Inter-Satellite Communications for Small Satellite Systems

Introduction

Small satellites are artificial satellites with lower weights and smaller sizes. Usually a large satellite has a mass greater than 1000 kg. European Space Agency (ESA) defines small satellites as satellites having a mass of 350-700 kg. At University of Surrey, satellites having a mass of 500-1000 kg are considered as “small”. In the study conducted by Academy of Astronautics, broadly classified small satellites in to different classes based on their mass as shown in Table 1.

Miniaturization of satellites helps to overcome the traditional barriers to space exploration and development. One of the major reasons for miniaturizing satellite is the reduction in cost. It has less mass and thus smaller and lighter launch vehicles can be used. It can be piggy backed on larger vehicles and takes shorter time from development to launch. The small satellites can be launched in various formation flying patterns to collect data from multiple points. It offers attractive features with respect to the design aspect and rapid technology infusion. Because of the agility of sensor mechanisms, new approaches to observations and calibration are possible using small satellites (Committee on Earth Studies, 2000). With the advances in technology, new missions can be developed and launched that may require a shorter development time. Proba-3 is the ESA’s (presentation by Tallineau. J) first step towards deploying satellites in close formation flying. Proba-3 is currently scheduled to be launched in 2017. Its main mission is to validate the technologies that are required for formation flying of two or more space vehicles. One of the challenges of small satellites are low power compared to large satellites and thus shorter life time because it cannot carry large batteries and the size of the solar panel cannot support high power transmission and reception. The design of various subsystems in small satellite should be done in such a way that each of the subsystem consumes less power and thus ensuring longer life time.

Small and relatively inexpensive satellites have become exclusive domain for scientific and amateur groups. Major advances in microelectronics have made small satellites an effective alternative to large and expensive satellites. There are many organizations and universities (EPFL, STUDSAT) that support small satellite research. Their main research focuses on the design aspect of small satellites. To the best of our knowledge, there are no studies devoted to inter-satellite communications for various formation flying patterns. The authors, Bedon, Negron, Llantoy, Nieto, and Asma (2010) propose the possibility to implement TCP/UDP protocols over satellite links. They have tried to focus on generating and simulating two scenarios of the constellation of satellites based on the QB50 proposed project. The proposed protocol corresponds to the transport layer which is used in Ethernet applications and they have not discussed the protocol they have used for medium access. Hence this remains an open issue. In this paper, we propose and evaluate the Medium Access Control (MAC) layer and routing layer protocols for inter-satellite communications in small satellite systems.