Burning up all of that satellite junk

London: Humanity has littered the space around Earth with a staggering amount of orbital junk from broken-up old rockets and satellites. Nasa estimates that there are 500,000 pieces of debris larger than a marble and 20,000 larger than a softball (one feet in circumference).

All pose a threat to spacecraft; this month, for example, flight controllers had to move the International Space Station out of the way of a fragment of an American Minotaur launcher.

Many proposals have been made to address the space debris problem, from shooting junk down to clearing it with a gigantic net, though none of the ideas is yet close to being used in an operational mission. The most advanced is a project called e. Deorbit, which the European Space Agency (Esa) is working up into a design to put to ministers of its member countries for approval next year.

The e. Deorbit craft would capture a derelict satellite before it breaks up into smaller pieces, which are far harder to remove, and would then burn up both the satellite and itself through a safe, controlled re-entry into the atmosphere.

The plan is to make the technology cheap and simple enough to fly many times, once the feasibility of the e. Deorbit approach has been proved in a demonstration mission. This could take place in 2021, if Esa’s Council of Ministers endorses what is likely to be at least a 150 million euro project at its meeting in December next year.

The project team looked at several options for disposing of redundant satellites. The original idea of lifting them into safe, higher orbits was dropped in favour of “downward deorbiting”. An early proposal for e. Deorbit to harpoon the satellite has been dismissed too, at least for the time being.

Instead, it is likely to capture it with robotic arms or perhaps in a net. The craft will need excellent sensors to detect and grab or enmesh its target safely, with no risk of an accident that could turn both e. Deorbit and its target into new space junk.

“I am very pleased with the progress we are making,” says Robin Biesbroek, project manager. “We are now going into detail on the concept of operations, e. Deorbit’s subsystems design and, especially, the capture and deorbit phases ... We need versatility to capture large and small satellites, including ones that are spinning rapidly.”

So far there have been surprisingly few disastrous collisions in space, given the amount of junk up there and the potential for damage. A loose 1 centimetre nut from a satellite, travelling at many thousands of kilometres per hour, can hit with the force of a hand grenade. The problem is most serious in low orbits hundreds of kilometres above Earth.

The “geostationary” orbits 36,000 kilometres high, occupied by many communications and weather satellites, are less cluttered.

Probably the worst crash so far came in 2009 when a defunct Russian Kosmos satellite destroyed a functioning US Iridium communications satellite — adding more than 2,000 pieces of trackable debris to the inventory of space junk, according to Nasa.

But no one should feel complacent about the future, as satellites are launched at an ever-increasing rate. “We are getting collision warnings almost every week for some of our satellites,” says Biesbroek. “We really need to do something.”

At the same time Esa is telling the space industry to “design for demise”: by making future satellites intended for low orbits in a way that minimises the risk of their ending up as hazardous debris. They must be built in a way that makes it possible either to bring them down safely or to boost them into an uncluttered high orbit when their operational life is over.

Satellites destined for eventual deorbiting should be designed to burn up safely and completely in the atmosphere on re-entry, without the need to avoid the risk of damage from intact pieces by targeting them at uninhabited parts of the world such as the open Pacific Ocean.

“It has become obvious that achieving this in a systematic way implies wholesale evolution of low-orbiting satellite platforms,” says Luisa Innocenti, who heads Esa’s Clean Space Initiative.

Financial Times