Computer Aided Approach on Optimizing Solar Array Circuitry on CubeSats

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1 Computer Aided Approach on Optimizing Solar Array Circuitry on CubeSats P. Günzel, D.Wei, A.Gritsch, A.Hoehn, M.Langer Institute of Astronautics, Technische Universität München Despite their evolution in the past 16 years, CubeSats missions often are still restricted to payloads with low energy demand due to their limited solar array surface. Originally built as six- ar cells on each side of the cubes could easily be assigned to one of the typically 3 battery charge regulators (BCR) provided with the sophisticated electrical power system boards available as commercial off the shelf hardware. Nowadays, CubeSats are trending towards more complex payloads and larger geometric sizes. The once straightforward electrical wiring concepts, based on the simple cubic design with always opposing solar arrays, are replaced more and more by missions using deployable structures for solar arrays with different orientations and resulting in a variety of sun angles on the solar cells of the satellite. Despite the possibility of 3-axis stabilization on CubeSats missions nowadays, most CubeSats are currently not yet designed with sun-pointing solar arrays and therefore the sun and shadow conditions on each cell and string have to be taken into account. Furthermore, commercial-off the shelf and university developed electric power systems often offer only a limited number of maximum power point tracking battery charge regulators with a dedicated range of allowable input voltages and currents. Therefore, while dealing with more complex designs featuring deployable solar wings and multiple unit (2, 3 and even 6U) configurations on CubeSats, it becomes necessary to carefully examine possible solutions on how to optimize the solar cell distribution and connectivity across the satellite and across the available battery charge regulators during the early design process of the satellite. Manual process analysis and optimization of the circuitry often becomes challenging due to the number of possible wiring arrangements between the individual cells, the interface constraints coming from the electrical power system and electrical losses e.g. bypass diodes. This paper examines the potential of computer-based optimization algorithms for solar cell wiring to multiple battery charge regulators. Our approach is to model the solar cells and their wiring within an algorithm, where radiation input power for each cell in different orbit and attitude scenarios, including non-stabilized tumbling, is fed into a solar cell model to convert power into current and voltage. Every combination and permutation possible for the given solar array architecture with respect to maximum and minimum tolerable voltages and currents is then evaluated. The best solution based on the overall harvested power with regards to input restrictions is then selected. The results show that the entire process is manageable even on desktop CPU's leaving room for improvements such as optimized program architecture and more sophisticated algorithms. The circuit layout can easily be adapted to even the most complex geometric designs in considerable short time. In addition to simulating certain defined (static) circuit layouts, circuits which dynamically switch solar cell associations appear feasible with this or similar algorithms. Such a dynamically configurable solar array and BCR association could possibly enable a new level of on-board solar array optimization.

2 S-Band, UHF and VHF Communication System for Cubesats including Ground Station Software Ralf Wilke, Matti Reiffenrath, Kai Parow-Souchon, Dirk Heberling Institute of High Frequency Technology, RWTH Aachen University, Aachen, Germany In the last 5 years the working group at the Institute of High Frequency Technology (IHF) of RWTH Aachen University has developed a communication system suitable for CubeSats. This includes a flexible flight hardware as well as extensive ground station software and hardware for data handling and decoding. State-of-the-Art algorithms and architectures are used to assure maximum downlink capacity at all communication scenarios during a flyover of the CubeSat. The system will be flown on the DragSail-CubeSat built by FH Aachen und RWTH Aachen IHF. We will show the system architecture and implementation details of both hardware and software enabling the community to take advantage of the latest research on communication systems for CubeSats. This includes also antenna measurements and test results from space radiation immunity test with Cobalt 60.

3 OSIRIS: High-Datarate Optical Downlinks for Small Satellite Platforms Christopher Schmidt, Fabian Rein, Martin Brechtelsbauer, Christian Fuchs Institute of Communications and Navigation, German Aerospace Center (DLR) Direct optical communication links might offer a solution for the increasing demand of transmission capacity on small satellite platforms. Although direct space-to-ground links suffer from limited availability due to cloud coverage, the achievable data rates can be higher by orders of magnitude compared to traditional RF communication systems. DLR is developing OSIRIS, the Optical Space Infrared Downlink System. OSIRIS is an experimental optical communication system optimized for small satellites. DLR s BiROS satellite and the Flying Laptop from University of Stuttgart will be the first scientific missions equipped with an OSIRIS terminal. This paper will give an overview about the OSIRIS payload for both missions and an outlook on the next generation of OSIRIS in the 100kg-satellite-class as well as for Cubesat missions.

