Link analysis for BILSAT-1

BILSAT-1, a 130 kg micro satellite, is Turkey´s first low Earth orbit Earth (LEO) observation satellite. The project was started in August 2001 at Surrey Satellite Technologies Limited (SSTL)´s facilities in Guildford, UK and BILSAT-1 was launched successfully from Plesetsk Cosmodrome, Russia in 27 September 2003. The main objective of the mission is remote sensing. The communications subsystem is a core system for Earth observation satellite. It is generally used for telemetry/telecommand signaling, software uploading and image/data transfer. The BILSAT-1 communications subsystem is composed of VHF/UHF (amateur space band) and S-Band (commercial space band). Link analysis is essential for design of any satellite communications subsystem to observe the quality of the link. The link budget should be calculated; the positive link margin has to be guaranteed at all elevation angles that the proposed design requires before the actual manufacturing process starts. For BILSAT-1 communications subsystem, the link budget calculator program has been developed at pre-design phase. The program calculates the received Eb/No and the required Eb/No, and gives the difference as the link margin with respect to the elevation angles. The communications subsystem parameters such as RF output power, antenna size/type, power consumption etc. both at ground station and on board have been optimized according to the simulated links. These parameters ultimately effects overall project cost and time schedule. Also, to aid pre-launch/in-orbit test and to observe in-orbit link quality, some status points have been made available at BILSAT-1 satellite telemetry system. The measurements include a received signal strength indicator (RSSI) that provides an indication of the total signal power received. By using this data, the reliability of the link budget calculator program can be verified. In this paper, the above-mentioned link budget calculator program will be presented and the calculated an- - d the actual link margins will be given and compared