On 25th August 2012 one of the most significant events in human history took place, yet it occurred so far away that not a single human being was there to witness it. In terms of exploration, this is about as colossal as you’re going to get. A journey that is still ongoing after a staggering 43 years and roughly 22.6 billion km (14.1 billion miles).
Shortly before the end of August in 2012, with the world still basking in the afterglow of a successful Summer Olympics in London, Voyager 1, NASA’s space probe launched in 1977, finally crossed the imaginary boundary that forms the Heliopause. To simply call the event historic would be a monumental understatement.
Now that might not be a word that too many have ever come across and probably for good reason, because it denotes an area that is so unimaginably far away, it’s difficult for us Earth-dwellers to wrap our heads around. The Heliopause, roughly 18 billion km (11.1 billion miles) from Earth, marks the very edge of our Solar System, the point at which the Sun’s solar winds begin to lose strength and where objects enter the Interstellar Medium – the matter and radiation that exists between stars.
It was at this point in August 2012, that an object that had originated on Earth, became the first to leave our Solar System and to venture into the great unknown. And nine years later, this intrepid little explorer is still hurtling through interstellar space.
It’s a little difficult to get your head around the fact that right now, roughly 22.6 billion km (14.1 billion miles)from Earth, an object built by humans is travelling at a speed of 61,000 km/h (38,000 mph) through interstellar space and is now so far away that it takes light just over 21 hours to reach the probe from our sun. It’s hard enough to picture space and other planets, but when you add in interstellar travel, you begin to get a sense of just how extraordinary this journey really is.
Yet this is not just about where it is now, but where it’s been and the things it’s seen since its launch on 5th September 1977. While it was not the first probe to visit Jupiter and Saturn, the images it sent back of the two giants and their moons were by far the most impressive and comprehensive images we had ever seen. Perhaps its most famous image is the ‘family portrait’, a series of pictures taken in 1990 put together to create a collage showing six separate planets and their positions in the Solar System.
The lifespan of the mission has already extended well beyond expectations but it’s generally assumed that we won’t be able to communicate with Voyager 1 past 2025. But even then, that won’t be the end of Voyager 1. We might not be able to communicate it with it, but this space probe is set to continue for some time to come.
The Space Race
As the Space Race began heating up in the late 1950s and through the 1960s, understandably much of the early focus was on the planets in our immediate vicinity and of course our moon. The 1970s saw some of the most dramatic events in space exploration. We’ve recently done a video on the Soviet mission to Mars that blasted off in 1971 and which became the first object to land on the Red Planet. In 1975, the Soviets also became the first nation to successfully photograph the surface of Venus from its Venera 9 and 10 spacecraft.
The Americans were also busy, but it’s noticeable how quickly public interest fell away after the first moon landing in 1969, with the irony being that the most-watched space event after it was the successful failure of Apollo 13 – again a topic we’ve had covered on Megaprojects, so if you fancy getting stuck into the Space Race then this is the place to do it.
The Grand Tour
Back in the days when we humans were bound by the constraints of our Earth, the Grand Tour was a 17th and 18th Century upper-class romp through aristocratic Europe. For many young men of the age, this was a right of passage, a way of seeing the world before returning to one’s roots and commencing adulthood.
In the 1960s, NASA commenced a program with the same name, intending to visit our distant planetary cousins. The idea was to launch four space probes, two of which would visit Jupiter, Saturn, and Pluto, while the other two would visit Jupiter, Uranus, and Neptune. If you’re wondering why it’s mixed like that, it’s because of planetary orbits and their location to each other when the probes pass.
With things swinging into gear in the early 1970s, the cost of the program ballooned to nearly $1 billion (around $6.7 billion today). Unfortunately for the Grand Tour Program, it had to compete for budget with another program that would go on to define NASA and space travel – the Space Shuttle Program. In December 1971, the decision was taken to cancel the Grand Tour and instead send only two probes that would be part of the existing Mariner series.
The Mariner Program had already achieved several notable successes. The first flybys of Mercury, Venus and Mars and also the first to successfully photograph Mars as well as performing the first gravity assist manoeuvre in space.
The ten mission series came at a cost of $554 million ($3.7 billion today) and once the Grand Tour was cancelled, the anticipated probe that would venture towards Saturn and Jupiter became known as Mariner 11 but was later changed to Voyager 1 as its mission profile began to differ considerably from the other Mariner missions.
Around the same time, its sister mission also received a name change and became Voyager 2. Just to confuse things, Voyager 2 would blast off before Voyager 1, but because of its trajectory and mission profile, it would be overtaken by Voyager 1 while in space.
