From Space Debris to NEO, Some of the Major Challenges for the Space Sector

Society’s reliance on space assets has grown to the point that today these are part of every modern country’s infrastructure. Services provided thanks to space technologies such as for example, Global Navigation Satellite Systems have become critical (Hesse and Hornung, 2015) for smooth operations in a variety of sectors, from telecommunications to transport to banking, and the list could continue. Even the general public has become accustomed to using satellite services like satellite television or the satnav on mobile phones. Hence, any threat to our space assets is a very significant issue for society. As of February 2020, there were about 5,500 satellites in space1 but only about 2,300 were actually functioning, which means about 3,200 defunct satellites are still orbiting Earth, together with upper stages and fairings of rockets and a variety of smaller objects produced by break-ups, explosions, collisions, degradation or other anomalous events that resulted in the production of fragments. Under the collective name of space debris, these objects have a size distribution that ranges from large intact bodies (e.g., parts of rockets or large satellites with a size larger than 10m and weight of several tons) down to millimeter-sized fragments like scales of paint or solidified droplets of coolant. Early 2020 estimates showed that there were 34,000 objects larger than 10 cm, 900,000 objects from >1 to 10 cm, and a staggering 128 million objects from >1mm to 1 cm. Given their high velocity and consequent high kinetic energy, even small pieces of debris pose a significant threat to operating satellites, as they could hit them with catastrophic consequences and the loss of potentially critical services. At the same time, high energy collisions between larger bodies can produce real explosions that can create thousands of fragments. These, in turn, can collide with other orbiting objects, triggering a chain reaction and a snowball effect that could render whole orbits unusable. This extreme scenario (Kessler Syndrome), initially studied by Kessler in the ’70s (Kessler and Cour-Palais, 1978), is not far from reality, as a handful of collisions have already happened. Perhaps the most famous is the one between Russian military communications satellite Cosmos 2,251 and a satellite of the Iridium constellation (Wang, 2010), which produced a step increase in the debris population. With more satellite applications currently being developed that demand a growing number of satellites (e.g., constellations of hundreds of satellites are being deployed to provide worldwide connectivity or a World Wide Web), the issue of space debris is becoming more significant (Virgili et al., 2016).