Page:The Case for Space Environmentalism.pdf/13

 40,000 satellites, debris growth is dramatic and there will be hundreds of disabling collisions within a few years (Figure 6b). After a few decades, it is likely that satellites will be disabled faster than they are launched. These calculations were performed for a Starlink population, and a similar calculation was carried out for the OneWeb constellation at 1,200 km. The results were subtly different but equally disturbing.



''Fig. 6. 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. Calculations made by authors using the JASON model [4], and using the same parameters as those in Fig. 20 of that report.''

Further modelling [26] looks more specifically at the collision rate likely in the de-orbiting zone, and finds that even with current debris density, each Starlink satellite has a roughly 50% chance of a collision each year from untracked debris. This collision probability would rise dramatically with any increase in debris.

Atmospheric pollution

Atmospheric effects are discussed by Boley & Byers [26]. All rocket launches result in emissions with negative impacts on the atmosphere, including CO2, NOx, soot and H2O in the mesosphere. So far these are minor contributors to the global budget, but the huge number of launches required to build and maintain constellations of thousands of satellites will increase pollution by a large factor. Future rocket types may also deposit other materials that could increase global warming directly in the stratosphere. Re-entering satellites and debris also deposit fine particulates during their burn-up. In particular, aluminium will be deposited at a rate that exceeds that from naturally entering micro-meteoroids, and may have an effect on the Earth's albedo. Ongoing climate change may also alter thermospheric density enough to significantly increase orbital decay lifetimes in LEO [27].

Ground and airspace collision