Mission to Mars Horizon

This is one of the most sophisticated space vehicles

ever built.

Curiosity is a billion-dollar rover.

In six days' time, it will attempt to touch down on Mars.

Landing a big rover is a tough business.

It means that everything about the system gets bigger and therefore harder.

This will be no ordinary landing.

It will be winched down by a crane hovering in the Martian sky.

It's so ambitious, it's so audacious, it's so unconventional.

Horizon has been behind the scenes with NASA's team as they follow

their rover across 350 million miles of space.

When Curiosity comes over the horizon,

this guy is already pointed that direction and as she comes up, then we're talking.

Curiosity's mission is to discover

if Mars could ever have supported life.

But the Red Planet has become known as the Bermuda Triangle of space.

Two-thirds of missions there have ended in failure.

In just under a week, the world will learn

if Curiosity can overcome the odds and touch down on Mars.

SPEECH OVER RADIOS

It's 10pm at the Jet Propulsion Laboratory in California.

OK, copy and we'll make that report to the surface team

when they come onboard.

The team behind the Curiosity mission are locked

in a crucial test at the space flight control centre.

We're now about five and a half minutes to entry.

They're practising for a landing they know is the most audacious

ever attempted on another planet.

Three minutes to entry.

They've been rehearsing and testing day and night for months,

running through each individual step of the mission in painstaking detail.

Confirming that we have parachute deploy.

Brian Portock is the flight director for the 350 million-mile journey to Mars.

Ann Devereaux helped devise a way to stay in touch with the rover.

Adam Stelzner will mastermind the daredevil landing.

And leading this test is Chief Engineer, Joel Krajewski.

The fate of this mission is central to everybody's soul, really.

Most folks have worked on this for three years, five years, eight years.

You don't get to do many in a given career.

You only get to do a few if you're lucky.

So the stakes for everybody are as high as they can be.

This is just a rehearsal,

but on the 6th of August, they'll be doing it for real,

hoping the Curiosity rover

will arrive safely at its destination.

Mars, the Red Planet.

It's become known as the Bermuda Triangle of space.

Since the launch of the first rocket there in the 1960s,

two-thirds of all missions have ended in disaster.

The mission logs make scary reading.

"Failed to launch."

"Missed the planet."

"Lost radio contact."

"Lost on arrival."

The team knows Curiosity might never reach the surface of Mars.

It's Joel Krajewski's job to make sure this mission is a success.

His day may begin like many Californians...

but then he heads to NASA's Jet Propulsion Laboratory.

Like anyone else, I drive into work every morning

but every morning as I do so, I pinch myself because

I get to work on a space mission and that is, that is pretty cool.

For more than a decade,

Joel has been engineering rovers to send to the Red Planet.

Before I got into working on rovers, of course like anybody else

I thought it was going to be a kind of a tricky business.

It sounds hard throwing things up into space

and exploring other planets.

Once I got into it, I learned that it's even harder than I thought.

This is the third rover that Joel has worked on.

But even for a Mars veteran like him, Curiosity has been a huge challenge.

Curiosity is the most complex vehicle we have sent to Mars.

Hundreds of people have worked on it for more than eight years

and we're still working on it.

Different people understand different aspects of it, but nobody knows it all.

As the real Curiosity hurtles through space,

its clone is hidden in a garage at the Jet Propulsion Laboratory.

It runs on its very own nuclear generator.

Its components can withstand forces greater than those

exerted on a supersonic jet.

And its electronics are designed to work at temperatures far lower

than the coldest places on Earth.

It's the most advanced moving vehicle ever sent into space.

Today, Joel's team are testing the wheels of Curiosity's twin.

-They're low class.

-Is that what we call them?

That's what we call them.

It's just one of hundreds of tests the rover has been through in the past nine months.

That's great.

The scientists want to land on Mars and explore.

They want to explore where we land and then also explore

kilometres away from where we land, and that means we have to drive.

We'd like to be able to drive over big rocks

so that we can drive close to a straight line,

not too much meandering around, and therefore we designed a big rover.

That makes it tricky.

The reason Curiosity is so big and expensive

is because of the science it will be conducting on Mars.

