The Trouble with Space Junk Horizon

'Down, I see her. Right cable is down.'

'OK to go for configuration, Steve.'

'Thank you, Al.'

220 miles above the Earth on 12th March 2009,

was a day like any other on the International Space Station.

'Two and three stowed.'

It was mid-morning and I was getting ready to exercise.

And we were just sort of getting into our mid-morning routine, if you will.

'OK, Nick. On my way.'

But then they got an unusual message.

We got a call that we were having "a red conjunction".

We were looking around, "What is a red conjunction?"

Because we hadn't really trained for it.

A red conjunction is a warning code

that the space station could be hit by some orbital debris.

It was a little bit chaotic,

because this was the first time we had had one of these.

The space station was travelling at nearly 8km per second.

The space junk was travelling at the same speed

in the opposite direction.

If they hit, the consequences could be catastrophic.

It gets hit by something relatively small...

..penetrates, but because of the pressure inside,

it just forces the modules to open up just like a balloon bursting.

And that happens extremely quickly,

with no chance that an astronaut in that module could ever get out.

'Copy, Al. You're on your way to the station.'

Nasa was taking no chances

and scrambled astronaut Sandra Magnus to the Soyuz life raft.

All she could do then

was sit and wait.

And it's either going to hit or it's not going to hit.

And so worrying about it doesn't help you.

Was this just an isolated incident

or was it a sign of a growing threat to life in space...

..and modern life on Earth?

'And liftoff.'

'First stage move. Propulsion performing normally.'

Space...

..endless and empty.

At least that's what we used to think.

In the last few decades,

orbits around Earth have become crowded with satellites

and littered with space junk.

So space junk is all the stuff that we've launched into orbit

that no longer serves a useful purpose.

So it's satellites, it's rocket bodies,

it's, you know, old gloves.

It's toolkits that astronauts have accidentally dropped.

Basically, litter that we've left in space.

But littering space is much more dangerous than it is on Earth.

Those objects are going at 17,000 miles an hour.

And when you're going 17,000 miles an hour,

it does not take a big piece of debris to ruin your day.

Satellites are virtually defenceless against high-speed orbital debris.

And they are crucial to modern life on Earth.

We are far more connected and far more dependent upon satellites

than most people really know.

The ability to make phone calls,

the way we do it now was just a dream less than 100 years ago.

We're all connected to the internet.

Weather satellites, navigation systems,

it's almost impossible to get lost,

despite what the guidance says on the GPS about turn left and turn right.

All of that and more is becoming increasingly vulnerable.

Unless we tackle the debris problem,

there is going to be no weather forecast,

there is going to be no news story from the other side of the world.

You're not going to be able to turn on the television and see the World Cup.

But how did space become littered with dangerous debris?

'Today, a new moon is in the sky.

'A 23-inch metal spear placed in orbit by a Russian rocket.'

Space was a pristine environment,

until the launch of Sputnik in 1957.

But in the first decades of spaceflight,

every time a rocket or satellite was launched,

it left behind some debris.

No-one thought it was much of a problem until this man,

Donald Kessler, did some calculations.

He was working for Nasa in the late '60s and early '70s,

when he discovered that leaving junk in orbit

wasn't like dumping junk on Earth.

People tend to think of orbit like a road through space.

I mean, as long as you stay on your road, you're not going to get hit.

It would be more accurate to think of the Earth as being

one big paved planet.

And when you want to go someplace,

you drive in a straight line from one place to another

and, of course, with no stop lights and no place to stop

and you're going to be running into each other in all kinds of directions.

And that's exactly what you've got in orbit.

So I headed up with an equation where I could write the spatial density,

its apogee and inclination.

Then you can do neat things like...

His calculations predicted that,

if bits of junk started smashing into each other at such huge speeds...

If you want to know the flux, the spatial density...

..they'd create a cascade of collisions

that would litter orbits with dangerous debris.

The integral of S squared...

This became known as the Kessler Syndrome.

..integrated over the volume.

In other words, if you never launch anything else in space,

there will still be this cascading phenomena that continues to grow

and, actually, it continues until you essentially grind up all the satellites into small dust particles.

