The different aspects of space situation awareness; space weather, near Earth objects, and tracking objects in Earth orbit, are frequently treated separately, but they are of course linked.
Recent assessments of solar activity, hinting at a forthcoming “grand minimum” in solar activity, imply that “space climate” may be of great significance of the coming decades.
Predictions of the future debris population in Earth orbit vary, depending on the assumptions made in a variety of areas, including the size of the “sub-10cm” debris population, which is highly uncertain. The NASA forecast illustrated here aims to assess the influence of different “post mission disposal” (PMD) scenarios, but there is another aspect of these plots that deserves attention.
The “11-year ripple” that is apparent on the above plot assumes that the solar activity levels follow the pattern that has been observed for the past 300 years. At the peak of each solar cycle, the energy delivered to the Earth’s upper atmosphere causes it to expand, increasing the drag on all objects, and causing the ones in the lowest orbits to re-enter the Earth’s atmosphere, thereby decreasing the total population.
Suppose, however, that the Sun does enter a “grand minimum” which is comparable to the “Maunder Minimum” period between 1650 and 1720, when there were virtually no sunspots observed.
In this scenario, the periodic heating of the atmosphere does not occur, the drag does not increase, and the debris population is not reduced.
This underlines the need for better SSA and effective post mission disposal, as the debris situation may be worse than anticipated if the Sun does not help us.
