Orbital Hub: A concept for human spaceflight beyond ISS operations

Abstract

The International Space Station (ISS) is the greatest endeavour in low Earth orbit since the beginning of the space age and the culmination of human outposts like Skylab and Mir. While a clear schedule has yet to be drafted, it is expected that ISS will cease operation in the 2020s. What could be the layout for a human outpost in LEO with lessons learnt from ISS? What are the use cases and applications of such an outpost in the future? The System Analysis Space Segment (SARA) group of the German Aerospace Center (DLR) investigated these and other questions and developed the Orbital Hub concept. In this paper an overview is presented of how the overall concept has been derived and its properties and layout are described. Starting with a workshop involving the science community, the scientific requirements have been derived and strawman payloads have been defined for use in further design activities. These design activities focused on Concurrent Engineering studies, where besides DLR employees also participants from industry and astronauts were involved. The result is an expandable concept that is composed of two main parts, the Base Platform, home for a permanent crew of up to 3 astronauts, and the Free Flyer, an uncrewed autonomous research platform. This modular approach provides one major advantage: the decoupling of the habitat and payload leading to increased quality of the micro gravity environment. The former provides an environment for human physiology experiments, while the latter allows science without the perturbations caused by a crew, e.g. material experiments or Earth observation. The Free Flyer is designed to operate for up to 3 months on its own, but can dock with the space station for maintenance and experiment servicing. It also has a hybrid propulsions system, chemical and electrical, for different applications. The hub’s design allows launch with just three launches, as the total mass of all hub parts is about 60,000 kg. The main focus of the design is on autonomy and reducing crew maintenance and repair efforts, and reducing the need for extravehicular activities. Following a description of the design approach and technical details, a cost estimation and a detailed discussion of the use cases for such a station concept, along with the possible scenarios of international cooperation, are also presented in this paper.