Three passed SV and 26.

No time critical commanding.

No satellite conjunctions. Good on step six.

All data feeds to externals are open and both communication lines to the site are good.

No applicable sieves or TPs. You're good to execute.

Copy that, ma'am.

The prospect of this nightmare scenario was so worrying that,

in the early '80s,

the American Air Force started cataloguing space junk.

The technology only allowed them to track objects

slightly bigger than a cricket ball.

Give level one a call on the TTC-56.

They started at 6,000 pieces.

And that number grew slowly to 10,000 over the next two decades,

helped by an international agreement calling for used rocket bodies

to be returned to Earth and burned up in the upper atmosphere.

OK, stand by.

It kept the risk of any major collision very low.

But in 2007,

all that changed.

The Chinese launched a missile

that took out one of their own defunct old satellites

in low Earth orbit.

The American military were under no illusions about what this meant.

Well, I think they did that because they realised

that the United States military

is critically dependent on space.

And they felt like if they were going to be able

to effectively respond to whatever challenges they had in the future,

they needed to develop a way to challenge our space capabilities.

Basically, there's not a single military operation

that takes place in the world today

that is not critically dependent on space capabilities.

And if space goes away,

we do not fight as effectively as we would otherwise.

As Kessler predicted,

collisions in space are more dangerous than those on the ground.

As demonstrated in this computer model.

After the collision, you see quite a compact debris cloud at the start.

But then, because some of the fragments are thrown into higher orbits

and some are thrown into lower orbits, the speed is different.

So you see the debris clouds stretch out and it forms this ring.

Now, because the Earth is not spherical,

it causes that debris ring to start to stretch out.

It moves the orbits around the planet.

So it goes from this kind of compact debris cloud right at the start

to the situation where all of that debris

ends up being distributed all the way around the planet.

Before China took out its old satellite,

the American Air Force were tracking 10,000 objects

in their debris catalogue.

After it, they were tracking an extra 3,000.

The debris field collisions create

is a massive concern for the general

who is in charge of all of America's space operations.

If you go to war in space, then it becomes a kinetic war.

You create a debris field that is just unmanageable

and you can't operate or fly in it.

So I hope to never go to war in space.

But at the same time, if we're threatened,

we have to be able to defend ourselves

and we have to be able to defend ourselves right now.

But the debris problem got worse in 2009

when an Iridium satellite collided

with an out-of-control Russian Kosmos satellite.

Now they were monitoring 17,000 pieces of junk.

At that number, Kessler's calculations

were forecasting a major collision on average every five years.

And really the situation you start to worry about is that's just one event.

You know, if you start to say,

"We're going to have one of these events every five years

"and that each one is going to generate thousands of fragments,"

then you end up in the situation where it's basically, you know, a lottery,

in terms of whether or not your satellite is going to be hit.

We see thousands and thousands of near misses every single day

as a result of all the junk that we've put up there.

But that average of one collision every five years

might not be much of a guide to what happens in the future.

So let's say that you're on a soccer team

and your average is one goal per game.

A 20-game season, you score 20 goals

because you've scored one goal a game.

So, of course, you're very reliable.

However, you could just as well have scored ten goals in two games

and were useless the other 18 games.

Your average is the same,

but the confidence that I have of what you're going to do the next game is going to be much lower.

I don't know whether or not you're going to have a ten-goal game

or a zero-goal game.

The same problem right now having to do with space.

We know the average.

We don't know if the next event's going to occur

in one day or one decade.

So the stakes couldn't be higher.

But until last year,

no-one knew exactly what happened to spacecraft when they collided.

Until this...

This is the work of Patti Scheaffer.

She's a key part of the team that fired a baked bean can-sized object

into a tank roughly the same size as the upper stage of a rocket.

And size mattered.

Well, this was the size of the object.

It was maybe a little bit shorter

but, basically, a large hollow object

is more representative of something that's actually in space,

like maybe a small satellite or a piece of a small satellite.

It also had to be a full-scale test.

Lots of people fire things like that, for instance,

and many things, many physical phenomenon

do not scale with size very well.

