Heterogeneous Spacecraft Networks: Wireless network technology assessment

Abstract

Constellations of small satellites are useful for a number of earth observation and space exploration missions. The Heterogeneous Spacecraft Network project is defining operations concepts and promising technology that can provide greater capability at lower cost. Typically, such spacecraft can communicate with each other in orbit and with ground stations for spacecraft operation and downlink of science data. However, small spacecraft often cannot utilize the capability delivered by networks such as the Universal Space Network, even if the mission could afford the cost. Small spacecraft have significant constraints in terms of power availability, attitude stability and overall mass and volume, requiring innovative technology for implementing highly functional satellites. A major challenge for such missions is selecting communications technology able to function in the space environment, able to meet the requirements for both inter-satellite and space-to-ground data links and fit within the resources available on small satellites. Moreover, the cost of the technology needs to be as low as possible to facilitate participation by a broad range of organizations. Finally, the communications networks should conform to standards allowing broad adoption and the use of common infrastructure for multiple missions. Communications technology based on the IEEE 802 family of local area and metropolitan area network standards can be adapted to meet the needs of such missions. This paper will identify possible development paths for improved communication between small satellites and to the ground by reviewing and evaluating standards-based technology for use by small satellite missions. Methods for greatly extending both range and data rate will be proposed and analyzed. It will review and evaluate the IEEE 802.11 wireless network standards, the ITU WCDMA 3G cell phone standard and the IEEE 802.15.4 Personal Area Network standard. A simple set of communication requirements will define the trade offs between standards and identify the technical capability needed for such missions. Specifically, the improvements needed to the Physical Layer to extend range to 1200 Km and the ability to comply with spectrum management constraints will be investigated. Authentication and encryption will be addressed along 1with adjustments to the Media Access Control layer that can optimize data transfer rates over a broad range of distances and conditions. The paper concludes with recommendations for standards-based communication technology development for small satellites supported by the results of this trade study. The primary objective is to greatly reduce the cost of data communication for small satellites by establishing a common infrastructure able to meet the needs of most missions.