DW: Do we need garbage removal in space? How high is the risk that a satellite could get hit by a piece of space debris?

Manuel Metz: Actually, there is a risk. There are a lot of objects in orbit. We know about 22,000 objects larger than 10 centimeters. There are about 750,000 objects larger than one centimeter and about 150 million objects larger than one millimeter.

That's incredible. Where do all these objects come from?

They come from all the space activities from the past: satellites have been launched into orbit and they have to be left there after their mission. Sometimes you have explosions in orbit, especially of upper stages of rockets. And those events produce all this space debris.

And with every collision I suppose the problem gets even bigger, right?

Absolutely. It seems that we are currently at the rim of a process where debris collides with each other and produces more and more debris, even if we would not launch any more satellites into orbit.

Is there a chance to protect the satellites from a collision?

We can only protect satellites from collisions with small pieces of debris.

By installing shields?

Exactly, by installing some kind of shield. In an experiment here on earth, an aluminum plate was hit by an object which is of millimeter size with a speed of 250,000 kilometers per hour. The result was a large hole in the size of a finger.

And which orbit in space is the most messy one?

The most messy one is one at altitudes of about 800 to 1,000 kilometers.

So that's where all the weather and spy satellites are?

Exactly. Earth-observation satellites, for example the ESA satellite Envisat is in this orbital region.

Now the German Aerospace Center is planning to capture discarded satellites. How does your system work?

There's a satellite mission planned that is called DEOS, the German Orbital Servicing mission. It is a servicer satellite equipped with a robotic arm to capture another satellite tumbling in orbit. In the final phase of the mission, both satellites, firmly attached together, are de-orbited into the earth's atmosphere.

But that means that with every discarded satellite you capture you lose a DEOS system. That's pretty expensive, isn't it?

That would be absolutely correct. But the DEOS system has a second objective. We want to show that we are able to service satellites in orbit. To perform maintenance operations - refuelling, for example.