Aiming the rapid response of mega constellation of satellites to cover the increasing demand for Earth observation and communication, in-orbit manufacturing is a promising approach. Driven by the NewSpace, which is leading a paradigm change in the space industry, the project Space Factory 4.0 has been founded to establish new processes and technologies based on the Industrie 4.0 approaches for rapid satellite assembly on an in-orbit platform. One of its fundamental approaches and the main contribution of this paper is the Digital Twins. In the scope of a Space Factory 4.0, the Digital Twin is a holistic approach for supporting and controlling systems for in-orbit Assembly, Integration, and Test processes, as well as satellite operations, by establishing a bidirectional link to its physical counterpart. It is an essential approach to obtain a digital representation of the current state of the real product at any time, enabling the recognition of and reaction to disruptive parameters at an early stage. To model Digital Twins and to meet the specific requirements of a Space Factory 4.0, such as the capability of sending telecommands and processing telemetry data, an extension of Industrie 4.0 component, called Space Factory 4.0 component, is proposed. This paper discusses this concept, its implementation and the results obtained and concludes to discuss its benefits and potentials for the space industry.