Up To Boldly Go

We think of ourselves as a global species.

But our bodies can only survive unsupported

on a fraction of the Earth's surface.

We've evolved to live in a temperate climate at sea level,

yet our relentless desire to explore has pushed us higher and deeper,

to every corner of the planet.

'I'm Dr Kevin Fong.

'I study the limits the human body can endure.

'I've worked with NASA for 15 years,

'finding ways to keep people alive in orbit.

'And now I'm going to use my own body to demonstrate what happens

'when we go to the most extreme environments on our planet.'

Just stick with it.

140.

Feeling pretty heavy.

DR FONG: 'Oh, ten more miles!'

And that's gone.

'In this programme, we're going to explore what happens to us

'when we leave behind our comfortable sea-level home...'

And that's weightlessness.

'..and go up, through the atmosphere.'

We live in a very narrow layer of air

that's smeared across the surface of our planet.

It extends to only a few kilometres above sea level

and as we rise higher and higher

it becomes harder and harder to survive

and eventually, it becomes impossible.

This is the story of what happens to our bodies

as we ascend through the layers of the atmosphere

and how we developed the technology that allowed us to explore

its upper reaches,

and eventually go beyond into space.

Our natural habitat is just above sea level.

But it's not in our nature to stay here.

We've always dreamt of flying.

But ever since we first took to the air,

we've found that the higher we go, the harder it is for us to survive.

The principle of all of this really couldn't be simpler.

It hasn't changed in the best part of 250 years.

You take a bag,

you fill it with something lighter than the air around it

and it rises up into the atmosphere.

In this case, we're using heat.

You heat the air inside the balloons,

you make it lighter, less dense than the air around

and it pulls these vast structures up into the sky.

In 1783, the hot-air balloon became the first real flying machine

and ever since, we've been enchanted by their ability

to lift us effortlessly from the ground.

It's a very beautiful way to fly, really.

Apart from the occasional blast from the burner,

it's pretty silent up here.

And d'you know, you feel remarkably safe,

given that you're in a basket underneath a bag of hot air.

The balloon gave us a completely new perspective

on the world in which we live.

And crucially, it opened up a new frontier -

the air.

Pretty much as soon as people had mastered this -

this idea that you can float in the air,

in a basket, under a bag of hot air -

people started to try and push the technology and themselves.

In 1862, a pair of pioneers, James Glaisher and Henry Coxwell,

took off from Wolverhampton gasworks for a world record attempt.

They aimed to rise to the highest altitude

any humans had ever reached.

For the first 20 minutes the flight went brilliantly well.

They were two miles up,

they'd broken through that very simple boundary

that we take for granted - the clouds.

They were some of the first people to see them from above,

and now, two miles in the air,

they were in uncharted territory.

As they rose higher, it got colder...

they were expecting that.

But there was another unseen and unexpected threat.

After two hours, they were as high as the summit of Mount Everest

and that's when things rapidly started to go wrong.

At around 29,000 feet

they started to experience extreme difficulty with their breathing.

Glaisher began to lose his eyesight, he could no longer read his watch.

Shortly after that, he lost the power of his limbs,

became paralysed and slipped into unconsciousness.

Something about the altitude was causing their bodies to fail -

and they were still rising.

As their open basket reached 37,000 feet -

the height a modern airliner flies at -

it seemed certain they would die.

Coxwell too was now in trouble.

His colleague was unconscious in the basket next to him,

he was losing the power of his limbs,

and at the last moment,

he managed to pull the venting cord with his teeth.

Slowly but surely, they started to drift back down to Earth.

As they descended, escaping the lethal effects of high altitude,

they spontaneously began to recover.

They had flown higher than any other human would for nearly 80 years

and had become the first people to experience

the dangers of high altitude.

To understand what happened to those brave but foolhardy balloonists

we need to understand what happens to the body

as it rises up through the atmosphere.

And those changes start to happen remarkably close to the ground.

This is Chamonix in the heart of the Alps,

Europe's highest mountain range.

