Raumfahrt - Weltraummüll muss aus dem Orbit entfernt werden, sagt ESA


Space debris must be removed from orbit says ESA

It’s time to start actively removing space debris from orbit or risk disaster, says the European Space Agency


t was on 23 August at 17:07 GMT that spacecraft operators at the European SpaceAgency’s (ESA) control centre in Darmstadt, Germany, noticed something was going wrong. Their flagship Earth observation satellite, Sentinel-1A, had suddenly jumped into a slightly different orbit and a slightly different orientation.

More seriously, the electrical power had dropped, and was not returning to normal. The spacecraft was only in its third year in orbit. Activating on-board cameras that had been used two years earlier to monitor the deployment of the solar panels, the operators found the problem.

It was enough to make an engineer’s blood run cold. There was a 40-centimetre-wide damaged area on one of the solar panels. 

The spacecraft had been hit by a piece of space debris. Subsequent computer simulations of the damage indicated that the solar panel had been hit from behind and that the size of the impacting object was no more than just a few millimetres.

It packed such a punch because it was travelling at orbital velocities, which are measured in kilometres per second. It was lucky that the debris wasn’t any larger. If it had been, the entire solar panel could have been shattered and the mission ended. Worse, the fleck could have struck the main body of the satellite.


The picture shows Sentinel-1A’s solar array before and after the impact of a millimetre-size particle on the second panel. The damaged area has a diameter of about 40 cm, which is consistent on this structure with the impact of a fragment of less than 5 millimetres in size. Photograph: ESA

In that case, “the outcome might have been much more severe,” said Holger Krag this week at the opening of the 7th European Conference on Space Debris, which was held at ESA’s Space Operations Centre (ESOC) in Darmstadt, Germany.



Krag is Head of the ESA Space Debris Office. His team monitors the 10 satellites that ESA currently operate in low Earth orbit to protect them from the swarm of human-made debris that now surrounds our planet.

On average there is a high risk alert of a potential collision every week, and every ESA satellite has to be manoeuvred to avoid a collision once or twice a year. “It’s just normal life now,” says Krag.

Radar stations track 18,000 objects in orbit. Of these, only 7% are operational satellites. The rest is space debris. And radar only sees the big stuff.

Using observations and computer models, Krag estimates that there are around 5,000 objects larger than 1m, 20,000 objects larger than 10cm, 750,000 larger than 1cm (he calls these “flying bullets”), and a whopping 150 million larger than 1mm (or about the size of the piece that damaged Sentinel-1A).

Space debris comprises spent rocket parts and fragments from defunct spacecraft: old batteries can explode, leaks can occur in coolant systems that solidify into pellets, occasionally satellites actually collide. Worryingly each collision produces more fragments and exacerbates the problem.

And it’s not just satellites that are at risk. So too are human lives. The conference was addressed by ESA astronaut Thomas Pesquet, via a satellite link from the International Space Station (ISS). 

Just like other satellites, the space station has been manoeuvred out of harm’s way in the past. Chillingly, however, if the collision alert comes with less than 24 hours warning, there is nothing that can be done.

Pesquet described how the astronauts must close all the hatches between the various modules and then wait in their Soyuz spacecraft, ready to perform an emergency evacuation to Earth if needed.

This procedure has been enacted four times in the 19-year history of the ISS. The latest was in July 2015, when the three man crew received just 90 minutes warning that a collision was possible. Thankfully, the space debris sailed cleanly by and to date no catastrophic debris strike has taken place.

But it’s set to get worse. So called mega-constellations of satellites are planned by companies such as One Web, Boeing, SpaceX and Samsung to bring Internet access to all sectors of the globe. These will loft more than ten thousand satellites into orbit.

By way of comparison, since the launch of the world’s first spacecraft, Sputnik One, in 1957, only 7000 spacecraft in total have been launched in the entire 60-year exploration of space.

The nightmare scenario that space debris experts contemplate is called the Kessler syndrome, after American astrophysicist Donald Kessler. In 1978, while working for Nasa, he published an analysis that showed frequent collisions exponentially increased the amount of space debris, leading to many more collisions, leading to much more debris until we lose the use of certain orbits because anything we put there would certainly be hit.

Krag showed the conference a graph of the radar-tracked fragments and said that since 2002, “The growth has entered into the more feared exponential trend.”

There can be absolutely no doubt that the time to do something about space debris has arrived, and this is what the experts have spent the week discussing. At the conclusion of the conference today, Jan Wörner, ESA Director General, committed the Agency to leading European activities to combat space debris.

This includes detection, tracking, and development of automatic collision avoidance systems for satellites, and new binding guidelines on satellite design. He went further saying that there had to be a concerted effort to reduce and remove the space debris that is already there.

ESA knows this is challenging. Their own debris removal mission, called e.deorbit, failed to get the backing of enough European governments last year and so was not funded.

Addressing this point at the conference, Brigitte Zypries, German Federal Minister for Economic Affairs and Energy, said that the mission would be re-tabled at the next ministerial meeting in four years time.

Wörner also said that he would not tolerate any excuse for non-participation. Clearly there is palpable determination in the agency, and a growing interest around the world. For the first time in its history, the conference was oversubscribed, and had to turn researchers away.

But unless a global community comes together quickly to tackle this problem, it will inevitably end up being too little too late.

Quelle: theguardian

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