One of the design requirements of the International Space Station (ISS) is that each year accelerations of one micro-g cannot be exceeded at the ISS internal payload location for 6 periods of not less than 30 consecutive days. Although there are other causes, this study deals only with the accelerations caused by atmospheric drag. The critical ambient neutral density, computed using the Marshall Engineering Thermosphere Model, required to produce accelerations of one micro-g on the ISS, is estimated using an atmospheric drag acceleration equation. Results show that the design requirements may be difficult to meet during periods of extremely high solar activity; the planned reboost and altitude strategies for the ISS may have to be revised to allow for the uncertainty in the prediction of neutral atmospheric density within the 100-day period established for orbital decay before reboost.

In the recent years we have witnessed unprecedented increase in both active and expired space missions (debris) – a scenario, if continued, that can lead to generation of even more debris through possible ‘satellite-satellite’ collision, ‘satellite-debris’ collision and/or ‘debris-debris’ collision (Kessler effect), especially in the heavily used low Earth orbit (LEO). Consequently, the possibility of a risk-free utilization and sustainability of space is significantly threatened because of the predisposed risk to both manned (e.g., the ISS) and unmanned active spacecrafts in this region of space. Space weather-enhanced atmospheric drag (and consequent increase in the rate of orbit decay) makes the risk even more worrisome. In this work, we investigate atmospheric drag effect on the trajectory of identified LEO objects (debris) during the 25th solar cycle and perform collision risk analysis for the International Space Station (ISS) operating at h≈415 km. We present relevant results and observations from this effort that are beneficial for orbit sustainability in LEO.