A mecca for mountain sports.

Today, the mountains are an idyllic holiday destination.

But until 150 years ago, they were regarded as a no-go zone

and treated with fear and trepidation.

Even now, three quarters of the world's population

lives below 500m

and there's a very good reason for that.

We're up here at 2,300m, looking down the Chamonix Valley.

Already, there's a very stark illustration

of how much harder life is at altitude.

The treeline there gives way to the sparse vegetation of the meadows

and as you get right up the mountain,

there's really nothing but rock and ice.

All life finds it harder

as you go higher and higher up the mountain

and that includes us.

Even at this very modest altitude, you feel much more out of breath

than you would at sea level.

And that is because the barometric pressure

has dropped by about...25% here.

And that means that every single breath I take

has fewer molecules of oxygen in it,

making the work of everything I do much harder.

It's the decreasing amount of oxygen in the air

that explains the effects of altitude on our physiology.

The higher we go, the less oxygen there is to breathe.

And with the help of a little technology,

it takes only minutes to reach altitudes

at which our bodies struggle to cope.

Here, another thousand metres higher,

the amount of oxygen in the air has dropped by a third.

And even fairly light exertion -

like running up a flight of steps -

leaves me feeling physically sick.

And it's all because my body's oxygen supply system

is feeling the strain.

As I breathe in, air rushes through my nose and mouth,

down my airways and deep into my lungs.

Here the oxygen dissolves in liquid

that lines the walls of the millions of tiny sacs called alveoli.

From here, the oxygen is picked up by red blood cells

that squeeze through the tiny vessels that surround my lungs.

Driven by the relentless beating of my heart,

those red blood cells are pumped round my body

where they release the oxygen to my cells,

which use it to produce the energy that keeps me alive.

This oxygen delivery system is incredibly efficient.

It runs for 24 hours a day, 7 days a week, for all of our lives.

For most of us, this whole system is calibrated

to the oxygen levels we find at sea level.

But at altitude, our bodies

are constantly struggling to harvest enough oxygen.

HE PANTS

Now, you can get an idea of what that's doing to me using this thing.

This gives you an idea of how much oxygen

there currently is in my bloodstream.

It's an oxygen saturation probe

and it's reading round about 88% at the moment.

It should read 100%.

And that lack of oxygen - hypoxia - is bad for you.

Oxygen is what keeps us alive.

If I saw a patient in a hospital with this sort of number,

I'd be worried.

And in the same way as it makes a patient in hospital sick,

it makes us at altitude sick

and that we call, "Acute Mountain Sickness."

Acute Mountain Sickness can be incredibly debilitating.

The lack of oxygen causes headaches,

lethargy, nausea and vomiting.

And unchecked, the lack of oxygen

would prevent us climbing much above 3,000m.

But today - just a few days after arriving in the Alps -

I'm going to try and climb to over 4,000m.

It's a beautiful day out here.

The Allalinhorn is just as beautiful, I reckon.

The Allalinhorn is one of Europe's highest mountains

and certainly the highest I've ever climbed.

The only reason I stand any chance of reaching the summit

is that since I arrived at altitude,

my body has been recalibrating itself

to survive on the lower levels of oxygen in the air.

The first change was that my brain automatically increased

the rate and depth of my breathing

to shift more air through my lungs.

But I've also undergone a series of more subtle physiological changes.

My heart is beating faster to help pump more blood round my body.

Non-essential functions - like digestion -

have slowed down to prioritise the delivery of oxygen

to more vital organs, like the heart and brain.

As time goes on, my kidneys produce a hormone called erythropoietin,

that stimulates the production of more red blood cells.

It's a process called "acclimatisation"

and it means that within a matter of days,

my body has changed its physiology to become much better

at harvesting oxygen from the thinner air.

Ooh, yes!

It definitely feels like harder work.

Stunning views over Switzerland from here.

-HE PANTS

-I certainly feel the work.

I think I've acclimatised a little over the last three or four days.

Still much more breathless on a slope like this...

