EARTH AND SPACE
Q Which is the more beautiful view from the ISS–Earth at night or Earth during the day?
A The planet is stunning–both by day and by night. During my mission some of the things I loved observing at night were thunderstorms and the aurora. During the winter months we were fortunate to witness many spectacular aurorae. This was due to an increase in solar activity, which causes charged particles from the Sun to penetrate Earth’s magnetic field and collide with atoms and molecules in our atmosphere. The result was a magnificent display of eerie green-and-red streaks of light that would snake beneath the space station or dance on the horizon.
At night, thunderstorms viewed from space were particularly impressive, too. On Earth, we only ever get to witness storms within our immediate local area of perhaps 50 or 60 km. From space, you can see entire storm fronts, stretching hundreds of kilometres. What’s remarkable is the sheer quantity of lightning strikes that are occurring at any one time within a storm system. I remember seeing one storm front that stretched for several hundred kilometres along the coast of South Africa. The lightning was so intense that it resembled a strobe light continuously illuminating the night sky.
Also at night-time we get to see cities illuminated and signs of human habitation. Whilst this may look very beautiful from space, it’s a reminder of just how much light pollution is caused by some of the vast urban areas of the world. By daytime it is much harder to pick out signs of human habitation. Instead we see the vast geological features of Earth, spanning entire continents and sculpted by four and a half billion years of nature’s slow but steady grind. Some of the least-known regions of our planet make for the most stunning vistas from space: the volcanoes of Kamchatka, the glaciers of Patagonia, the dunes of the Sahara and the remote mountains of Kazakhstan and China all spring to mind.
There is certainly no denying the beauty of planet Earth. If I had to choose, I would say that Earth is most stunning by day. It really is a blue jewel, an oasis of life that shines out in stark contrast against the black void of space. I can only imagine that for those who have ventured farther out into space, such as the Apollo astronauts who went to the Moon, that view of ‘home’ must have felt even more precious.
This chapter is devoted to our home planet and the unique perspective gained by viewing it from space. But it is also devoted to the other view from the Cupola window–the vast inky vacuum, and the shimmering panorama of stars and planets that may one day be our new home. In order to survive in both of these environments we must learn to respect and protect them. And to do that, we need to understand the remarkable science that underpins it all.
Q Can you see Earth’s atmosphere from the space station–and what’s it like?
A Yes, we can see Earth’s atmosphere from space. However, what struck me when I first saw the atmosphere was not the same feeling of serenity, awe and wonder that I experienced when looking down on the planet for the first time. Instead I remember thinking, ‘Is that it? You’ve got to be kidding me! Life on Earth owes its existence to that thin strip of gas and… it’s tiny.’ Earth’s atmosphere is really thin–if you imagine the planet as the size of a football, then the atmosphere is as thick as a sheet of paper. Most of the air is contained in a band only 16 km high. That’s not even halfway across the English Channel from Dover to Calais!
To see the atmosphere in daytime, we have to look to the horizon where the curvature of Earth meets the blackness of space. Earth’s atmosphere appears as a very thin band that looks white against Earth’s surface, then gradually becomes light blue, dark blue and finally mixes with the black of space. The colours that we see are caused by the scattering of sunlight off the molecules of the atmosphere, called ‘Rayleigh scattering’. If we look straight down or obliquely onto the planet, then we don’t see the atmosphere–we just see the natural colours of Earth’s surface. But we can also see clouds, weather systems, volcanic ash and sandstorms, which constantly remind us that there’s a very active atmosphere down below. I was surprised one day, looking out over the Mediterranean, to see an enormous sandstorm stretching from the Sahara Desert across into southern France, Spain and Portugal. I watched as we moved around Earth and could see, when the sandstorm was on the horizon, how that part of the atmosphere appeared hazy with an orange hue, as the Sun reflected off the fine particles of sand.
At night we can only see the very top of the atmosphere. This appears as a thin greenish-orange strip of light and I was able to capture it in several photographs. This visual effect is called ‘airglow’ and is caused by a faint emission of light in the upper part of the atmosphere. Various processes create this emission, such as luminescence (caused by cosmic rays striking the atmosphere), chemiluminescence (caused by oxygen and nitrogen reacting with ions) and the recombination of atoms photoionised by the Sun during the day. Because this ‘airglow’ effect takes place in the upper part of atmosphere, when we see Earth’s atmosphere at night it appears thicker than it does by day.
