Temperature effects on satellite power systems performance

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. 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. 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.