The Voyager Program
During the early 1960s, a project was planned to tour the gas planets of our solar system. This mission eventually became known as the Voyager Program, which was launched in the late 1970s. Originally, their mission was to study Jupiter and Saturn, but the mission has changed due to its continual success.i The voyager probes were able to study Jupiter, Saturn, Neptune, and Uranus and are now continuing to the outer reaches of the solar system. The Voyager program is now called the Voyager Interstellar Mission. The spacecraft was designed to make close-up observations of the planets and their moons. The spacecraft also carries a golden record with the sounds and pictures of Earth. The Voyagers have made many discoveries, including 23 moons, active volcanoes, planetary rings, and magnetic fields.
The Voyager mission was designed to take advantage of the rare geometric arrangement of the outer planets during the late 1970s. This arrangement of planets only happens once every 175 years. Scientists determined that the late 1970s was going to be the optimal time in which a flight path could be designed to study all the gas planets in one trajectory. The spacecraft used the gravity of the planets to sling shot them to the next planet.ii Over 10,000 trajectories were analyzed before they decided on the best one.iii
Originally, the vision was to have a Grand Tour of the outer planets, but due to budget cuts, the program was scaled down. The Voyager probes were going to be the Mariner 11 and Mariner 12, but were moved into their own program in 1977 because the design of the spacecraft had changed so dramatically.iv When all was said and done, the Voyagers were only meant to study Jupiter and Saturn, Saturn's rings, and the large moons of both planets. The mission was a huge success. The Voyagers studied 4 planets, 48 moons, the planets rings, and the magnetic fields.v Voyager 1 and 2 are currently[update] still in operation, making them the longest-lasting mission of the U.S. National Aeronautics Space Agency.
The new missions, the Voyager Interstellar Mission, objectives are to study the ultraviolet sources from the stars, explore the boundary between the sun and interstellar space, find the limits of the suns magnetic field and the outward flow of the solar wind. The mission is now determining the outer solar systems environment and searching for the heliopause boundary. Currently, they are in the heliosphere, which is a magnetic bubble around the solar system. The VIM is broken up into 3 phases: terminal shock, heliosheath exploration, and interstellar exploration. The mission's continual success is partly due to the Voyagers design.
The spacecrafts have a 3 axis stabilized system. They were designed to make observations of the planet's atmosphere, magnetosphere, rings, and moons. They were built to last 5 years, but are now over 33 years old.vi They are about the size of a compact car and weighed about 1 ton at launch, but this weight has gone down due to its loss of hydrazine. There are many instruments which make up the Voyager 1 and 2.vii
The Imaging Science Subsystem includes the Imaging Narrow Angle and the Imaging Wide Angle cameras. They study the atmosphere of each planet and look for circulation. There are a couple particle detectors, the plasma subsystem and the cosmic ray subsystem. They look for low energy particles and high energy particles to study the solar wind, terminal shock, and magnetospheric plasma from the gas planets. The ultraviolet spectrometer looks for certain colors of ultraviolet light and can determine if any are missing from normal sunlight, with this data scientists can determine properties of a planet's atmosphere. The infrared spectrometer and radiometer, IRIS, is basically a thermometer which determines the temperature of an object, can detect certain types of elements on a surface or in an atmosphere, and can measure the reflection of an object.viii
The photopolarimater can determine the properties of the properties in an atmosphere. There is also the low energy charged particle detector, the high gain antenna (12' diameter), which transmits data to earth, and the bus, which carries the various subsystems and instruments. The low field magnetometer and high field magnetometer measure changes in the Sun's magnetic field with distance and time. This is also the instrument which determines the planets magnetic field. The Voyagers have 3 radioisotope thermoelectric generators, which provide all the power.ix
The Voyagers also carry a "message in a bottle" for other life forms, if it is ever found. The 12 inch gold plated phonograph record contains 115 images, which are encoded in analog form, and sounds from Earth (wind, rain, thunder), to include animals (birds, whales), greetings in many languages, and a 90 minute music selection which includes a wide variety of music, including Beethoven. Carl Sagan led the committee which selected the contents of the disk.x
On one side of the disc is the record recording itself, while the other side has pictures and diagrams on how to decipher and play it. The left hand corner describes how to play the sounds. There is a phonograph record showing where to place the stylus, along with code on the speed the disc needs to be rotated. The right hand corner shows how to decode the signals so they can construct the pictures in the right format. There is another picture on the record which shows our solar system location in reference to 14 pulsar stars. A drawing of the hydrogen atom is also shown to indicate the time scale for the record.xi
