Destination Mars E-Book

Andrew May

• Herausgeber: Icon Books
• Kategorie: Wissenschaft und neue Technologien
• Serie: Hot Science
• Sprache: Englisch
• Veröffentlichungsjahr: 2017

Seitenzahl: 223

Beschreibung

Mars is back. Suddenly everyone – from Elon Musk to Ridley Scott to Donald Trump – is talking about going to the Red Planet. When the Apollo astronauts walked on the Moon in 1969, many people imagined Mars would be next. However NASA's Viking 1, which landed in 1976, was just a robot. The much-anticipated crewed mission failed to materialise, defeated by a combination of technological and political challenges. Four decades after Viking and almost half a century after Apollo technology has improved beyond recognition – as has politics. As private ventures like SpaceX seize centre stage from NASA, Mars has undergone a seismic shift – it's become the prime destination for future human expansion and colonisation. But what's it really like on Mars, and why should anyone want to go there? How do you get there and what are the risks? Astrophysicist and science writer Andrew May answers these questions and more, as he traces the history of our fascination with the Red Planet.

Leseprobe

DESTINATIONMARS

DESTINATIONMARS

The Story of Our Quest toConquer the Red Planet

ANDREW MAY

CONTENTS

Preface: From Science Fiction to Science Fact

1   The Lure of the Red Planet

2   How to Get to Mars

3   Martian Robots

4   From a Small Step to a Giant Leap

5   Big Plans

6   Private Enterprise

7   Living on Mars

8   The New Space Race

Recommended Resources

List of Abbreviations

Index

PREFACE: FROM SCIENCE FICTION TO SCIENCE FACT

It’s the year 2031. The six astronauts making up the crew of Ares 1 blast off into Earth orbit, where they proceed to link up with the recently completed Hermes Mars transit vehicle. Looking like a small-scale version of the ISS – the International Space Station – Hermes boasts something the ISS never had: a nuclear-powered ion engine. Nothing like as powerful as the chemical rocket that lifted the crew off the Earth’s surface, this is only capable of producing a tiny acceleration … but it’s an acceleration that can be kept up for months on end. That’s enough to take Hermes all the way to Mars, putting it safely into orbit around the Red Planet later the same year.

All six crew members transfer to the small Mars descent vehicle, which takes them down to the surface. After entering the thin Martian atmosphere, their descent is slowed first by a large parachute – like a Soyuz space capsule returning to Earth – and then by a powerful downward-pointing rocket engine, like a scaled-up version of the one on the Apollo lunar lander. The Ares 1 crew don’t just land anywhere, but in a carefully prepared spot. A series of earlier, uncrewed missions has already delivered everything they need for their 30-day stay, including a pressurised habitat with food, air and water, two surface rovers and a variety of scientific instruments. Most important of all, ready and waiting for them when they arrive is the Mars ascent vehicle, which has been busy making fuel for the trip back up to Hermes by mixing hydrogen with carbon dioxide from the Martian atmosphere.

This first human journey to Mars passes without a hitch, and the Ares 1 crew return safely to Earth – to be followed two years later by Ares 2 on a similar mission. Then after another two years … well, perhaps Ares 3 won’t go quite according to plan. It doesn’t in Andy Weir’s 2014 novel The Martian, which was turned into a blockbuster movie by Ridley Scott the following year. That’s the source of the scenario that’s just been described – and for Weir and Scott it serves to set up one of the most exciting survival stories of modern times. But is it really just fiction?

Most of the technology portrayed in The Martian already exists. The Saturn V rocket of the 1960s could lift more than a hundred tonnes of payload into Earth orbit, and there are several launchers in development which will be able to match that. The 400-tonne ISS shows that it’s possible to build large-scale structures in Earth orbit – and that humans can safely live and work in space for a year or more.