So we really wanted to get a full-scale, full-sized test.

It was the culmination of years of work.

But it was over in a flash.

"Is that T minus ten?"

"Yes, that's T minus ten."

"Nine, eight..." And then you hear this...

And the building literally shakes a little bit.

But I think a lot of it is me, you know, just being freaked out.

And then you see your screen flash up and it's over.

All that work is turned into this.

Travelling at 7km per second...

the can made a huge mess.

So this piece of modern art here is what the tank looks like.

Now, this was the top of the tank.

Right here, it folded after it flew through the inside.

But you can see it's all splayed out.

The intense heat from the explosion vaporised huge chunks of metal.

And when it condensed and cooled, she made a startling new discovery.

Flakes of aluminium, which came from bits of the can and the tank.

They might look benign, but in space they'd be lethal.

Now that's about, er...

What is that? 250 milligrams.

That's a little bit bigger, heavier than a ibuprofen pill.

And the energy that would have on orbit

at, say, 14km per second would be, er...

Well, the momentum would be about the same

as a hot-loaded .357 Magnum.

So that's a lot of momentum.

And the energy would be more like

a .50-calibre Browning machine gun sniper round.

So if you're going to think about how dangerous this is on orbit,

think .357 Magnum, .50-calibre sniper round.

Somewhere in there.

And she discovered that the collision generated

hundreds of these flakes.

No-one knew that vaporised metal could be so dangerous.

So if there are many more particles produced than we thought,

10 times, 100 times, 1,000 times more,

then it has a snowball effect,

because each one of those particles,

if there's ten times more, there could be ten times more strikes.

And each one of those makes ten, so that's ten times ten, which is 100.

If there's 100 times more, then each one of those can make strikes,

which is 100 times 100, which is 10,000.

So it snowballs rapidly.

The question is, how rapidly is it going to snowball?

And the only way we can know that

is to know how many of these particles we can't see

are actually made.

But if there are more objects in orbit than previously thought,

there should be more bullet-sized holes

in the biggest thing up there...

..the space station.

'The thing we showed you is still in the socket caddy when you get there.'

'It'll be right of the front module. It'll be right of the front module.'

'You can see almost everything from that vantage point.'

Astronaut Jim Reilly was on a spacewalk

to repair an external radiator on the station

when he spotted something he had never seen before.

And as we're tilting back, we're going past this radiator.

I noticed right out on the end of it,

there were three what looked like bullet holes

about the size of a 7.62 millimetre round.

And it's about the size of my thumb. Three of them, just about that size.

There was a fourth hole on the flight immediately behind mine.

A fellow named Rick Mastracchio was working on the same area.

And down by Rick, there's a fourth bullet hole on there.

The space station can absorb hits from small pieces of junk

because it has a specially constructed hull

made up of an ingenious layering system called a Whipple shield.

What you see here is a mock-up of the Columbus module

of the European Space Agency,

which is on the International Space Station.

And here you see on the outer surface

the Whipple shield has been implemented everywhere.

You see here a cutaway part

and you can see the outer wall, the bumper,

then you have some stuffing shown here

and the inner wall, which is finally supposed to stop the particle.

The layers absorb and dissipate the energy of any strike,

but the protection is only effective

for objects up to one centimetre in size.

Unfortunately, the American Air Force

only has the technology to track objects bigger than ten centimetres,

slightly bigger than a cricket ball.

And that leaves a huge and worrying gap in the space station's defences.

Objects between one centimetre and ten centimetres, roughly,

they can neither be avoided nor shielded.

So there is a dark risk that remains

even for the International Space Station.

If the space station was hit by a piece of debris

of this kind of size...

..it could be devastating.

So the space station is a pressurised module.

That means the pressure inside is greater than the pressure outside.

It's a vacuum outside the space station.

And the equivalent down here is a balloon.

You know, you blow air into a balloon,

the pressure is greater inside the balloon than outside the balloon.

And we all know what happens if you stick a pin into a balloon.

If you look at that balloon bursting in slow motion,

as the pin goes in, the balloon unzips.

And that's one of the things that could happen on the station.

