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Messenger spacecraft at Mercury

To boldly go: the history of space exploration

Image credit: Nasa

With further wonders of the universe still untouched, we remember the ground-breaking space missions of the past and discover how they are helping to unlock the secrets of our Solar System today.

As Nasa called out in vain to the Dawn spacecraft on All Saint’s Day in 2018, the space world held its breath. After more than a decade venturing into orbits unknown, capturing never-before-seen images and making discoveries that touch the far reaches of our Solar System, Dawn’s fuel had finally run out. Despite its muted end, the mission was an overwhelming scientific success, not merely because it represented an apex. Dawn wasn’t just 11 years in the making – the precision needed, the advanced sensors and the way its development transcended disciplines and countries was the culmination of centuries of technological advances, while the mission lived up to its name by ushering in a new dawn of space exploration.

As Nasa explains: “Each mission is part of a continuing chain of innovation. Each relies on past missions for proven technologies and contributes its own innovations to future missions.” This chain allows scientists to push the boundaries of what is possible to the point we find ourselves today – robots searching for life on Mars, 40-year-old missions journeying through interstellar space and the Parker Solar Probe ready to rendezvous with our Sun.

To put man on the Moon, Nasa required an accurate navigation system, controlled via computer. In the early 1960s, computers were so large they could occupy entire buildings, so the agency turned to emerging technology, found in the form of microchips. To fast-track its development, Nasa bought thousands of these chips, almost single-handedly kickstarting an entire industry. Over the next 10 years this technology proved critical, up to the point when Nasa’s most ambitious launch to date, the Voyager mission, made its lift-off in 1977.

Nasa had already sent probes past Venus and Mars during the 1960s. It journeyed to Jupiter twice in the early 1970s, under the Pioneer mission, and landed on the Red Planet with its Viking lander in 1976. With Voyager, the agency was aiming higher. Its two spacecraft were to journey further and deeper than any craft before, carrying the most advanced sensors made to date.

Despite its name, Voyager 2 was the first of Nasa’s twin spacecraft to launch in August 1977, 16 days before Voyager 1. It received its moniker because it would reach the mission’s destinations of Saturn and Jupiter later than its sibling. The crafts journeyed past Jupiter in January 1979, onto Saturn, Uranus and Neptune the year after, and on Valentine’s Day 1990, the last images of the mission were captured as Voyager 1 orbited 13 billion miles from the Sun.

Taking innovations from the Pioneer missions, the scope of the instruments on board Voyager was unprecedented. Its narrow- and wide-angle cameras would go on to capture the first shots of the Earth and Moon in the same frame. Its infrared and ultraviolet spectrometers revealed a treasure trove of data about planetary atmospheres, while its cosmic-ray detectors began unlocking the secrets of orbits and radiation belts. It didn’t just borrow technology from past missions, either. The knowledge gained proved equally invaluable. Pioneer 10, for instance, was the first spacecraft to fly through the asteroid belt, giving the Voyager team a wealth of data on its dangers. It captured the first images of Jupiter, providing analysis of the planet’s magnetic field, both of which assisted in the Voyager mission’s trajectories.

The photos Voyager took are still the only collection to show Venus, Earth, Saturn, Jupiter and Neptune as a ‘family portrait’ and, between them, Voyager 1 and 2 explored all the giant outer planets, their rings, magnetic fields and 48 of their moons.

In August 2012, Voyager 1 entered the interstellar medium making it the most distant, longest-serving spacecraft from Earth. Today, its 40-year-old instruments continue to send back data to Nasa scientists and this is expected to continue until 2025. Jupiter was again targeted in 2011 when Nasa turned its attention to Juno. This advanced craft took previous technologies a step further, upgrading the probe’s camera to a coloured sensor called JunoCam.

Five years after launch, in July 2016, this camera captured the first images of the planet’s north pole. Its on-board energetic particle detector was enhanced with extra foil shields to protect the instrument and, having learnt more about the planet’s magnetic field via Pioneer, Voyager and Galileo, Juno was fitted with a gravity science system to help understand how the planet formed. JunoCam has since captured stunning views from storms in the south to closeups of Jupiter’s Great Red Spot and continues to be in operation.