The huge, nuclear-powered Hermes spaceship seen in the movie is far more sophisticated than it needs to be (for a trip to Mars, that is – it’s about right for a Hollywood blockbuster). The issue here, though, is one of unnecessary cost and extravagance rather than lack of technological feasibility. It would certainly be possible, for example, to produce artificial gravity by rotating parts of the spacecraft – but whether that’s necessary or cost-effective, on a mission designed to last little more than a year, is a different matter. Similarly, the ‘ion drive’ propulsion system – identified in the novel as being of the VASIMR (Variable Specific Impulse Magnetoplasma Rocket*) type – is technically feasible, and the subject of current research, but it’s probably unnecessary. Conventional rockets should be able to do the job well enough.

The crew-carrying Hermes would be preceded by various supplies sent in advance – robotic missions of the kind that are already routinely sent to Mars whenever a launch window opens up. This ‘split-mission’ approach was promoted in the 1990s by aerospace engineer Robert Zubrin, under the title Mars Direct – which also included the idea of in situ fuel production, as portrayed in The Martian. With various permutations, Zubrin’s basic mission architecture is echoed in most current proposals for the human exploration of Mars, whether from government agencies like NASA or from private companies like Elon Musk’s SpaceX – and of course in fictional portrayals like The Martian.

So a journey to Mars is technically feasible – but is it going to happen in the next 20 years? During the 1960s, many people were confident there would be humans on Mars before the end of the 20th century. Sadly, that didn’t happen, for a variety of reasons, ranging from money and politics to conflicting priorities within the space and science communities. Despite that, progress has been made. We’ve got the football-field-sized ISS, maintaining a continuous human presence in space since the first year of this century. We’ve seen NASA put the Curiosity rover – a mobile science laboratory the size of a small city car – on to the surface of Mars, and then drive it up the side of a mountain. And we’ve heard big-business entrepreneurs like Musk making bullish predictions about reaching the Red Planet on private funds alone. The race to Mars may have had a slow start, but it’s definitely hotting up now …

__________

* A list of abbreviations is included at the end of the book (see page 155).

THE LURE OF THE RED PLANET

1

Our Solar System neighbour

May we attribute to the colour of the herbage and plants, which no doubt clothe the plains of Mars, the characteristic hue of that planet, which is noticeable by the naked eye, and which led the ancients to personify it as a warrior? Are the meadows, the forests, and the fields, on Mars, all red? … The land cannot be all over bare of vegetation, like the sands of the Sahara. It is very probably covered with a vegetation of some kind, and, as the only colour we perceive on Mars’s terra firma is red, we conclude that Martian vegetation is of that colour.

So wrote the French astronomer Camille Flammarion in 1873. That was a time when telescope technology had just got to the point of discerning a few surface features on the Red Planet – and people like Flammarion let their imaginations run wild. Their writings sparked a worldwide surge of interest in Mars, and before long its alleged ‘red vegetation’ was joined by a complex system of artificial canals and malevolent bug-eyed monsters. It was just the latest phase in humanity’s fascination with the Red Planet, which stretches back to antiquity.

Mars is one of Earth’s closest neighbours in space, the next planet out from the Sun. Before the invention of the telescope, it was one of just five planets that could be seen in the night sky. The others are Mercury and Venus, both orbiting closer to the Sun than Earth, and Jupiter and Saturn out beyond Mars. Only Venus ever gets closer to the Earth than Mars.

The Earth’s orbit takes it all the way round the Sun once a year. The orbit isn’t a perfect circle, but it’s close enough, with an average radius of about 150 million kilometres. For convenience, this distance is sometimes referred to as an ‘astronomical unit’, or AU, to make it easier to compare distances within the Solar System. Venus, for example, travels around the Sun on a near-circular orbit of 0.72 AU radius, so its closest approach to Earth is just 0.28 AU, or about 42 million kilometres.

The situation with Mars is more complicated. Its orbit is distinctly non-circular – an oval shape called an ellipse. Its distance to the Sun at perihelion, or closest approach, is only about four-fifths of that at aphelion, the furthest point of its orbit. Actually, all the planets move on elliptical orbits – that’s Kepler’s first law of planetary motion – but in the case of Earth and Venus, perihelion is only slightly closer to the Sun than aphelion.

