Temperature effects on satellite power systems performance M. Bekhti, M. N. Sweeting, Abstract - Alsat-1 is the first small satellite for the Centre of Space Techniques (CTS) – Algeria. It was designed, built, assembled and tested at Surrey Satellite Technology Limited (SSTL) at the University of Surrey, with the participation of 11 Algerian engineers covering all aspects of micro satellite engineering within a technology transfer programme between SSTL and the CTS. Alsat-1 is an enhanced micro satellite weighing 100kg (launch mass). The satellite measures 60 by 60 by 62.5 cm, and is powered by four body mounted GaAs solar panels, with a total power rating of 60 watts. The solar panels are the primary source of power to the satellite. Twenty two 4Ah Nickel Cadmium cells are used to power the satellite during eclipse.[9] The power system on Alsat-1 has met or exceeded prelaunch predictions excepting for the NiCd battery pack which started showing signs of defects in August 2005. [8][10] This paper shows how, from August 2005 until now, teams from SSTL and CTS have been working together to monitor battery health and performance in particular with regard to its charging cycles. The key points affecting the battery thermal condition including power consumption during eclipse, heat generated by the battery itself and the depth of discharge of the battery are discussed. Some recommendations and ideas regarding thermal design and battery protection are presented. Keywords - micro satellite, system performance, degradation, depth of discharge, temperature, thermal conditions. I. Introduction Small satellites have already been launched with considerable success by many institutions in the developing countries. Their attraction lays in the promise of low cost and short development timescales made possible by the use of proven standard equipment and off the shelf components and techniques. Coupled with realistic and focussed goals, such satellites make it possible for a country with even a small research budget to participate in their development, launch and operation. Small satellites thus present an ideal opportunity for training students and engineers in different disciplines, including engineering, software development for on board and ground computers. The Algerian engineers were trained at Surrey through the AlSat-1 project with specializations in the following disciplines: System Engineering, ADCS, Power, RF, OBDH, Mechanical and Launch Interface, Earth Observation Payload, GPS, Operation, TTC and Propulsion. [8] Manuscript received July 20, 2010. This work is part of a research project on power systems on board small satellites. M. Bekhti, Centre des Techniques Spatiales, BP 13, Arzew 31200, Algérie. Tel: +213 41 47 38 26 - Fax: +213 41 47 36 65, Email: m_bekhti@yahoo.fr M. N. Sweeting, Surrey Satellite Technology Limited,Tycho House, 20 Stephenson Road , Surrey Research Park , Guildford GU2 7YE , United Kingdom, Tel: 44 (0)1483 803803 - Fax: 44 (0)1483 803804, Email: m.sweeting@sstl.co.uk . II. Alsat-1 platform architecture: The spacecraft is cubical in shape with four body-mounted panels, with the remaining sides including the spacecraft launch adaptor, sensors, payload apertures and antennas (figure 1). The structure is based on aluminium and aluminium honeycomb panels and was been designed to be compatible with a range of launchers. The stack of trays carries an optical platform and between the stack and the panels, the battery pack, the wheels and the propulsion system are carried. A propulsion system is required in order for the spacecraft to carry out initial launcher injection corrections, spacecraft separation into the final orbital slot, altitude maintenance and finally an end-of-life manoeuvre to remove the spacecraft from the operational system. [9] Fig 1 Alsat-1 platform architecture. III. Alsat-1 power system description The primary power to the satellite is supplied via 4 solar panels (figure 2). The power from each of the four solar panels is fed into a dedicated Battery Charge Regulator (BCR), i.e. one BCR per solar panel. The output of the BCRs is connected to a 22 cell, 4Ah NiCd battery, the Power Distribution Module (PDM) input and the Power Conditioning Module (PCM) Advances in Communications, Computers, Systems, Circuits and Devices ISBN: 978-960-474-250-9 57