Welcome to a journey of a different kind:
one which brings us back to Earth.
The objects we encounter along the way are manmade.
Originally designed to explore the universe,
these are now a challenge for modern space flight.
We pass Pioneer 10 on its way to interstellar space.
Now defunct, it has provided us with fundamental insights into our Solar System.
Space debris is not a concern out here, so let’s rush on.
Our gas planets have seen probes flying by.
Only Jupiter and Saturn have had orbiting satellites.
To prevent contaminating the planet’s environment with terrestrial forms of life,
they are safely disposed of.
We are entering the region of the rocky planets.
Besides Earth, Mars is the most observed.
We can track the location of active probes orbiting the red planet
but not of their inactive predecessors.
These uncontrolled spacecraft could become a risk to other missions.
Before we enter our home planet’s zone of influence,
we pass by the so-called Earth-Sun Lagrange Points.
Here, a balance between forces, allows spacecraft to move synchronously with Earth.
Despite growing demand for the Lagrange points, especially for space telescopes,
there is no risk of congestion.
The balance of forces is only perfect at precisely one spot,
and the slightest deviation will cause the objects to drift away.
To prevent a return to Earth,
ESA’s former Herschel and Planck space telescopes have used their remaining fuel
to bring them into an orbit around the Sun.
The risk of a return is now close to zero.
The next objects we encounter are on highly eccentric orbits
reaching from a few thousand to more than 100,000 kilometres altitude.
These orbits are very sensitive to perturbing forces caused by the Sun and the Moon.
To prevent long-term interference with frequently used regions
due to drifting and uncontrolled reentry,
ESA has modified the orbits of active missions such as Cluster-II and Integral.
The satellites will now re-enter within the next 25 years at safe latitudes.
Let’s continue and visit one of the most congested regions in space:
the geostationary ring.
This is the only orbit on which satellites move synchronously with Earth.
An ideal choice for meteorological and telecom satellites.
The average distance between two objects here is only 190 km.
Defunct spacecraft in geostationary orbit can drift and endanger satellites in their vicinity.
This is why experts recommend to retire these objects at least 300 kilometers higher,
to a so-called graveyard orbit.
With a successful lift, they should no longer interfere with the Geostationary Orbit.
But can this be guaranteed for all times?
Aging satellites are known to release debris
and explosion can occur due to residual energy sources.
The resulting fragments can be thrown back and cross the Geostationary orbit.
The release of residual energy, once the nominal mission is completed, is therefore fundamental.
Launcher stages used to deliver spacecraft into the geostationary ring
often remain on their transfer orbit and could interfere with active missions.
Consequently, debris mitigation guidelines foresee that these stages
should be maneouvered out of the geostationary ring and other frequently used regions.
Further along, we pass through the region used by constellations for satellite navigation.
Like layers of an onion,
four different constellations make use of four different altitudes.
Inside these layers, we also find defunct satellites and upper-stages.
Stable graveyard orbits are difficult to find here.
Fortunately, no explosive break-ups have taken place so far.
As we move even closer to Earth,
we see that the number of objects around us is growing.
This is the region of the Low Earth Orbits.
Two-thirds of all large manmade objects are concentrated here.
About 600 active satellites provide us with science and Earth data, and telecommunications.
They are surrounded by thousands of defunct satellites, rocket stages and fragments.
Plus, this area is facing a surge in spaceflight activity.
Smaller and more cost-effective satellites are increasingly launched to low earth orbit.
The only chance to ensure the future use of these orbits
is to strictly apply debris mitigation measures.
The first is to monitor the environment while spacecraft are still active.
ESA satellites like Cryosat-2 have to perform 1 to 2 maneuvers per year to avoid collisions.
The second measure to combat the harsh rigors of years in space
is to release residual onboard energy by depleting fuel,
venting pressure tanks and discharging batteries.
Finally, the longer spacecraft stay in orbit,
the higher the risk of collisions becomes.
Experts fear that one day a cascading effect of collisions
and follow-on collisions
might set in making spaceflight in this orbit extremely difficult.
A maximum of 25 years in orbit after mission completion is, thus, recommended.
This can be achieved by moving the spacecraft downwards
into the denser layer of Earth’s atmosphere.
In 2011, ESA successfully conducted such a disposal maneuver with ERS-2
lowering it from an operational altitude of 800km to 600km,
where the remaining fuel was burned.
Instead of otherwise 200 years, ERS-2 will now re-enter in less than 10.
On their way down, objects pass through the altitude of another manmade object,
our human outpost in space: the International Space Station.
Although the environment here is relatively clean, it is not risk-free,
as shown by the many impact chips on its surface
and the regularly conducted collision avoidance maneuvers.
In even lower altitude, uncontrolled objects are bound for a re-entry.
To minimize risk, larger spacecraft must be brought down using a complex,
controlled manoeuver to a selected, safe spot on Earth.
Without such a manoeuvre, the time and location of reentry, are not under control.
The uncontrolled re-entry will start after a final orbit revolution at about 100 kilometers.
First, the aerodynamic forces
will cause exposed external parts of the spacecraft to be sheared off.
During deceleration, the object will be exposed to extreme heat.
Some materials, such as aluminum, will begin to melt.
The outer shell is gradually destroyed.
Internal elements are released to the airflow and dissolve.
In addition, strong aerodynamic deceleration enhances the destruction process.
With complete disintegration only components made of heat resistant material
like titanium or glass will have survived.
They cool down, and fall with a terminal velocity of about 300km/h
mostly into the vast seas.
Occasions to find space debris objects on the ground are very rare.
And, unlike meteoroids, they do not form craters.
We have reached the end of our journey.
Spaceflight has put mankind forward in the endeavor to understand our Universe.
It provides us with unique insights into our home planet
and makes us aware of our responsibilities towards it.
To ensure future exploration and exploitation of space,
we need to tackle the challenge of space debris.
The counter measures described in this film are a first step.
With joint and continuous efforts of all space faring nations
we will be able to achieve this goal.