So, yes, we can see Earth’s atmosphere–it is beautiful, but also incredibly thin and fragile; we’d do well to look after that precious band of life-supporting gas.
Q Which destinations would you now like to visit for the first time on Earth, having seen them from up in space?–Anonymous
A I’ve been fortunate to visit many beautiful places on Earth. I must be a sucker for punishment, as I tend to prefer cold, rugged and remote landscapes for my adventures. Some of my fondest travel memories are from a three-month expedition to Alaska at the age of 19, with a charity called Operation Raleigh (now Raleigh International). This is a sustainable development charity that works in remote rural areas to help communities manage natural resources, improve access to safe water and sanitation and protect vulnerable environments. In addition to their invaluable contribution to remote communities and the environment, Raleigh expeditions provide volunteers with amazing opportunities to build self-confidence and leadership through adventure and scientific exploration. Alaska certainly left a lasting impression on me, and during my time in space I always made a special effort when we passed the Aleutian Islands to grab a camera, head to the Cupola window and marvel at the striking beauty of Alaska’s mountains, glaciers and rugged coastline. Each time was like taking a trip down memory lane.
Perhaps that teenage encounter with the great outdoors will go some way to explaining this list of places that I would now love to visit, having seen them from space (see photographs 31–34):
• The Andes, South America
• The volcanoes of the Kamchatka Peninsula, in the Russian Far East
• Nam Co Lake, China. In Mongolian it is known as Tengur nuur, meaning ‘Heavenly Lake’
• Coast Mountains, British Columbia
• Lake Alakol and the Almaty province, Kazakhstan
Q Can you see aircraft or ships from space?
A It’s not easy to see small objects with the naked eye from space. An exceptionally good human eye has a visual acuity of around one arc minute (or 1/60th of a degree). By doing some calculations, you can determine that at a distance of 400 km, the smallest resolvable size for the human eye (this is like the smallest pixel size of a screen) is 116 metres. This means that for the shape of an object on Earth to be discernible from the ISS, it would have to be bigger than 116 metres. But the real answer is more complex–just because you cannot determine something’s shape doesn’t mean you can’t see it. The brightness of an object will also determine whether or not it can be seen. For example, you can look out on any clear night and see small satellites, no more than 10 metres in size, passing overhead in orbits more than 1,000 km high. This is because they are shiny and reflect sunlight at an observer.
In order to see a large container ship or even have a chance of spotting an aircraft from space, you need to know exactly where to look. One way to do this is to first pick out a ship’s wake or aircraft contrails and then follow these telltale signs back to their origin. Then, if your eyes are better than mine and are feeling particularly fresh and sharp, you might be able to make out the tiny speck of a ship or an aircraft! At night, ships will sometimes stand out as tiny, single sources of light in an otherwise black ocean–or, in the case of fishing boats in the Gulf of Thailand, they can light up vast stretches of water with their green spotlights directed into the sea. From space, this looks as if some alien life-form is emerging from the depths, as the fishermen try to lure phytoplankton, which in turn attracts squid.
Much easier, of course, is spotting aircraft or ships using one of the many telephoto camera lenses that we have on board the ISS. These lenses have varying focal lengths to choose from, which give a magnified image. Anything larger than a 400 mm lens will enable you to see aircraft or ships in photographs. I took a picture of the port of Antwerp with a 500 mm lens, and not only can you see container ships clearly, but (unbeknown to me at the time) there was an aircraft passing overhead and you can clearly make out the contrail, followed by the tiny white outline of an aircraft. We also have stabilised binoculars on the space station, which are very useful for viewing approaching spacecraft, but there are no telescopes on board.
Q In your photos of aurorae, is this how they appear to the naked eye or are the colours more intense because of the camera exposure?
A For photographing the aurora, I found that a 0.5-second exposure and a light sensitivity setting (ISO) of 6400 gave a very close image to what we were seeing with the naked eye, in terms of colour and intensity. If anything (and I hate to disappoint you here) we see a more spectacular image with the naked eye. The camera doesn’t do justice to the way the aurora eerily snakes and ripples, changing in both intensity and colour from the darkest part of the night orbit until daylight approaches.
Q Can you see stars and planets from the space station, and do they look different?
