Voyager 2: Travelling Towards The Immensities Of Interstellar Space

NASA’s Voyager 2 spacecraft, holder of many records!
Launched on August 20th, 1977 from Cape Canaveral aboard a Titan III rocket, it is still operational
after more than 40 years!
The orbit in which the probe was placed led it to flyby the two giant planets, Jupiter
and Saturn. During the journey, the technicians realized that they could use a rather rare
planetary alignment in order to make the probe reach Uranus and Neptune. From Voyager 2 comes
most of the information we have about these two planets.
On 5th November 2018, the Voyager 2 probe passed the heliopause, the border region between
the heliosphere and the interstellar medium. The heliosphere is the region of space around
the Sun where the ionized gas we call plasma comes mainly from the Sun. Researchers at
the University of Iowa, in an article in Nature in 2019, were able to ascertain the entry
of Voyager 2 into the interstellar space after noticing a marked increase in plasma density,
evidence of the probe’s transition from the low-density hot plasma characteristic of solar
wind, to the cold, high-density plasma of interstellar space.
During its long journey, Voyager 2 was the first spacecraft to have visited the four
gas planets of the Solar System: Jupiter was the first, on 9th July 1979: during the flyby
with the gas giant, it discovered its fourteenth moon. On August 26th, 1981 it was the turn
of Saturn. On January 24th, 1986, Voyager 2 visited Uranus, of which it discovered two
new rings and ten new moons. And finally on August 25th, 1989, the probe visited Neptune,
of which it discovered four rings, five moons, and the “Great Dark Spot”, a gigantic storm
in the planet’s atmosphere that has several aspects in common with the Great Red Spot
of Jupiter.
Voyager 2 was the first spacecraft to go beyond Uranus and Neptune. If you were astride Voyager
2 near Uranus or Neptune, how would you feel knowing that no one has ever gone so far from
the Sun before you? Write it in the comments!
The passages near Uranus and Neptune were instead the first (and still the only) close
encounters with these two planets. Since then the probe has been moving away from the Sun,
at a slower speed than Voyager 1, heading towards the boundaries of the Solar System,
by convention fixed on the outer limit of the Oort Cloud, a roughly spherical region
of space that extends between 20000 and the 100000 astronomical units from the Sun, and
which it is believed long-period comets come from, that is, those with orbital periods
greater than 200 years.
Given the good state of health of the spacecraft, the scientists decided to extend its mission:
on 11th December 2007 it was reported that the probe passed through the termination shock,
a zone of space after which the Sun’s magnetic field no longer has influence; Voyager 1 also
crossed the same area about three years earlier, but no reliable data was available due to
the non-functioning solar wind detector. Voyager 2 was therefore the first probe to have detected
and measured termination shock. The latest information indicates that Voyager
2 would have gone through termination shock in September 2007.
Voyager 2 is still functional and is the third most distant man-made object from Earth, after
Voyager 1 and Pioneer 10; the Voyager 2 will never overtake the first, while it should
overtake the second in 2023, a year estimated not considering the different gradual slowdown
of the two probes.
On 13th August 2012, Voyager 2 broke the longevity record held up to then by the Pioneer 6 probe
with 34 years and 340 days of service. On November 5th, 2018, the instrument detected
a sharp drop in the solar wind speed and since that date has not detected any solar wind
flow in the surrounding environment.
The confirmation of the exit from the heliosphere, made on November 5th, 2018, was provided by
the Plasma Science Experiment instrument, which uses the electric current of the solar
plasma to detect the speed, density, temperature, pressure and flow of the solar wind.
On September 15th, 2019, Voyager 2 began its journey into interstellar space at a distance
of 121367 astronomical anits (equivalent to 16,822 light hours or 18,214 billion km) from
the Sun. The probe is moving away from the Sun at a speed of 15,374 km/s, equal to 3,241
astronomical units per year; its speed is in very slight slowdown. Would you like to
travel that far? Write it in the comments!
On 29th October 2020, at Deep Space Station 43 (DSS43) in Canberra in Australia, following
maintenance carried out on the 70-meter diameter antenna, the operators of Voyager 2 sent a
series of commands to the probe, to test the new updated components of the antenna: in
particular, two new radio transmitters (one of the two, the one used to talk to Voyager
2 itself, had never been replaced for 47 years); and the antenna thermal control systems and
other obsolete electronic equipment. The probe has correctly responded with a return signal,
confirming that it has received the message from the DSS43.
Like its sister Voyager 1, Voyager 2 also had several scientific objectives, including
providing better estimates for the mass, size, shape of planets, satellites and rings of
gas giant planets; investigate the circulation, dynamics, structure and composition of planetary
atmospheres; characterize planetary morphology and geology and their satellites; and finally
determine the structure of the magnetic field and characterize the composition and distribution
of the particles and plasma trapped inside it.
Voyager 2 is a decagonal based prism 1,78 m wide and 47 cm high. A parabolic high gain
antenna is located on the top of the spacecraft. Most of the scientific instruments are located
on a trellis that extends 2.5 meters from the spacecraft.
