It was the year 1977 when NASA (National Aeronautics of Space Administration) launched its two spacecrafts, Voyager 1 and Voyager 2, from Cape Canaveral, Florida, USA. Both these spacecrafts are exploring the outer regions of our Solar System even today and hence they are the most distant objects in space exploring those regions where no human made object has ever gone. As said in the beginning of our beloved series of Star Trek - "to go where no man has gone before...".
Voyager 2 set another record of visiting more planets than any other spacecraft in history. If all goes fine then the twins are likely to survive for many decades and will continue to send us the information of the surrounding of the home of our planet - Earth.
When Voyagers were launched in 1977 to study and photograph the outer giant planets of the Solar System, the robot ship was expected to survive just four years, however the human expertise to put together the technological advancements makes the spacecrafts Super Machines which are still working without problems.
Another spacecraft called Pioneer 10 held the record for 25 years for being the most distant human made object in space, but in 1988 the baton got passed from Pioneer 10 to Voyager 1. On February 17, 1988 Voyager 1 cruised beyond the Pioneer 10 spacecraft and became the most distant human-created object in space. At that time, it was 10.4 billion kilometers from Earth (the distance between Earth and Sun is .15 billion kilometers (1.5 crore kilometers), also known as 1 AU - Astronomical Unit). Pioneer 10 and Voyager 1 are headed in almost the opposite direction from the Sun.
At present, at the end of year 2004, Voyager 1 spacecraft is 14.05 billion kilometers away from the Earth, 94 times the distance between the Sun and the Earth and Voyager 2 is a little less away at 11.24 billion kilometers from the Earth, 75 times the distance between the Sun and the Earth. The distances are so great that the signals transmitted from these spacecrafts takes 13 to 16 hours to reach Earth, even though the signals travel at the speed of light (3 lakh kilometers per second!).
Both the Voyagers have accomplished their primary mission of visiting the various planets and their satellites of our Solar System and make detailed study about them. They have discovered several new satellites of various planets like Jupiter, Saturn, Neptune and Uranus and even discovered new ring systems of all the Gas Monsters.
As stated earlier, the signals have to travel billions of kilometers to reach us. These signals are radio waves produced by a 20-watt radio transmitter; by the time they reach us they become so faint that they are around 20 billion times smaller than the power of a digital watch battery (button cell).
In the year 2002, when the Voyager 1 was 25 years old and 12.5 billion kilometers away from Earth, the signals from NASA station required 12 hours to reach. The Voyager team at NASA's Jet Propulsion Laboratory in Pasadena, California, sent commands to activate a spare sun sensor and star tracker to help the craft locate its position. The necessity of such an operation aroused because Sun was also just like a bright star for the craft, and it could collect very little solar power that it uses as its fuel.
The speeds at which these crafts travel are mind-boggling. Voyager 1 travels at the speed of 64,000 kilometers per hour and Voyager 2 escapes at the speed of 56,000 kilometers per hour. Voyager 2 is heading in the opposite direction of Voyager 1 and traveling at a slightly lower speed.
Pluto, the last and the farthest planet known to us was not visited by any of these two Voyagers and it is still remains unvisited. Voyager 1 did a close flyby of Jupiter and Saturn and than went on its way towards the outer edge of the Solar System and Voyager 2 also did flybys of Jupiter and Saturn and than marched ahead to examine Uranus and Neptune. Voyager 2 did a much better survey of all the gas giants of the Solar System and than headed into the opposite direction of Voyager 1 towards the edge of the Solar System. A little surprising fact is worth mentioning here, Voyager 2 was launched in August 1977 and 1 month later in September 1977 Voyager 1 was launched.
Our Super Machines are far beyond any planetary orbit, which means they are not going to encounter any known planets. So what are they doing now and what is their next mission?
Now the mission of the Voyagers is to extend the NASA exploration of the Solar System beyond the neighborhoods of the outer planets to the outer limits of the Sun's sphere of influence, and possible beyond. This is known as VIM (Voyager Interstellar Mission).
In other words VIM is an extension of the Voyager mission that was completed in 1989 with the close flyby of Neptune by the Voyager 2 spacecraft. Away from all planets both spacecrafts are still within the boundaries of the Sun's magnetic field – the Heliosphere. Voyagers are receiving signals, which scientists believe are coming from the outermost edge of the heliosphere, known as the heliopause.
The Sun emits a steady flow of electrically charged particles called the solar wind. As the solar wind moves at very high speed out into space it creates a magnetized bubble around the Sun – the heliosphere. The speed at which solar wind moves is 15 lakh kilometers per hour, somewhere far ahead in heliosphere solar wind slows down to around 4 lakh kilometers per hour speed, this happens in an area called Termination Shock, the first indication that the wind is nearing the heliopause.
Aim of both the Voyagers is to cross the Termination Shock area and later overcome the heliopause boundary where the Sun's influence wanes and the interstellar space begins. No spacecraft has ever visited the heliopause; the Voyagers may be the first to pass through this region, which is thought to be around 22 billion kilometers away from the Sun. The Voyagers should cross the heliopause 10 to 20 years after reaching the termination shock. The Voyagers have enough electrical power and thruster fuel to operate at least until 2020.
Super Machines not only carried different types of scientific instruments but also messages. Messages were put with an intention that other civilization may capture our Voyager and open it to see what is inside. Even if the Voyagers will go dead after may be a few decades, they will still continue to ride away from us at the same speed and eventually may run into the area of some intelligent civilization.
Each Voyager carries a 12-inch gold-plated copper disk. The disk has recorded on it sounds and images of Earth designed to portray the diversity of life and culture on the planet. Each disk is encased in a protective aluminum jacket along with a cartridge and a needle. Instructions explaining from where the spacecraft originated and how to play the disk are engraved onto the jacket. Electroplated onto a 2 cm area on the cover is also an ultra-pure source of uranium-238 (with a radioactivity of about 0.26 nanocuries and a half-life of 4.51 billion years), allowing the determination of the elapsed time since launch by measuring the amount of daughter elements to remaining U238. The 115 images on the disk were encoded in analog form. The sound selections (including greetings in 55 languages, 35 sounds, natural and man-made, and portions of 27 musical pieces) are designed for playback at 1000 rpm. The Voyagers were not the first spacecraft designed with such messages to the future. Pioneers 10 and 11, LAGEOS, and the Apollo landers also included plaques with a similar intent, though not quite so ambitious.
Some scientific results of the Voyager mission
Discovery of the Uranian and Neptunian magnetospheres, both of them highly inclined and offset from the planets' rotational axes, suggesting their sources are significantly different from other magnetospheres.
The Voyagers found 22 new satellites: 3 at Jupiter, 3 at Saturn, 10 at Uranus, and 6 at Neptune.
Io was found to have active volcanism, the only solar system body other than the Earth to be so confirmed. Triton was found to have active geyser-like structures and an atmosphere.
Auroral zones were discovered at Jupiter, Saturn, and Neptune.
Jupiter was found to have rings. Saturn's rings were found to contain spokes in the B-ring and a braided structure in the F-ring. Two new rings were discovered at Uranus and Neptune's rings, originally thought to be only ring arcs, were found to be complete, albeit composed of fine material.
At Neptune, originally thought to be too cold to support such atmospheric disturbances, large-scale storms (notably the Great Dark Spot) were discovered.
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