A rare astronomical event due to occur in the late 1970s inspired the desire to send a spacecraft to the most distant planets in our Solar System and beyond. That decision almost 40 years later has meant humans have created and launched a spacecraft which has travelled to the boundary of our Solar System. It is now in the vast space between the stars and has become the most distant man-made object in the Universe.
Gary Flandro, an engineer working at NASA’s Jet Propulsion Laboratory, proposed the idea of the ‘Grand Tour’ of the outer planets in 1965. A rare planetary alignment which only occurs every 175 years favoured the idea as the planets were close together. NASA had already been exploring the idea of using a planet’s gravity to change a spacecraft’s speed and direction when planning the Mariner 10 mission which visited Mercury and Venus in 1973/4. The alignment of the outer planets and the ability to use a planet’s gravitational field meant the craft could move from Jupiter to Saturn and then onto Uranus, Neptune and Pluto and observe all the planets in a single flight with minimum propulsion. The flight time using this gravity assist method reduced travel time to Neptune from 30 years to just 12.
Unfortunately due to finance problems the ‘Grand Tour’ was deemed too expensive, however a flight to Jupiter and Saturn and a flyby of their moons was possible and thus the Mariner Jupiter-Saturn project, later renamed as the Voyager Program, was developed (the Voyager name had already been taken for a plan to land hugely elaborate probes on Mars, but this project too was cancelled, freeing up the name) . To complete their mission two spacecraft were designed to last five years. In the August of 1977 the Voyager 2 space craft was launched, and a couple of weeks later Voyager 1 was launched, both raced skyward on board Titan-Centaur rockets. Both Voyagers were headed for Jupiter and Saturn but on different trajectories.
By 1979, both Voyagers had completed a close up approach with the largest planet in our Solar System, Jupiter. In 1980, Voyager 1 flew past Saturn and then continued its journey out of the Solar System. After flying past Saturn in 1981, Voyager 2 was still working so it was authorized and funding continued to propel it onto Uranus where it arrived in 1986. NASA also authorized it to continue onto Neptune where it travelled past this gaseous planet in 1989, 12 years after launch. The Voyager mission allowed scientists to find out more than ever before about the gas giants. Some of the highlights included observing Volcanic eruptions from Jupiter’s moon Io, viewing Saturn and its rings from behind (a view impossible from Earth), discovering many new moons of Uranus as well confirming the existence of Neptune’s rings. Thirty six years later, in September 2013, Voyager 1 continued to make headlines as it now has travelled out of the Solar System and into the realms of interstellar space.
The Voyager space-crafts are powered by Radioisotope Thermoelectric Generators. The energy released when the Plutonium on board decays is converted to heat, which is converted into electricity. Initially the Voyagers had 11 different measuring instruments on board. One of these instruments the Imaging Science System (ISS) included the cameras attached to the spacecraft which produced photographic imagery of the Gas Giants. Only 5 of these instruments are still working which does not include any ability to take pictures. However the Voyagers can still detect the slow moving plasma particles emitted from our Sun. Changes in measurements of these particles have allowed scientists to determine that the Voyagers are moving into new territory through an area called the termination shock and they are now traversing the Heliopause. Voyager 1 was launched on a faster trajectory and is now in an area in which the Sun’s influence is minimal at almost 19 billion km from the Earth. Voyager 2 is 15.3 billion km away. Both Voyagers have enough power to continue running until 2020. Powering down some of the remaining instruments may conserve some power up to 2025.
After the Voyagers power does finally run out 43 years after launch, they spacecraft will continue to drift through interstellar space. Beyond our Solar System is the Oort Cloud, the area in which comets are thought to originate. It has been estimated that it will take Voyager 1 three hundred years to reach the inner parts of the Oort cloud and potentially 30,000 years to fly beyond it. In about 40,000 years Voyager 1 will be closer to the red dwarf star AC +793888 in the constellation of Camelopardis than the Sun.
The Voyagers seem destined to drift further into space and should any other life form happen to come across these space craft, they both have on board a golden record with pictures, sounds and music from the Earth. The record will be a time capsule of the Earth or a message in a “bottle in a cosmic ocean” as noted by astronomer Carl Sagan. Should any other civilisations in 40,000 years happen to find this record, they will be treated to the delights of Bach and Beethoven, some Azerbaijan bagpipes and other traditional music as well some Chuck Berry and Louis Armstrong. There are also a number of Greetings recorded in 55 different languages on the record. Should these aliens speak in the Amoy dialect from an area in China, they will hear this greeting http://voyager.jpl.nasa.gov/spacecraft/audio/amoy.au which translates as “Friends of space, how are you all? Have you eaten yet? Come visit us if you have time.” If they speak French however it’s a simple “Hello everybody”. As well as sounds there are also simple images, of DNA, evolution, mankind as well as astronauts and a Titan-Centaur launch, all to help create an image of Earth.
The Voyager Interstellar Mission has so far proved very successful and provided us with some concrete evidence of the properties and characteristics of the Gas Giants as well a sense of scale of the Solar System as they drift further and further away. Although they will run out of fuel within the next 15 years, the Voyager space crafts are destined to endlessly drift into the unknown vastness of space clutching aboard memories of Earth to share with the Universe.
(Article by Martina Redpath, Education Support Officer)