The
Voyager 2 spacecraft is an
unmanned interplanetary space
probe launched on August 20, 1977.
Both the Voyager
2 and the Voyager 1 space
probes were designed, developed, and built at the Jet Propulsion
Laboratory
near Pasadena, California
. Identical in form and instruments with its
sister
Voyager program craft
Voyager 1,
Voyager 2 was
launched on a slower, more curved trajectory that allowed it to be
kept in the place of the
Ecliptic (the
plane of the
Solar System) so that it
could be sent on to
Uranus and
Neptune by means of utilizing
gravity assists during its fly-by of
Saturn in 1981 and of Uranus in 1986. Because of this
chosen trajectory,
Voyager 2 could not take a close-up
look at the large saturnian moon
Titan
like its sister space probe had. However,
Voyager 2 did
become the first and only spacecraft to make the spaceflight by
Uranus and Neptune, and hence completing the
Planetary Grand Tour. This is one that
is made practical by a seldomly-occuring geometric alignment of the
outer planets (happening once every 176 years).
The
Voyager 2 space probe has made the most productive
unmanned space voyage so far, visiting all four of the Outer
Planets and their systemes of moons and rings, including the first
two visits to previously unexplored
Uranus
and
Neptune.
Voyager 2 had two
sensitive vidicon cameras and an assortment of other scientific
instruments to make measurements in the
ultraviolet,
infrared,
and radio wavelenghts, as well as ones to measure
subatomic particles in outer space,
including
cosmic rays. All of this was
accomplished at a
proper fraction of
the amount of money that was later spent on more advanced and
specialized space probes "
Galileo" and "
Cassini-Huygens". Along with the earlier
NASA
Pioneer 10 and
Pioneer 11; sister probe
Voyager 1; and the more recent
New Horizons,
Voyager 2 is an
interstellar probe in that all five of
these are on one-way trajectories leaving the Solar System.
Mission profile
Voyager 2 was originally planned to be
Mariner
12, an extension of the
Mariner program of space
probes.
The
Voyager 2 spacecraft was launched on August 20, 1977, from
Cape
Canaveral
, Florida
, on board a
Titan IIIE/Centaur carrier rocket, in a flawless launch into the
correct trajectory. Some weeks later, the ground controllers
for the Voyager program became engrossed in a early post-launch
problem with
Voyager 1, and they forgot to send an
important updating code to
Voyager 2. (These space probes
had been programmed to expect a radio message of some kind from the
Deep Space Network at least once
per week to verify that their radio systems were still working.)
This failure to receive a radio message caused
Voyager 2
to shut down its primary radio receiver, and to switch over to its
identical back-up receiver, which had a subtle defect in it. In the
process of switching back and forth between the receivers a few
times, a fuse in the DC power supply of the primary receiver blew,
permanently disabling it. (Once a fuse blows in an unmanned
spacecraft, there is absolutely no way to repair or replace it.)
Thus the back-up receiver had to be relied upon for the entire
mission.
Fortunately, after waiting one more week,
Voyager 2
automatically switched to its back-up radio receiver once more, and
the Deep Space Network radio engineers were able to re-establish
contact through the spacecraft's back-up radio receiver. This radio
receiver has remained somewhat "finicky" ever since then, but it
has been "nursemaided" along technically, and it has never failed.
Also, periodically, files of procedures for
Voyager 2 to
follow in the future have been uploaded via the Deep Space Network
to give
Voyager 2 a sketchy plan of what to do for many
months, in case the radio receiver ever did permanently fail,
cutting off all messages from the Earth to
Voyager
2.However, the back-up radio receiver for
Voyager 2
has not failed, and it remains in operation as of November 28,
2009. As for the two radio receivers for
Voyager 1, there
never has been a problem with either one of those. Furthermore,
there never has been any problem with the X-band
traveling wave tube transmitters for
either
Voyager 1 or
Voyager 2.
Voyager 2's Launch Difficulties
Voyager 2's gyroscopes and its electronic
digital computer were operational during
its Titan/Centaur launch phase, monitoring the sequence of events,
in order for those systems to take over the space probe's
attitude control and other functions upon
separation from the
Centaur upper
stage. But at that point, the unexpected happened:
Voyager
2's computer experienced robotic "vertigo." In its confusion,
it helplessly switched to backup sensors, presuming its "senses" to
be defective.