In the movies we see great hulking spacecraft hurtling through interstellar space but we’re still a long way from that. Voyager 1 is relatively small, especially in comparison to more recent manned flights.
Voyager 1 weighs just 825.5 kg (1,820 lb) and is the shape of a decahedral bus, measuring 47 cm (1.5ft) in height and 1.78 metres (5.8ft) across. There is a 3.6 metres (11.8 ft) diameter parabolic high-gain antenna mounted on the top of the probe, while many of the scientific instruments onboard are located on a boom that extends 2.5 metres (8.2 ft) from the probe.
Located along this boom are the plasma and charged particle detectors with a steerable scan platform at the tip along with the imaging and spectroscopic remote sensing instruments.
A second boom extending out 13 metres (42.6 ft) from Voyager 1 houses the magnetometers while the third boom, which points down and away from the other scientific instruments has the spacecraft’s three radioisotope thermoelectric generators (RTGs). These RTGs are what powers Voyager 1 and each contains 24 pressed plutonium-238 oxide spheres. As of April 2021, Voyager 1 has 70.86% of the plutonium-238 that it had at launch and by 2050 that will be down to roughly half. By 2110, it will have 27.58% left and by 2167 it’s estimated that its plutonium reserve will run out. So basically as long as Voyager 1 doesn’t hit anything, it’s going to outlast us all. Lastly are two 10 metres whip antennas, each perpendicular to the other, used for the plasma wave and planetary radio astronomy investigations.
At the time of launch, the entire system generated just 470 Watts – equal to a low-end vacuum cleaner – but this has reduced even further over time and NASA now says Voyager 1 is running on 249 Watts. The probe is always transmitting and uses a 22.4-Watt transmitter (that’s the same kind of wattage as a fridge lightbulb) to send back information to Earth. But the distances are now so fast that by the time it reaches Earth, its strength has been reduced to 0.1 billion-billionth of a Watt and NASA needs to use the largest antennas at its disposal just to read the data.
Communications to and from Voyager 1 go through the Deep Space Network station on Earth, a series of three U.S communications facilities based in California, Spain and Australia. Information coming back from Voyager 1 is normally sent on either 2.3 GHz or 8.4 GHz frequency, while data sent out to it is sent at 2.1 GHz. At the moment, signals going to or coming from Voyager 1 take around 20 hours to reach earth.
Onboard are two cameras, a 200 mm focal length, low-resolution wide-angle camera, used primarily for spatially extended imaging, and a 1500 mm high-resolution narrow-angle camera.
Voyager 1 was launched on the back of Titan IIIE rocket on 5th September 1977, sixteen days after Voyager 2 left Earth but neither launch went exactly to plan. Voyager 2 experienced severe computer problems that nearly curtailed the entire mission. It’s thought that the probe experienced robotic “vertigo” in which it struggled to orientate itself correctly and even separated too early from its final stage booster. It was a nervy few minutes, but eventually, Voyager 2 managed to correct itself and roared off towards Jupiter.
With the Voyager 1 hot on the heels of Voyager 2, NASA engineers raced to address the computer issues that had almost been disastrous for the first probe. But as you would have it, the computer was the least of their worries.
A fuel leak in the Titan rocket meant that the second stage booster ran out before its scheduled cut out time, in response, the final stage, known as the Centaur, located on the space probe itself, began firing earlier than planned to counteract the loss. Voyager 1 was in a desperate race against time to get onto its Jupiter trajectory before its booster fuel ran out, and for many on the ground, it appeared as if the probe was about to fall just short. But as I’m sure you can guess what happened considering we’re still talking about Voyager 1. With just 3.5 seconds worth of thrust remaining, Voyager 1 made it onto its correct trajectory. The Centaur stage had effectively saved the day, and like its sister ship, Voyager 1 began heading for the largest planet in our Solar System.
On 19th December 1977, Voyager 1 overtook Voyager 2 within the massive asteroid field that separates us and Jupiter. To give you a good idea of the size of the asteroid belt, it would be almost another year until the space probe sped clear.
In January 1979 Voyager 1 neared the colossal planet Jupiter and immediately began photographing it. This was by no means the first images beamed back of the great ringed planet, with Pioneer 10 having sent back grainy images of Jupiter in 1973, but what came back from Voyager 1 was astonishing.