History

It began with Sputnik

As 1940s German and US engineers were taking V2 rockets to the boundary of space, the Soviet Union was lining up something much more dramatic. In October 1957, it launched the world’s first satellite, Sputnik, into Earth’s orbit. The launch took Western countries by such surprise, it became kindling that ignited the space age, leading to the creation of Nasa and fast-tracking the race to put man on the Moon.

Sputnik was a technological marvel of its age. Fitted with ‘whisker’ antenna and orbital trackers, this ball-sized sphere revealed the density of Earth’s atmosphere and the principles of space pressure during its short-lived, three-week mission. With haste, the US responded with the launch of Explorer 1 four months later.

Building on Sputnik’s design, the Explorer 1 satellite added a cosmic-ray detector, which led to the discovery of charged particles trapped in Earth’s magnetic field – the Van Allen Belts. All missions owe a debt to this research, without which these particles could have proved fatal to machinery and astronauts.

Lessons learned from these Jupiter missions are now being put to use for the launch of Lucy. In October 2021, when Juno plans to retire, Nasa will send this next-generation craft to a belt of unique Trojan asteroids that orbit the Sun and Jupiter. During its mission, Lucy will complete a 12-year journey, visiting seven asteroids believed to be ‘time capsules’ from the birth of our Solar System.

At the point Juno launched, Nasa had imaged seven of the then nine planets – Earth, Mars, Venus, Saturn, Jupiter, Neptune and Uranus – so the agency turned its attention to the extremes of our system. At one end, our innermost planet Mercury. At the other, Pluto.

These missions, however, posed their own challenges; Mercury’s intense heat meant its Messenger craft had to withstand extreme environments. Whereas Pluto is located 5.9 billion kilometres from Earth, 1.5 billion kilometres further than any planet Nasa had imaged at that time.

Messenger launched in 2004, entering orbit in 2011. During its four-year mission, it captured more than 250,000 images and used its seven scientific instruments to study the planet’s icy poles and magnetic crust. It deliberately plunged into Mercury’s atmosphere in 2015. The craft was protected from the planet’s raging 450°C temperatures thanks to a ceramic cloth called Nextel. This cloth was an advanced version of the material developed during the Space Shuttle missions and, it was so effective, Messenger was able to function at room temperature.

Nasa engineers fiddling with a spacecraft

Image credit: Nasa

The mission to Pluto was more complex. Launched in 2006, two years after Messenger and the same year the Astronomical Union demoted Pluto to a dwarf planet, New Horizons took nine years to reach its distant destination. Entering orbit less than two months after Mercury’s probe met its fiery end, the instruments on board New Horizons needed to meet its scientific objectives – to determine the composition of its atmosphere and study its geology – and last the distance to Pluto, past its moon Charon and onto the Kuiper Belt, a vast, mysterious region on the edge of our Solar System made up of the remnants of the early universe.

After its flyby of Pluto in July 2015, New Horizons homed in on one of these remnants, eventually making its closest approach, and making history, on New Year’s Day 2019 as it captured images of 2014 MU69, the most distant object ever explored. The mission was meant to last nine-and-a-half years, yet New Horizons is spending its 13th year journeying through the Kuiper Belt with enough fuel on board to make a third historic flyby if an appropriate target can be found.

During this time, Nasa was making a different kind of history orbiting a craft called Dawn around another dwarf planet, Ceres. Dawn launched in 2007 and became the first spacecraft to orbit an object – Vesta – in the main asteroid belt before leaving its orbit and heading to Ceres. Achieving a double orbit was an incredible feat of engineering, made possible by Dawn’s ion thrusters. By the time Dawn arrived at Ceres in 2015, it became the first craft to orbit a dwarf planet and, while in orbit, found the first signs of organic matter on such a protoplanet.

Despite ending its mission in November last year, Dawn has continued to influence missions. New Horizons may not have been possible without Dawn’s experience of dwarf planets, and members of the New Horizons team are now helping adapt the craft’s spectrometers and reconnaissance imagers ahead of the Lucy Trojan mission. Rosetta’s lander Philae may not have made its landing on Comet 67/P in 2014 without Dawn’s insight into the trajectories of space rocks, and the data Dawn obtained from Vesta has helped pave the way for OSIRIS-REx.

