Fig. 3 Visualisation of 4000 ASOs in various orbital neighbourhoods. The left-hand side plots objects in Cartesian space. The right-hand side plots the same objects in angular momentum space at the same instant. In both cases, the objects are colour coded according to orbit inclination with respect to the Earth’s equatorial plane. It can be seen that the ASO population naturally segregates into rings or orbital highways with LEO toward the bottom and GEO as a halo at the top. Data set from [11].
Over the years, some non-binding guidelines have emerged to try to minimise proliferation of debris, for example the IADC Space Debris Mitigation Guidelines, and the UN COPUOS LTS guidelines. NASA guidelines [12] state that during active life of satellites, operators should manoeuvre them to avoid collision; and at the end of spacecraft life, it is expected that a spacecraft is either, in the GSO case, moved to a higher storage orbit, or left in a lower orbit where it will decay due to atmospheric drag within 25 years.
Orbital space and the sky as environments
Meaning of environment
The Oxford English Dictionary defines environment first as “the surroundings or conditions in which a person, animal, or plant lives or operates”. Humans have carried out activities in outer space since 1957, and we have reached a point where these can have deleterious impacts both in space and on Earth's surface. There is therefore a strong case that the concept of environment should extend to orbital space, between 100 km and 36,000 km. The Outer Space Treaty of 1967 [13] and the Liability Convention of 1972 [14] set out general principles quite consistent with this idea, and the LTS guidelines explicitly note that Earth orbit is an environment worth preserving. Definitions of ecosystems could allow space to be included [15].
The radio interference environment
Satellites communicate with ground stations by radio signals. There is a legal obligation for many bodies such as the US FCC at the national level, and the International