A Yes, astronauts can see stars and planets. In fact, from space we see them clearly as steady sources of light, as opposed to the ‘twinkling’ starlight that we often see on Earth. This is because turbulence in Earth’s atmosphere causes most of that ‘twinkling’, as it refracts the light in different directions and makes the stars appear slightly less clear than when viewed from space. This is the reason why you find many of the world’s observatories on mountain tops–in an attempt to reduce the amount of atmosphere through which the light has to travel. Another benefit of mountains is that there tends to be less light pollution.
Of course we have no atmosphere outside our windows in space, and it seemed to me that the planets appeared to be slightly brighter than when viewed from Earth–certainly Jupiter, Mars and Venus did. I was able to photograph Venus rising over Earth and also Jupiter, Mars and Saturn. Most of our windows look down on Earth–so although we see the planets rising and setting, it’s much harder to see them when they’re above the space station. You can see my photo of Venus rising just ahead of the Sun in the photo section (photo 30).
What’s also interesting is trying to judge the distance of objects in space. Because there is almost no atmospheric interference, objects look sharper and clearer, even at a distance. When Cygnus, a commercial cargo spacecraft, departed from the space station after a resupply trip during my mission, we had the most spectacular view of it disappearing ahead of the space station. Of course it got smaller as it got further away, but it still looked incredibly sharp-focused and well defined, despite its increasing distance from us, which made it very hard to judge exactly how far away it really was.
Q Why is it that in some pictures space looks black, with no sign of any stars or planets?–Gill Lee
The reason you can’t see stars in daytime photographs from space is that, when lit by the Sun, any foreground objects–such as Earth, the space station or my spacesuit–are many thousands of times brighter than the stars in the background. Earth is so bright that it swamps out most, if not all, of the light from stars and other planets. The stars don’t show up because the camera cannot gather enough of their light in the short exposure times that we use for daytime photographs.
Our eyes work in a similar manner. The iris adjusts the central opening of our eye (the pupil), the diameter of which determines how much light strikes the retina. In bright daylight, our pupils contract in an effort to limit the amount of light entering the eye. In space, there is no chance during daylight of our eye being able to distinguish the paltry light from distant stars against the bright glare of the Sun. This is no different from being on Earth, where we would not expect to see stars in the daytime. It’s just that in space the sky is black during the day, and this looks unusual both in photographs and to our eyes, because we are used to seeing stars against a black sky.
At night, our pupils dilate, allowing more light to enter the eye, in addition to striking more of the light-sensitive rods on the retina. This enables us to see objects that are less bright than the Sun, such as stars. You can test this concept for yourself by observing how many stars you can see on a bright night when there is a full Moon, compared to a much darker night with no Moon.
To take pictures of stars and planets from space, we need to wait until we are in Earth’s shadow and then use longer exposure times (around 1–2 seconds) in order for the camera sensor to capture sufficient starlight. Because of the longer exposure times, we need to hold the camera extremely steady or the image will be blurred. Often for night photography I would use a stabilising ‘Bogen arm’–a camera mount with a friction knob that allowed me to secure the camera at the desired angle and hold it much steadier than a human hand could manage. Some of my favourite photographs from space were taken using this method: pictures of the Milky Way rising over the horizon, or time-lapse sequences of the aurora, thunderstorms and Earth by night.
Q Did being in space, and seeing Earth from space, change your perspective on the planet and life, or do you still feel the same?
That’s a great question and one that I get asked quite a lot. In some ways coming back down to Earth from space was, for me, a bit like visiting my old primary school. As a child your world is quite insular, usually revolving around home, school, family and friends. Your experiences at school are a huge part of those early formative years, but as you grow up and slowly become exposed to life outside that small bubble, your perspective changes. There’s nothing like a visit to your old primary school to bring those early memories flooding back and to make you realise just how different your perspective of the world is today than it was then.
Going into space certainly broadens your horizons… quite literally! You get a more holistic appreciation of Earth and begin to feel strangely familiar with the planet. It may sound odd, but there are so many places that I now feel I know very well, despite never having set foot in those countries. Part of our morning routine on the ISS was to check the daily orbits to see which parts of the planet we might like to photograph that day: the Himalayas, the Bahamas, Africa, Alaska, Indonesia. As I reel off those names now I can recall the features of each location (and so many more) with astonishing clarity. I can visualise their valleys and glaciers, volcanoes and islands, mountains and rivers–all firmly etched in my memory.