It will have to drive across difficult terrain

while carrying a lab full of equipment.

The scientists would like an infinitely capable vehicle.

But in the real world, the machine has to fit within a certain volume.

It has to fit within a certain mass.

We can only lift so much mass off the Earth

and have it land safely on Mars.

The rover is five times as heavy as any vehicle they've ever launched,

which makes landing it on another planet

more difficult than anything they've attempted before.

Landing a big rover is a tough business.

The landing system is more complex, parachutes are bigger,

everything gets much bigger and therefore harder.

# There's a starman waiting in the sky... #

NASA's engineers have never shied away from tricky landings.

# There's a starman... #

During the Apollo missions of the 1970s,

they weren't satisfied just to put a man on the moon.

But landing a car on Mars is an entirely different proposition.

Adam Stelzner has spent years working out how to do it.

He will take control of the rover as it begins to enter the Martian atmosphere.

He won't be able to rely upon the systems

that got the lunar rover down safely onto the surface of the moon.

Mars is tough.

The moon, where we've landed lunar modules on the moon before,

does not have any atmosphere

and it makes the process of getting down to the surface kind of simple.

You take a rocket engine, you turn it on and you slow yourself down until you touch down on the surface.

Unlike the lunar rovers,

Curiosity will have to battle an unpredictable atmosphere.

Historically, Mars has been evil.

You don't know what the weather's going to be like, you don't know

whether the atmosphere's going to be dense or diffuse.

Will it be a hot day and not so dense, or a cold and dense day?

If it's cold and dense, you slow down faster, you end up shorter.

If it's hot and low density, you end up flying farther.

The dangers of this unpredictable atmosphere are heightened

by the speed the spacecraft has to travel at to get to Mars.

It will arrive at 13,000 miles per hour.

We have enough energy of motion in the spacecraft that we could

vaporise the spacecraft in the atmosphere of Mars

just by slamming into that atmosphere and developing

so much friction that the vehicle would burn up.

So it's a challenge.

The rover will be tucked inside a spacecraft

when it reaches the dangerous Martian atmosphere.

Its first line of defence will be the world's biggest heat shield.

Next, the team have to stop it

from crashing head-on into the Red Planet.

So they have designed the biggest supersonic parachute ever made.

In NASA's giant wind tunnel near San Francisco, they put it to the test.

'Five, four, three, two, one...'

The parachute must be deployed at twice the speed of sound.

Good chute, good chute!

The tests confirmed the huge canopy should survive the enormous forces

it will encounter as it's dragged through the Martian atmosphere.

Finally, Curiosity's engineers

tested the most risky part of the landing procedure...

I think we are ready to go.

..a bizarre hovering crane

that will have to lower the rover down the final 20 metres to the surface.

CHEERING

The sky crane took the engineers years to perfect.

It has never been used to land anything before.

But although all of Curiosity's individual landing stages

passed their tests on Earth before launch,

they have never been tested all together.

The Red Planet's evil environment

will be the first place the whole procedure is ever attempted.

MUSIC: "Pumped Up Kicks" by Foster The People

Planning the journey was the first challenge for Joel Krajewski's engineering team.

Go, go, go, go, go!

-Nice job!

-APPLAUSE

As Flight Director, Joel's colleague Brian Portock is, in effect, the mission's quarterback.

CHEERING # Robert's got a quick hand... #

It's Brian's job to aim and throw the spacecraft across the solar system to a moving receiver...

..Mars.

PLAYERS SHOUT

Everything's in motion in space.

Run in, run in!

Mars is moving round the sun and the Earth is also moving round the sun,

and their motion relative to each other is changing.

Go, go, go, go!

Similar to a receiver running out for a pass is in motion...

Ball!

..and the quarterback needs to stand back and throw a ball...

Really good shot!

..so that the receiver and the ball meet at a point in space

and a time that's the correct one so that they can catch it.

Oh, nice!

CHEERING

They need to figure out how far the ball needs to travel depending on where the receiver is.

-Go, go, go!

-How fast the receiver's running in that direction.

Most quarterbacks don't sit down and calculate that on paper.

