The Voyager Program: History and Mission

The Voyager program is an American scientific program developed by NASA that launched in 1977 two robotic space probes: Voyager 1 and Voyager 2. The scope of the mission was to study the outer part of the Solar system and gain knowledge about the outer planets and their moons. At first the mission was quite simple: Voyager 1 had to study the planetary systems of Jupiter and Saturn and Voyager 2 had to study Uranus and Neptune.

Currently the Voyager space probes are exploring the outer boundary of the heliosphere in interstellar space. As a result of their success, the space probes mission has been extended three times as they continue to transmit useful scientific data. It was confirmed that on August 25, 2012, Voyager 1 had become the first man-made object to exit the Solar system and enter interstellar space. A few years later it was also confirmed that Voyager 2 also indicated its enter into the interstellar space in 2018.

The Voyager space probes are powered by radioisotope thermoelectric generators, a type of nuclear battery. This is a type of battery that is perfect for missions needing energy over a long period of time – which would be too long for fuel cells or battery – and that can’t rely on solar energy. It allows us to organize very long missions to happen. As such it’s predicted that the batteries will no longer be functional from 2032 on, i.e 55 years after the launch of the space probes, which is quite remarkable. However as time passed by, various functions and systems of the probes had to be switched off to keep the main system in working order. Consequently they’ll be able to keep its current set of scientific instruments on until 2025.

The history of the Voyager space probes

The space probes were initially conceived as part of the Mariner program whose purpose was to launch various robotic interplanetary probes from 1962 to 1973 in order to investigate Mars, Venus and Mercury. But as their mission has been changed to go study Jupiter and Saturn, they were removed from the Mariner program. At first they kept their original name and were called the Mariner Jupiter-Saturn space probes. However due to their evolution from the Mariner space probes, their name was quickly changed to Voyager.

This new program took over many elements of the Grand Tour program. As indicated by his name, the Grand Tour program, developed by NASA, aimed to sent two groups of robotic probes to all the planets part of the outer Solar system: Jupiter, Saturn, Pluto, Uranus and Neptune. Yet this program was deemed too expensive, around 1 billion dollars. Consequently it was cancelled and replaced with the Voyager program.

For this reason the Grand Tour program had a major influence on the Voyager program, as it fulfilled a lot of the planned objectives for the Grand tour, with the exception of a visit to Pluto.

The missions of the Voyager program

The Voyager program used the favorable alignment of Jupiter, Saturn, Uranus and Neptune which occurs only once every 175 years and was set to happened in the late 1970s. The space probes used gravitational assists, namely the use of the relative movements and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft and thus saving propellant and reducing expense. Through gravity assistance, it’s possible to either accelerate a spacecraft, decrease its speed or redirect its path.

While Voyager 2 was launched first, on August 20, 1977, Voyager 1 was launched on September 5, 1977, on a faster and shorter trajectory.

Originally, the Voyager space probes were to conduct closeup studies of Jupiter and Saturn, its rings and their larger moons. As this mission was a real success and as the probes were in good condition, scientists decided to go and explore Uranus and Neptune.

The Voyager space probes made it possible to recover a lot of data and photographs of the most distant planets, thus allowing us to have precise details, which were until then still unknown, about the four giant planets and their Moon.

For instance, we were able to observe Jupiter’s cloud forms, its wind and storm systems, as well as to discover the volcanic activity on its moon Io. It was the first time that active volcanoes had been seen on another body in the Solar system. It was also discovered that seven percent of the upper atmosphere of Saturn is helium and the rest is hydrogen. Titan, Saturn’s largest moon, was also studied in depth. Among the major discoveries was the discovery of a magnetic field around Uranus and ten of its moon, but also the discovery of three rings and six unknown moons of Neptune.

Furthermore Voyager 1 and 2 sent us a lot of close up photos of the giant planets. Among them is the Pale Blue Dot, taken in 1990 by Voyager 1, and popularised by Carl Sagan. This famous photography pictures planet Earth from a distance of about 6 billion kilometers. Planet Earth appears as very small blue dot, lost in the vastness and greatness of space. As Sagan described: “The Earth is a very small stage in a vast cosmic arena“.

As the main mission of the Voyager program was achieved in 1989 when Voyager 2 flew by Neptune, it was decided to extend their mission through the Voyager Interstellar Mission. The goal was to extend the exploration of the Solar system beyond the outer planets, and if possible, beyond the “limits” of the Solar system, beyond what we call the heliopause boundary. It can be defined as the limit where the solar wind from the Sun is stopped by the interstellar medium. Reaching after the heliopause will allow the space probes to make measurements of the interstellar fields, particles and waves which are unaffected by the solar wind and thus giving us major informations.

As part of the deep space exploration, both space probes carry a golden record that contains pictures and sound of Earth, as well as data detailing the location of Earth. At the same time it’s a time capsule and an interstellar message to any civilisation that may recover the space probes. The content of the record was selected for NASA by a committee. There are 115 images and sounds such as wind, thunder, animals but also songs from different cultures and eras, greeting in 55 languages but also the sound of laughter. The images depict mathematics, the Solar system, DNA, human anatomy, animals, insects, landscapes but also food, architecture. The goal was to depict Earth and humanity in the broadest range possible and represent the different cultures.

As of today, the probes continue to send important data to scientists. Currently they mainly study ultraviolet sources among the stars and they explore the boundary between the Sun’s influence and interstellar space.

Recently a published study showed that the space probes detected a new type of electron burst. Thus a new mechanism in the physics of cosmic radiation and solar shock waves has been discovered. In fact, solar flares cause violent shock waves which accelerate the particles. Although this idea is already known to scientists, the date collected by the space probes has shown that the particles seem to accelerate beyond the heliopause. But above all, they made it possible to concretely observe an interstellar shock wave in a new environment.

It is clear that the Voyager program is a real success. The program has made it possible to collect an enormous amount of data and images on our Solar system, which have allowed to gain a more precise knowledge of the deep space. But above all, Voyager space probes have now become the testament of humanity traveling through space.