When I first arrived on the space station our commander, Scott Kelly, had already been there for nine months. It was his second long-duration mission and his fourth spaceflight. I thought I was doing well when I could look out of the window and identify most of the major countries of the world. Scott floated past the window one day and casually noted, ‘Ah, there’s that nice beach on the coast of Somalia.’ I’m not sure I ever got to that level of familiarity with the planet, but after six months there were not many places that I didn’t recognise.
On the one hand, this fresh comprehension of the planet might be attributed to receiving a fairly extreme tutorial in geography. However, my experience involved far more than simply acquiring a talent for identifying locations on Earth. Seeing Earth from space gives you a sense of awareness and understanding as to our place within the solar system, the Milky Way and even the universe. Many astronauts have previously reported the same phenomenon and it has even been given a term: the ‘Overview Effect’–a cognitive shift in awareness while viewing Earth from orbit or the lunar surface. I wouldn’t dare to compare my experience of viewing Earth from 400 km with those of the Apollo astronauts, who travelled nearly 400,000 km away from Earth, to a point where the planet appeared as a minuscule disc occupying just a small fraction of a spacecraft window. But I think that both time and distance away from Earth contribute to this ‘Overview Effect’ and I certainly gained a new perspective of, and appreciation for, our small and fragile home during my time in space.
Perhaps Monty Python’s ‘Galaxy Song’ sums up this feeling better than I have been able to articulate here–if you haven’t heard it, then it’s certainly well worth a listen, to add a bit of perspective to life!
A This is a favourite question of mine and yet one of the hardest to answer. That’s because yes, space does smell… but exactly what it smells of is much harder to put your nose on.
I smelt space on a number of occasions. The first time was after just a few days on the Space Station, when I was helping astronauts Tim Kopra and Scott Kelly back in after their spacewalk. Subsequently there was a strong and distinctive smell whenever we opened the airlock after it had been exposed to the vacuum of space. I noticed the same odour each time I used the Japanese airlock, when transferring small satellites through it for launch or recovering experiments that had been outside the space station for several months.
The mystery scent is the topic of much light-hearted debate among astronauts. It has been described as seared steak, hot metal, welding fumes and barbecues, to name but a few. There are some suggestions that the smell may originate from the spacesuit itself, with certain components ‘off-gassing’, having been exposed to vacuum and thermal extremes. However, I smelt the exact same smell a couple of times inside an empty Japanese airlock following re-pressurisation. In my opinion, the smell of space is like static electricity. For example, when you take off a shirt or jumper and sometimes get a large static discharge–it has that kind of burnt metallic smell.
Actually what you’re most likely smelling with static electricity is ozone. Ozone can occur naturally when high-energy ultraviolet rays (from the Sun, lightning or static electricity) strike oxygen molecules, splitting the molecule into two single oxygen atoms. A freed oxygen atom then combines with another oxygen molecule to form O3–ozone. Although ozone is present in the lower part of the stratosphere at around 20–30 km above Earth, it is not present at 400 km, so why would we smell it in space? Well, atomic oxygen is present in space. In fact, between 160 and 560 km, what little atmosphere there is consists of about 90 per cent atomic oxygen. It’s possible that atomic oxygen is being introduced to the airlock when it is exposed to space, and on re-pressurisation it’s reacting with oxygen molecules from the space station atmosphere, thereby creating ozone.
Perhaps the most wistful theory is that the smell of space is the leftover aroma of dying stars. There’s an awful lot of combustion going on in the universe. Stars mostly comprise hydrogen and helium gas, powered by a nuclear-fusion reaction that can last for billions of years. At the end of its life, as the hydrogen fuel is used up, a star will collapse on itself and undergo a violent supernova explosion, during which heavier elements such as oxygen, carbon, gold and uranium will be produced. All this rampant combustion produces smelly compounds called ‘polycyclic aromatic hydrocarbons’. These molecules are thought to pervade the universe and float around for ever. So are we smelling the leftovers from some of the earliest stars, when we stick our nose into the airlock? Who knows.
Either way, I found it a rather pleasant smell and it reminded me a little of a British summer barbecue, burning sausages on a charcoal grill…
A Well, I’m not sure if this refers to ‘out in space’ or inside the space station, so I’ll answer both. First, it’s impossible for sound to travel through the vacuum of space. Sound waves need something to pass through, such as a solid, liquid or gas. Of course on Earth we are most used to hearing sound travelling through air. Sound is a vibration, where particles vibrate and collide with adjacent particles, propagating the sound as an audible mechanical wave. In the rarefied atmosphere of low Earth orbit, there are simply not enough particles to cause collisions and propagate the noise.