Set, go!

It's all done in their head instinctively, without thinking about it.

For spacecraft, we do it on paper, or these days, on computers.

PLAYER SHOUTS

The other thing a quarterback does is put spin on the ball.

Spiral so that the ball flies in the correct trajectory.

So we also are spinning our spacecraft...

so it maintains its attitude...

..and so that we can point the solar rays back at the sun and communicate back to the Earth.

And so, the actual rotation of the ball

is similar to the rotation of the spacecraft.

They make it sound simple,

but firing a spacecraft across the solar system

involves some really complex ballistic calculations.

The craft must escape the pull of the Earth's gravity.

It must contend with solar winds that could blow it off course....

cosmic radiation which can disrupt radio contact...

..and the craft is constantly being dragged from its course

by the gravitational pull of other planets.

Just a tiny error could result in Curiosity missing Mars altogether.

To get the distance scales approximately similar,

the quarterback here is throwing a pass 30 metres, 40 metres away.

Brian's target of Mars is hundreds of millions of kilometres away.

It's similar to if this quarterback here were throwing a football

to a receiver in, say, London, and needing to hit his mark.

APPLAUSE

-It'd be the wrong kind of football. LAUGHS:

-Yeah!

In November 2011, at Kennedy Space Centre,

the rover made its way to the launch pad on an Atlas rocket.

For the mission team, the launch is the moment of no return.

While the craft is on the ground, final fixes can always be made.

But once it's in the air, a fault could mean the end of the mission.

There's so much energy involved with launching.

SPACECRAFT BLASTS

All the little piece parts on the spacecraft

are designed to survive that vibration and those forces.

Just the fact that it gets into space

and we start talking to it for the first time is an incredible achievement.

-It's spacecraft separation.

-APPLAUSE

It's the first big step on the way to Mars.

But any damage caused by the launch to Curiosity's components might not be immediately obvious.

So, for the past eight months,

the engineers have needed to stay in careful contact,

to check its course and its vital signs.

'Re-transmit... Six, three, eight...'

They need to be sure that they receive every message sent back by the rover...

and that every instruction they give will be heard loud and clear.

MUSIC: "Sweet Child O' Mine" by Guns N' Roses

To communicate with Curiosity,

the team have to rely on equipment hidden deep in the Mojave desert.

Ann Devereaux helped engineer the systems that allow the team to stay in touch.

Now that the spacecraft is nearing the end of its voyage,

she feels the distance between her and her rover more than ever.

It's very much akin to having a kid in college.

We raised her, we taught her everything she knows,

we gave her all the gear that she needs to investigate her new world, but now she's gone.

And, you know, we gave her a calling card. We told her to call often,

but we don't get to talk to her all the time, and, you know,

we don't know what she does every day until she's in contact with us.

# Whoa, whoa, whoa Sweet child o' mine. #

Curiosity can call home using two ultra-high-frequency radios.

But the distance between Mars and Earth,

together with the rover's limited power,

makes it difficult to pick up the signal.

It's a problem anyone with a car radio knows well.

RADIO INTERFERENCE WARPS MUSIC

We're about a hundred miles outside of Los Angeles.

In the car, I've got the radio going,

but my favourite radio station is almost gone.

I'm not that far, certainly compared to Mars,

and the radio station that I listen to has a 90,000-watt transmitter,

and so you'd wonder why I can't pick up the station here.

The problem is my little antenna

is just not capable of picking up the signal at this distance,

no matter how powerful it seems the transmitter back at home is.

MUSIC: "Spread Your Love" by Black Rebel Motorcycle Club

In space, power is in short supply,

and Curiosity will need to use almost all of its energy

to drag its near-ton weight across the surface of Mars.

That means the rover's transmitters have to get by with just a fraction

of the 90,000 watts used by a radio station on Earth.

She only has a ten-watt transmitter, and she's MUCH further away.

We're about 140 kilometres from Los Angeles -

Curiosity is going to be 250 million kilometres at Mars.

We need something bigger for an antenna.

# Spread you love like a fever

# Spread your love like a fever

# Spread your love like a fever

# Spread your love like a fever. #

The DSS14 antenna is the biggest dish

in NASA's Deep Space Communications Network.

