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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 Laboratorymarker near Pasadena, Californiamarker. 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 Canaveralmarker, Floridamarker, 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 NASAmarker 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

  1. Planetary Voyage NASA Jet Propulsion Laboratory - California Institute of Technology. 23 March 2004. Retrieved 8 April 2007.
  2. Case Western Reserve University: "Voyagers (1977-present)"
  3. Case Western Reserve University: "Galileo (1989-2003)"
  4. 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
  5. Nasa
  6. Croswell, Ken, Planet Quest: The Epic Discovery of Alien Solar Systems (1997), pg. 66
  7. Voyager 2 Proves Solar System Is Squashed NASA.gov #2007-12-10
  8. Voyager 2 finds solar system's shape is 'dented' # 2007-12-10, Week Ending December 14, 2007. Retrieved 12 Dec 2007.
  9. Voyager Mission Operations Status Report # 2009-06-26, Week Ending June 26, 2009. Retrieved 21 August 2009.
  10. Distance in light years derived from 3.26/measured parallax of 0.38002 arcseconds as of 2008-01-01
  11. Notes on Voyager 2 Quick Look Data: Data after November 29, 2006


Bibliography

  • Nardo, Don (2002). Neptune. Thomson Gale.


External links




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