The Voyager's journey has been a long one, but it all started back in 1977, aboard a Titan-Centaur rocket.xii Voyager 2 was launched first, on August 20, 1977 from Cape Canaveral, Florida. Voyager 2 was designed to fly by Saturn and go towards Uranus. Voyager 2 flew by Jupiter in July 1979, then Saturn in August 1981. After this flyby, it was determined that everything was in good condition, so NASA added additional funding to keep everything operational and continue onto Uranus. It then Passed by Uranus in January, 1986 and passed by Neptune August 1989.xiii It was the first spacecraft to observe Neptune. On September 5, 2007 it crossed the terminal shock and is now in the heliosheath, traveling 470 million miles a year.xiv
Voyager 1 was launched on September 5 from Cape Canaveral, Florida. On that same day, it returned a photo of the Earth and Moon. Voyager 1 was designed to pass the large moon Titan and behind Saturn's rings.xv Voyager 1 passed by Jupiter in March, 1979, then Saturn in November 1980. After studying those planets, it began its voyage out to the edge of the solar system. On February 17, 1998, Voyager 1 passed Pioneer 10 and became the most distant human made object.xvi On December 18, 2004, Voyager 1 crossed terminal shock and is traveling in the heliosheath. It is travelling at 320 million miles a year.xvii
The Voyager program is one of the most scientifically productive missions of all time. Since they have explored all the giant outer planets of our solar system, 48 of their moons, the unique rings and magnetic fields those planets possess, and now, the edge of the solar system, they have sent an enormous amount of data back to Earth which has led to many discoveries.xviii The Voyagers were the only probes to ever visit Uranus and Neptune, and the second probes to visit Jupiter and Saturn.xix The probes gathered detailed data and imagery of these planets and their moons, which has led to a much better understanding of how these planets' atmospheres and magnetospheres function.xx
The Voyagers discovered much about the planets and their moons. Studying Saturn's rings were one of the primary objectives of the mission, and it was discovered that the rings were very complex. It was discovered that Saturn's atmosphere is mostly hydrogen and helium and that there are winds of 1,100 miles an hour. Both of the Voyagers also measured Saturn's rotation, which is 10 hours, 39 minutes, 24 seconds.xxi Voyager detected 10 previously unseen moons with unique surfaces orbiting Uranus, and two new rings. It also showed that Uranus's magnetic field was unusual and the planets rate of rotation to be 17 hours, 14 minutes, and was orbiting oddly and sideways.xxii It was found that Neptune had the fastest winds in the solar system and its moon Triton contained icy volcanoes.xxiii On Jupiter, they discovered that the great red spot was a giant volatile storm, and volcanic activity on Io, a moon of Jupiter which scientists thought to be dead and cratered.
Now that the Voyagers are past the terminal shock, and are in the heliosheath, they are discovering even more about our solar system and giving us great insight. Data from the Voyager 2 spacecraft indicates that the solar system is not round, it has a squashed shape.xxiv Scientists have known that the solar system is passing through an interstellar cloud, but this has baffled physicists for some time. According to scientists, this local cloud of ours should be crushed by outside high pressure supernova exhaust. The Voyager spacecrafts data have led to us figuring out that there is strong magnetic field outside the solar system. This magnetic field holds the interstellar cloud together. Also, the sun's magnetic field, which contains solar wind, makes a magnetic bubble. This is known as the heliosphere, and it helps protect us from galactic cosmic rays and interstellar clouds. The two Voyagers are located in the outermost layer of the heliosphere, where the solar wind is slowing down. xxv As of August 2010, Voyager 1 was at a distance of 17.1 Billion Kilometers from the sun and Voyager 2 at a distance of 13.9 Billion kilometers.xxvi
They are now heading for the heliopause, the boundary between interstellar space and our solar system, which has never been reached by any spacecraft probe before. If everything goes well, we will be able to communicate with the two spacecraft for another 10 years or so, until their radioactive power sources can no longer supply enough electrical energy to power critical subsystems. After that our contact with them will be lost forever. As long as the Voyagers keep on going there will be more discoveries. In about 40,000 years Voyager 1 will pass by a star in the constellation of Camelopardalis and in 296,000 years Voyager 2 will pass by (4.3 light years) Sirus.xxvii
Even though the Voyager mission had a bumpy start with mission changes and budget cuts, it has been one of the most successful missions of all time. Being able to use the rare geometric arrangement of the planets back in the 1970s and 1980s to tour all of the gas giants turned out to be very beneficial for us. The design of the spacecraft turned out to last much longer than anyone ever imagined and since it was built so well, it has led to many discoveries and new missions. For now, both spacecraft will continue to study ultraviolet sources and the boundary between the sun and interstellar space. If mankind is ever wiped out, the Voyager and it's golden record may be the only thing left to prove that we were ever here.