It's their switchboard for every spacecraft in the solar system.

But all this interplanetary chatter means that Ann can't just pick up

the phone to Curiosity any time she likes.

There's a lot of spacecraft out there, and they all want to talk back home, too, right?

They all want to call home.

And so, we have to schedule time at one of these antennas, like here at DSS14,

and tell the people that we need to talk to Curiosity and this is how long we want to talk to her for,

and they point the antenna so when Curiosity comes over the horizon,

this guy is already pointed in that direction and as she comes up, then we're talking.

But a queue for the phone is not the only thing that could kill

the conversation between the rover and the team back home.

Once it arrives at Mars,

the whole mass of the planet will stand in the way.

Mars itself rotates as the Earth rotates,

and so sometimes, even if we wanted to talk to Curiosity, we couldn't.

Because we just have the whole planet between us and Curiosity.

A Martian day lasts 24 hours and 40 minutes.

For half of that time,

the rover will drop behind the red planet's horizon,

out of view of Earth's antennas.

When Curiosity arrives, night will be falling on Mars.

Midway through its perilous landing procedure,

the team will lose direct contact with the spacecraft.

But NASA can rely on help from some previous Mars missions.

We have an ace in the hole. In fact, we have two.

It's called Mars Reconnaissance Orbiter and Mars Odyssey.

So, these are two orbiters that we have around Mars already.

They're sitting there, they're waiting for their sister to come.

As the Martian night obscures the rover from Earth's view,

Odyssey will attempt to relay its vital messages

back to the control room.

This is just one of hundreds of risky procedures

that must go right for Curiosity to land safely.

In designing the most complex landing ever attempted in space,

the team have had to go out on a limb, staking their reputations

on a system that has never been used before.

It's so ambitious. It's so audacious. It's so unconventional.

It doesn't feel like there's a lot of shelter.

You can't say, "Oh, I'm doing what they did before

"and it just didn't work out, I didn't get lucky."

No, we're not doing what we did before.

We're doing something completely novel, hanging it way out there.

Um...

You feel exposed.

As chief architect of Curiosity's landing sequence,

Adam Steltzner has gone through each part of it

over and over in his head.

But for now, it only exists in his imagination.

And in this NASA animation.

We show up at this near six-kilometre-a-second speed.

We burn a hole in the sky of Mars for about 100 kilometres long.

We start out at six kilometres a second,

and we're still going about a kilometre a second.

We're not slowing down very much, because there's not enough atmosphere to help us out.

So eventually we have to pop a parachute.

That slows us down more. But still not enough.

It takes us down to about 100 metres a second.

200 miles an hour, almost.

You don't want to hit the surface of Mars like that.

So, about a couple of kilometres from the surface,

we decide it's time to look for the surface with our radar.

And once we've seen it, we take this great leap of faith.

And cut ourselves free,

light our rockets and start our descent to the surface.

We slow ourselves all the way down,

and then, 20 metres above the surface,

we do this kind of crazy thing...

called the sky crane manoeuvre.

Zzz-zzz...

The average person on the street thinks it's crazy.

Even the team that's working it, sometimes we think it's crazy.

The strange part is,

it's actually the result of reasoned engineering thought.

Six days from now,

the team hope Curiosity will execute this unlikely manoeuvre.

Back on Earth,

they will be waiting for the message they have all dreamed of...

..it's safely down.

The purpose behind all this daredevil engineering

is to send the biggest payload of scientific equipment

ever to leave Earth

to uncover the secrets of Mars.

It's the latest step in mankind's love affair

with this curious red light in the night sky.

Ever since Galileo built his first telescope,

astronomers professional and amateur alike

have peered through their lenses at the red planet.

Oh, yes.

Do you see it?

I see it.

-I see some bright colours.

-You see some bright colours?

-I think it's Mars.

-You think it's Mars?

I think you might be right.

It's Mars, for goodness' sake - now how could you not be interested?

It's just beautiful.

Mars has, you know, intrigued people

for so many years.

I think it's that red colour that attracts people,

and it's just... just the romance of it.

