Flexible access for a space communications network with IP functionality
The vision for the future space network involves a scenario where all scientific spacecraft form a distributed network to provide real-time information transfer to users on the ground. This scenario will require sensors and instruments on spacecraft to become addressable nodes in a communication network. To enable this vision, there is critical need for advanced communications and dynamic network connectivity to provide broad coverage and intelligent-based real-time data delivery to scientists. These new missions will introduce a number of complex routing, network control, scheduling, data management and communication problems that need to be studied in detail. We describe the potential advantages of a dynamic mission's operations concept and the need to develop a dynamic bandwidth allocation enabling more efficient use of the space resources. In this scenario, a number of spacecraft, each with several instruments on-board, are sending data to ground stations through the NASA relay system. Our objective is to provide an optimal or near-optimal t utilization and fair allocation of bandwidth of the downlink channel while guaranteeing specific QoS requirements for different service classes. We try to understand the traffic profiles that need to be supported and propose a suitable hybrid Time Division Multiple Access (TDMA)-based protocol. We formulate and study an assignment problem for optimal timeslot scheduling. By using simulation, the protocol performance is analyzed and compared with that of the existing static fixed-assignment scheme. We also address the benefits of increasing spacecraft availability using a Direct-to-Ground communications option that can be enabled in an IP-based network. By addressing these issues we try to contribute in the development of the next generation space network infrastructure that will serve as an enabler for better space exploration.