nd,
1977 from the Cape Canaveral, Florida to flyby the planets Jupiter, Saturn, Uranus and
Neptune. It is has the record of longest travelling space craft. Voyager 1 was launched by the rocket
Titan Centaur with utmost priority of studying the Saturn’s moon Titan. The
magnetometers and the camera on board have provided valuable information about
the 48 moons of the giant planets, active volcanoes on Jupiter’s moon its myriad
cloud formation, winds and storms; Saturn’s intricate rings which are found to
have kinks, braids, ringlets and spokes. Voyager 2 fathomed the details of the
Uranus and its 10 moons, Neptune’s three rings- its widely distributed auroras
and the magnetic fields.
After accomplishing the primary mission of flying by the
planets Jupiter and Saturn, Voyager1 has set out for Voyager Interstellar
Mission (VIM). The main objective of this mission is to enable National
Aeronautics and Space Administration NASA’s exploration of solar system beyond
the neighbourhood of the outer planets to the outer limits of the Sun’s sphere
of influence. Voyager 1 is at distance of 18.9 billion kilometres (125.3 AU)
and Voyager 2 is 15.3 billion kilometres (102.6 AU) away from Sun. One AU or
the astronomical unit is distance between Sun to earth equal to 149 million
kilometres. VIM has three distinct phases, termination shock, heliosheath
exploration and interstellar exploration phase. Voyager 1 escaping at the speed
of 3.6 AU per year 35 degrees north from the Solar Apex (solar motion relative
to other stars), Voyager 2 moving at speed of 3.3AU per year 48 degrees from
the elliptical plane to south.
Both the Voyager spacecrafts are designed to carry the Golden
Record Cover containing a combination of time capsule and an interstellar
message to alien civilisation. It contains a phonograph record, a 12 inch gold
plated copper disk containing sounds and images portraying the diversity of the
earth. Should they encounter any life form, the record has sounds selected by a
committee headed Dr. Carl Sagan, which included, spoken greetings in fifty five different
languages, 115 images of earth and a variety of natural sounds; music from
different eras and cultures. A Hindustani Classical composition titled "Jaat
Kahan Ho" sung by the legendary vocalist Surshri Kesarbai Kerkar is a part of
the illustrious music collection. It is played as a kind of encore (closing
number) due to its popularity. There are five different instruments to record
the magnetic field intensity, plasma waves, low energy charged particle and
plasma density. These instruments are monitored by five different specialised
scientific investigation teams.
Though Voyager 1 has reached the
interstellar space last year, NASA made the announcement of the important
milestone in space exploration on 12 September 2013. They were unable to arrive
at a satisfactory conclusion until an unexpected coronary mass ejection or
solar outburst of the wind and magnetic fields erupted from the sun in March
2012 and reached the Voyager 1 after 13 months, in April 2013. It recorded the
oscillations just like the violin string waves. The pitch of the oscillations
helped in determination of the density of the plasma which is roughly 40 times
greater than in the heliosphere. Similar wave oscillations of much lower
intensity were recorded in Oct and Nov 2012. Extrapolation of the measured
oscillations helped in the determination of the location of Voyager 1 which
indicated that it has entered interstellar space in Aug 2012. It was precisely
on Aug 25th 2012, scientists observed a change in the charged
particles and plasma density which is on expected levels indicating that
Voyager1 has crossed the heliopause. Scientists have been making their conclusions
on the basis of difference between the direction and strength of magnetic
fields of earth and space. As the Voyager1 entered the interstellar space the
levels of galactic cosmic rays has increased and levels of charged particles of
the heliosphere decreased by a factor of 1000. These were expected changes when
Voyager1 crossed the heliopause, the boundary of heliosphere and interstellar
space. It is the boundary where Sun’s solar winds are stopped by the
interstellar medium
Voyager mission continue to
receive small signals every day, but the emitted signals from the Voyagers are
of low intensity roughly 23 watt, power of the refrigerator bulb. By the time
they reach earth they are reduced by billionth-billionth of a watt. Typically
Voyager 1 now transmits 160 bits per second and signals take 17 hrs to reach
earth. These signals are captured by the NASA’s Deep Space Network Stations.
The electrical power is provided by the Radioisotope
Thermoelectric Generators (RTG) fuelled by Plutonium-238. The availability of
power will gradually decrease owing to the degradation of the radioactive
material. It has enough electrical energy to continue working till 2020 and then
to conserve its energy, each of the instruments will be slowly turned off till
the last instrument which will be turned by 2025. Gyro operations will be deactivated
for Voyager 2 in 2015 and Voyager 1 in 2016. Gyro operations enable the
spacecraft to turn 360 degrees six times per year to measure the magnetic
field. Till 2025 the electrical power and altitude control propellant would be
available later scientific instruments will be devoid of any power. Thereafter
Voyager 1 might escape in the direction of Alpha Centauri, AC +793888 a star in
constellation of Camelopardalis and Voyager 2 after 40,000 years will pass star
Ross 248. Voyagers perhaps might remain as remnants of mankind’s unquenchable
quest to unravel the mysteries of space and the eternal Milky Way.
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