That's wonderful.

Curiosity's planetary scientist Ashwin Vasavada

has shared this fascination since he was a boy.

Looking at Mars through a telescope, you can see some wonderful things.

You can see the planet, you can see the polar caps come and go with the seasons.

I love looking through telescopes, but really, they're almost like

using a record player for someone who grew up with the internet.

In 1976, we moved beyond mere telescopes.

When the Viking space probe beamed back the first-ever images

from the surface of Mars,

it inspired a whole generation of space scientists.

This image is an image taken by the Viking lander in 1976,

and it kind of is a special image for me,

because I saw this image in a book I was reading as a young kid.

And it's the first time I really noticed that planets were other worlds.

You could stand on a planet, look out and see rocks

and you could walk off the horizon of the image you're looking at,

and you wonder what's across that hill.

It just blew me away, and maybe it's the moment I became a planetary scientist.

The Viking mission tapped into the public's fascination with Mars.

It was inspired by one of the most intriguing questions in science.

Are we alone?

It's about searching for life in the universe,

it's about asking this profound question of whether we're alone,

whether we're all that there is.

And the only way we can do that, even in this technological age,

is just by stepping out to our nearest neighbour planet,

the one next furthest out from the sun, and asking the question there.

But really, it's going to tell us this profound reality,

whether we're alone or we're not.

NASA's Viking mission was hugely ambitious.

It was their first ever attempt to land robotic probes

on the surface of Mars.

And it was going to search for life itself.

It has an arm, so it can extend out into the area around it

and pick up sand to bring back to the other laboratories which are on board the lander.

The Viking landers were equipped with these state-of-the-art biological laboratories

and they scooped up soil and analysed it.

They tried to feed any microbes that would be in the soil

and do very sophisticated experiments to detect life.

CHEERING

The delight of landing safely

and receiving these extraordinary pictures

was followed by what seemed to be an incredible discovery.

Initial observations suggested that they had detected microbial life

in the Martian soil.

But as the euphoria subsided

and the scientific data was analysed, a new realisation dawned.

Viking had in fact failed to find life on Mars.

And the results were either negative or just ambiguous

and it made us realise that it's not going to be this easy.

Since the 1970s, other missions have told us much more about Mars.

Successful Rovers and orbiters have produced detailed maps

of the red planet's surface and breakdowns of its atmosphere.

They have revealed just how hard it would be for life to survive

in the planet's extreme environment.

The surface of Mars today is a very harsh place to life.

There's a lot of things that are hazards to life.

Now we're interested in knowing whether those same hazards

were there in the past

and maybe early Mars as opposed to present Mars was the place to look for life.

Today, Mars is an inhospitable desert.

Its thin atmosphere leaves its surface exposed

to lethal solar and cosmic radiation.

Average temperatures of minus 55 degrees Celsius

would make it very hard for life as we know it to survive.

That's why Curiosity is not expecting to find life here and now.

Instead, it will try to discover

if life could have survived there millions of years ago.

Which means the Rover not only has to travel all the way to Mars,

it has to travel back in time.

This desert, 200 miles outside Los Angeles

has become a second home for the Curiosity team.

It's an ideal place not just to test the Rover,

but also to design the mission's science.

Chief scientist John Grotzinger is in charge of the experiments

that will enable the Rover to see into the past.

Not by looking for bones or fossils, but by trying to find

elements crucial for life.

Simple things, like liquid water.

What we're going to do is an acid test.

Take a few drops, put it on the rock and see if it fizzes.

And yes, cool, it fizzes.

And what that tells us is that this work is made out of

a mineral called carbonate.

And carbonates on Earth form in lots of water,

and that tells us that this dry desert that we are in here today,

600 million years ago, there was an ocean.

It was liquid water in ancient lakes and seas

that allowed life to take hold.

So Curiosity's scientists have carefully chosen a Martian landing site

similar to this spot in the Mojave Desert.

Curiosity will hunt for the same evidence of a wetter past

in the Gale Crater on Mars.

Here's Gale Crater, with Mount Sharp majestically rising above the plains.