It gets hit by something relatively small, penetrates,

but because of the pressure inside,

it just forces the modules just to open up,

just like a balloon bursting.

And that happens extremely quickly,

with no chance that an astronaut in that module could ever get out.

The space station can manoeuvre out of the way

of any bigger pieces of junk.

But as astronaut Sandra Magnus knows,

it's not like turning the wheel of a car.

You have to program the kind of burn you want to do.

You have to program the manoeuvre

the station needs to get to do the kind of burn you want to do

based on which jets you're using.

It takes several days.

They may have gotten it down faster than that,

but it's not just, "OK, flip a switch, let's move the station."

It's not that straightforward.

In 2014, the station had to move three times

to avoid large chunks of space debris.

But as Sandra Magnus discovered in March 2009,

sometimes there's not enough time to move the station.

It was mid-morning and I was getting ready to exercise

and we were just sort of getting into our mid-morning routine, if you will.

And we got a call that we were having "a red conjunction."

We were looking around, "What is a red conjunction?"

Because we hadn't really trained for it.

A red conjunction is a warning code

that the space station could be hit by some space junk.

This warning is only issued when there's no time to move the station.

It wasn't predicted.

It was a little bit chaotic

because this was the first time we had had one of these.

'Copy, Al. You're on your way.'

Ground Control were tracking a 13cm chunk

of a Delta II rocket body,

about the size of a CD, apparently heading straight for the station.

And Sandra was sent to the Soyuz capsule,

the space station's life raft,

in preparation for a possible evacuation.

When the Soyuz docks to station, it's put in sort of a sleep mode,

because you really don't need it while you're on station,

because it's, you know, your delivery vehicle

and your go home vehicle.

But when you're getting ready to evacuate from the station,

whether it's nominal or a contingency,

you have to power all that stuff up.

And there's a certain sequence of things you have to go through to do that.

But she wasn't panicking.

It's either going to hit or it's not going to hit.

And so worrying about it doesn't help you.

All you have to do is just prepare everything that you need to prepare

so that, if it hits, then you're in the best possible configuration.

And if it doesn't hit, well, then, you just go and do it anyway.

The Soyuz has a small window.

And as she sat and waited, she couldn't stop herself looking out.

So I'm looking out the portal thinking, "Oh, maybe I can see it."

You know, your view is like this, right?

It's like looking out of a peephole of a door.

I was laughing to myself, "Go on, there's no way."

Because if I saw it, it would be really bad, because it'd be right there.

Fortunately, the junk sailed by and the station was undamaged.

But the crisis did force the astronauts and Nasa

to re-evaluate what they would do if it happened again.

We got through it. It was all good.

So it wasn't that everybody didn't know what's needed to be done.

But it's like, what order do you communicate?

What's the most important thing you communicate? Who communicates what to who?

So there was a lot of refinement that needed to happen

and so we instituted that after this.

'OK, hatch opened and stowed.'

Since that near miss in 2009,

the amount of trackable orbital debris has gone up by over 20%

to 22,000 pieces.

'Before receiving, gate closed and locked.'

But scientists calculate that there are hundreds of millions of pieces of debris

that are too small to track

hurtling round in the orbits close to Earth.

'How about just one more check on the reel?'

Most of them don't present any threat to the space station.

But they do to the people who live and work up there...

..the astronauts.

For emergency doctor Kevin Fong,

who worked at Nasa in their human spaceflight programme,

astronauts are at their most vulnerable on the spacewalk.

'OK, we checked all four systems.'

'Modulation all four and clean with the go.'

These guys are out there tumbling around the Earth

holding onto the space station,

travelling at 17,500 miles an hour

250 miles off the ground

with nothing between them and death

but this multilayered suit and a visor.

I mean, that's... that's walking in space.

'Oh, my goodness, something's fallen out.'

Throw space junk travelling at similar velocities into the mix

and the dangers start to get bigger.

At that speed,

something as small as a fleck of paint could be life-threatening.

Just how dangerous has been tested in this special lab

at the University of Kent.

This strange-looking assembly of pipes and tubes

is actually one of the most powerful guns in Britain.

