Voyager: Trailblazers of the Galaxy

Intro

‘In this bitesize episode, we’re going to be talking about a topic that I have been very excited to do as I went through a phase of being absolutely obsessed with space and space missions when I was in my early twenties. So I hope you enjoy it and find it as interesting as I do!

‘In 1977, two identical spacecraft were launched two weeks apart by the US space agency NASA. Their mission: to go where no human made object had ever gone before – the outer planets of our solar system. This so-called Grand Tour was to include Jupiter and Saturn, and if all went well perhaps even Uranus and Neptune, and would take advantage of a rare alignment of these large gaseous planets. The two pioneering probes that were to be sent on this Grand Tour of our solar system were known as Voyager.

‘The two spacecraft are today the furthest man-made objects in history, venturing far beyond their original missions to explore the outer realms of our solar system, which was completed in 1989. Voyager 1 is currently nearly 25 billion kilometres from Earth and its sibling has clocked up just over 20 billion kilometres, and both of them have now entered interstellar space, the space between the stars. Despite their vast distance from their homeland, NASA is still in contact with both probes, extracting invaluable data that tracks their trajectories through the void. What makes the probes even more special, is that they both carry a golden record—a time capsule of Earth’s sights and sounds—intended as an intergalactic greeting to any interstellar wanderer they might encounter. Let’s talk about these trailblazing spacecraft in more detail.’

Planning the mission

‘Originally part of the NASA Mariner programme that sent probes to the inner planets of our solar system Mars, Mercury and Venus, the Voyager probes were originally named Mariner 11 and Mariner 12. However, as their design progressed beyond the Mariner family’s scope, they were renamed and incorporated into the Voyager Program. This program was to be known as the Planetary Grand Tour, which was conceived in the late 1960s and early 1970s, aiming to take advantage of a rare alignment of the outer planets and explore them using gravitational assists of the planets to increase acceleration of the spacecraft, also known as “a gravitational slingshot”. Due to funding issues from Washington, the Grand Tour was shortened to flybys of just Jupiter and Saturn, with a possibility of an extension to Uranus, and Neptune if the mission was a success and resources allowed.

‘The two Voyagers were designed and built by the Jet Propulsion Laboratory, a special division of NASA tasked with robotic exploration of the solar system. They were fitted with 11 scientific instruments to study things like atmospheres, magnetic fields, and particles in space and a camera to take pictures. For communication with Earth, Voyager was fitted with a 3.7 metre antenna to send and receive messages through radio waves. It could connect with Earth using NASA’s Deep Space Network, a worldwide network of large antennas placed in strategic locations in the US, Spain and Australia to ensure uninterrupted communication with deep space probes. If Voyager couldn’t talk to Earth directly, it would be able to save data on a recorder to send later. At its current distance, it now takes more than 22 hours for signals from Voyager 1 to reach Earth.

‘To power its operations, Voyager was fitted with three special radioactive generators called radioisotope thermoelectric generators (RTGs). These generators create electricity using plutonium-238, a special material that emits steady heat due to its natural radioactive decay. Over time, their power decreases, but they will keep working to support Voyager’s activities until at least 2025, and possibly 2030.

‘Voyager’s cameras were controlled by one of the spacecraft’s digital computers, called the Flight Data Subsystem (FDS). The computer command subsystem (CCS) helps control these cameras, managing commands and making sure everything runs smoothly. Another important system, the Attitude and Articulation Control Subsystem (AACS), helps it stay steady and keep its radio antenna pointed towards Earth.

‘NASA then selected a team led by astronomer Carl Sagan to create The Voyager Golden Record, a phonograph record (which was actually made of gold-plated copper) which would be sent into space aboard both Voyager spacecraft. It was a deliberate attempt by NASA to communicate with potential extraterrestrial life forms. It includes greetings in 55 languages, sounds of Earth, diverse music, images of Earth’s locations, scientific information, and even a message from the then-US President Jimmy Carter. This eclectic mix was curated to  showcase humanity’s cultural, scientific, and biological diversity, serving as a snapshot of life on Earth for any intelligent beings that might encounter it beyond our solar system.’

Launch and primary mission

‘The decision was taken to launch Voyager 2 first, in order to take advantage of a rare alignment of Jupiter, Saturn, Uranus and Neptune (which only happens once every 176 years). This trajectory would be slower and more circular and in order to take this trajectory, Voyager 2 was launched first on 20 August 1977 from Cape Canaveral in Florida. Voyager 1 was launched 16 days later on 5 September, but because it followed a much faster trajectory, it overtook its sister probe just three months later on 15 December and would be the first to reach Jupiter, hence the reason they were launched in the wrong order. Both spacecraft were launched aboard ​​Titan-Centaur rockets from Cape Canaveral.

‘The start of the Grand Tour, however, was fraught with problems right from the start. Voyager 2’s launch was delayed by a double computer failure, and once in space, it grappled with issues like robotic “vertigo” and malfunctioning sensors. Similarly, Voyager 1 encountered its own share of troubles, including jammed scan platforms and malfunctioning thrusters. But despite these setbacks, both spacecraft persevered, as they ventured into the unknown.

