The subject of this thesis is the development of attitude control systems for modular satellites. Modular, reconfigurable space systems are being investigated for two reasons: on the one hand, to achieve a faster, more flexible and cost-effective development of space systems in times of massively decreasing launch costs. On the other hand, systems have to be made serviceable in order to avoid becoming space debris and modular systems promise certain advantages in this regard. But there is a lack of knowledge about modular space systems since so far, hardly any have ever been developed. The objective of developing a catalog of modules for several satellites instead of one satellite for a specific mission also requires a completely novel approach and methods in satellite design. The aim of this work is therefore: 1. to generate knowledge about the design of modular space systems with focus on attitude control, 2. and to develop methods to assist in the design of such systems. This PhD thesis aims to lay a foundation of knowledge by focusing on the attitude control of satellites in low earth orbit. This subsystem is well suited as a starting point for entire modular space systems as it is in principle coupled with the other subsystems such as the structure, power system or data handling. These subsystems need to be taken into account but the parameters only need to be known very roughly which also helps to get started with the design automation of modular space systems. In a first step, a comprehensive literature review on attitude control systems in modular spacecraft was conducted. This includes the general systems concept and the navigation algorithms used today. In addition, design methods for space systems were collected and investigated in this thesis. Subsequently, a minimum set of requirements for the modular ADCS were defined. Based on these requirements, several concepts for modular space systems were developed. This includes the development of algorithms for the calibration of sensors and actuators in reconfigurable space systems. These concepts were then analyzed mathematically with a focus on their scalability. For the selection and evaluation of the developed concepts, different module catalogs were designed based on the defined requirements. The design of catalog of modules was only possible with the help of design automation due to the number of possible module combinations. Therefore, in this thesis a new method was developed to generate and evaluate module catalogs automatically. Afterwards, the developed algorithms for modular systems were validated and verified. With the help of the design algorithm, a number of modules and modular space systems were then generated in order to obtain concrete information about the performance of the developed modularity concepts. As an example, two reference missions with the different concepts were generated. Additionally, a tradespace analysis of generic mission scenarios was conducted as a method to select the best performing modules from the module catalog. In summary, this thesis analyses and evaluates the scalability and performance of different concepts of attitude control systems. In addition, a design automation method was developed and tested to design module catalogs for space systems.