This document@ when followed in its entirety@ will yield a robust EPS design suitable for very high-reliability space missions. This document specifies general design practices and sets minimum verification and validation requirements for power systems of unmanned spacecraft. The focus of the document is on earth orbiting satellites using traditional photovoltaic/battery power@ but does not exclude other primary power generation and storage methods. This document does not address specific launch vehicle requirements however much of the design philosophy used here is applicable to launch vehicle power systems.