Voyager 2's disoriented flight-control computer remained
disconnected from
Voyager's powerful thrusters at this
point, so it did not cause damage to the launch during the
launching itself. The Centaur's attitude-control system stayed in
charge, suffering no "vertigo" and, as planned, it electronically
correcting the disequilibriam of the
Voyager's computer
just before separation.
From the spacecraft's control center, engineers and technicians
helplessly watched the antics of
Voyager 2's disoriented
computer. One hour and 11 minutes after lift-off,
Voyager
2's own dedicated solid rocket fired for 45 seconds to supply
the final increment of
momentum that it
needed to get to Jupiter.
One-and-one-half minutes after
Voyager 2's key rocket burn
ended, the three-meter-long articulating arm holding the television
camera and other remote-sensing instruments unlatched and deployed
as planned. After this,
Voyager 2's computer once again
sensed an emergency for some reason. This time it switched to a
different set of thrusters and activated valves to control the tiny
bursts of gas that stablized its attitude in space. Voyager's
robotic "alter ego" (its executive program) then challenged
portions of its own computer in a frantic attempt to correct the
orientation failure that it sensed.
At this point,
Voyager 2 followed the normal procedures
that the JPL engineers had installed in the computer to cope with
the most dreaded emergency for a robot spacecraft in deep space --
attitude-control disorientation. Voyager shut down most
communications with the Earth in order to begin its
reorientation.
Seventy-nine minutes passed while
Voyager 2 struggled
alone and unaided to find the Sun with a light sensor and to
establish a known orientation point. Finally,
Voyager 2
radioed back to the Earth that it was operating normally. It was
unknown this point if the redundant sensors were malfunctioning, or
its on-board digital computer was defective.
The fault protection in
Voyager 2's computer was operating
at this point on the now-painful assumption that it would be
triggered only by a hardware failure hundreds of millions of miles
from Earth. In that event,
Voyager 2 would be unable to
establish even emergency communications with its human flight
controlers, who could not help it much at that distance, in any
case.
Voyager 2 had been programmed to virtually shut off
communications with the Earth during such deep-space emergencies
and to attempt to fix itself. Somehow, these procedures had been
triggered right after the launching, when they should not have
been. There had been no hardware problems in the computer -- just a
slight but serious missetting of attitude-control parameters in the
con-board computer.
Encounter with Jupiter
The closest approach to
Jupiter occurred on
July 9, 1979. It came within 570,000 km (350,000 miles) of the
planet's cloud tops. It discovered a few
rings around Jupiter, as well as volcanic
activity on the moon
Io.
The
Great Red Spot was revealed as a
complex storm moving in a counterclockwise direction. An array of
other smaller storms and eddies were found throughout the banded
clouds.
Discovery of active volcanism on the
moon
Io was easily the greatest unexpected discovery at Jupiter. It
was the first time active volcanoes had been seen on another body
in the Solar System. Together, the Voyagers observed the eruption
of nine volcanoes on Io, and there is evidence that other eruptions
occurred between the two Voyager fly-bys.
The moon
Europa displayed a large
number of intersecting linear features in the low-resolution photos
from
Voyager 1. At first, scientists believed the features
might be deep cracks, caused by crustal rifting or tectonic
processes. The closer high-resolution photos from
Voyager
2, however, left scientists puzzled: The features were so
lacking in topographic relief that as one scientist described them,
they "might have been painted on with a felt marker." Europa is
internally active due to tidal heating at a level about one-tenth
that of Io. Europa is thought to have a thin crust (less than 30
kilometers or 18 miles thick) of water ice, possibly floating on a
50-kilometer-deep (30 mile) ocean.
Two new, small satellites,
Adrastea
and
Metis, were found orbiting just
outside the ring. A third new satellite,
Thebe, was discovered between the orbits of
Amalthea and Io.
Encounter with Saturn
The closest approach to
Saturn occurred on
August 26, 1981.
While passing behind Saturn (as viewed from Earth),
Voyager
2 probed Saturn's upper atmosphere with its radio link to
gather information on atmospheric temperature and density profiles.
Voyager 2 found that at the highest pressure levels (seven
kilopascals of pressure), Saturn's
temperature was 70
kelvins (−203 °C), while
at the deepest levels measured (120 kilopascals) the temperature
increased to 143 K (−130 °C). The north pole was found to
be 10 kelvins cooler, although this may be
seasonal (
see also Saturn Oppositions).
