Academic Reading — Test 70

Reading passage

Since the launch of the first artificial satellite in 1957, humanity has placed thousands of objects into orbit around the Earth. Many of these remain useful, providing communications, weather forecasting and navigation. A great number, however, no longer serve any purpose. Spent rocket stages, defunct satellites, fragments of metal and even flecks of paint now circle the planet at tremendous speeds. Collectively, these unwanted objects are known as orbital debris, and their steady accumulation has become one of the most pressing concerns facing the modern space industry. The danger posed by such debris arises not from its size but from its velocity. In low Earth orbit, objects travel at roughly eight kilometres per second, far faster than a rifle bullet. At these speeds, even a small fragment carries enormous kinetic energy. A fleck of paint a few millimetres across can chip a spacecraft window, while a piece the size of a marble can disable a satellite entirely. A collision involving an object only ten centimetres wide would be catastrophic, capable of destroying a functioning satellite outright and generating thousands of new fragments in the process. Because the consequences scale with relative speed rather than mass, engineers must treat almost every particle as a potential threat. Tracking this material is a formidable task. Ground-based radar and optical telescopes can reliably follow objects larger than about ten centimetres, and several agencies maintain catalogues of these larger pieces. The vast majority of debris, however, is simply too small to be observed from the ground. Estimates suggest that there are tens of millions of fragments smaller than one centimetre, none of which can be individually monitored. Operators of crewed spacecraft and valuable satellites therefore rely on statistical models of debris density rather than direct observation, manoeuvring out of the way only when a tracked object is predicted to pass dangerously close. A particular worry among scientists is a scenario first described in detail by the American researcher Donald Kessler in 1978. He proposed that, above a certain density of objects, collisions between pieces of debris would produce yet more debris, which would in turn cause further collisions. This chain reaction, now widely referred to as the Kessler syndrome, could in principle render certain orbital regions unusable for generations. Importantly, the cascade need not begin immediately; it could unfold slowly over decades, gathering pace as the population of fragments grew. Some researchers fear that the most crowded altitudes may already be approaching this critical threshold. Several measures have been proposed to slow the growth of the debris population. The most widely accepted is mitigation: designing spacecraft so that they create less rubbish in the first place. International guidelines now recommend that satellites in low orbit be removed from space within twenty-five years of the end of their working lives, either by guiding them down into the atmosphere, where they burn up, or by lifting them into a higher disposal orbit, sometimes called a graveyard orbit. Mitigation alone, however, cannot reduce the debris that already exists. For that reason, engineers are investigating active removal, in which a dedicated vehicle would capture and de-orbit large defunct objects using nets, harpoons or robotic arms. Such missions remain technically demanding and expensive, and none has yet been carried out on a large scale. The problem is further complicated by questions of law and economics. Space is a shared environment, yet no single nation owns it or bears clear responsibility for cleaning it. Under existing treaties, an object generally remains the property of the country that launched it, which means that one state cannot simply remove another's defunct hardware without permission. This legal arrangement, though designed to protect ownership, can hinder cleanup efforts. Meanwhile, the recent trend towards launching large constellations of small satellites, sometimes numbering in the thousands, has sharply increased the number of objects in orbit and intensified concern about future collisions. Whether humanity can continue to exploit near-Earth space safely will depend not only on clever engineering but also on international cooperation and a willingness to share the costs of keeping the orbital environment clean.