IELTS Reading: Multiple Choice (Single Answer)

The space immediately surrounding Earth — the region between the upper atmosphere and about 2,000 kilometres altitude known as low Earth orbit (LEO) — has become, over six decades of space activity, one of humanity's most cluttered environments. Radar tracking networks operated by the United States Space Surveillance Network currently monitor approximately 27,000 objects larger than 10 centimetres in LEO, including defunct satellites, spent rocket stages, and fragments from collisions and breakups. Below this threshold, an estimated 500,000 objects between 1 and 10 centimetres and millions of particles smaller than 1 centimetre are thought to orbit Earth, too small to track reliably but travelling at velocities of 7 to 8 kilometres per second — fast enough for even a centimetre-sized piece of debris to deliver an impact equivalent to a small explosive. The debris problem has self-accelerating properties that alarm orbital mechanics specialists. In 1978, NASA scientist Donald Kessler proposed a scenario — now known as the Kessler Syndrome — in which collisions generate debris fields that trigger further collisions in a cascade, progressively filling orbital shells with fragments and rendering certain orbital altitudes unusable for generations. Crucially, this process does not require any new launches to continue; once initiated, it is self-sustaining. In 2009, the accidental collision between an operational Iridium communications satellite and a defunct Russian Cosmos satellite — the first hypervelocity collision between intact satellites — added approximately 2,000 tracked fragments to the debris population and illustrated the plausibility of Kessler's scenario. Current debris mitigation guidelines, developed by the Inter-Agency Space Debris Coordination Committee (IADC) and adopted by major space agencies, recommend that objects in LEO should deorbit within 25 years of completing their mission. In practice, compliance remains incomplete, and the guidelines themselves are insufficient to stabilise the debris environment given current launch rates. Active debris removal (ADR) — the development of spacecraft capable of capturing and deorbiting debris objects — is widely discussed as a necessary complement to mitigation guidelines. Several technologies are under development, including robotic arms, harpoons, drag nets, and electromagnetic tethers. The regulatory and legal framework for ADR is, however, significantly underdeveloped: under current space law, debris objects remain the property of the launching state, creating uncertain liability for any state or private entity that removes or damages another nation's debris.