It can fire objects at roughly ten times the speed of a bullet.

But today, they're not firing anything as big as a bullet.

This tiny one-millimetre steel ball is what most space junk looks like.

In space, small is what's frequent. Large is not very common.

The ball wrapped in wax

and similar in size to a tiny piece of debris

or a fleck of hardened paint is loaded.

It's the most likely kind of thing to hit an astronaut on a spacewalk.

'237 in lift.'

'OK, I am ready to receive it.'

One of the most vulnerable parts of the spacesuit

is the astronaut's visor.

This is a piece of plastic, a polycarbonate,

which is typically used in space,

for example as a shield across the visor of the helmet

an astronaut might wear.

So he'd be looking out through it, protecting him from the environment.

What we're going to do with it here is we are going to put it in the gun

and fire one of our very small particles at 14,000 miles an hour towards it.

The polycarbonate is the same thickness as the visor.

So would the visor survive?

So this is our polycarbonate after the impact experiment.

So our one-millimetre object travelling at 14,000mph

has punched straight through the front.

At the back, there's a slightly larger whole.

So it's gone through and removed material from the rear surface.

And that's kept on going and hit what's on the far side,

potentially an astronaut.

'OK to go. I have my gate closed and locked.'

'With that you are go to release the cutters from the internal bearing.'

The visor's going to be almost non-existent as an obstacle.

The tiny amount of that energy,

a fraction of that energy that particle has gets taken up by shattering the visor.

And in terms of what it would look like to the astronaut,

well, it's probably going to be the last thing that they see.

The energy contained within a single fleck of paint

travelling at these enormous velocities,

it is much more akin to the energy you see

contained within a high explosive.

For astronauts like Jim Reilly, who's walked in space five times,

the dangers of space junk are part of the job.

You know, at some point, you get hit by something of any size,

it's pretty much game over.

But, you know, we accept those risks even here on Earth.

You know, you can get hit by a bus and it's just, it's your day, right?

So you accept that.

'Good to go to close the thermal hatch.'

Of course, the astronaut's suit

presents a much bigger target than the visor.

But that's more protected.

'Get all the routing back to the structure itself.

'Are you good on that?'

It has a layering system that helps slow down any small objects

that might pierce the fabric.

And it also has a built-in safety mechanism.

The suit can sustain a hole somewhere between an eighth and a quarter of an inch

and that will still have enough volume within the oxygen tanks

to give you about 15 minutes to get back into the airlock.

The problem on the station, though, is that you can be 15 minutes away and further

when you're doing some of your work.

'Your left hand is off just now.'

'OK, captain, complete.'

ASTRONAUTS TALK INDISTINCTLY

Spacesuit is kind of a bit of a misnomer.

It's not a suit.

It's the world's smallest spacecraft.

You depend upon it entirely for your life,

because inside that suit is an atmosphere that you can breathe,

a warmth enough to keep you alive

and something that can repel heat when it's out there.

FEMALE ASTRONAUT SPEAKS INDISTINCTLY

And it all looks great and it all looks nice and floaty.

But actually these are some of the most terrifying moments

in all of human space exploration.

This is the maximum exposure that an individual can have out there.

This is where they are stripped of all of the protections

that have been engineered over years.

It's hard to think of an environment or a situation

in which you would be more vulnerable.

MALE ASTRONAUT SPEAKS INDISTINCTLY

Up till now, no astronaut has ever come to grief in a spacewalk.

But for some scientists, the past is no guide to the future.

When the space age started, Nasa designed the spacesuits

so that the astronauts could survive impacts of very small dust.

But as the space age has gone on and bits of paint are flaked away from the outside of spacecraft

or sometimes a disused satellite explodes and showers space with very fine debris,

there is more and more debris about the size we've been shooting here today.

Sooner or later in the next decade or two,

an astronaut will be struck by something this size.

But maybe in the future,

people won't have to risk their lives on the final frontier.

At the European Space Agency's lab in Holland,

Dr Andre Schiele is suiting up

to test the next generation of astronaut.

He's wearing a high-tech sleeve,

which is remotely linked to a robot arm.