..than I would be down there.

The effects of altitude are pretty obvious.

I'm hoping my body will withstand the altitude.

But it's by no means guaranteed.

Although the changes my body has made

are helping me cope with the thinner air,

those changes can also seriously damage my health.

Because the lower oxygen levels also cause physical changes

to my circulation.

My blood pressure rises, and the capillaries -

the finest blood vessels in my body -

can begin to leak, causing fluid to seep out

into the surrounding tissues.

If that happens in the lungs, the fluid builds up in the alveoli,

causing blood oxygen levels to plummet.

And if it happens in the brain, it can causing swelling

that leads to headaches, confusion and paralysis.

Exactly the symptoms suffered by Coxwell and Glaisher

on their record-breaking balloon flight.

Both conditions can be rapidly fatal

if you don't return to lower altitude immediately.

And they can occur at altitudes well below 4,000m.

HE PANTS

We're at 3,950m.

This is about as high as I've ever been on a mountain.

And I can honestly say...

..it's one of the most beautiful places in the world I've ever seen.

But by now, every step is a huge effort

and I'm breathing as hard as I can

but it still feels like I'm going to be out of breath forever.

50 metres to go.

It gets harder the higher you go.

Here we go, on the summit.

-Well done.

-Thank you.

Congratulations.

Thank you. 4,000 metres.

4,000m and a bit, brilliant.

Wow, now that is a view.

It's amazing up here. I can see why you like this as your office.

Yeah, it's an awesome place.

Very, very amazing place to be.

From up here,

these high Alpine peaks seem to be the very roof of the world.

And in many ways, for our species, that is exactly what they are.

We're surrounded here by mountainous peaks

running from 4,000 to nearly 5,000 meters.

And you can climb up here, it's fantastic climbing up here.

But that altitude, 5,000 meters,

has special significance for our species.

It's our high altitude limit.

There are no permanent habitations above 5,000 meters.

So for us, as the human race, this is it. This is our ceiling.

It is, of course, possible to climb above 5,000 meters,

but our stays at these heights can only be temporary

because of the serious effects extreme altitude has on our health.

Those effects are best seen

in the climbers who take on the world's tallest mountain,

Mount Everest.

As soon as they get to base camp, which at 5,300 metres

is already 1,000 metres higher than the Allalinhorn,

even the fittest climbers start to suffer,

losing weight as their bodies start to break down their muscles.

From here it's another three and half kilometres vertically up

to the summit.

And the final ascent

is one of the most demanding physical challenges

we can put our bodies through.

As soon as you go above 8,000 metres

you enter what climbers call the death zone.

One of the people who has made it to the top is my friend and colleague,

Dr Dan Martin.

So, Dan how does all this compare to your days climbing Everest?

Well, it's a little different,

little bit more vertical than Everest.

We never had to do anything like this

on the way up to the summit, thankfully.

Ooh, ice!

The physiological challenges are far greater

than any other mountain on Earth.

It's the highest and it really wears you down,

all that time at high altitude.

I can remember the final...trudge, is the only way I can think of it,

to the summit, just this sort of very slow, one foot,

then stopping and panting for ages, and then the other foot,

and then the other foot.

You kind of feel like you're never going to get there.

By the time you reach the summit

you're really at the end of what you can tolerate,

both physically and mentally.

On the summit of Everest, at 8,848 metres,

the air contains only a third of the oxygen that it does at sea level.

It's well into the death zone.

You can't survive here for long

because your body's deteriorating by the second.

Hundreds of people have died trying to climb Everest.

Dan's ascent was part of a medical expedition

to find out why some people are so much better at coping

in the tenuous atmosphere.

What never ceases to amaze us when we go to the mountain

is that very fit, sporty type people,

who are really fit at sea level,

can tend to do very badly at high altitude.

We've learnt that the amount of oxygen you deliver around your body

doesn't really give a good indication of how well you perform.

Which goes against the classic teaching

that we're all taught in physiology books,

the more oxygen that goes round the better you are.