This is a pretty cool thing to witness in the vacuum of space. During a spacewalk, for example, I could knock my metal tether hook against a metal part of the space station and I would not hear a thing. The same metal-on-metal collision would cause a loud noise back on Earth. That is not to say that inside the spacesuit it is blissfully quiet. On the contrary, the spacesuit is working hard to keep you alive. This requires pumps, fans and airflow, all of which create quite a din. We wear a communications cap inside our helmet that incorporates a headset and microphone, in addition to providing some noise protection. So for astronauts working in the vacuum of space, things are not as quiet as you might imagine.
Things aren’t much better inside the space station. We don’t have to wear communications caps, but the space station does have a plethora of ventilation fans, pumps and electrical equipment, all of which contribute to a fairly noisy environment. The background noise level varies around the space station, although I didn’t really notice these variations much when floating between modules. The one exception was if someone was exercising on the treadmill. The treadmill generates a large amount of noise, as high as 85 decibels (recognised as the limit beyond which hearing protection should be worn), if someone is pushing themselves and running at high speed. To put that into perspective, most fighter pilots are exposed to about 80 decibels whilst wearing standard hearing protection inside a modern jet cockpit. To that end, astronauts exercising on the treadmill have specially moulded hearing protection that allows them to listen to some music or watch a movie/TV programme on the laptop, whilst at the same time protecting them from treadmill noise. Generally, the rest of the space station is a more comfortable 50–60 decibels (comparable to a busy office environment) and our crew quarters have additional soundproofing in the walls and doors that reduce that further, to around 45–50 decibels.
A It’s a common misconception that there is no gravity in space. In fact, gravity is everywhere! The great Sir Isaac Newton published his law of universal gravitation in 1687, supposedly after a close encounter with an apple. Newton described gravity as a force, stating that a particle attracts every other particle in the universe with a force that is directly proportional to the product of their masses, and inversely proportional to the square of the distance between them. This means that the force of attraction between two objects reduces (rather rapidly) the farther apart they are, but it never completely disappears. In this sense, gravity is the force that connects all matter in the universe.
Forces are nice, easy things to comprehend and we can understand the pull of the Sun that keeps the planets in their orbits, or the pull of Earth on the Moon. However, in 1916 another genius, Albert Einstein, complicated matters somewhat when he published his theory of general relativity. This had big implications for gravity. In essence, we now understand gravity not as a force, but rather as the curvature of space-time. Matter causes space-time to bend, warping the shape of the universe. Gravity is the effect that particles feel as they travel through this curved space-time on their journey through the universe. Newton’s law still remains an excellent approximation of the effects of gravity in most cases, but when there is a need for extreme precision, or when dealing with very strong gravitational fields, then Einstein’s relativity is required.
So you cannot travel through space without feeling the effects of gravity everywhere. On the International Space Station we are most definitely being affected by Earth’s gravity, just as we are by the Sun’s, by that of the other planets in the solar system and the supermassive black hole at the centre of the Milky Way (called Sagittarius A). Even as you read this book, the mass of your body is causing a small amount of curvature in space-time, which will be having an effect on the orbit of the ISS (admittedly, this is a rather small effect!).
The story of gravity is far from complete. Einstein’s theory of general relativity has so far stood the test of time, and now scientists are in search of things like gravitational waves and gravitons, and are musing on the concept of gravity propagating through the universe at the speed of light. However, we still don’t really know what gravity is; we only know how it behaves.
Q Why do you appear ‘weightless’ on the International Space Station?
A We appear weightless on the ISS because we are actually falling at the same rate as everything around us. Therefore if we were to try and stand on some scales in space, the scales would be falling with us and so they wouldn’t register any weight at all–great news for anyone on a diet! By travelling very fast around Earth (about 27,600 km/h), we don’t escape Earth’s gravity but instead, as we fall towards the planet, Earth curves away beneath us and we never get any closer to it. Our rate of falling exactly matches the curvature of Earth and we ‘fall’ the entire way around the planet. Since the space station and everything inside it is falling at approximately the same rate, we float and appear ‘weightless’. We call this environment ‘microgravity’.