After the saturnian fly-by, the camera platform of
Voyager
2 locked up briefly, putting plans to officially extend the
mission to
Uranus and
Neptune in jeopardy. Fortunately, the mission's
engineers were able to fix the problem (caused by an overuse - that
temporarily depleted its lubricant), and the
Voyager 2
probe was given the go-ahead to explore the uranian system.
Image:Saturn (planet) large.jpg |Saturn taken by Voyager 2.Image:Iapetus by Voyager
2.jpg |Iapetus by Voyager 2
spacecraft, August 22, 1981.Image:Enceladus from Voyager.jpg |Color
image of Enceladus, almost full
disk.Image:Titan voyager.jpg |Titan.
Encounter with Uranus
The closest approach to
Uranus occurred on
January 24, 1986, when
Voyager 2 came within 81,500
kilometers (50,600 miles) of the planet's cloud tops.
Voyager
2 also discovered 10 previously unknown
moons of Uranus; studied the
planet's unique atmosphere, caused by its
axial tilt of 97.8°; and examined the uranian
ring system.
Uranus is apparently the third largest (heaviest?) planet in the
Solar System. It orbits the Sun at a distance of about 2.8 billion
kilometers (1.7 billion miles), and it completes one orbit every 84
years. The length of a day on Uranus as measured by
Voyager
2 is 17 hours, 14 minutes. Uranus is unique among the planets
in that its axis is tipped so far that sometimes it seems that
Uranus is rolling around the Sun on its side. This extremely-large
tilt of its axis is thought to be the result of a collision between
the accumulating planet Uranus with another planet-sized body early
in the history of the Solar System. Given the odd orientation of
its axis, with the polar regions of Uranus exposed for periods of
many years to either continuous sunlight or darkness, planetary
scientists were not at all sure what to expect at observe or
measure Uranus.
Voyager 2 found that one of the most striking effects of
the sideways orientation of Uranus is the effect on the tail of the
planetary magnetic field. This is itself tilted about 60 degrees
from the uranian axis of rotation. The planet's magnetotail was
shown to be twisted by the rotation of Uranus into a long corkscrew
shape following the planet. The presence of a significant magnetic
field for Uranus was not at all known until
Voyager's
arrival.
The radiation belts of Uranus were found to be of an intensity
similar to those of
Saturn. The intensity of
radiation within the uranian belts is such that irradiation would
"quickly" darken - within 100,000 years - any methane that is
trapped in the icy surfaces of the inner moons and ring particles.
This kind of darkening might have contributed to the darkened
surfaces of the moons and the ring particles, which are almost
uniformly dark gray in color.
A high layer of haze was detected around the sunlit pole of Uranus.
This area was also found to radiate large amounts of ultraviolet
light, a phenomenon that is called "dayglow." The average
atmospheric temperature is about 60 K (−350 degrees
Fahrenheit/−213 degrees Celsius). Surprisingly, the illuminated and
dark poles, and most of the planet, exhibit nearly the same
temperatures at the cloud tops.
The uranian moon
Miranda, the
innermost of the five large moons, was discovered to be one of the
strangest bodies yet seen in the Solar System. Detailed images from
Voyager 2's flyby of Miranda showed huge canyons made from
geological faults as deep as 20
kilometers (12 miles), terraced layers, and a mixture of old and
young surfaces. One
hypothesis suggests
that Miranda might consist of a reaggregation of material following
an earlier event when Miranda was shattered into pieces by a
violent impact.
All nine of the previously known uranian rings were studied by the
instruments of
Voyager 2. These measuremenst showed that
the Uranian rings are distinctly different from those at Jupiter
and Saturn. The uranian ring system might be relatively young, and
it did not form at the same time that Uranus did. The particles
that make up the rings might be the remnants of a moon that was
broken up by either a high-velocity impact or
torn up by tidal effects.
Image:Uranus.jpg |Uranus viewed from 18 million
kilometers.Image:Uranus Final Image.jpg |Uranus Final
Image.Image:Uranian_rings_PIA01977_modest.jpg |Voyager 2 shot of
the Uranian rings.Image:Miranda
HiRes Mosaic 2.jpg|Miranda
Encounter with Neptune
Voyager 2's closest approach to
Neptune occurred on August 25, 1989. Since this was
the last planet of our Solar System that
Voyager 2 could
visit, the Chief Project Scientist, his staff members, and the
flight controllers decided to also perform a close fly-by of the
lone large neptunian moon,
Triton, to
gather as much information on Neptune and Triton as possible,
regardless of what angle that Triton would fly away from Neptune
at. This was just like the case of
Voyager
1's encounters with
Saturn and its
massive moon
Titan.