On average, Mars is about 50 per cent further from the Sun than Earth. It also takes significantly longer to complete an orbit, following the third of Kepler’s laws which states that a planet’s orbital period increases with its distance from the Sun. A Martian ‘year’ is 687 days long, or just a few weeks short of two Earth years. During this time, the distance between Mars and the Sun varies between 1.38 AU at perihelion and 1.67 AU at aphelion.

Due to a combination of its orbital eccentricity and lack of synchronisation between the Martian year and our own, the distance to Mars – and hence its appearance in the skies of Earth – fluctuates enormously over time. There are two technical terms that help with a discussion of this: conjunction and opposition. While amateur astronomers will be familiar with these words, outsiders should note that the way they are used in this context is counterintuitive in the extreme.

Naively you might think that ‘conjunction’ refers to the point in their orbits when Earth and Mars are closest to each other, on the same side of the Sun, while ‘opposition’ means they are as far apart as possible, on opposite sides of the Sun. Unfortunately, it’s the other way around. This may sound crazy, but there’s an obscure kind of logic to it. The terms go back to ancient times, when everyone thought the Sun and all the planets moved in circles around a stationary Earth. In this model, ‘conjunction’ means that Mars and the Sun are close to each other on the same side of the Earth, while ‘opposition’ means they are on opposite sides of the Earth.

Opposition is the best time for observing Mars, because it’s closer to Earth and thus appears larger and brighter than usual. Oppositions occur roughly every 25 or 26 months. Even at opposition, however, the distance to Mars can vary considerably depending on whether it’s near perihelion or aphelion. The very best observing opportunities occur at perihelion opposition, when Mars is just 0.38 AU from Earth, or approximately 56 million kilometres. Oppositions of this type only come round once every 15 to 17 years – the best-case scenario from an observer’s point of view. At the opposite extreme, the worst-case scenario is aphelion conjunction, when Mars is a very distant 2.67 AU from Earth – 400 million kilometres.

The distance between Earth and Mars varies between two extremes as the planets orbit around the Sun.

It’s only since the invention of telescopes that people have been able to see Mars clearly, even at close opposition. Before that it was just another small point of light in the sky, not too different from a bright star or one of the other planets. Even in those days, however, there was something special about Mars. It has a distinctly reddish colour, and the enormous fluctuations in its brightness – between conjunction and opposition, and between perihelion and aphelion – were a baffling mystery to cultures that believed the Earth was the centre of the universe, and that everything in the heavens ought to be perfect and unchangeable. To the ancients, Mars was a symbol of violence and conflict – even our modern name for the planet comes from the Roman god of war – and at one time a bright perihelion opposition was considered a portent of bloodshed to come.

The invention of the telescope in the 17th century did nothing to diminish the fascination with Mars. In fact, it made the Red Planet look even more intriguing, particularly when compared to its Solar System neighbours. Telescopes revealed Mercury to be a small, rocky world like the Moon. Venus, although similar in size to the Earth, is shrouded in thick clouds suggestive of a crushingly dense – and hellishly hot – atmosphere. The outer planets Jupiter and Saturn are huge balls of gas – as are Uranus and Neptune, which are so far away they weren’t even discovered until the advent of the telescope. From a human point of view, none of those planets could be described as inviting. But Mars is different.

Viewed through a telescope, Mars resembles a smaller- scale version of our own planet, with a radius of 3,390 km compared to Earth’s 6,370 km. Because it’s further from the Sun, it receives less of its light; at its brightest, Martian sunlight is about half the intensity of that on Earth. But the length of a Martian ‘day’ is almost the same as one on Earth: Mars rotates on its axis once every 24 hours and 39 minutes. To avoid confusion with 24-hour Earth days, astronomers call the Martian day a ‘sol’.

