I have been collaborating with colleagues, in particular Dr Hugh Lewis and a graduate student Arrun Saunders, at the University of Southampton over the last few years to attempt to answer these questions. Arrun’s hard work, as part of a PhD programme, has recently confirmed the findings of other researchers in the field, suggesting that indeed the density in the upper atmosphere is declining by a few percent per decade.
Why is this relevant? Well, the drag on orbiting satellites is directly dependent on the atmospheric density, so as the density decreases, then so does the drag. This in turn means that the orbital lifetime of satellites increase, which results in an increasing number of space debris objects on orbit. The international space-faring community need to wake up to this density trend in the high atmosphere where satellites (and space junk) orbit. If not taken account of in the development of debris mitigation guidelines, then the effectiveness of such guidelines will be compromised. Perhaps more importantly, as the community begins to consider the necessity of actively removing debris objects from orbit to stabilise the debris environment, the neglect of this trend in the operational planning will have a significant negative impact in achieving a beneficial outcome.