Through repeated computerized test simulations of trajectories
through the neptuniam system ahead of time, the flight controllers
found that the best way to route
Voyager 2 through the
Neptune-Triton system. Since the plane of the orbit of Triton is
tilted significantly with respect with to the plane of the
Ecliptic, through mid-course corrections,
Voyager 2 was directed into a path several thousand miles
over the north pole of Neptune. At that time, Triton was behind and
below (south of) Neptune (at an angle of about 25 degrees below the
Ecliptic), close to the
apoapsis of its
elliptical orbit. The gravitational pull of Neptune bent the
trajectory of
Voyager 2 down in the direction of Triton.
In less than 24 hours,
Voyager 2 traversed the distance
between Neptune and Triton, and then it observed the northern
hemisphere of Triton as
Voyager 2 passed over the north
pole of Triton.
The net and final effect on the trajectory of
Voyager 2
was to bend its trajectory south below the plane of the Ecliptic by
about 30 degrees.
Voyager 2 is on this path permanently,
and hence, it is exploring space south of the plane of the
Ecliptic, measuring magnetic fields, charged particles, etc.,
there, and sending the measurements back to the Earth via
telemetry.
While in the neighborhood of Neptune
Voyager 2, discovered
the "
Great Dark Spot", which has
since disappeared, according observations by the
Hubble Space Telescope. Originally
thought to be a large cloud itself, the "Great Dark Spot" was later
hypothesized to be a hole in the visible cloud deck of
Neptune.
Neptune's atmosphere consists of hydrogen, helium, and methane. The
methane in Neptune's upper atmosphere absorbs the red light from
the Sun, but it reflects the blue light from the sun back into
space. This is why Neptune looks blue.
For decades, beginning in the late 19th century, it was widely
thought that an unseen planet (dubbed "
Planet
X") was influencing the orbits of Uranus and Neptune, by
perturbing them, since their observed
and their positions predicted by calculations differed somewhat.
This notion might have brought about the 1930 discovery of
Pluto, but the actual discovery of Pluto by
Clyde Tombaugh in 1930 was an accidental one
that occurred while a few astronomers were scanning areas of the
sky for "Planet X".
The notion of a "Planet X" has persisted, because over the decades
since 1930, it became increasingly clear that Pluto could not
possibly have the mass to account for the observational
discrepancies. When
Voyager 2 flew-by Neptune, it became
possible to much more precisely measure Neptune's mass. Neptune was
evaluated at about 0.5 percent less massive than was previously
believed, which is a difference comparable to the complete mass of
Mars. When the orbits of Uranus and Neptune orbits were
recalculated using the more accurate mass figure, it was found that
that the erroneous mass number for Neptune - and not the gravity of
an unseen planet - caused the orbital discrepancies that had long
caused concern by planetary astronomers.
With the decision of the
International Astronomical
Union to reclassify
Pluto as a "
dwarf planet" in 2006, the flyby of Neptune by
Voyager 2 in 1989 became the point when every large planet
in the Solar System had been visited at least once by a space
probe.
Image:Neptune.jpg|Voyager 2 image of NeptuneImage:Triton_moon_mosaic_Voyager_2_(large).jpg|Voyager
2 image of Triton
Escaping the solar system
Since its
planetary mission is over, Voyager 2 is now described as
working on an interstellar mission, which NASA
is using to
find out what the solar system is like
beyond the heliosphere. Like
Voyager 1 around three years before,
Voyager 2
crossed into the heliosheath, the last section of the heliosphere
before interstellar space, in October 2007.
On August 30, 2007,
Voyager 2 passed the termination shock
into the
heliosheath, approximately 1
billion miles (1.6 billion km) closer to the Sun than
Voyager 1 did. This is due to the local
interstellar magnetic field of deep space. The southern hemisphere
of the solar system's heliosphere is being pushed in.