So what would we really weigh on board the space station, if we weren’t in constant freefall around the planet? Well, let’s imagine we could build a tower 400 km high (the same altitude as the ISS) and weigh ourselves. Interestingly, we would still weigh 89 per cent of our weight on Earth–that’s certainly not weightless! This is because 400 km is really pretty close to our planet, and the gravitational acceleration we feel from Earth is still 89 per cent of what it would be if we were standing on its surface. We calculate our weight by multiplying mass by gravitational acceleration; and so since Earth’s gravitational acceleration hasn’t reduced that much at the top of our 400-km tower, our weight hasn’t changed that much, either.
Now imagine that you had taken a lift to the top of that tower. If the cable snapped and it fell back to Earth, then (if we ignored air resistance) you would be in freefall inside the lift and would enjoy the same feeling of weightlessness that astronauts do on board the space station–that is, up till the point at which you smash into the ground!
Q How do you weigh yourself in space?–Michael, aged 29
A That is a very logical question to ask, Michael–how do you weigh yourself in weightlessness? Well, in space we can’t measure our weight directly, because we are in freefall and so our weight is essentially zero. However, we can measure how much of us there is, that is… our mass. By measuring our mass, we can determine what our weight on Earth would be. To measure our mass, we used a Russian device called a Body Mass Measurement Device (BMMD), which is a bit like a pogo-stick with a compressed spring. Astronauts first curl their body around the BMMD, hold on tight and then release the spring, gently travelling up and down whilst the device measures the frequency of oscillation. By first calibrating the BMMD and by knowing the stiffness of the spring, the device can accurately determine an astronaut’s mass. We would do this three times and then average the result, although often the readings were within 0.1 kg of each other, such was the accuracy of the BMMD. Astronauts would usually ‘weigh’ themselves once every month whilst in space, a procedure fondly known as ‘riding the donkey’!
Q When you were in space, was there a risk of the ISS being hit by a meteor or piece of space junk?
Actually, the space station gets hit by very small particles of debris quite frequently. Space debris encompasses both natural debris (micrometeoroids) and artificial (man-made) debris. Micrometeoroids orbit the Sun, whilst most artificial debris orbits Earth. Most of the time these impacts have no serious effect, and the space station is well protected by special shields that cover the pressurised modules that astronauts live and work in. However, there is a risk that something larger will strike the space station and cause damage. We see evidence of this on spacewalks, usually on handrails that have been struck by space debris and have left a small impact crater, often with sharp flayed metallic edges. Astronauts have to be particularly vigilant not to slide a glove over these razor-sharp protrusions and puncture their spacesuit. One of the Cupola windows has also suffered a debris strike, resulting in a small chip in the windowpane. But whilst no one likes to wake up and find a crack in a space-station window, it’s not as bad as it looks. Each of the Cupola’s seven windows has four panes of fused silica and borosilicate glass (made from silica and boron trioxide, which makes it particularly resistant to thermal shock), with a total glass thickness of more than 7 cm, and the chip has barely penetrated the first layer.
The problem is that when objects are travelling at hypervelocity, they don’t need to be very large to cause significant damage. The chip in the Cupola was probably caused by a fleck of paint or a small metal fragment around a few thousandths of a millimetre across. So if something so tiny can cause damage to the space station, imagine what something 10 cm in diameter would do. Well, it would cause cataclysmic damage, penetrating straight through the space station with secondary effects that would shatter it into pieces.
The good news is that there are experts in Mission Control who warn us if there is a risk of collision–established as debris intruding into an imaginary pizza-box shaped ‘keep-out zone’ around the ISS (1.5 × 50 × 50 km). Some 23,000 pieces of space junk are being tracked by ground-based radar systems such as the US Space Surveillance Network and the European Space Agency’s Space Debris Office in Darmstadt, Germany. When the risk of collision is high enough, the space station has to perform a ‘Debris Avoidance Manoeuvre’ (DAM), using thrusters from the Russian segment or a docked spacecraft to change the ISS orbit and avoid an impact. But an avoidance manoeuvre usually takes around 30 hours to plan and execute. If the debris has been spotted too late for the ISS to perform a DAM, the crew will be instructed to close all hatches between the various modules and shelter in their Soyuz spacecraft until the risk of collision has passed. The latest ‘shelter-in-place’ procedure was implemented in July 2015, when the crew received just 90 minutes’ warning that a collision was possible.
