The Free Flyer as first item of the Orbital Hub scenario is docking to existing ISS during its first mission.
DLR (CC BY-NC-ND 3.0).
The small and modular Base Platform provides basic functionality to accommodate a crew of three astronauts permanently.
After ISS, the Orbital Hub consisting of crewed Base Platform and autonomous Free Flyer ensures continuation of human space flight in Low Earth Orbit.
Orbital Hub: Multi-Purpose Platform for Continuation of Human Spaceflight on Low Cost in LEO
For decades the International Space Station (ISS) has demonstrated not only long-term international cooperation between 14 partner governments but also a significant engineering and programmatic achievement mostly as compromise of budget, politics, administration and technological feasibility.
All ISS partners agree to utilize the orbital research facility until at least 2024. However, there is a common understanding that a platform in LEO is crucial for continuous research, technology demonstration, Earth observation and monitoring, commercial use as well as preparing the next steps for going to Moon and Mars.
In general, a transition to a new concept without a critical loss of know-how takes up to 10 to 15 years. Therefore, the conceptualization regarding technical layout, creating a road map and development of a follow-on outpost in LEO is crucial and time critical.
The system-analysis study “Post ISS” of DLR`s Institute for Space Systems in Bremen is a national preparatory work for the establishment of future programs in the field of human spaceflight and to secure long-term research and astronautical activities in LEO. The engineering concept study was conducted by a team of DLR internal and external experts, industry (e.g. Airbus, Bigelow Aerospace) as well as ESA and NASA astronauts. The baseline question was:
How could we continue with space research and space technology development after the ISS utilization period (~2024)?
To answer this, the following objectives were defined among others within the study:
User requirements for LEO-platforms
Requirements regarding a future Mini-platform in LEO have been collected from German scientists and engineers. Several research disciplines participated in the user workshop and contributed recommendations for payload definitions. In addition to traditional µg-research, an extended focus was placed on Earth observation, atmospheric physics and technology demonstrations for human-rated platforms. The top-level science driven expectations based on detailed quantitative requirements can be summarized as follows:
Engineering Concepts for Modular LEO Platform
In total the study team identified 13 options including sub-options fitting to the aforementioned concept framework. Four of them were chosen for detailed evaluation regarding political, social, technical and economic criteria. A lean multi-purpose platform with dockable module was evaluated to be the most promising option from a European and German point of view. It is called “Orbital Hub” and stands for the basis or core element of a “space city” idea: on the hub, spacecraft can dock and be serviced, or goods (e.g. propellant or experiments) can be distributed.
The selected concept aims to employ only the minimum functionality required for a scientific astronautical base platform in LEO with a permanent crew of three members. The Orbital Hub consists of two main parts: the crewed platform and the free-flying modules (referred to as “Free Flyer”).
The Base Platform consists of three main modules: the docking node, the service module and the expandable habitat. The docking node is the approach point for any crew-/ cargo visiting vehicle with four available docking ports. Additionally it accommodates a cupola, crew training equipment and subsystems for communication, data storage and contingency propulsion. Attached to the docking node is the service module, as the central part of the Base Platform. It houses the basic bus functionalities (mainly power supply, thermal control), a toilet and the externally mounted Control Momentum Gyros (CMGs) for platform orientation. The Expandable Habitat uses the BA330 by Bigelow Aerospace as a baseline design. It ensures a comfortable living and working environment with sufficient space for the crew. It contains three crew quarters, food provision, storage, workstations, manufacturing and laboratory racks for human physiology. A small airlock is included for contingency cases when EVAs are inevitable.
The Free Flyer has three functional elements: the pressurized laboratory, the external platform and the service module. The pressurized laboratory is the only area of the Free Flyer which is accessible by the crew and additionally only in docked state to the Base Platform. It provides sufficient volume for payload which needs to be pressurized, e.g. material sciences, crew workstation for experiment preparation plus maintenance and an airlock to equip the attached External Platform. The External Platform is a truss element with standardized payload interfaces providing mechanical connection, power and data supply as well as thermal conditioning. The External Platform is serviced by robotic means using a mobile robotic manipulator. The service module section is a direct extension of the truss structure and, similar to the Base Platform counterpart, accommodates mainly power, thermal, propulsion and data handling systems. The Free Flyer is the active part of the Orbital Hub scenario during assembly phase and rendezvous and docking, requiring impulsive thrust. Furthermore, during the free-flying campaigns the payloads demand an undisturbed environment and high quality microgravity, which leads to the necessity of continuous thrust. For this reason, the Free Flyer is equipped with a hybrid propulsion system with both chemical and electrical thrusters to meet the different thrust requirements of the multiple applications.
Conclusion and Next Steps
The feedback from many scientists and engineers has shown continuous high interest in using the Low Earth Orbit on a multi-purpose mini platform. It is a common understanding that a space laboratory offers unique possibilities and therefore is not replaceable. Europe and Germany have achieved a technological system competence by developing, constructing and operating research facilities in space (e.g. Columbus, ATV and the Orion Service Module).
The modular Orbital Hub concept represents the highest degree of maturity based on current technologies, operational / logistical systems, current commercial developments and financial aspects. The Orbital Hub is a realistic opportunity as it is based on existing European technologies in human spaceflight and could be realized with moderate budgets and timeframes thanks to its simple approach. By foreseeing a sequential implementation, e.g. the Free Flyer as first element in orbit in cooperation with the still existing ISS, a smooth transition between ISS and future platforms could be realized. However, a significant involvement and commitment of Europe and international (commercial) partners is required.
In general, it is expected that future LEO architectures will be smaller, more modular and flexible than the current ISS. Complementing payloads such as Earth Observation, technology demonstration, commercial application as well as opportunities for preparation of human exploration will add to the conventional scientific utilization. The interest of the user community in a research laboratory and an observation platform in LEO serves as a basis for the architecture`s design open for future commercial involvement. The Orbital Hub would represent an affordable possibility to continue human space flight in LEO and a reliable basis regarding long-term human space exploration beyond LEO.