A Scheduling System for Small Ground Station Networks

Abstract

Ground station networks promise great potential in improving the operation of small satellites by sharing resources. Especially in the field of pico and nano satellites many contact windows for communication and simplified data collection are desirable. One major issue is finding a good solution for scheduling the links between the satellites and the available ground station. This paper addresses the specific needs of academic ground station networks and introduces the CUSS scheduling system developed at the University Wuerzburg. Exemplary cases are presented to characterize the performance of the scheduling system. Nomenclature n = number of satellites m = number of ground stations = satellite request number i = ground station number k = starting time of contact window = ending time of contact window = set of all Candidates of Service to request i I. Introduction n efficient operation of multiple satellites in orbit depends on the quality of coordination of the infrastructure on ground. In the last five years the amount of pico and nano satellites launched into orbit significantly increased. This had as consequence the implementation of a significant amount of additional ground stations at university institutes for communication with their satellites. The integration of these university ground stations into a coordinated network of distributed ground stations offers interesting potential to increase the contact periods to the satellites as well as the reliability of satellite operations. For such amateur ground stations, the planning and scheduling needs differ from the processes of professional space organizations like NASA or ESA, as the performance and the average availability of these inexpensive ground stations is much lower. Thus, schedules for the stations in the network can be planned ahead only for a relatively short period of time. This has to be compensated by the amount of available stations. Therefore, the scheduling mechanisms of the space agencies are hardly transferable to such academic networks, as they are based on few, but very reliable high performance stations, Therefore, in this contribution a scheduling system for academic ground station networks is presented, focusing on the special needs of the small satellite community. Priorities can be allocated to different satellites and for each ground station. As a consequence, research emphasis was on fast re-scheduling capabilities in order to take into account less reliable individual stations. The paper is arranged as follows. The second chapter starts with a more detailed description of the Satellite Range Scheduling problem. Chapter 3 deals with the scheduling requirements in this specific case and explain the problem specification. Chapter 4 introduces the CUbesat Scheduling System (CUSS) with emphasis on the software architecture, basic functionality and implemented search algorithms. A basic scheduling scenario and the results obtained from the CUSS system are presented in chapter 5, a conclusion follows in chapter 6. The last part concludes with some remarks about the future work.