What can we do with unwanted satellites?

April 30, 2015 by Stephen Hobbs, Chiara Palla And Jennifer Kingston, The Conversation
It’s crowded up there - the many objects tracked in low Earth orbit. Credit: ESA

There are thousands of satellites in Earth orbit, of varying age and usefulness. At some point they reach the end of their lives, at which point they become floating junk. What do we do with them then?

Most satellites are not designed with the end of their life in mind. But some are designed to be serviced, such as the Hubble Space Telescope, which as part of its final service was modified to include a soft capture mechanism. This is an interface designed to allow a future robotic spacecraft to attach itself and guide the telescope to safe disposal through burn-up in the Earth's atmosphere once its operational life has ended.

Thinking about methods to retire satellites is important, because without proper disposal they become another source of – fragments of old spacecraft, satellites and rockets now orbiting Earth at thousands of miles per hour. These fragments travel so fast that even a piece the size of a coin has enough energy to disable a whole . There are well over 100,000 pieces this size or larger already orbiting Earth, never mind much larger items – for example the Progress unmanned cargo module, which Russian Space Agency mission controllers have lost control of and which will orbit progressively lower until it burns up in Earth's atmosphere.

We don't know exactly how many or where they are. Only the largest – about 10% of those fragments substantial enough to disable a satellite – can be tracked from the ground. In fact damage to satellites is not unknown, with Hubble and the Solar Maximum Mission (SMM) satellites among those to have coin-sized holes punched into them by flying debris. There is a risk that over the next few years there will be other, perhaps more damaging, collisions.

The soft capture mechanism was installed to prevent more space debris. Engineers worldwide are devising ingenious ways to try to limit the amount of debris orbiting the planet – for good reason. Predictions show that if we don't tackle the problem of space debris then many of our most useful orbits will become too choked with flying fragments for satellites to safely occupy them.

A hole punched in the side of the SMM satellite by flying orbital debris. Credit: NASA

At some point, there may be enough debris in a given orbit for debris-satellite collisions and debris-debris collisions to cascade out of control. This is known as the Kessler syndrome, as shown (in somewhat exaggerated fashion) in the film Gravity.

Given the degree to which we rely on satellites these days – for communication, GPS and time synchronisation, upon which in turn many vital services such as international banking rely – it's crucial we prevent near-Earth space from reaching this point. And like it or not, one of the important steps required is to remove large defunct satellites that could become the source of many more chunks of debris.

Designed for disposal

Satellites such as the UK's TechDemoSat-1 (TDS-1), which launched in 2014, are designed for end-of-life disposal. TDS-1 carries a small drag sail designed and built at Cranfield University that can be deployed once the satellite's useful science life is over. This acts like a parachute, dragging the satellite's orbit lower until it re-enters the atmosphere naturally and burns up high in Earth's atmosphere.

TDS-1 is small enough to burn up – larger or higher satellites will require other ways of moving them away from the most important, valuable, and busy orbits. It's possible, with enough fuel on-board (and all systems functioning after perhaps decades in space), for satellites to de-orbit themselves. Other, more exotic solutions include tug satellites using nets, tethers, and even high power lasers.

However, space debris isn't just an engineering problem. Suppose Europe develops a tug satellite and tries to de-orbit old Russian satellites, or passes close to an active US spy satellite. Clearly this could get political. Simply put, we haven't yet found a way to use space sustainably, and the problem is almost as complex as finding ways to ensure sustainable development on Earth. What we need are practical solutions – and soon.

Bag it and bin it - ESA’s e.Deorbit project may use nets to collect debris and drag it into the atmosphere to burn up. Credit: ESA

So what will happen to Hubble, perhaps the most well-known case of a satellite that requires a retirement plan? One day, perhaps in the early 2020s, a small spacecraft will be launched to rendezvous with the space telescope. It will attach using the soft capture mechanism and then fire its engines to guide Hubble toward re-entry over the South Pacific. For a satellite as large as Hubble, it's likely that some parts will survive re-entry so a large uninhabited region over the ocean is best suited to avoid risk of damage or casualties.

The re-entry can be tracked carefully from other satellites, aircraft, and ships – all will capture the moment that Hubble itself, having spent decades watching the heavens, will become a bright shooting star for other telescopes to capture. It somehow seems fitting that a mission as remarkable and long-lived as Hubble should itself end in a blaze of glory.

One that got through: part of the Delta rocket fuel tank that came back to Earth in 1997. Credit: NASA

Explore further: ESA experts assess risk from exploded satellite

Related Stories

ESA experts assess risk from exploded satellite

March 5, 2015

After studying the recent explosive break-up of a US satellite, ESA space debris experts have concluded this event does not increase the collision risk to nearby ESA missions in any meaningful way.

Swiss craft janitor satellites to grab space junk

February 15, 2012

The tidy Swiss want to clean up space. Swiss scientists said Wednesday they plan to launch a "janitor satellite" specially designed to get rid of orbiting debris known as space junk.

A blueprint for clearing the skies of space debris

April 17, 2015

An international team of scientists have put forward a blueprint for a purely space-based system to solve the growing problem of space debris. The proposal, published in Acta Astronautica, combines a super-wide field-of-view ...

Space debris expert warns about dangers of orbital junk

January 12, 2015

The emerging problem of floating space junk becomes more and more evident and bothersome. Spacecraft and satellites are currently subject to high-speed impacts by more than 19,000 trackable objects, mainly old satellites, ...

Recommended for you

After a reset, Сuriosity is operating normally

February 23, 2019

NASA's Curiosity rover is busy making new discoveries on Mars. The rover has been climbing Mount Sharp since 2014 and recently reached a clay region that may offer new clues about the ancient Martian environment's potential ...

Study: With Twitter, race of the messenger matters

February 23, 2019

When NFL player Colin Kaepernick took a knee during the national anthem to protest police brutality and racial injustice, the ensuing debate took traditional and social media by storm. University of Kansas researchers have ...

Researchers engineer a tougher fiber

February 22, 2019

North Carolina State University researchers have developed a fiber that combines the elasticity of rubber with the strength of a metal, resulting in a tougher material that could be incorporated into soft robotics, packaging ...

A quantum magnet with a topological twist

February 22, 2019

Taking their name from an intricate Japanese basket pattern, kagome magnets are thought to have electronic properties that could be valuable for future quantum devices and applications. Theories predict that some electrons ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.