A. Lawrence, M. L. Rawls, M. Jah, A. Boley, F. Di Vruno, S. Garrington, M. Kramer, S. Lawler, J. Lowenthal, J. McDowell, M. McCaughrean

“ 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. ”

“ Ground and airspace collision
It is unlikely that all de-orbited satellites will burn up completely, or that all surviving rocket parts, including unspent fuel, will be successfully dumped in the sea, so damage to property and even life will be an increasing risk. Disposing of satellite remnants in a marine environment has environmental risk, which has been successfully challenged in the past [28,29] . The risk to life and impact on the environment is non-trivial. ”

“ Medium Earth Orbit (MEO) is at altitudes around 20,000 km, within a broad range. This is the regime of global navigation satellite systems such as GPS and GLONASS, but also recently of some internet communications systems such as O3B. Satellites in MEO take around 12 hours to orbit the Earth, and each satellite can communicate with a fairly large portion of the Earth’s surface. From the perspective of a person on Earth, a spacecraft in MEO will move across the sky much more slowly, and remain in the field of view for an hour. ”

“ Adequately addressing the problems detailed above will require a holistic approach that treats orbital space as part of the environment, and worthy of environmental protection through existing and new policies, rules and regulations at national and international levels. We urge decision- and policy-makers to consider the environmental impacts of all aspects of satellite constellations, including launch, operation and de-orbit, and to work with all stakeholders to co-create a shared, ethical, sustainable approach to space. ”

“ It is reasonable to claim that access to the night sky environment, including unobstructed views of the stars, can be considered a basic human right for all people. Satellites will also significantly affect amateur astronomy and citizen science, which have become relevant particularly in recent years as an integral part of scientific exploration. For a typical 7 degree binocular field of view, taking our model 2030-era population, around eight satellites will be visible everywhere you look and they will typically be the brightest objects in the field of view. ”

“ Many human activities have a locally constrained environmental impact. Most space activities are however inherently global. A satellite may launch from California, but an hour later it is flying over France. Conversely, a Chinese or Russian system will soon appear in the sky over the USA. A coordinated international approach is therefore crucial, but this has to start with each sovereign state recognising its global responsibility. ”

“ A radio astronomy antenna is sensitive to a range of directions typically a few degrees across — the ‘main beam’ — but also has reduced sensitivity in very different directions — the “sidelobes”. Likewise the satellite antenna emits most of its power in a main beam, but also some in sidelobes. The worst effects, which can potentially damage sensitive electronic receiver systems, are for an alignment between the astronomical and satellite main beams — this rules out radio observations close to GSO targets, and should be avoided even for fast-moving LEO satellites. ”

“ Without avoidance methods, the current debris density means there will on average be one collision per satellite every 50 years in LEO, with a piece of debris that is 10 cm or larger [4] . However, large objects are tracked and orbital elements made publicly available, so that potential collisions can be predicted and actively avoided. ‘Conjunctions’, where one satellite passes within a few km of another, happen many times every year, but so far only one major accidental collision has taken place. ”

“ Collision impacts on space operations
Growth of space debris The space community loosely divides objects in space into ‘active satellites’, ‘dead and leftovers’ such as derelict satellites and rocket stages, and ‘debris’, resulting from fragmentations, explosions and collisions. As described above, debris can in turn be divided into ‘tracked debris’, down to 10 cm size, and smaller ‘untracked’ debris, which can only be estimated. ”

“ In some observations, finely detailed maps are made by combining signals from many interlinked antennas, but the noise problem affects each antenna individually, which physics dictates will always be sensitive to a broad range of directions and frequencies. Unlike optical images, the effect is not a localised streak, but a complex effect across the whole map, which can be hard to recognise and remove — it is like trying to listen to very quiet music in a noisy room. ”

“ Impact on astronomy
In considering the impact of satellites on astronomical observations, we have to bear in mind that individual sources of light pollution may be billions or even trillions of times brighter than those that astronomers study, and that many of the most scientifically important observations concern unrepeatable time sensitive or transient events — such as the detection of Near Earth Objects, Supernovae, or Fast Radio Bursts.
Optical astronomy
ASOs can be seen from Earth because they reflect sunlight. ”

“ Damage to the orbital space environment has problematic features in common with other types of environmental issue. First, the observed and predicted damage is incremental and complex, with many contributors. Second, whether or not space is formally and legally seen as a global commons, the growing commercial exploitation of what may appear a ‘free’ resource is in fact externalising the true costs. ”

“ However, there is a growing sense worldwide that we should be explicitly considering the sustainability of space activities, and considering orbital space as an environment. For example, the recent G7 summit issued a statement on space sustainability and the World Economic Forum has partnered with the European Space Agency and the University of Texas at Austin, amongst others, to develop a Space Sustainability Rating. ”

“ The incremental impact of any single proposal for a satellite constellation may be relatively modest, but if all such proposals are allowed because their individual impact is deemed to be modest, the cumulative effect could nevertheless be extremely serious. Furthermore, because of complex interdependencies, the emergent behaviour is not a simple addition and is extremely hard to predict. ”

“ Satellites can even have their electronics overloaded and be permanently disabled. With the huge increase in the number of satellites and the increased collision risk, active collision avoidance by many satellites will be frequent. If satellites are disabled, even temporarily, they will lose the ability to manoeuvre around hazards and the collision risk will increase dramatically every time a satellite enters “safe mode” or is disabled. ”

“ The frequency and intensity of solar storms varies in an eleven-year cycle and the next Solar Maximum, when solar activity will be at its peak, is predicted to be in 2024-2025. The population of satellites by then is expected to be several times higher than it is today and it is worth noting that a relatively minor geomagnetic storm resulted in an unexpected descent and burnup of 40 Starlink satellites in February 2022.
Conclusion
We have laid out the argument that there is an urgent need for orbital space to be considered part of the human environment. ”

“ Only some satellites are visible above the horizon at a time. For our 2030-era population, roughly 4,300 are above the horizon at any one time, and they cross the sky in about 13 minutes. For a small field of view, there may be only a few percent chance of being affected by a streak, but the observation could be completely wasted and need to be repeated [18] . The more serious impact will be on wide field survey instruments. ”

“ Calculating the likelihood of disabling damage by debris with size > 1 cm to active satellites is a complex problem requiring many physical variables. Note that disabling a satellite leaves an uncontrolled derelict that may then be a danger to other spacecraft. ”

“ Even so, a significant number of satellites at the margins of visibility may create an unsettling effect of constant wriggling and squirming.
In addition, for many Indigenous people, the night sky is an active and vital part of culture, storytelling and inheritance from one generation to another. ”

“ Descending debris also poses a risk to aircraft. From the same UN presentation, predictions suggest a 1 in a 1000 chance of an aircraft being struck each year, but with some 300 passengers per aircraft, that means 0.3 casualties per year. A possible population of 100,000 satellites increases the casualty rate by many times. The first aircraft strike or ground casualty is only a matter of time. ”

“ The evolution of the satellite population, debris population and cumulative collisions for two possible satellite constellation scenarios at a height of 600 km with frequent deorbiting. a. 2,000 launches per year aimed at a stable population of 10,000 satellites. b. 10,000 launches per year aimed at a population of 40,000 satellites. ”

“ They will move across the field of view in about ten seconds, continuously being replaced by new ones. Meanwhile, many amateur astrophotographers will suffer the same problem as professional astronomers — streaks in most of their images. ”