So, just being an Olympic athlete isn't enough?

No, sadly not, and it may count against you.

It's believed that at very high altitude

the most important thing is not how much oxygen you extract

from the air, but how efficiently you use it.

So, just below the summit Dan's team stopped to take blood samples

to see just how little oxygen they were surviving on.

The results surprised even the experts.

We found some fairly astonishing numbers when we got back.

When we calculated the oxygen saturation,

which is comparable to what we see on the probe,

mine was 34%.

34%? Yeah.

That's absolutely shocking.

I've never seen those levels in a living patient....

Me neither.

..With those numbers.

Dan's blood oxygen level

was the lowest ever recorded in a living human being.

Somehow, his body was surviving on levels of oxygen

that would be fatal to most people.

It's not clear how he was able to do this.

But one intriguing possibility is that his body was remembering a time

when it had to cope with much lower levels of oxygen.

As an unborn baby,

you had to rely on sharing the oxygen from your mother's blood.

And there was much less of it to go around.

In fact, the oxygen levels in the womb are almost exactly the same

as those on the top of Everest.

In order to cope, your body's physiology was modified,

allowing it to use that tiny amount of oxygen

as efficiently as possible.

It may be that the only reason

we're able to stand on the summit of the world's highest mountain

is that our bodies are able to reactivate those metabolic pathways

that we last used in the womb.

But Everest is our limit.

If it was just 100 metres higher,

we wouldn't be able to survive on the summit

without taking additional oxygen.

Mount Everest is the highest point on Earth that we can climb to.

But it is not the end of our upward ambition.

In fact, it's just the beginning.

The 20th century gave us technology that allowed us to leave the ground

and conquer the air, taking us and higher and higher.

The first aeroplane only flew in 1903.

And those earliest machines

could only stay in the air for less than two minutes.

But within a few decades, we had mastered the skies.

World War II brought a revolution in aviation

with the demands of the military ushering in faster,

more powerful planes,

creating a whole new range of physiological challenges

for the crews who flew in them.

These aircraft are remarkable,

marvels of engineering,

that's the B17 flying fortress and just behind, the B24.

They were manufactured with a specific purpose in mind,

to deliver bombing loads during World War II.

This changed aviation for ever -

more air crew flying higher and faster than they ever had before.

These planes were capable of flying higher than the summit of Everest,

up to heights of 40,000 feet, over 12,000 metres.

Just getting ready to take off here.

Those engines, incredibly loud.

We're just taxiing to get into position on the runway.

This is the radio room of this B17...

..very cramped, this was not built for comfort.

It's almost like the crew were an afterthought.

And if you were one of those World War II bomber crews,

this would be the start of a day...

..that would last a very, very, very, very long time.

This remarkable plane, the 909,

is one of only 13 B-17s still flying today.

And it's been painstakingly restored

to be exactly as it was in the Second World War.

Well, there's so little room to move,

and you're in amongst the clockwork of all of this

all the way this all the way through.

Wow, look at that!

That is incredible.

During the war, tens of thousands of B-17s and other bombers

flew missions over Europe.

While the British bombers flew at night,

the American air force preferred to fly in daylight.

But although it allowed them to see their targets,

it also put them in plain sight of the enemy guns on the ground.

On board were crew like 90-year-old Frank Tedesco,

who in 1942 was just 20 years old.

When we approached the target

we could see up ahead large volume of explosions, called flak,

and we knew we had to fly through it.

I don't care how good a pilot you are, you can't avoid flak.

So, hopefully, you don't get damaged.

To avoid the dangers of the flak and enemy fighters,

the planes were designed to fly higher and higher.

But as they did so, they catapulted the crew deep into the death zone,

to altitudes where their lives were in danger.

That airplane has no form of heat for the crew.

The temperatures we experienced

were anywhere from 30 to 50 degrees below zero Fahrenheit.

It got to the point where you almost used to dread the cold

as much as the anti-aircraft fire.

But it wasn't just the cold that threatened the crew.