Topographically, Mars resembles a dryer version of Earth. Its surface features are only hazily visible through a terrestrial telescope, but they give a desert-like impression. It’s clear, too, that Mars has an atmosphere – though thinner than that of Earth. The actual density and composition of the Martian atmosphere remained a mystery until the first space probes visited the planet. But even through Earthbound telescopes, astronomers could see that Mars has its own weather – from the occasional wispy cloud to huge dust storms. Like Earth, Mars has ice caps at the north and south poles – although once again, a proper understanding of these had to wait until the space age.

Another Earth-like feature that can be observed on Mars is its regular seasonal cycle. The Earth’s seasons come about because its axis of rotation (once every 24 hours) is tilted at 23 degrees relative to its orbit round the Sun (which takes 365 days). Around June, the northern hemisphere is tilted towards the Sun, producing summer in the north and winter in the south. In December the situation is reversed, with winter in the north and summer in the south.

Mars has an axial tilt of 25 degrees, close to that of Earth, so it exhibits a similar cycle of seasons. They’re roughly twice as long as Earth seasons, because the Martian year is longer – 687 Earth days, or 669 Martian sols. There’s another difference too, caused by the greater ellipticity of Mars’s orbit. Perihelion – the closest approach to the Sun – occurs during southern summer and northern winter, while aphelion occurs during southern winter and northern summer. This means that seasonal variations are more pronounced in the southern hemisphere, which tends to have hotter summers and colder winters than the northern hemisphere.

Mars’s seasonal variations can be seen from Earth with the aid of a telescope. They’re reflected in the expansion and contraction of the ice caps – particularly the southern one – and in changes in the colouring of surface features. In particular, dark areas can be seen to spread out during summer and shrink back in winter. When astronomers first observed this phenomenon in the 19th century, some of them wondered if they were seeing seasonal changes in native Martian vegetation. This led to one of the most intriguing speculations of the telescopic age: is there life on Mars?

Comparison of key data for Earth and Mars

Earth

Mars

Radius (km)

6,370

3,390

Surface gravity (g)

1

0.4

Solar irradiance (watts per square metre)

1,360

590

Atmospheric pressure (kilopascals)

101

0.6

Perihelion distance to Sun (AU)

0.98

1.38

Aphelion distance to Sun (AU)

1.02

1.67

Length of year (days)

365

687

Length of day (hours)

24

24.6

Axial tilt (degrees)

23

25

Another Earth?

The year 1877 saw a perihelion opposition of Mars, when the Red Planet was just 56 million kilometres from Earth. This rare opportunity was seized on by an Italian astronomer named Giovanni Schiaparelli, who made detailed observations of the Martian surface. Like all astronomers of the time, he recorded his findings by drawing what he saw through the eyepiece of his telescope. Photography was still in its infancy, and it would be well into the 20th century before cameras were considered reliable enough to be used for professional astronomical work.

Among other surface features, Schiaparelli drew a complex network of straight lines, which he referred to by the Italian word canali. Translated into English, this can either mean ‘channels’ – implying a natural phenomenon – or ‘canals’, implying an artificial one. Schiaparelli was probably using the word in the first sense, but English-language accounts of his work preferred the more evocative term ‘canals’.

A detailed map of Mars showing its supposed ‘canals’, produced by Schiaparelli in 1888.

One person who took the idea of Martian canals to heart was the French astronomer Flammarion, who – as described at the start of this chapter – already had a fanciful notion of the Red Planet. Even more ardent was the American Percival Lowell, who made detailed maps of the canals over a period of years, including during the perihelion opposition of 1892. Lowell was convinced the Martian canals were artificial constructions – the work of intelligent creatures who were battling to bring water from the seasonally melting ice caps to the increasingly arid Martian desert. Lowell promoted this view in a series of popular works, starting in 1895 with a book simply titled Mars.