‘Voyager 1 reached Jupiter in March 1979 after a silent, lonely journey of 18 months travelling at around 125,000km an hour. As it approached the gas giant, it captured breathtaking images, unveiling the intricate details of Jupiter’s swirling clouds and the iconic Great Red Spot that has been raging continuously since it was discovered in the 17th century. These close-up pictures offered scientists unprecedented insights into Jupiter’s atmosphere and weather patterns. During its closest approach, Voyager 1 soared 280,000 kilometres above Jupiter’s cloud tops. Moreover, it discovered previously unknown moons and witnessed volcanic activity on Jupiter’s moon Io, highlighting the dynamic nature of the Jovian system. The images transmitted back to Earth by Voyager 1 captivated the public all over the world, cementing the spacecraft’s legacy as a trailblazer in exploring the outer solar system. Voyager 2 arrived four months later in July, passing within 350,000 kilometres of the planet’s cloud tops. Both spacecraft utilised Jupiter’s gravitational pull to “sling-shot” them onto a faster trajectory onto the next stop – Saturn.

‘Voyager 1 flew by Saturn twenty months later in November 1980, with Voyager 2 arriving nine months later in August 1981. These encounters with Saturn provided detailed insights into the planet, revealing that Saturn’s atmosphere is mostly hydrogen and helium, with winds blowing at high speeds, especially near the equator. The probes also took photos of the gas giant, which revealed the intricate patterns and textures within the rings, showcasing their complexity and beauty in ways never seen before. Voyager 2 also made significant discoveries about Saturn’s largest moon, Titan. It found that Titan’s atmosphere is mostly nitrogen, with traces of methane and other gases. This discovery suggested that Titan might have conditions similar to those on early Earth, raising the possibility of organic chemistry and even the presence of liquid methane lakes or seas on its surface.

‘During  the flyby of Saturn, Voyager 1 was slung down underneath the gas giant at a very high velocity and upwards out of the ecliptic plane of the planets orbiting the sun. Voyager’s 1’s planetary mission was over. However, Voyager 2 was only half way through.’

Voyager 2 extended primary mission

‘After the successful flyby of Saturn, Voyager 2 used a gravitational sling-shot to propel itself further along the ecliptic plane to the next planet – Uranus. Voyager 2’s flyby of Uranus occurred in January 1986. During this encounter, Voyager 2 passed within approximately 81,500 kilometres of the ice giant’s cloud tops.  provided valuable data about Uranus’s atmosphere, unique magnetosphere, and discovering ten new moons and two new rings, scientists were somewhat disappointed with the planet’s appearance. Uranus appeared as a featureless, pale blue sphere with little visible detail, unlike the vibrant atmospheres of Jupiter and Saturn. This lack of distinct features was unexpected and left scientists wanting more detailed information about the planet’s composition and structure. Despite the disappointment in its appearance, Voyager 2’s observations greatly expanded our understanding of Uranus and its unique characteristics including its oddest feature: a chaotic magnetosphere, with the icy giant rotating on its side at about 98 degrees.

‘Voyager 2 then continued further out to the furthest planet of our solar system, Neptune. Voyager 2’s flyby of Neptune occurred three years later in August 1989. The probe passed within approximately 4,950 kilometres of Neptune’s north pole. The spacecraft provided detailed observations of Neptune’s atmosphere, revealing features such as its dynamic cloud patterns and the Great Dark Spot, a large storm similar to Jupiter’s Great Red Spot. Voyager 2 also discovered five new moons and four rings surrounding the planet. The flyby of Neptune marked the end of Voyager 2’s primary mission to explore the outer planets of the solar system, concluding its historic journey with remarkable discoveries about this distant ice giant.’

Interstellar mission

‘12 years after they were launched, these trailblazing probes began exploring the space beyond the planets. In 1990 and at a distance of 6 billion km from the sun, Voyager 1 was ordered to turn its cameras back towards home for one final picture. It captured a series of 60 images that would be pieced together to become the iconic image known as the “Family Portrait.” It depicted six of the Solar System’s planets, including Earth, as small, pale dots against the vast darkness of space, with the blue   pixel sized dot of Earth becoming known as “The Pale Blue Dot”. This image provided a humbling perspective of our place in the universe. 

‘Since then, both Voyager spacecraft have continued their journey into interstellar space, but their ageing systems have posed challenges. Instruments have had to be turned off one by one to conserve power as the two spacecraft travel farther from the Sun, with the last remaining instruments expected to be powered down by 2025. Each Voyager is now being powered by around 250 watts of energy from their RTGs. To put that into context, that’s the same amount of energy that is needed to power small to medium sized household appliances. It is only because of the exponential improvement in technology back here on Earth that NASA has been able to stay in contact with the probes. Despite the limitations, Voyager’s remarkable mission has provided invaluable insights into the outer reaches of our solar system. Voyager 1 crossed the heliopause—the boundary of the Sun’s magnetic field—on 25 August 2012, followed by Voyager 2 on 5 November 2018. 

‘As they continue their odyssey, the Voyagers will eventually encounter other stars. In about 40,000 years, Voyager 1 will approach AC+79 3888, one of the fastest moving stars in the Milky Way relative to the Sun. In about 296,000 years, Voyager 2 will come close to Sirius, the brightest star in the sky. The Voyagers are destined to drift through the stars until either the end of time or until they are encountered by an extraterrestrial intelligent life form. This life form will then be able to use the Golden Disk to learn about our tiny but plucky little planet called Earth that dared to go where no one thought possible.’

Outro

‘I hope you found the story of the Voyager spacecraft interesting! I would like to do more on space and so do let me know on social media if that is something you’d like to see! I would also like to pay tribute to all the amazing scientists and technicians at the Jet Propulsion Laboratory in California for accomplishing this incredible feat of pioneering science and technology, you guys are the real trailblazers! Thanks very much for listening and see you next time, goodbye.’