There was so little oxygen at those altitudes

that even the engines struggled to function.

If you look out the window there, that engine is turbo charged.

It uses the exhaust gases to drive a turbine

to compress air to enough of a mixture to get it to burn

at 40,000 feet, the upper limit of operation of this aircraft.

The engines found it difficult to breathe and so did the crew.

This is the oxygen system for this aircraft, very basic.

You draw your oxygen off that compressed cylinder there

into this demand valve.

That's all that protected the crew from the lethal hazards

of the thin atmosphere at the huge altitudes these aircraft flew at.

The failure of these oxygen systems

was a major cause of death on those bombing missions.

Many crew died in their seats

without realising anything was wrong.

And to find out why,

I'm going to put myself through the same experience.

These are the laboratories of QinetiQ in Hampshire,

operated by Dr Henry Lupa and his team.

The room I'm sitting in, is a decompression chamber.

Any second now, all the air is going to be sucked out of it,

leaving me at an equivalent altitude of 25,000 feet.

All military pilots have to do this training

so they become familiar with the effects of sudden hypoxia.

Just confirm you're happy to proceed.

Yeah, very happy, thank you.

Stand by for rapid decompression in 5, 4, 3, 2, 1.

As the pressure drops, the chamber suddenly fogs up

as the moisture condenses out of the air.

A lot colder in here now, some condensation in the cabin.

25,000 feet.

While I've still got my breathing mask on,

I can function fine at this altitude.

So still on oxygen at this point

and the oxygen saturation probe there is showing me 99% saturated.

OK, you're feeling all well?

Feeling good.

'But when the time comes to take my mask off,

'I'll be suddenly exposed to air

'with only a third of the amount of oxygen in it.'

What I would like you to do is drop your mask

and then switch the regulator off.

'This is rapid decompression. Unlike in the mountains,

'there's no time to acclimatise to the lack of oxygen

'and the effects are very different.'

'Whilst initially I can easily perform normal functions

'like writing my name and address,

'my blood oxygen levels are falling dramatically.'

'And within a couple of minutes,

'I'm struggling to perform even simple tasks.'

'But although I was struggling to perform these tasks,

'I really didn't care.

'The over-riding sensation I was feeling

'was one of euphoria and well-being.

'But after three minutes, I can't even write properly.'

'I'm now in great danger

'and not even registering anything that's said to me.'

'Without help with that mask, I would've passed out in my chair.

'I'd been without my oxygen supply for less than four minutes.'

How was that? Did you enjoy the experience?

You do feel quite euphoric during it.

That's one of the biggest dangers of hypoxia,

in that it is actually quite an enjoyable...

People enjoy the euphoria of it.

Certainly watching your face, you seemed quite happy,

jovial for most of the time.

Towards the end,

you could see that you were slumping forward in the chair.

I was a bit concerned you were going to collapse.

I don't think I would've guessed

that you get that hypoxic that quickly.

It's very easy to get to a state where even if you recognise it,

you just don't care.

You lose your self-criticism, you lose your judgement

and you don't do anything about it.

And then it'll kill you.

The first bit of writing seemed like a bit of trivial nonsense.

The second bit, I didn't care what it looked like,

I didn't realise it looked quite that bad.

I mean, there's me, normal bad doctor's handwriting,

there's me, hypoxic doctor's handwriting.

Barely intelligible,

didn't get to the second and third line of the address.

'It was exactly this creeping mental deterioration

'that affected so many of the bomber crew during the Second World War.

'A brief period of euphoria followed by unconsciousness and death.'

And because they flew higher, at 40,000 feet,

when their oxygen failed,

they would've slipped into unconsciousness within 30 seconds.

It casts into sharp relief that video you always ignore

at the start of a commercial flight,

where they show the yellow masks dangling from the ceiling

and explain to you how to put them on and to put them on quickly.

If you don't get them on quickly, you've got seconds.

After that, you're not going to care,

the people around you aren't going to care

and everyone's going to do pretty badly.