i Voyager, "Mission", http://voyager.jpl.nasa.gov/mission/mission.html (accessed February 24, 2011).
ii Voyager, "Planetary Voyage", http://voyager.jpl.nasa.gov/science/planetary.html (accessed February 24, 2011).
iii Voyager, "Planetary Voyage", http://voyager.jpl.nasa.gov/science/planetary.html (accessed February 24, 2011).
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v Voyager, "Fast Facts", http://voyager.jpl.nasa.gov/mission/fastfacts.html (accessed February 24, 2011).
vi Voyager, "Planetary Voyage", http://voyager.jpl.nasa.gov/science/planetary.html (accessed February 24, 2011).
vii Voyager, "Instruments", http://voyager.jpl.nasa.gov/spacecraft/instruments.html (accessed February 24, 2011).
viii Voyager, "Instruments", http://voyager.jpl.nasa.gov/spacecraft/instruments.html (accessed February 24, 2011).
ix Voyager, "Instruments", http://voyager.jpl.nasa.gov/spacecraft/instruments.html (accessed February 24, 2011).
x Voyager, "Golden Record", http://voyager.jpl.nasa.gov/spacecraft/goldenrec.html (accessed February 24, 2011).
xi Voyager, "Golden Record", http://voyager.jpl.nasa.gov/spacecraft/goldenrec1.html (accessed February 24, 2011).
xii Voyager, "Fast Facts", http://voyager.jpl.nasa.gov/mission/fastfacts.html (accessed February 24, 2011).
xiii Voyager, "Fast Facts", http://voyager.jpl.nasa.gov/mission/fastfacts.html (accessed February 24, 2011).
xiv Voyager, "Planetary Voyage", http://voyager.jpl.nasa.gov/science/planetary.html (accessed February 24, 2011).
xv Voyager, "Planetary Voyage", http://voyager.jpl.nasa.gov/science/planetary.html (accessed February 24, 2011).
xvi Voyager, "Planetary Voyage", http://voyager.jpl.nasa.gov/science/planetary.html (accessed February 24, 2011).
xvii Voyager, "Planetary Voyage", http://voyager.jpl.nasa.gov/science/planetary.html (accessed February 24, 2011).
xviii Voyager, "Fast Facts", http://voyager.jpl.nasa.gov/mission/fastfacts.html (accessed February 24, 2011).
xix The Planetary Society, "The Story of the Mission", http://www.planetary.org/explore/topics/voyager/objectives.html (accessed February 24, 2011).
xx NASA, "Frequently Asked Questions", http://voyager.jpl.nasa.gov/faq.html (accessed February 24, 2011).
xxi NASA, "Saturn", http://voyager.jpl.nasa.gov/science/saturn.html (accessed February 24, 2011).
xxii NASA. "Uranus", http://voyager.jpl.nasa.gov/science/uranus.html (accessed February 24, 2011).
xxiii NASA. "Neptune", http://voyager.jpl.nasa.gov/science/neptune.html (accessed February 24, 2011).
xxiv The Outer Planets, "Voyager 1 & 2", http://lasp.colorado.edu/education/outerplanets/missions_voyagers.php (accessed February 24, 2011).
xxv NASA. "Voyager Makes an Interstellar Discovery", http://science.nasa.gov/science-news/science-at-nasa/2009/23dec_voyager/ (accessed February 24, 2011).
xxvi NASA, "Interstellar Mission", http://voyager.jpl.nasa.gov/mission/interstellar.html (accessed February 24, 2011).
xxvii NASA, "Interstellar Mission", http://voyager.jpl.nasa.gov/mission/interstellar.html (accessed February 24, 2011).
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