Mount Sharp is a Martian mountain,

rising 18,000 feet above the centre of the massive Gale Crater.

The scientists believe their Rover could find carbonates here, proving

this Martian crater was also filled with water in its ancient past.

But that's not the only similarity that Mount Sharp has

with the mountains here in the Mojave Desert.

In both places, the team can use the rock itself to travel back in time

to any moment in the geological past.

The mountains are formed of layers, built up gradually over millennia.

Testing each one will reveal what the environment was like there

at the particular moment in time it was laid down.

What we see here is a stack of layers that tell us

about the early environmental history of the Earth,

representing hundreds of millions of years.

They read like a book of Earth history and they tell us about

different chapters in the evolution of early environments and life.

And the cool thing about going to Mount Sharp at Gale Crater

is going to be there, we'll have a different book

about the early environmental history of Mars that will tell us

something equally interesting, and we don't know what it's going to be yet.

The team believe the place they've chosen to land is

the perfect spot to look back in time.

They want to know if Mars could have supported life

at any point in its history.

So that Curiosity can discover all the information the scientists need,

the engineers have designed it to work just like

a human exploration team would back here on our own planet.

What Curiosity can do as we begin to explore Gale,

is pretty much what a geologist would do on Earth,

but it's also bringing along a chemistry lab.

The official name of the mission is Mars Science Laboratory.

And with good reason.

We have three different camera systems.

We have another instrument that involves a laser that gives us

the ability to zap out and understand

the composition of the environment around us.

We've got instruments that can ping things down in the subsurface

and tell us if there's water down there.

And then we've got other instruments that can actually tell us

about the laboratory conditions, like what we would do on Earth.

It's this chemistry lab, right in the belly of the Rover,

that makes the mission really special.

What Curiosity can do, which has never been done before on a Rover mission,

is to actually drill a hole in the rock,

take the powder and put it into the chemistry laboratory which is inside the Rover.

And that I'm really excited about, because it takes us

to a whole other level with science analysis on Mars.

This is a clone of an essential piece of Curiosity's mobile chemistry kit.

It was constructed here at the Goddard Space Laboratory

by planetary scientist Paul Mahaffy and his team.

This equipment, known as SAM,

can reveal the chemicals present in the Martian rock.

But for it to work,

SAM needs to be fed the right sort of rock samples, correctly prepared.

So Curiosity will first have to use all the other tools it has at its disposal.

The very first tools are the very high resolution cameras

on the mast of Curiosity.

And then, when we get even closer to a sample

that we might see in the distance and then approach,

we'll start using other tools.

For example, on the mast is an experiment

called ChemCam.

ChemCam will point at a rock and fire a laser.

And then look at the emissions that come off from that rock,

and that's really important

because it can tell the differences between different types of rocks.

So if we come across a rock that looks substantially different

from rocks we've looked at before,

then we might want to approach those samples,

put out the arm, and start interrogating that rock or that outcrop

with instruments that are on the arm.

An element analyser and a very nice microscope,

and if we examine the outcrop or the rock with those tools

and decide it's worth even further exploration,

then what we do is we sample the rock.

We drill into the rock, we create some powder with the sampling system

and then we deliver that powder into SAM.

The chemical analysis of this powdered rock

is one of the most important tests in the mission.

That's why the team are still running tests on SAM's twin back here on earth.

We've put a bit of powdered rock into the oven of SAM,

and we slowly heat it up from ambient temperature

to very hot temperature, about 1,000 degrees centigrade.

And as the sample is heated up, at different temperatures it releases

different simple gases or complex gases, and that helps us determine

what the mineralogy, what the mineral composition of the rock is.

SAM can look for the chemical signatures of water

and it can also detect organic compounds - the building blocks of life.

Our very first job on getting to Mars will be to understand

if there are organic compounds that we can even detect.

Mars is a very harsh environment.

Ultraviolet radiation penetrates right down to the surface

because there is less of an atmosphere than on Earth.

The same is true for very energetic cosmic radiation

that pounds in and really has the potential to destroy

fragile compounds that are very close to the surface.

So that's a very first-order question -

are there organic compounds on Mars? Can we detect them with SAM?

