Green and confused: What happens to old satellites?

Q.On the anniversary of the Apollo Moon landings, my eight-year-old son asked what happens to the old satellites and other debris in space. Will they eventually fall to Earth?

Your son has put his finger on what is becoming quite an environmental problem. First, tell him not to worry: he doesn’t have to go round with a hard hat on for fear of a wayward satellite flattening him. Most space debris, if it falls back to Earth, burns up as it re-enters the atmosphere.

However, there is a great deal of junk out there, zooming along at speeds of up to 25,000mph. At such a velocity, a mere flake of paint can do considerable damage to a satellite. Nasa frequently has to mend windows on its spacecraft because of penetration by minuscule flying objects.

No one is sure of the exact amount that has accumulated since the launch of the first satellite, the Soviet, in 1957, but over the years, millions of pieces of debris from space missions and satellites have contributed to what has become a revolving scrapyard way above our heads. Objects range from jettisoned spacecraft parts to tiny fragments of fuel and urine.

A United Nations body called the Inter-Agency Debris Co-ordination Committee uses sophisticated radar and monitoring equipment to track the debris and is able to detect objects (about 9,000) bigger than a tennis ball. Smaller objects can’t be tracked but are growing in number. One of the problems is that as these objects collide or break up, more debris is created. A discarded launch arm can wipe out a multimillion-dollar satellite. A bolt dropped during a space station repair could puncture the skin of a spacecraft and cause a catastrophe.

On occasions a space launch has had to be delayed until scientists were certain that the rocket would enter a “junk-free” zone. Now engineers are looking for ways to vaccuum up the debris before disaster strikes. It’s a bit like the mounting pile of rubbish deposited on Everest by climbers — the more we explore, the more junk is amassed. Man leaves an environmental footprint everywhere, even in space.