OPINION: The Voyager 1 and Voyager 2 unmanned spacecraft were launched within weeks of each other 34 years ago.
Travelling at 17 kilometres per second, the two are currently heading in different directions out of our solar system.
Voyager 1 is the more distant of the two and is now the farthest human-made object from Earth. It is so far away that any radio signal sent to it takes 16.5 hours to get there.
That means if you want to change the direction of the spacecraft by increasing thrust on a motor or you want to alter a camera position, 16.5 hours will pass from the time you decide on the manoeuvre to it actually taking place.
The spacecraft weighs 722 kilograms and, like its sister, Voyager 2, it is equipped with all the systems required to undertake such a long mission. This includes 16 rocket thrusters with eight backups, gyroscopes for measuring and maintaining the orientation of the spacecraft, and instruments to allow star positions to be determined so that its radio antenna remains pointed towards Earth.
Electrical power is provided by the heat delivered from the radioactive decay of plutonium oxide. It is used to power three generators, delivering a total power of 470 watts - about the same as a household refrigerator.
The objective of both Voyager missions was to exploit a rare alignment of the planets Jupiter, Saturn, Uranus and Neptune, to fly close by and study them and some of their moons.
By careful calculation of the trajectory, a spacecraft can use the energy of the gravitational pull of a planet to provide the acceleration to assist it towards the next planet. The technique, referred to as a gravitational slingshot, saves a lot of fuel.
Between 1977 and August 1989, Voyager 2 flew past Jupiter, Saturn, Uranus and Neptune and several of their moons. It was a spectacularly successful mission and the science derived from it profoundly changed our understanding of the solar system.
Between 1977 and November 1980, Voyager 1 flew by Jupiter and Saturn and provided sensational views of five of Jupiter's moons, including witnessing the eruption of a volcano on the moon Io, and flying by five of Saturn's moons.
The solar system ends at the outer edge of the heliosphere.
This is a huge bubble formed by the charged particles spat out of the Sun by the violent nuclear reactions in its interior.
At present, Voyager 1 is at the outermost reaches of the heliosphere. The limit will be detected by a change of direction in the Sun's magnetic field in this region. This occurs because the fast charged particles (the solar wind) encounter the incoming interstellar wind - that is, charged particles from distant stars.
The result of this interaction is the slowing of the solar wind and a change in the magnetic field direction.
When that change is detected, scientists will know the spacecraft has moved beyond the solar system and into the vastness of space between the stars.
No-one knows when the edge of the solar system will be reached, but it could be years away. All being well, the passage into interstellar space will be detected before Voyager 1's power runs out in 2020 or thereabouts.
Voyager 1 will be the first human-made object to leave the solar system, after which it will continue to move into interstellar space. It is heading in the general direction of a star called AC+79 3888 in the constellation of Camelopardalis, which it will pass in 40,000 years from now, at a distance of 10 trillion kilometres. Voyager 2's "closest" encounter with a star will be in 296,000 years, when it will pass within 40 trillion kilometres of Sirius, the brightest star in the sky.
After that, the Voyagers will move into deeper space for many millions of years, long after they are technically able to let the inhabitants of Earth (if there are any) know about it.
Even if either of the two Voyager spacecraft could maintain their present speed of 17km/sec, they would not reach the edge of our galaxy, the Milky Way, for 490 million years. Given that the current best guess is that there are at least 200 billion galaxies in the universe, it will not be short of places to explore in the very, very distant future.
- © Fairfax NZ News
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