Collision risk analysis for nanosatellite cluster launches

Nanospacecraft are usually launched in clusters from a single launch, in which they are hosted as secondary payloads. The nanospacecraft, e.g. CubeSats, are usually released simultaneously in small groups from one single container, in order to simplify the launcher interface manufacturing and the launch operations. The release sequence must be designed to minimize the risk of collisions between the nanospacecraft and the primary payload and the risk of impacts among the nanospacecraft themselves. Considering the increasing number of micro and nano-satellites in the recent space activity, establishing a methodology for the collision risk analysis and determining appropriate tools for release systems design is of interest. This paper describes the collision risk analysis for a nanosatellite cluster deployment, comparing results obtained with different release mechanisms, procedures and orbital dynamics modeling assumptions. The in orbit collision risk in the first orbits after launch depends on the orbital perturbations differential effects on the spacecraft trajectories and mostly on the in orbit injection initial conditions, such as release time delay among successive releases, relative initial position and velocity, which directly reflect on the satellite dispenser configuration, interface concept and mechanical parameters. The assumption is made that the spacecraft have no orbit control capabilities, therefore no collision avoidance maneuvers can be performed after the satellite release. The analytical model used for the analysis is based on the Encke equations for the relative motion, considering the main perturbations acting on the satellites, such as Earth gravitational field higher harmonics, Moon and Sun third body perturbations, solar radiation pressure, atmospheric drag. The risk of collisions is assessed performing Monte Carlo simulations based on the numerical integration of the equations of motion. The main variables of the simulations are the in orbit injection initial conditions, implemented in terms of release devices configuration and performances and including the effects on separation system faults or non nominal performance. The final results provide the collision risk assessment and the influence that the release devices configurations have on this risk. A case study is also described in detail, concerning the launch of a cluster of nine CubeSats in standard CubeSat dispensers and a heavier primary payload. Copyright ©2010 by the International Astronautical Federation. All rights reserved.