The bad news is that there is a ‘black zone’ in terms of unknown risk of collision. Any object greater than 1 cm in diameter is large enough to cause catastrophic damage to the ISS and potential loss of life. This is the debris that the ISS is most at risk from, those pieces of 1–10 cm diameter that are hard to track, but highly likely to spoil your day. Using observations and computer models, it is estimated that there are 725,000 of these ‘space bullets’ between 1 and 10 cm in orbit around Earth. So, now that we know there is a risk of the space station being hit by a piece of space junk, the next question is highly relevant…
Q What would happen if the space station was hit by space debris?
A Let’s imagine a larger object, say 2 cm in diameter, hits one of the space-station modules. Our first line of defence is the Micro-Meteoroid Orbital Debris (MMOD) shields. There are many hundreds of MMOD shields protecting parts of the space station and they differ in the materials used, mass, thickness and volume. Typical defences are Whipple and ‘stuffed’ Whipple shields. The basic principle of these shields is to have an aluminium ‘bumper’, which the debris strikes first. In addition to absorbing some of the impact, the bumper is designed to break the debris into smaller pieces, which then have less chance of penetrating the pressurised hull. Ideally you want as large a gap as possible between the bumper and the hull so that the broken-up fragments are spread over a wider area. The ‘stuffed’ Whipple adds some additional ceramic cloth and Kevlar fabric into this gap–materials often used in bulletproof clothing.
The European module, Columbus, is at the front of the space station and therefore at higher risk of a debris strike. However, even with shields of greater mass and a larger standoff distance, they will not stop a 2 cm-diameter object penetrating the hull. The first thing the crew will know about this is a big ‘bang’ from a strong acoustic shock wave as the hull perforates. If a crew member is unlucky enough to be in the same module, then they may witness an intense flash of light, before being struck by bits of the inside module wall breaking off (called ‘spallation’), in addition to small fragments of the original debris. Some of these aluminium fragments burn quite actively, and the heat generated by the impact will also create a risk of fire. The perforation will typically be accompanied by rapid temperature changes and a decrease in air pressure, which can cause an internal fog. If the crew is unlucky, the perforation may be so large that a rapid crack growth occurs and the module ‘unzips’ or breaks apart completely. Such a dramatic break-up would probably be catastrophic for all crew members. However, assuming that the module maintains some sort of integrity, then the space station will begin to lose pressure, probably quite rapidly, and the crew would feel their ears ‘pop’ with the rapid change in pressure.
As a crew, we spend many hours training for a ‘rapid depressurisation’ emergency. In the scenario I’ve just described, it would be obvious to the crew which module had been struck and the most likely response would be for someone to shut the hatch immediately, sealing off that module and preventing the space station from going to vacuum. A similar situation occurred on 25 June 1997 on board the Mir space station. However, the rapid depressurisation was not the result of an impact with space debris, but of an impact with an approaching Progress resupply vehicle. Russian cosmonaut Vasily Tsibliyev had been instructed to remotely dock the cargo vehicle using a video image and a laser rangefinder. The problem was that none of the other crew members could see the Progress spacecraft through any of the windows, in order to use the rangefinder and report back its range. And without knowing how far away Progress was, it was impossible to calculate how fast it was approaching. The video image alone was useless in trying to judge the rate of closure and by the time Tsibliyev realised that the Progress was, in fact, approaching very rapidly, it was too late. Despite braking urgently, Progress collided with Mir with a great thump, rupturing the space station and knocking it into an uncontrolled spin.
Having seen the point of impact, Tsibliyev knew that it was the Spektr module that was leaking, but that module had not been readied for an easy hatch closure. It took the crew several minutes to cut the many cables that were strewn through the hatchway, until the module could finally be isolated to save the remainder of Mir. A lot was learnt from that near-disaster. Every hatch on the ISS is now designed to be closed in a matter of seconds. Normally, cables and other items are not permitted to be strewn through hatchways. Where this is unavoidable, a method of ‘quick-disconnect’ exists so that a hatch can be sealed with minimum delay.
The crew train for a rapid depressurisation in a very methodical fashion. First, having accounted for everyone and gathered in a safe haven, we work out how much time we have to deal with the problem until the pressure drop requires a complete evacuation of the space station. Then we check the integrity of the Soyuz spacecraft and try to establish which module is leaking. A slow leak may be hard to find, but by closing each hatch sequentially and monitoring to see if the pressure continues to drop or remains steady, it is possible to work our way through the entire space station until we find the leak. Of course we always work back towards our Soyuz spacecraft, being careful never to get on the wrong side of a closed hatch that would isolate us from our escape vehicle.