Every movement he makes with his hand and arm

is mimicked by the robot.

In space, it's a very hostile environment for humans to be

for several reasons.

There is debris that can hit astronauts

when they are doing activities outside.

If a robotic system is struck by a small part,

it will probably break,

but we are not facing life loss.

So it is much safer to do this

and we can actually control those robotic systems

from either inside the safe and shielded environment of the space station

or even from the ground.

This cutting-edge technology is still being developed

and won't come online for a number of years.

But even when it does,

Dr Schiele doesn't envisage replacing humans in space.

We strongly believe at Esa

that the combination of astronauts and robots

can be the most powerful one.

Where not one replaces the other,

but every system exploits its optimal characteristics.

So a robot is very good at repeating tasks,

at doing tasks in very hostile environments.

And humans are very good at planning tasks,

at understanding random situations.

So with the system that we show here, in the telerobotics lab at Esa,

we are combining the human intelligence

with the preferences of a robotic manipulator by tele manipulation.

But orbital debris threatens life on Earth as well as in space.

And that's because modern life

is increasingly dependent on satellite technology...

..from GPS

to television

to the weather forecast.

And in the future,

we're only going to get more dependent on space technology.

Our use of space is going to grow.

We're already relying on many services

that are provided by satellites already.

That situation is unlikely to change.

You know, we're only going to place more demands

on satellites into the future.

And, you know, if that happens in combination with a growing debris problem,

then there're going to be issues arising.

And that debris problem could be about to get worse.

Scientists have only recently begun to understand the risks

of 17 old Russian SL-16 rocket bodies

orbiting within 50km of each other.

They're big. About the size of a railway carriage.

We showed that there is a one in 400 chance over the next ten years

of two of those SL-16 rocket bodies colliding.

So you may ask, that doesn't sound like that's too bad.

I'm not sure how many of you would go and take the subway tomorrow into work

if there is a one in 400 chance that that subway wasn't going to make it into work.

So far, those old rocket bodies haven't come close to each other.

But could there be an even greater danger

threatening our dependence on space?

What I'm really more concerned about is kind of like the canary in the mine.

I don't care about the big breakups.

I care about the satellites that are failing for unknown reasons

because, statistically, you know you have many more

of the lethal, non-trackable objects

than you do of the trackable fragments

that are going to break things up.

So what a precursor should be,

an indicator that we're getting close to the Kessler Syndrome

is that we have many more satellites that have anomalies for unknown reasons.

'It's coming off. Go for deploy.'

'Oh, roger. Liftoff and the clock is started.'

This huge satellite was built in Britain in 2002...

..for the European Space Agency.

LAUNCH COUNTDOWN IN FRENCH

It was the largest civilian Earth observation satellite

ever fired into space.

And it was very successful.

But in April 2012...

..it suddenly stopped working.

So all of a sudden it went from generating huge amounts of data for scientists down on the ground

to basically one of the biggest pieces of junk that we see on orbit.

Some scientists suspect Envisat

might have been disabled by space junk.

Sometimes there is no clear indication and it's just a suspicion

that smaller particles have impacted the satellite and done some damage.

You can cut a cable easily or you can damage some structural parts.

So it certainly will happen. And it has happened in space.

Envisat is now hurtling around the world at over 7km per second,

in the same orbit as all of the other Earth observational satellites.

But the much greater threat of a collision with some junk

was highlighted when scientists built a computer model of its path

through the largest debris field.

So what we're seeing here,

this is the view from Envisat as it's travelling around the Earth.

These are all the other debris objects that we can currently track from the ground.

As we're moving along the orbit here,

what you see is there are plenty of objects that are passing in front of Envisat.

In some cases, passing right next to Envisat.

Now, when we get to the poles like this,

you can see just how crowded the environment actually is.

And Envisat is just going through that now without any kind of control.

So there's no way it can manoeuvre to avoid any collision.

You know, some of these things passing at 14km per second.

Huge amounts of energy's involved.

Removing Envisat from its dangerous orbit

is obviously a pressing problem.

The satellite company Airbus

is at the forefront of the race against time

to bring Envisat back to Earth.