And if there are, then the fun really starts.

The discovery of organic compounds on Mars

would cause huge excitement right across the globe.

Together with liquid water, they are regarded as essentials for life.

Curiosity's other tests will reveal

whether the ancient Martian environment

could have allowed life itself to form from these building blocks.

Even in the best-case scenario,

the environment on early Mars would still have been pretty hostile.

So to understand if extraterrestrial life could have formed,

astrobiologists like Lewis Dartnell need to find out

the most extreme conditions in which life could still survive.

They do it by looking for the limits of life here on Earth.

Searching out harsh, dangerous environments,

places where we used to think life could never exist.

A lot of what we're trying to do

is understand the limits of terrestrial organisms.

What's the survival envelope

of Earth life, so places that are very hot and acidic

or are very cold and dry, like Antarctica,

or some very high-pressure, very high temperature places,

like the black smokers and the hydrothermal vents on the sea floor.

Because it's by understanding life in these most hostile environments on Earth

that we understand a lot about the possibility of there being life

on other worlds, and in similar environments.

This decaying train line is one of these hostile environments on Earth.

It's a strange, alien landscape,

cut through by one of the world's most extraordinary rivers.

Now, that's...

That is blood, blood-red.

That's incredible.

The Rio Tinto is 100 kilometres long,

running from the mountains of Andalusia to the Gulf of Cadiz.

It is been used by NASA to test life-detection equipment

for Mars missions.

Rio Tinto is one of those places that you read about time and time again.

It's commonly used as an example of a Mars-like environment here on Earth.

I've seen loads of photos in journal papers and books, textbooks,

but it's only when you come here

and see with your own eyes that it just jumps out at you.

That is... That is an alien colour for a river, that is, blood red.

To understand what Mars might have been like millions of years ago,

astrobiologist first try to understand these desolate places on earth.

Actually, the reason that the waters here in Rio Tinto are blood red

is because the substance is the same.

The oxidised iron in our blood is the same stuff as in that river

turning it that grotesque, off colour.

It's absolutely amazing.

It had always been thought

that this strange red colour was a result of pollution,

that the water had been tainted by iron and other metals

washed downstream from the mines

that have existed here since Roman times.

Well, I can't see anything obviously alive,

and there's clearly no fish swimming around in here.

There are no visible signs of life.

And the Rio Tinto's waters hold another secret,

which made people think there was no hope

of even the tiniest life forms ever existing here.

So, I've got a PH meter here, and I'm going to test the acidity

of the water in the Rio Tinto at this place here.

Now, a normal river, a healthy river, would be PH7 - that's neutral.

And, obviously, the lower the number, the greater the acidity is.

So I'm going to take a sample...

here...

..dunk in the PH probe and we see that it's dropped below 3 already,

2.7 and it's levelling off at about 2.65, so that's acidic.

That's about 100,000 times more acidic than a normal river.

And that's almost as acidic as stomach acid.

That is one acidic river.

If liquid water ever existed on Mars,

it might well have been a metallic acid river like this.

It seems unlikely to think that life

could have emerged in such a hostile environment,

but scientists have discovered this blood-red river

is actually teeming with microscopic bacteria.

This is a microscope photograph of the river water

and you can see these thin, hair-like threads

down the microscope, and these are the microbial filaments themselves,

these are the cells, these are the life in this water.

These extraordinary bacteria

are not just tolerating the strange river conditions -

they're actually creating them.

They simply don't behave like life as we know it.

The community, the ecology of the extremophiles living in this river,

they don't need to eat complex organic molecules

like our cells have to, like human cells or animal cells,

they've got far simpler requirements,

and all those cells need to munch on are fundamental things

like iron and sulphur dissolved in the water,

and they're reacting together

and use that chemical reaction to power themselves,

and a by-product - a waste product, if you like - of that living process

is the sulphuric acid and that's why Rio Tinto is so phenomenally acidic.

So life can find ways to survive

even in conditions people thought would mean instant death.

That raises hope that similar microbes could exist on other planets.

So scientists are waiting with bated breath

to see what Curiosity will tell us

about the conditions on ancient Mars.