During its closest approach on 5th March 1979, at a distance of about 349,000 kilometres (217,000 miles), the most detailed images of the surface of Jupiter we’ve ever seen began to emerge. Along with this were countless images of many of Jupiter’s moons, including two new discoveries Thebe and Metis. Some of the most remarkable images came from the moon Io, which revealed a ferocious amount of volcanic activity and it is now regarded as the most geologically active object in the Solar System.
But like any grand tour, the time came to bid farewell to the Jovian (Jupiter) system in April 1979 and after successfully performing a boost to set it on a gravitational assist trajectory, Voyager 1 set its sights on the next mega planet – Saturn.
The space probe reached Saturn in November 1980 and was at its closest on 12th November when it came within 124,000 kilometres (77,000 miles) of the planet. Once again, the images and data sent back from Voyager were mesmerizing with pictures of Saturn’s rings revealing complex structures inside, composed mostly of water ice, with some pieces estimated to be anywhere between 10 metres (32.8ft) and 1 kilometre (0.6 miles) in thickness.
Voyager 1 revealed that Saturn’s helium content in the upper atmosphere was 7%, compared to 11% on Jupiter while also showing the presence of strong winds that typically blew eastward. It also found aurora-like ultraviolet emissions of hydrogen located in both the polar regions of the planet and mid-latitudes also – a fact that continues to puzzle scientists because similar events on Earth only happen at high latitudes.
Apart from Saturn itself, another huge event was the flyby of the planet’s largest moon, Titan. This had in fact been chosen instead of a flyby of Pluto because of the appearance of gravity on Titan and that it may even be one of the more inhabitable places in the Solar System. Unfortunately, a thick haze swirling around Titan prevented detailed images of the surface from being taken, but nonetheless, readings from scientific instruments onboard lead to increased speculation that lakes of liquid hydrocarbons could exist on the surface.
As Voyager 1 blasted clear of Saturn, it had effectively completed its mission. The analysis of the two giant planets had been a huge success, now, all that was left was to continue you on until its power ran out and Voyager 1 finally fell silent.
But that was nearly 40 years ago now and still Voyager 1 creeps on. In 1990, as it neared the extremities of our Solar System, the space probe turned in space and took a series of pictures that have come to be known as the family portrait. The picture is actually 60 separate images in a mosaic, with Venus, Earth, Jupiter, Saturn, Uranus and Neptune all present, along with the distant Sun. This is also where the famous Pale Blue Dot image of the Earth comes from and was taken 6 billion kilometres (3.7 billion miles) from our planet.
On 17th February 1998, Voyager 1 overtook another object from Earth, Pioneer 11, to become the furthest man-made object from Earth. As the next millennium began to progress, the next question was, when exactly would it become the first object to leave our Solar System?
Things get complicated when we’re talking about distances so impossibly difficult to comprehend. But when we think about the Solar System, we need to imagine a bubble around us, which we call the heliosphere. Essentially, this is a cavity in space caused by the sun and the plasma coming from it. Radiation levels are very different inside and outside the bubble as is the presence of solar wind coming from the sun.
Towards the edge of this bubble is an area known as the Termination Shock, the point where solar winds slow considerably and where the heliosheath begins, a transitional area where our Solar System meets true interstellar space.
Voyager 1 entered the Termination Shock in February 2003 but this was not fully confirmed until several years later and by the end of 2011, those back on Earth knew that Voyager 1 was approaching the very edges of the Solar System and was now travelling through an area named, somewhat appropriately, Cosmic Purgatory.
It was not until the summer of 2013, that NASA revealed that Voyager 1 had passed through the heliopause region and was now travelling through the interstellar medium. It was showing significant changes in the charged particles in space, most of which are normally affected by solar winds coming from the sun, along with an 80 fold increase in electron density.
In 2017, NASA fired up the four trajectory correction manoeuvre thrusters for the first time since 1980, a quite remarkable fact considering they hadn’t been used in 37 years. This boost enabled the Voyager 1 team to keep the antenna pointed back towards Earth and should enable communication for the next few years.
But as I mentioned earlier, when Voyager 1 ceases communication, that won’t be the end – far from it. Even after its power supply runs out, the probe will continue through space, destined to wander aimlessly for eternity or until something hits it. We expect it to reach the Oort Cloud, a massive grouping of icy objects in space, in around 300 years and from there it’ll take only around 30,000 years to pass through it. Add another 10,000 years on to that, and Voyager 1 should pass relatively close to a sun named AC +79 3888.
Long after all of us are gone, and either we’ve saved the planet or completely destroyed it, Voyager 1 will continue to travel through interstellar space. The greatest journey that any man-made object has ever undertaken, is really only just getting started.