A reliable oxygen supply has been a must for pilots

for the last 70 years.

Since then, aviation technology

has produced jets that fly even higher and faster,

breaking the sound barrier and climbing to over 15,000 metres.

But flying these machines exposes the crew to other hazards,

not least G-forces,

the immense forces of acceleration the pilots endure

while manoeuvring these planes.

And now I'm going to experience those forces for myself.

This centrifuge was built in the 1950s

to recreate the high G-forces experienced by fighter pilots.

It's capable of generating up to 9G,

a level that leads to unconsciousness

and risk of fatal accidents in pilots.

But it's what fighter crews need to tolerate.

What's going to happen to me now?

What we're going to do is gradually spin you up

with an acceleration of 0.1g per second.

We keep going until your vision begins to fail,

which is one of the early signs of inadequate oxygenation of the brain.

How am I going to know when enough is enough?

In front of you are three lights.

As soon as you start to see the peripheral lights disappear,

I'd like you to press that button.

-This button here.

-That will stop the centrifuge.

All right, I guess I sort of look forward to it, see how we go.

Stand by, 0.1g per second onset rate.

As the G load increases,

blood moves away from my head down into my legs.

The force is so strong that my heart is pulled

a couple of inches down inside my chest,

making it even harder for it to pump blood to my head.

And among the first organs to suffer will be my eyes.

Starved of oxygen, my colour vision will fail as I go through greyout,

which for most people, happens at between 3 and 4G.

What happens shortly afterwards is G-loc -

G induced loss of consciousness.

It's consequences when flying a plane are predictably disastrous.

And I'd rather avoid it even in this centrifuge.

So I'm going to bail out before it happens to me.

4G.

You actually did very well, you got up to about 4.7G,

something like that. Very good, in fact.

I did better than average, but I could still only stand 4.7G.

Fighter pilots need to be able to withstand much higher forces.

And the only way they can do that is with the help of technology

and with the invention of some very special trousers.

-How does that feel?

-That feels great actually, yeah.

So what do these do, Henry?

What they do is inflate

and stop blood going down into the legs whilst you're pulling G.

They also pressurise the abdomen and stop the heart descending,

because it does descend a few centimetres

while pulling high levels of G.

This is the flight suit worn by the pilots of the RAF's

most advanced plane, the Typhoon.

And with its protection,

I'm going to see if I can really push my G-tolerance.

2G.

My suit automatically inflates as it detects the increasing G force,

squeezing my legs and abdomen

and forcing the blood back towards my heart and brain.

5G.

With the gondola spinning at nearly 70mph,

we reach 5G, a level that would render most people unconscious.

6G.

But with the suit's help, I'm still going strong.

In response to the rising G, the breathing system

detects the G-force and increases the pressure of air

pushed into my lungs, enhancing my G-tolerance even further.

Well, you did fantastically well - that was 8G.

So it's quite incredible.

You can feel that really squeezing

and the pressure comes up from your legs,

pushing all the way up into your abdomen and, I guess,

trying to help you return blood to your brain.

And, you know, it definitely works.

It took you well above 3G,

above what I'd experienced before, more than 3G.

There's not a chance I could have got there

relaxed and unprotected before

so the suit definitely works.

They really are magic trousers.

It's protective clothing like these anti-G suits

that has helped pilots fly high into the atmosphere.

By the 1950s, some jets were flying above 70,000 feet,

over 20,000 metres, where the air is so thin

that the pressure is less than 10% of that at sea level.

At these heights, the curvature of the Earth spreads out below us

and above, we can see the blackness of space.

But we still hadn't reached the top of our atmosphere.

In fact, we weren't even halfway there.

And in our quest to go higher, we had to go back

to the oldest flying technology of all.

In 1960, Joseph Kittinger, a military test pilot,

boarded a gondola strapped under a massive helium balloon.

It took him up through the atmosphere, and up and up

to 30,000 metres.

With 99% of the atmosphere below him,

he was at the very edge of space.