They might not have been all that different

to some of the places extreme life survives on Earth.

But before Curiosity can begin its scientific mission,

..it first has to touch down safely on the Red Planet's surface.

With landing day now looming close, the responsibility weighs heavily

on the shoulders of lead engineer Joel Krajewski.

All engineers are aware, of course, of the risks of a mission like this,

and the pressure of that, or the stress of that awareness,

different people handle in different ways.

I go surfing.

You spot a good wave...

..paddle hard, feel the lift behind your feet,

dig a heel in...

..and the wave takes you all the way in to shore.

But no matter how much you've practised...

..nature can surprise you.

You can see a good wave...

..paddle hard for it...

..and - wham!

That's a wipe-out.

I would not want to wipe out in space.

Back at NASA's Jet Propulsion Laboratory...

..it's not just Joel who is feeling the pressure.

Although Curiosity is only weeks from arrival,

the team is working harder than ever.

Any loose ends that are going to be messy?

Like, you know, the eyes not closed, any of that kind of stuff

-that we're going to have to deal with?

-The eyes are all closed.

With most of the testing now complete,

it's no longer machine failure that is worrying Joel.

It's the possibility of human error.

We have done all of the instrument and engineering check-outs on the vehicle,

so we know the vehicle survived the launch experience well

and it's healthy.

Of course, what's not quite ready is us - we, the team.

We have to operate this vehicle through the landing event

and then in the science mission after that,

and for that, of course, we have to train ourselves.

RADIO CHATTER

With 80 days to go until landing,

the team are carrying out their toughest test.

A complete rehearsal of the Rover's landing, in real time.

The spacecraft is now reporting,

radio has reached entry interface and things are nominal.

Although it's a simulation, it feels just like the real thing.

This is the big day, which is to say the big night.

We've gone through five days of approach,

but now here, we have only a few hours left until landing

and so it's kind of... This is for the money!

As they simulate the Rover's final approach to Mars,

the atmosphere in the control room is good.

Even the scientists have arrived to watch the show.

It's going really well.

We're just under 30 minutes until we touch down on the surface of Mars.

Everything's looking good.

But Joel wants to give the team a real test,

so this rehearsal won't go perfectly.

Hidden in the wings, a team of gremlin engineers

is making it appear as if the spacecraft is encountering problems.

So we're going to learn, all together now,

how well the whole team is able to navigate through problems

and make good choices, precisely in the state of extreme exhaustion.

You get caught up in it because the screens look the same

as when we're looking at the real spacecraft,

the people are sitting in the same positions -

I'm in the chair I'm going to be in - you're doing the night shift.

You're kind of tired and kind of on edge

and so when you see, like, monitors go red and everything,

for a second... (GASPS) It's very compelling.

As the simulation of the landing begins,

it's Adam Stezlner's turn to practise guiding Curiosity

safely onto the surface of Mars.

I feel like a fisherman who's caught a whale

and I just don't know... Can I do this? Am I up for this?

The huge distance between Earth and Mars

means that once the team has sent the instruction to land,

there will be no going back.

The spacecraft has reached entry interface and things are nominal.

Any message they send to Curiosity takes 14 minutes to get there,

so for the final stages the Rover will be on its own.

For them the landing will be like

the longest roller coaster ride they've ever taken.

Stand by for parachute deploy.

Effectively they make their bet and they say, "OK, go,"

and it's hands off and the actual landing itself - going through the atmosphere...

Confirming that we have parachute deploy.

..jettisoning hardware...

Heat shield has been jettisoned.

..firing thrusters...

Powered flight has begun.

..that all has to happen autonomously by the vehicle,

which is actually harder for people, I think.

It's only a rehearsal, but there is still a tense wait

as the Rover performs the last of the landing manoeuvres.

Eventually, Curiosity touches down safely.

APPLAUSE

The team did really well

and they kept their heads under pressure

and we're still working really well under pressure,

and so that's all I could ask.

The rest is in the hands of the fates.

The team are now preparing

to go through this procedure one final time.

In six days, we'll find out if they can do it for real.

Subtitles by Red Bee Media Ltd