Mitigation measures for large constellations

Large constellations of satellites in Low Earth Orbit (LEO) will provide important communications and broadband internet services to large parts of the world where the necessary terrestrial infrastructure is lacking. These services are also likely to have a significant effect on the space economy. At the same time, there is considerable potential for negative impacts on the space environment and other space users unless appropriate space debris mitigation measures are incorporated into the design and operation of the constellations. Recent modelling work by the authors has shown that the robust implementation of post-mission disposal (PMD) to orbits with short lifetimes, in combination with other constellation and satellite design decisions, can help to reduce the negative impacts of large constellations operating for decades in LEO. However, further modelling work is needed to understand the possible impacts emerging from the simultaneous operation of multiple constellations at relatively similar altitudes in LEO. In addition, it is likely that these constellations will move away from ideal Walker-type geometries in an effort to reduce the collision risk between satellites in the same constellation. Consequently, a new simulation study has been performed, with the aim of improving the understanding of the impacts arising from the operation of several large, non-typical constellations in LEO. This new study was focused primarily on the arrangement of orbital planes in two large constellations. In particular, the separations in altitude and inclination were evaluated for their influence on the collision risk to other same-constellation satellites and non-constellation objects, and to assess the potential for collisions between satellites from the different constellations. The DAMAGE evolutionary model was used to evolve the population of objects >= 10 cm in LEO from 1 January 2013 over a 200-year projection period with an optimistic assumption for the behaviour of the constellations and the background orbital population with respect to the commonly adopted debris mitigation measures. The results show that the effect of these measures was to reduce the number of objects and collisions in the LEO environment compared with previously reported results, which represented the implementation of the existing and commonly adopted debris mitigation guidelines. These benefits persisted even for a scenario with two constellations operating in relative proximity. The effects of separating the orbital planes of large constellations were not clear and further work is needed to ensure that the evaluation of large constellations is achieved in a robust fashion.