The key difference between Dawn and OSIRIS-REx is that while the former orbited an asteroid, the latter is finalising plans to ‘touch’ one – a near-Earth asteroid known as Bennu. Like Rosetta, OSIRIS-REx will use pinpoint precision to come into contact with a space rock as it hurtles thousands of kilometres an hour through space. Unlike Rosetta, however, OSIRIS-REx won’t land on Bennu, instead using the contact to obtain a tiny, yet significant, sample of rock. Having worked directly with the Rosetta team, OSIRIS-Rex scientists successfully guided its craft into Bennu’s orbit last year and are now surveying its surface for a sample location.

Once OSIRIS-Rex launches, Lucy will build on its successes by hiring members of the OSIRIS-REx team to adapt its thermal spectrometer for the journey to the Trojan asteroids. Beyond the scientific data it obtained, Dawn’s successful use of ion thrusters, which made it possible to escape Vesta’s orbit and enter Ceres’, is similarly likely to prove crucial in helping Lucy enter and leave multiple orbits around its target asteroids, as well as influence future supply missions to Mars.

‘Each mission is part of a continuing chain of innovation’.

Nasa

Space agencies have had a presence on the Red Planet since 1971, when the Soviet Union launched its Mars programme. Some 15 missions have successfully journeyed to, and in the majority of cases, landed on, Martian soil – alongside many missions that failed – in the decades since.

Nasa’s Mars Science Laboratory – consisting of its Opportunity and Curiosity rovers, as well as MAVEN and Odyssey orbiters – has obtained tremendous amounts of data on Mars’s atmosphere and geology. The lab’s latest addition, the InSight rover, plans to reveal what lies in Mars’s crust, mantle and core. Having landed in November 2018, InSight has already detected what scientists believe to be the first Marsquake, and its ‘mole’ heat probe has started digging into the planet’s heart ahead of the Mars 2020 rover touching down next year.

With Mars 2020, Nasa plans to launch one of the most scientifically advanced crafts in its history, with 24 sensors fitted to seven instruments. It has built on the landing technology of the Curiosity rover to improve entry and touchdown, and its tyres are more durable, have more traction and are narrower to help it climb higher than ever before. The Mars 2020 rover’s advanced microphones will capture more of the planet’s sounds, and it will be the first rover to store rock samples – like those stored by OSIRIS-REx – for future missions to analyse.

Further down the line, having explored planets, comets, asteroids and moons, our next frontier is the most dangerous yet. The Parker Solar Probe, which launched in August last year, is an ambitious mission to be humanity’s first attempt at visiting the Sun. It will spend the next six years using Venus’s gravity to propel it closer to its destination before aiming to make its closest flyby by 2026. At this point, the probe will reach speeds of 430,000mph and face temperatures of 1,377°C in its bid to solve the mysteries of its prodigious energy.

Borrowing from missions that came before – including how to survive extreme temperatures from Messenger and data from Cassini as it too used Venus gravity assists – the team has built four unique instruments, specially designed for this mission. Just as Nicolaus Copernicus posited six centuries ago, the Sun holds the key to unlocking the Solar System’s secrets. If the Parker Solar Probe achieves its lofty aims it could take the baton from Dawn and propel the next era of space exploration to the stars, literally.

Astronomy

The fathers of space exploration

Our fascination with exploring our universe began long before a rocket drawing was ever penned. After the ‘father of astronomy’, Nicolaus Copernicus, theorised our Sun was at the heart of our Solar System in the 15th century, Galileo Galilei and fellow telescope pioneers Johannes Kepler and Christiaan Huygens spent the decades that followed peering beyond the horizon, spying exploding stars, spots on the Sun and entire planets. These learnings lay the groundwork for Albert Einstein’s space-travel theories in 1905, and this sparked a fire that spent the next 50 years taking hold. Without this quartet’s work on speed, velocity, inertia and the principle of relativity, today’s rockets wouldn’t have made it through Earth’s atmosphere, let alone reached Voyager 1’s record-breaking distance of interstellar space.

 

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