As of June 26, 2009,
Voyager 2 was at a distance of around
89.41
AU (13.375
billion km, 8.311
billion miles, or 0.001413 ly) from the
Sun, deep in the
scattered disc, and
travelling outward at roughly 3.27 AU per year.
It is more than twice as far from the Sun as Pluto, and far beyond the perihelion of 90377 Sedna, but not yet beyond the outer limits of the orbit of the dwarf planet Eris.
Voyager 2 is not headed toward any particular star. If
left alone, it should pass by star
Sirius,
which is currently about 2.6 parsecs from the Sun and moving
diagonally towards the Sun, at a distance of 1.32
parsecs (4.3
ly, 25
trillion
mi) in about 296,000 years.
Voyager 2 is expected to keep transmitting weak radio
messages until at least 2025, over 48 years since it was
launched.
| Year |
End of specific capabilities as a result of the available
electrical power limitations |
| 1998 |
Terminate scan platform and UV observations |
| 2007 |
Termination of Digital Tape Recorder operations (because it was
no longer needed due to a receiver failure. Please explain.) |
| 2008 |
Power off "Planetary Radio Astronomy Experiment" (PRA) |
| 2015 approx |
Termination of gyroscopic
operations |
| 2020 approx |
Initiate "instrument power sharing" |
| 2025 or slightly afterwards |
Can no longer power any single instrument |
Each
Voyager space probe carries a
gold-plated audio-visual disc in the
event that either spacecraft is ever found by intelligent
life-forms from other planetary systems. The discs carry photos of
the Earth and its lifeforms, a range of scientific information,
spoken greetings from the people (e.g. the Secretatry-General of
the United Nations an the President of the United States, and the
children of the Planet Earth and a medley, "Sounds of Earth", that
includes the sounds of whales, a baby crying, waves breaking on a
shore, and a variety of music.
Current status
Locations and approximate trajectories
of
Pioneer and
Voyager spacecraft, as of
2007
Voyager 2, as of November 1, 2009, was at -54.59°
declination and 19.733 hrs
Right Ascension, placing it in the
constellation
Telescopium as observed
from Earth.
On November 30, 2006, a telemetered command to
Voyager 2
was incorrectly decoded by its on-board computer - in a random
error - as a command to turn on the electrical heaters of the
spacecraft's magnetometer. These heaters remained tuned on until
December 4, 2006, and during that time, there was a resulting high
temperatures above 130° C (266° F), significantly higher than the
magnetometers were designed to endure, and a sensor rotation away
from the correct orientation. It has not been possible to fully
diagnose and correct for the damage caused to the
Voyager
2's magnetometer, although efforts to do so are
proceeding.
Information about continuing telemetry exchanges with
Voyager
2 is available from
Voyager Weekly Reports. Information on the
current location of Voyager 2 can be found at
HeavensAbove.
See also
References
Footnotes
- Planetary Voyage NASA Jet Propulsion Laboratory -
California Institute of Technology. 23 March 2004. Retrieved 8
April 2007.
- Case Western Reserve University: "Voyagers
(1977-present)"
- Case Western Reserve University: "Galileo
(1989-2003)"
- The details of the problems with the two radio receivers of
Voyager 2 space probe are well-documented in space
communications textbooks, in magazines like "Scientific American"
and "Discover", in publications about the Voyager programs
that were written by NASA and printed & sold by the U.S.
Government Printing Office, in electrical engineering magazines
published by the IEEE, and
more. I don't have any of these at my fingertips now, but the
information is absolutely incontrovertable and well-documented.
Anyone who is skeptical is welcome to research in places like the
above and to see with your own eyes. The problem with the back-up
radio receiver in
- Nasa
- Croswell, Ken, Planet Quest: The Epic Discovery of Alien
Solar Systems (1997), pg. 66
- Voyager 2 Proves Solar System Is Squashed NASA.gov
#2007-12-10
- Voyager 2 finds solar system's shape is 'dented' #
2007-12-10, Week Ending December 14, 2007. Retrieved 12 Dec
2007.
- Voyager Mission Operations Status Report #
2009-06-26, Week Ending June 26, 2009. Retrieved 21 August
2009.
- Distance in light years derived from 3.26/measured parallax of
0.38002 arcseconds as of 2008-01-01
- Notes on Voyager 2 Quick Look Data: Data after
November 29, 2006
Bibliography
- Nardo, Don (2002). Neptune. Thomson Gale.
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