There are thousands of satellites in Earth’s orbit, all of varying age and usefulness. Sooner or later they reach the end of their operational 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. There are exceptions, such as the Hubble Space Telescope, which, as part of the final space shuttle servicing mission in 2009, was modified to include a soft capture mechanism. This is an interface that will 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 working life ends.
It’s important, because without proper disposal they become another source of space debris — fragments of old spacecraft, satellites and rockets now orbiting Earth at thousands of miles per hour. These pieces travel so fast that even one the size of a coin has enough energy to disable a whole satellite upon impact.
There are well over 100,000 pieces this size already orbiting Earth, never mind the much larger items out there. For example, the Progress unmanned cargo module, which the Russian Space Agency has lost control of, will orbit at progressively lower altitudes until it eventually burns up in Earth’s atmosphere.
We don’t know exactly how many or where they all are. Only the largest — about 10 percent 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 had 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.
While the soft capture mechanism was installed to prevent future space debris, engineers worldwide are devising ways to try to limit the debris already orbiting the planet, and with good reason. Predictions show that if we don’t tackle the problem soon then many of our most useful orbits will become too choked with flying fragments for satellites to occupy them.
There may also be enough debris in a given orbit for collisions between the debris itself to cascade out of control
At some point, there may also be enough debris in a given orbit for collisions between the debris itself to cascade out of control. This is known as the Kessler syndrome, as shown (in somewhat exaggerated fashion) in the film Gravity.
Our reliance on satellites cannot be overstated. We use them for communication, GPS and time synchronisation, upon which in turn many vital services such as international banking rely. So 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.
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.
While TDS-1 is small enough to burn up, larger satellites, or those in higher orbit, will need to be moved away in different ways from the most valuable and busy orbits. If there is enough fuel on board and all systems are functioning after perhaps decades in space, it’s possible for satellites to de-orbit themselves. Other, more exotic solutions include using tug satellites with 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.