At the end of this trellis a camera and a spectroscope (imaging and spectroscopic remote
sensing instruments) are mounted. The magnetometers, on the other hand, are located on a 13 m long
arm on the opposite side of the trellis. A third pylon houses the radioisotope thermoelectric
generators. Two other 10 m long antennas, perpendicular to each other, are used for
investigations in the radio band.
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Due to its enormous distance from Earth and the resulting delay in communications, Voyager
2 was designed to operate in autonomous mode. To do this and implement the complex sequences
of operations for attitude control and scientific instruments, three interconnected on-board
computers were used. The Computer Command Subsystem (CGS) had the
task of storing the commands for the other two on-board computers and launching them
at set times. The Attitude and Articulation Control Subsystem
(AACS) managed the attitude control of the spacecraft.
The Flight Data Subsystem (FDS) monitored the instruments, including changes in their
configuration and telemetry. All three on-board computers had redundant
components to ensure continued operation. The AACS included redundant star sensors and
solar sensors.
Voyager 2 is powered by a radioisotope thermoelectric generator that will allow it to operate, albeit
to a limited extent, until 2025.
According to forecasts, after having reached and analyzed the heliopause a few years after
Voyager 1, which reached it in August 2012, it should subsequently reach and analyze interstellar
space and the hypothetical hydrogen wall (located between heliopause and bow shock); assuming
that it travels at its current speed, it can be estimated that this zone will be reached
in 2052, but in reality it will take more time due to the progressive slight slowdown
of the probe.
In about 40000 years it will pass about 1,7 light years from the star Ross 248, 10,32
light years away from the Sun, located in the constellation of Andromeda (at that time
Ross 248 will be the closest star to the Sun, at about 3 years light); moreover, in about
296000 years it will pass about 4,3 light years from the star Sirius, which is 8,6 light
years away from the Sun.
In addition to the scientific instrumentation, Voyager 2, like its sister Voyager 1, carries
a rather special load on board: on its back there is a circular golden aluminum case,
bearing the instructions to make the contents of the disc contained in it accessible to
anyone. The actual support looks like a copper plated gramophone record, with a diameter
of about 30 cm: it contains sounds, songs and images that represent human civilization.
If a new spaceship similar to Voyager 2 would be built, what would you write in the disc?
What kind of pictures would you load in it? Write it in the comments!
The idea of launching a “message in a bottle” in cosmic immensities dates back to the early
1970s. In March 1972 the Pioneer 10 probe was launched.
The vehicle carries an aluminum and gold alloy plate, showing the image of a naked man and
woman; also engraved are a series of diagrams and schemes designed to exemplify a conventional
unit of measurement that leads to the exact location of the planet Earth. Creators of
the message, some scientists and science communicators from the SETI project, including Frank Drake
(known for the equation of the same name) and the famous Carl Sagan.
Although simplistic and controversial, the idea of the plates is of great impact and
stimulates a new conception of space research, aimed at establishing a first, timid contact
with distant civilizations. In 1977 the times are surprisingly ripe: the film “Close Encounters
of the Third Kind” is shown in cinemas, a true manifesto of a a new awareness and message
of hope towards a hypothetical cosmic brotherhood. How would you feel if the golden plate onboard
Voyager 2 would be found by an extraterrestrial intelligence? Write it in the comments!
The Voyager probes are about to embark on a long journey, bringing with them what in
the intentions of the creators of the “Golden Record” will be humanity’s calling card for
alien civilizations and men of a distant future. Greetings and best wishes in dozens of languages
open the disc, which also features classical music symphonies, ethnic songs and memorable
pop music pieces such as Chuck Berry’s “Johnny B. Goode”. A sequence of indefinite sounds,
then, hides the codes to visualize the lines (and sometimes the colors) of over one hundred
photos that portray men, animals and plants.
Carl Sagan himself, father of the scientific research of intelligent life in Space, summarized
the concept and meaning of the disc: “The probe can be found and the recording displayed,
only if there are advanced civilizations traveling in interstellar space. The launch of this
bottle into the cosmic ocean is a message of great hope regarding life on this planet.
Predictably, the romantic concept of a human message thrown adrift in space has inspired
artists, singers and directors. The cinema didn’t fail to mention the Voyager probes:
just two years after the launch of the latter, the film “Star Trek – The Motion Picture”
(1979) dusts off the spaceship Enterprise and its famous crew, grappling with a threatening
Voyager gone mad. In 1984 the director John Carpenter directed
“Starman”, a love story between a terrestrial woman, in mourning for the loss of her husband,
and an alien: the adventure of the extraterrestrial begins immediately after having found and
decoded the messages reported on the disc of Voyager 2.
Adrift in an ocean of stars and planets, some man-made spacecraft are about to embark on
a long and lonely journey to destinations we can’t even imagine. Something of us has
reached the edge of the solar system, on the abyss of an unknown edge. It is a simple recorded
record. Or the poetic hope that someone out there will find him.
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