Q How problematic is space debris?–Thomas Santini, from Robert Gordon’s College in Aberdeen
A Space debris is a huge problem. In addition to any naturally occurring micrometeoroids, for 60 years and more than 7,000 launches humans have been littering the orbital pathways around Earth with space junk–from rocket boosters and defunct satellites to tiny fragments and flecks of paint. There are estimated to be a whopping 150 million pieces of space debris larger than 1 mm, all trapped within a few thousand kilometres of Earth’s surface. When launching satellites today, it is naïve to think that an attitude of ‘big sky, small bullets’ will prevent a significant impact from occurring–it’s simply a matter of time. On 23 August 2016, operators at the European Space Agency’s control centre in Darmstadt noticed that one of their Earth observation satellites, Sentinel 1A, had suddenly dropped electrical power and changed its orbit slightly. In just its third year of operation, this flagship satellite had been struck by debris and suffered damage to a 40 cm-wide area of the solar panel. It could have been much worse. The more we rely upon space-based assets in our day-to-day lives and for national security, the more serious the consequences of such collisions will be.
In 1978, NASA scientist Don Kessler recognised the danger posed by the high density of objects in low Earth orbit and the possibility of this creating a cascading chain reaction of collisions. Dubbed the ‘Kessler Syndrome’, the effect featured in the opening scenes of the 2013 film Gravity, as a cloud of debris destroyed a Space Shuttle and subsequently the ISS. Unfortunately the Kessler Syndrome is not just the stuff of science fiction. Half of all near-misses today are a result of debris from just two incidents. In 2007, China destroyed one of its own satellites with a ballistic missile. And in 2009, a US commercial communications satellite collided with a defunct Russian weather satellite. In spite of all this, the ISS is actually in an orbit where the amount of space debris is relatively low.
With the number of satellites in orbit looking to more than double in the next decade (to well over 18,000), this problem is only going to get worse. No single nation or entity is responsible for space. However, currently 85 countries are members of the Committee on the Peaceful Uses of Outer Space (COPUOS), set up in 1959 by the United Nations. Today various international organisations, space agencies and governments are working hard to understand the problem of space debris and make efforts to clean up space. The European Space Agency is at the forefront of developing and implementing debris-mitigation guidelines. Moreover, as part of their Clean Space initiative, ESA are planning the first-ever active debris-removal mission, e.Deorbit, with the goal of capturing a heavy ESA-owned item of debris and then destroying it in a controlled atmospheric re-entry. The US Defense Advanced Research Projects Agency (DARPA) is leading military efforts to find better ways of tracking space debris with a new ground-based 90-tonne Space Surveillance Telescope, which can track thousands of small targets and search an area larger than the size of the continental US in seconds. And since 2002, the Federal Communications Commission now requires all geostationary satellites to commit to moving to a graveyard orbit at the end of their operational life.
There is still an awful lot to do to reduce the threat posed by space debris, but doing nothing is no longer an option.
Quick-fire round:
Q How many times did you go around Earth during your flight?
A You can work this out for yourselves. First, you need to know how long I was in space–186 days. Then you need to know that the ISS orbits Earth 16 times a day; or, more precisely, 15.54 times a day. So that’s 186 × 15.54 = 2,890 orbits.
Q How far did you travel during your time in space?
A Well, distance is equal to velocity × time. We travel at 27,600 km/h. Then you need to work out how many hours there are in 186 days. The distance will be 186 × 24 x 27,600 = 123,206,400 km.
Q Can you see the Great Wall of China from space?
A Unfortunately not with the naked eye. I did try, but I couldn’t make it out. However, once you know where to look, you can of course use an 800 mm focal-length camera lens and then take a photo of the Great Wall of China. Similarly, the Pyramids are impossible to spot with the naked eye. However, you can see the Nile delta easily, which stands out against the desert like a sprig of broccoli and provides a great lead-in feature for knowing where to point the camera for that elusive Pyramid shot.
Q Is there a formal protocol for ‘first contact’ with aliens?
A This question made me laugh, although it’s a great question to ask! The short answer is, disappointingly, ‘No’. I would have loved to have sat through a briefing on what to do, should an alien life-form approach the space station but, alas, it was not forthcoming.
