As satellite technology has been highly advanced, it has become difficult to assure dependability of satellite systems. Currently, dependability of satellite systems is mainly supported by various risk analysis and verification. However, sometimes it is not clear why such analysis and verification result are required for dependability of the satellite systems. In particular for development of micro satellites, due to time and cost constraints, management of risk analysis and verification has been done in ad-hoc manner. This paper presents a strategic development of a micro satellite using assurance cases. Assurance case is a documented body of evidence that provides a convincing and valid argument that a system is adequately dependable for a given application in a given environment. In Europe, assurance cases are widely used as regulation in safety- critical areas such as defense, avionics, rails, etc. In this paper, we take "Discharge and Charge system of Hodoyoshi-3 microsatellite" as an example. We conduct a writing experiment of assurance cases for the system and report how the assurance cases are used for quality assurance of the system.