Historical growth of quantities affecting on-orbit collision hazard

Abstract

Over the last 34 years over 22,000 man-made Earth-orbiting objects have been cataloged by the U.S. Space Command Space Surveillance Center. Nearly 7,000 of these objects remain in orbit While only 6% are operational satellites. The thousands of pieces of derelict hardware and fragmentation debris pose a collision threat to each other and the several hundred functioning payloads. The probability of collision (PC) between an Operational satellite in low-Earth orbit and the orbital debris environment is mainly a function of spatial density of the debris population, collision cross section, relative impact velocity, and mission duration. Routinely, only changes in spatial density are used to account for changes in the PC as a function of altitude and time. Historical changes to the on-orbit population that would affect the relative velocity and collision cross section are identified. Changes in the relative kinetic energy of an impact are also calculated. The analysis shows that the average relative velocity, collision cross section, and relative energy of impact have increased over time due to changes in the cataloged population. Whereas changes in spatial density are found to have a dominating effect on PC values, the other factors studied have a small effect on the PC but substantially influence the energy of representative impacts. This paper examines the relative importance of factors that influence the collision hazard from the resident on-orbit population. -