For a few minutes, he was further from the Earth

than any human had ever been before.

And then...

..he jumped out.

But Kittinger's altitude record was only to last a few weeks.

Because mankind was about to enter the Space Age,

developing the most impressive machines ever built

in an attempt to leave the planet altogether.

'50 seconds and counting.'

'45 seconds.'

This is the Saturn V.

It's the most powerful rocket ever built.

This vast structure, 110 metres long,

is a symbol of how much effort and energy we need

to extend our reach into the extremes of space.

This entire vehicle,

everything up until here, is just fuel and engines.

'We have the power transfer.'

There's a simple reason why rockets like these need so much fuel.

And that's because to escape the Earth's gravity

they need to create a huge amount of thrust.

All told, the Saturn V carried 2,500 tonnes of fuel.

Enough for the vast engines

to produce the seven million pounds of thrust required

to send the rocket to the moon.

But delivering enough power to escape the Earth

was only half the problem.

A much bigger challenge was keeping the crew alive on the journey.

Project Apollo was about more than just brute force.

The first problem was that your crew were sitting on top of a rocket

with the explosive capacity of a small nuclear weapon

and if they survived the launch, the engineers then had to find

a way to protect them against the void of space

and provide them with something in the way of life support.

The success of human space flight

depended on finding ways for people to survive in space.

Completely removed from the safety of the Earth's atmosphere,

astronauts would have to be provided

with everything they needed to stay alive.

And from the start, it was a process of trial and occasional error.

In April 1960, Russian Yuri Gagarin became the first man

to successfully orbit the Earth.

He was followed into space just three weeks later

by the American astronaut Alan Shepard

on his Mercury-Redstone rocket.

Shepard was in space for just 15 minutes, but he and Gagarin

had proved that mankind could survive in the vacuum of space

by taking an artificial atmosphere with them.

This is a real Mercury capsule.

This carried Gordon Cooper into space in 1963

and look at it, it's tiny.

There's about the space of a telephone box in there,

carrying an astronaut around the Earth.

To survive in space, you need to bring enough oxygen with you

with enough pressure behind it to make it breathable.

The Mercury system solved this

by filling the capsule with 100% oxygen.

And that worked well, that kept the astronauts alive.

But it came with an enormous risk.

The use of pure oxygen systems survived into the Apollo programme,

the mission that was to land men on the moon.

The first stage of that mission was due to launch in February 1967,

carrying three astronauts -

Gus Grissom, Edward White and Roger Chaffee.

They would orbit the Earth to test the Apollo hardware.

But just three weeks before launch,

the crew entered the craft for a full systems check.

It's not clear what happened next,

but it's thought a stray spark from the electrical system

started a small fire,

which in the 100% oxygen atmosphere quickly turned into an inferno.

Trapped in their capsule,

the astronauts burned to death in seconds.

Pure oxygen atmospheres were never used again.

By the time the next manned mission, Apollo 7, launched in October 1968,

the cabin was filled with a mixture of oxygen and nitrogen,

more like the air we breathe on Earth.

Only when in orbit in the vacuum of space

was the atmosphere replaced with pure oxygen,

but at such a low pressure it didn't pose the same fire risk.

But for these longer Apollo missions

where the crew would live in their capsules for more than a week,

there were other problems to solve.

If you want to survive in space,

it's not enough just to provide oxygen.

You need to remove the waste gases,

the gases of respiration, carbon dioxide.

If that accumulates, it causes drowsiness, confusion,

later coma, and eventually death.

In 1970, the crew of Apollo 13,

Jim Lovell, Fred Haise and Jack Swigert,

encountered a catastrophic failure of their life support system,

an explosion which left them short of oxygen and without the ability

to remove enough carbon dioxide from their atmosphere.

And that would lead to one of the greatest dramas

in the history of human space exploration.

'Houston, we have a problem here.'

-Say again, please.

-'Houston, we've had a problem.'

The crew of Apollo 13 were on their way to the moon

when an explosion in an oxygen cylinder

caused the command module to lose power and life support.