The idea of Martian canals was always controversial – not just because it implied the existence of intelligent creatures on Mars, but also because only a handful of people claimed to be able to see them. Many astronomers, looking through telescopes just as good as Schiaparelli’s and Lowell’s, couldn’t see any linear features at all. The matter came to a head at the next perihelion opposition in 1909, when the French astronomer Eugène Antoniadi made the most detailed drawings of Mars to date. There were no canals in Antoniadi’s drawings, and he suggested they were nothing but an optical illusion – aided no doubt by wishful thinking:

The more or less rectilinear, single or double canals of Schiaparelli do not exist as canals or as geometrical patterns; but they have a basis of reality, because on the sites of each of them the surface of the planet shows an irregular streak, or else a broken, greyish border.

That should have been the end of it – and for most professional astronomers, it was. But for the public at large, Martian canals retained a fascination which persisted until space probes established their non-existence beyond any doubt. The canals’ popular appeal owed a lot to Lowell’s conception of highly intelligent creatures struggling to survive on an increasingly barren planet. The suggestion was that Martian civilisation was older and more advanced than that on Earth. As Lowell himself wrote in his 1895 book:

Quite possibly, such Martian folk are possessed of inventions of which we have not dreamed, and with them electrophones and kinetoscopes are things of a bygone past, preserved with veneration in museums as relics of the clumsy contrivances of the simple childhood of the race. Certainly what we see hints at the existence of beings who are in advance of, not behind us, in the journey of life.

Just two years after Lowell wrote these words, a new serial by H.G. Wells made its appearance in Pearson’s Magazine. It was called The War of the Worlds, and its very first pages portray a vision of Mars almost identical to Lowell’s – a dying world populated by super-intelligent Martians. But Wells goes one logical step further than Lowell. If the Martians have advanced technology, and if their planet is dying, wouldn’t they start looking for a new one to conquer? Wells’s Martians set their greedy sights on Earth, in science fiction’s first – but far from last – alien invasion story. The Martians portrayed in The War of the Worlds are hideous, tentacled, bug-eyed monsters – a striking, and disturbingly xenophobic, image that would come to dominate mass-market science fiction for decades to come.

A more positive – if less credible – picture of Mars can be found in another magazine serial 15 years after The War of the Worlds. Edgar Rice Burroughs’s novel A Princess of Mars began to appear in All-Story Magazine in February 1912. It’s the first in what turned out to be a long series of novels, like the same author’s better known stories about the jungle hero Tarzan. The Tarzan books may be far-fetched, but the Barsoom novels put them in the shade. ‘Barsoom’ is the Martians’ own name for Mars, as the hero of the first book, John Carter, discovers when he travels there. He doesn’t need a spaceship to do that – he simply finds himself teleported to the Red Planet by mystical means. On arrival, he discovers the air is thin but breathable, and Martian topography is much like the American south-west.

During his adventures on Mars, Carter encounters numerous intelligent species, all of them humanoid (unlike Wells’s tentacled monsters) – and some virtually indistinguishable from Homo sapiens. So indistinguishable, in fact, that Carter eventually marries the eponymous ‘Princess of Mars’. Preposterous as it is on the face of it, Burroughs’s vision of Mars has one significant feature in common with those of Lowell and Wells – he portrays Mars as a dying world that has seen better days. As the Princess explains in the first novel: ‘Were it not for our labours and the fruits of our scientific operations there would not be enough air or water on Mars to support a single human life’.

Credit for the first ‘hard’ science-fictional treatment of Mars – i.e., in which the science is as painstakingly accurate as the exigencies of the story allow – is usually given to Stanley G. Weinbaum’s short story ‘A Martian Odyssey’, published in Wonder Stories in July 1934. This deals with the first trip to Mars – not by mystical teleportation, as in A Princess of Mars, but by nuclear powered rocket – as in The Martian. And just like Project Ares in The Martian, Weinbaum’s rocket is called Ares, after the Greek god of war (and counterpart to the Roman god Mars). For modern readers, Weinbaum’s description of Mars may come across as full of errors, but it was perfectly respectable in terms of the scientific knowledge of the time. The planet is portrayed as a cold, desert-like place with thin air, which is breathable after special training – not unlike the highest mountains on Earth.