They build some of the world's most sophisticated and complex satellites

in their high-tech clean rooms.

But they're figuring out how to solve the Envisat problem

in much more humble surroundings...

..the company's converted bike shed.

And what they've come up with is deceptively simple.

They plan to harpoon it.

This demonstration allows us to prove that we can target a small object,

a very lightweight object very accurately.

If we can do that, then we can certainly go and capture very big objects and very heavy objects,

which is essentially the main targets that we want to capture.

They hope to launch a chaser satellite,

which would carefully approach Envisat

or any other defunct satellite

and then fire the harpoon.

So this system will capture those items of debris,

tow them out of the orbits where they might collide with active satellites

and allow them to burn up safely in the atmosphere.

So the idea is to have a system which takes them away from where they cause a problem

and basically destroy them safely.

It sounds great in theory,

but it may not be easy in practice.

You're firing something, it's going to be travelling pretty quickly.

It's going to hit the other spacecraft.

OK? And that's kind of the situation that we're trying to avoid in the first place.

We're artificially generating a collision here.

The whole point of this spacecraft,

of, you know, removing that big junk

is that we reduce the number of objects that we have on orbit.

So we don't want to be generating any new debris.

The harpoon strike could have a much bigger unintended impact.

Where on that spacecraft are you going to fire your harpoon?

There are all sorts of things inside there that,

you know, potentially you can have problems with.

On the inside of the satellite, we have things like propulsion lines,

which you can see here, which carry the propellant for the thrusters.

And electronics boxes and various other bits of equipment.

So when we punch through this panel,

we need to take into account that there might be this sort of equipment on the other side.

Hitting the extremely volatile propellant with a harpoon

would almost certainly cause an explosion.

So Dr Jamie Reid and his colleagues

have been poring over the blueprints of Envisat

to make sure they can target

precisely where they want the harpoon to land.

But there's a final obstacle that might prove insurmountable.

This is a pretty big spacecraft.

It needs to be big because we're kind of manhandling this one.

You know, you're not going to send a mouse to grab an elephant.

So this spacecraft is big.

That means it's going to go onto a big rocket.

And that rocket is going to cost a lot of money.

So we've invested huge amounts of money into this.

And its job, essentially, is to grab a bit of junk and then burn it up.

You know, so it's not really performing any science, anything else.

That's what its job is for and we're spending huge amounts of money to do that.

It's certainly true that if you had one satellite

to go and catch one piece of debris, it would be very inefficient.

So the advantage of the harpoon design

is we can have one chaser satellite

that has lots of different harpoons on it

and it can go and capture multiple pieces of debris.

There are other plans to remove defunct satellites,

including capturing them in a net...

..sticking a magnetic thruster onto the body...

..physically grabbing drifting spacecraft...

..firing a laser beam to change their orbit...

..and even using solar radiation to sail them off to safety.

But the debris problem is so huge

that it might be beyond all of these solutions.

If I take off a certain number of objects over a certain period of time,

I'm going to reduce the probability of collision.

Unfortunately, from the analysis that's been done,

it's about 35 to 50 removals to prevent one collision.

That's not great, right?

A lot of people think, "I remove one object, I've stopped one breakup."

That is not the way it's going to work.

It's statistical in nature, it's being very proactive.

It doesn't mean we shouldn't do it. But it's not one for one.

It's going to be a huge, huge cost.

Do we spend the money on removing all these objects?

Or let's not spend the money.

Let's leave all the objects in orbit

and then we take the risk that some of those are going to be hit,

they're going to generate more fragments

and we end up in the situation where, you know,

Earth orbit is completely congested,

full of fragments and we can't launch new space missions.

Of course, satellites continue to be launched at about 120 a year.

But that's not what has scientists most concerned.

They're worried about these things.

CubeSats.

They're far cheaper than your conventional large spacecraft.

And what that means is we can put up more of these

and they can perform the kind of space missions

that we wouldn't be able to contemplate with a larger spacecraft.

What helps keep the cost down is that they're so small

they can be launched as part of the payload of a bigger satellite

or even from the space station.

They're quite simply thrown into orbit.

