“…Some clusters detections during these later missions could be attributed to human spaceflight activities, in particular, to specific firings of solid rocket motors (SRMs) (e.g., Schobert and Paul, 1997). SRMs produce large amounts of solid combustion products in the form of micron-sized aluminium oxide particles, which, if used for geostationary orbit (GEO) insertions or retrograde LEO deorbiting manoeuvres, can create circumterrestrial streams of micro-debris with lifetimes of up to months (Bunte, 2003;Stabroth et al, 2008). As the use of orbital SRMs ramped up in the late 1970s and 1980s (to enable utilization of the GEO, see e.g., McDowel, 1997;Wegener et al, 2004), they gained attention for their potential to cause hazard to spacecraft through their generated micro-debris trails (Mueller and Kessler, 1985;Akiba and Inatani, 1990)-amidst the growing awareness of the space debris problem in general (Kessler and Su, 1985;Kessler, 1991).…”