'We had a pretty large bang

'associated with the caution and warning.'

It forced the crew to evacuate to the lunar landing module, the LM.

'I want you to get some guys

'figuring out minimum power in the LM to sustain life.'

Although the LM was capable of making the return journey to Earth

and the crew had enough oxygen and food,

there was a crucial flaw in the plan.

The LM didn't have enough filters

to remove the carbon dioxide from the air.

And the spare filters from the command module

wouldn't fit the LM's systems.

If they couldn't find a way to remove the CO2,

the crew would suffocate and die long before they reached home.

What followed was the greatest piece of DIY in space history.

The command module filters were adapted

with cardboard and sticky tape.

Around the world, millions watched,

breathlessly waiting to see if the improvised filters

would work well enough to bring the crew safely back to Earth.

'Houston, you're looking good.'

-'Welcome home.'

-'Thank you.'

Since then, we've got better and better at sending people into space.

We can now not just keep people alive for a week or so,

we can keep a presence in space permanently.

For more than ten years, astronauts have been living and working

on the International Space Station,

supported by an artificial atmosphere just like the Earth's.

50 years after we first started going into space,

we now live and work there,

we explore and we do science, and to do that,

we've had to create much more sophisticated life support systems.

The International Space Station does a pretty good job

of creating what we're used to down here on Earth.

One atmosphere of pressure, enough light, heat, water,

21% oxygen - something that looks an awful lot like home.

And to have achieved that in orbit,

in an environment so uniquely hostile to human life,

is a tremendous achievement.

The International Space Station is a home away from home.

But although we can replicate an Earth-like atmosphere,

living in space for extended periods

presents another serious challenge to our physiology.

Simulating the effect of being in orbit

is almost impossible on the Earth.

But there is one place we can go, where for just a few seconds,

we can experience what it's like to be in space.

This Airbus 300 is used by the European Space Agency.

It's been specially modified for what's known as parabolic flight.

First, the pilots fly the plane steeply upwards,

before guiding it over the top of the arc into an equally steep dive.

As the plane falls away...

..it's as though gravity disappears.

(LAUGHS)

And that's weightlessness.

'It doesn't last long, but for just 20 seconds,

'it's as though we've escaped the pull of the planet.'

Now that's fun!

So fantastic and really hard to describe.

All of those dreams you ever had of flying are just suddenly for real.

'Nothing in our evolutionary past has prepared us for this.'

So this looks like pretty good fun. And it is.

When gravity disappears temporarily, it's fantastic.

But like anything else, you can have too much of a good thing.

When you have to live in weightlessness,

it can have serious consequences for your body.

For astronauts on the International Space Station,

who are weightless for months at a time,

there are many potential hazards.

For a start, simple necessities like eating,

washing and going to the toilet become fraught with difficulty.

But removed from gravity, our physiology also changes.

Released from the constant pull of the Earth,

our muscles start to waste away

and our bones, no longer bearing weight, lose calcium,

becoming weaker and brittle.

And since the heart doesn't have to work so hard to pump blood

to our head, it too becomes weaker.

Because of these changes, the astronauts on the Space Station

have to exercise for hours every day, to retain their strength.

In time, we hope to travel further into space,

and we'll need more elegant ways to cope with the lack of gravity.

But in the meantime, our colonisation of orbit

is a remarkable stepping stone.

It's extended our habitable range to hundreds of miles

above the Earth's surface and made us a space-faring species.

A remarkable journey when you consider

that not even 250 years ago, no-one had even left the ground.

That journey that takes us away from the surface of the Earth

out into the atmosphere and beyond into space

is the purest expression of our desire to explore.

And it's that urge that makes us want to find ways to explore

new, extreme environments.

It's extended our reach from the narrow but comfortable envelope

of sea-level to the deepest reaches of our ocean,

to the top of our atmosphere and eventually, out into space.

And in the future, who knows where that will take us?

Possibly to completely different worlds.

Subtitling by Red Bee Media Ltd

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