The disadvantage is that they're not manoeuvrable.

In the end, the problem is similar to a collision, if you like.

The release event of these objects

is more or less identical

to the large release of a cloud of fragments,

because these CubeSats are not manoeuvrable.

They cannot avoid collisions.

Even though the CubeSat is small,

there's is probably sufficient mass in here

that if it was to hit a larger spacecraft,

you know, at 10km per second,

it would cause a catastrophic breakup of that spacecraft.

You know, the mass of these could be

anywhere between 3kg all the way up to 20kg

and that's enough mass

to completely destroy a satellite like Envisat.

Around 100 of these mini satellites were launched in 2014.

And that number is only set to increase.

There is no law governing space operations

and that's primarily because space isn't divided up by national boundaries.

Space, in the end, is a resource. It needs to be shared globally.

There is no space above your country that you can reserve.

Spaceflight happens by orbiting around the full Earth.

So you have to share the whole space.

You need to have consensus globally

on what we do with this precious space.

Consensus isn't always possible to achieve.

So the United States, the most powerful spacefaring nation,

is taking matters into its own hands.

It's not going to break the bank by investing in unproven technology

to clean up the debris problem.

But the Federal Government is spending a billion dollars

on a new tracking system called Space Fence.

Space Fence will provide the capability

to detect, track and catalogue objects

all the way from the baseball size

down to sort of marble size,

depending on the altitude.

So instead of just tracking 22,000 large objects,

Space Fence will now allow the Space Surveillance Network

to track up to 200,000 much smaller objects.

To be honest, a lot of people would say,

"Well, let's just put our head in the sand and ignore the problem."

Well, that's just an irresponsible way to look at the problem.

If you can see that debris and if you can avoid that debris,

you need to do everything you can to do that.

Because every one of those events that is a collision

creates thousands of other pieces of debris now that you have to track.

This new system is called Space Fence

because it produces a fence-like radar beam.

It's the size of the radar and the huge increase in its frequency

that allows it to track much smaller objects.

When an object crosses that fence, we detect it.

And then we can electronically steer this energy

so that we can track it very precisely.

And then once you develop a track on it,

at that point I can then use physics

to predict where it's going to be in the future.

So every time the object goes over the site,

we would then collect more information on it, more data,

which allows us to refine the estimate of where it is at,

again, so that we can predict where it's going to be in the future.

But there are limitations to this system.

There are millions of objects of varying sizes orbiting Earth,

but it's only the thousand or so operational satellites

that can be moved to avoid a collision.

So even with the latest technology,

can science make any worthwhile predictions

about what might happen in the future?

What I expect is going to happen is not going to be at all

what anybody else that you're going to film is going to say.

Because I don't know what the answer is.

So I'm just going to tell you you have to live with ambiguity

and I believe that it will not unfold

in a predictable, linear, consistent way from anyway that we believe.

It's going to be sporadic and it's going to be unpredictable

and we're all going to act surprised

and myself and Don Kessler and Hugh Lewis are going to go back and go,

"The variance is large. We told you."

MALE ASTRONAUT TALKS INDISTINCTLY

'Right, that looks like it's in there.'

If Kessler's calculations about the increase in the debris problem are right,

and so far they have been,

then scientists forecast that this is what the orbits around Earth

will look like in the next few centuries.

'OK, I am ready to receive it.'

We're using space all the time.

You know, when we look into the future, that's only going to continue

and we're going to make more use of space.

'It did wiggle.

'To set that to be effective,

'it needs to be pointed forward.'

You know, if we are connected via space all the time,

then space becomes our single point of failure.

And we've got to tackle that problem.

But there are also idealistic

as well as practical reasons

for wanting to preserve our access

to what's now one of our most precious resources.

I want my kids and my kids' kids to be able to explore space.

And if we ruin the environment, we can't do that.

And that would be tragic, because my passion for space

came when I was ten years old and I watched Apollo 11

and I watched Neil Armstrong walk on the moon

and that magic that created that feeling in me that said,

"I want to do space,"

I want my kids and my kids' kids to have that opportunity.

And if the space environment is ruined, that will never happen.