In this first of three short papers, I introduce some of the basic concepts of space engineering with an emphasis on some specific challenging areas of research that are peculiar to the application of robotics to space development and exploration. The style of these short papers is pedagogical and this paper stresses the unique constraints that space application imposes. This first paper is thus a general introduction to the nature of spacecraft engineering and its application to robotic spacecraft. I consider the constraints and metrics used by spacecraft engineers in the design of spacecraft and how these constraints impose challenges to the roboticist. The following two papers consider specific robotics issues in more detail.