ATV separation and departure strategy from uncontrolled International Space Station

The Automated Transfer Vehicle (ATV) is an unmanned cargo vehicle developed under European Space Agency (ESA) contract by EADS Space Transportation as prime contractor, to be part of the European contribution to the ISS (International Space Station) program. One of the main issues of the ATV flight scenarios design is the ISS safety in case of contingency. In some cases, it has been necessary to design specific scenarios dedicated to particular off-nominal situations. This paper presents a strategy that has been elaborated to ensure a safe departure in response to an emergency case where the ATV is captured by the Russian docking port but the docking mechanism cannot be rigidly locked and therefore attitude control of the ISS cannot be reactivated. We will first define the initial conditions at departure by analyzing ISS motion during the attached phase and its consequences in terms of communication unavailability with the Ground. These elements will enlighten the design of the separation and departure strategies that will be themselves successively defined. The safety of the resulting trajectories will at last be described.