The hero of ‘A Martian Odyssey’ meets a variety of life forms, all of which reveal a different approach to alien-creation compared to Weinbaum’s predecessors. Where Wells thought ‘I want to create Martians that are going to invade Earth’, and Burroughs thought ‘I want to create a beautiful princess that my hero can fall in love with’, Weinbaum thought ‘I want to create aliens that might have evolved on the planet Mars as it’s depicted in factual science books’.

As a result, Weinbaum’s Martians really are alien – with no points of similarity to anything that’s evolved on Earth, no interest in conquering humanity … and certainly no desire to mate with the protagonist. Perhaps for this reason, ‘A Martian Odyssey’ made far less impact on the public than either The War of the Worlds or A Princess of Mars, and it’s barely remembered today. Nevertheless, the story played an important role in inspiring a new generation of hard science fiction writers, including Isaac Asimov and Arthur C. Clarke.

Clarke went on to produce his own fictional account of the Red Planet – a novel called The Sands of Mars. It appeared in 1951, when Clarke was serving as chairman of the British Interplanetary Society. As such, he was as well-informed as anyone at the time, both about planetary science and about the practicalities of space travel.

The protagonist of The Sands of Mars travels to Mars in a nuclear-powered spaceship called Ares – just like ‘A Martian Odyssey’ before it and The Martian 60 years later. Clarke portrays the Martian atmosphere as ‘thinner than above the peak of Everest’ – requiring the use of a breathing mask but not a full pressure suit. Clarke’s Mars is an almost barren desert, with sparse vegetation and a few simple animals. ‘Simple’ in science fiction terms, that is – meaning about the level of a grazing herbivore (to a scientist ‘simple animal’ means something like a tardigrade, which needs a microscope to see it properly).

Arthur C. Clarke did his homework. The Sands of Mars is an excellent example of hard science fiction, representing the peak of scientifically accurate portrayals of Mars … until the first space probes arrived and changed everything. At one point in the novel, Clarke confidently asserts (in italics, no less) that ‘There are no mountains on Mars’. Oh yes, there are.

The real Mars

In 1971, 20 years after The Sands of Mars, NASA’s Mariner 9 became the first spacecraft to go into orbit around the Red Planet. Over a period of several months, it sent back thousands of photographs which transformed our understanding of Martian topography. In this respect at least, it turned out that science fiction had seriously underestimated Mars. As Arthur C. Clarke wrote a few years later in his non-fiction book The View from Serendip: ‘It has the most spectacular scenery yet discovered anywhere in the universe’. As for those non-existent Martian mountains, Clarke was happy to admit he’d guessed wrong. He pointed to the example of Olympus Mons – an extinct volcano towering 22 kilometres above the surrounding terrain, about two-and-a-half times the height of Mount Everest. Olympus Mons is one of five mountains discovered by Mariner 9 that are higher than anything Earth can offer. Equally spectacular is a giant rift valley, ten times the length and four times the depth of the Grand Canyon in Arizona. It was christened Valles Marineris, after the spacecraft that discovered it.

In the 40-plus years since Mariner 9, around a dozen other robot explorers – orbiters, landers and rovers – have visited the Red Planet. Equipped with sophisticated scientific instruments in addition to cameras, they’ve sent back vast quantities of ever more detailed data. As a result, we know a lot more about Mars than we used to.

The surface of Mars is mainly composed of volcanic basalt. That’s a rock that’s found on Earth, too, but Martian basalt is particularly rich in iron oxide – or rust, to use its non-scientific name. It’s what gives the ‘Red’ Planet its distinctive orange-brown hue. Seen by robot landers on the surface, the Martian sky is a reddish colour too, caused by fine dust particles suspended in the atmosphere. Dust is one thing Mars has plenty of – most of the surface is covered with it. Being a very dry planet, the dust gets blown around a lot; huge dust storms are the most distinctive and dramatic features of Martian weather.