Operational use of guided reentry capsules – system design solutions and mission safety considerations☆

Future utilization of the experimental facilities on-board the International Space Station (ISS) exhibits a demand for frequent sample return opportunities that can be provided by small, unmanned but controllable re-entry capsules. Based on the mission and system requirements for payload retrieval, a conceptual vehicle design down to subsystem level is presented. The vehicle is of a sphere-cone shape with an oblate bottom surface and equipped with a body flap. This configuration was established by means of extensive numerical analyses. A tether-assisted deorbit maneuver is considered, which yields significant mass savings over a conventional propulsive approach if applied in an operational scenario. For reentry guidance, which is a key technology for this type of vehicle, an explicit near-optimal guidance law is presented and its performance evaluated. Furthermore, mission safety issues in case of GNC system failures are addressed. Six-degree-of-freedom analyses simulating the loss of the control capability during re-entry flight indicate that the vehicle is capable to drastically reduce landing dispersions and thus to improve safety on ground, if proper on-board emergency procedures are implemented.