4 Developing a Next Generation CubeSat Radio Link Nicolas Appel 1, Rolf-Dieter Klein 2, Martin Langer 1 1 Institute of Astronautics, Technische Universität Müunchen 2 Multimedia Studio Dipl.-Ing. Rolf Dieter Klein, München nicolas.appel@tum.de Most of the currently available CubeSat hardware still carries the legacy of amateur radio technology. To remain compatible to available ground station equipment, many commercial CubeSat transceivers for the VHF/UHF bands use the AX.25 packet radio protocol and compatible modulations. These techniques were not designed for the use in satellite links and are generally more error-prone and bandwidth-inefficient than modern satellite communication systems. Ongoing research is carried out to replace packet radio and proprietary protocols in future missions. We therefore developed the Nanolink protocol, a data link layer protocol and a compatible transceiver. Nanolink was designed to provide reliable and efficient communication between a ground station and CubeSat. It is intended to operate in low bandwidth-delay radio links with high asymmetry and moderate to weak signal quality. In addition to the Nanolink protocol, we are developing a compatible CubeSat transceiver for the VHF/UHF bands. The transceiver uses direct conversion IQ modulation to make all digital modulations possible. The required signal processing is handled by an onboard FPGA. Since modulations with higher spectral efficiency are possible, the transceiver can handle data rates of more than bit/s. The transmitter output power is adjustable in a wide range and allows to also use it in situations where low power consumption is required. Together with the new protocol we hope to create a better radio link for CubeSats with more reliability and efficiency.

5 Creating Ground Segment Software based on the Fire Framework Slavi Dombrovski Zentrum für Telematik e.v. Usually an application (such as a ground station software) consist of multiple off-the-shelf software products (SQL server, web server etc.) and a main module, which is typically developed from scratch and is able to access those components. Depending on the physical constraints some software modules are bounded to a particular workstation, e.g. serial port handler for a TNC, transmitter, antenna rotator etc. In this case the application components are often distributed along different workstations, such that the need for custom network protocols arises. Moreover each component needs to be remotely accessible for monitoring, service and further purposes. The OS-independent Fire framework, developed by private flag, has three fundamental aims: define an interface which can be used to make any kind of software accessible, allow a seamless distribution of application parts (distributed computing) and allow dynamical creation, modification and visualization of applications at runtime. All software components are implemented as modules with connectable input and output ports. The ports can be (re)connected during the runtime allowing live modification of the data flow. The behaviour of each module can be configured by changing its settings. With the Fire GUI an application can be created live by dropping available modules onto the application space and connecting them with each other. Since modules can contain further sub-modules, the whole application is represented hierarchically by a so called application tree. With the integrated Fire ghosting technique an application tree (or its specific branch) can be automatically mirrored to a single or multiple remote Fire instances by forming a ghost branch within the remote tree. From the point of view of a developer there is no difference between a local and a remote application branch. Thus application parts can be seamlessly distributed along multiple physical systems.

6 A niche professional network for the Space industry Maxime Sixdeniers SpaceBoard The Space Network - maxime@spaceboard.eu Niche professional networks targeted networks customized to serve the exclusive needs of a niche audience are spearheading the concept of professional online networking. Such platforms have the edge over broader popular networks for their extremely focused and information-centric approach to interactions. They also benefit from the advantage of having little or no noise generated through posts irrelevant to the individual s professional needs. These networks are designed to bring important career-related content to the user s fingertips, to ease the sharing of knowledge and expertise among all professional levels of the industry. At the same time, they allow users to join in engaging discussions or simply browse the database to stay up-to-date. SpaceBoard is a niche professional network dedicated exclusively to the field of space. Its goal is to create a unified platform that serves all space industry players, promoting the advancement of space and fostering academic, professional and business opportunities. The platform will feature a broad set of functionalities specifically developed to create an attractive, interactive and easy-to-use online environment for space-networking purposes. These functionalities will enable users to create a personal board on the platform to publicize their competencies, connect with like-minded peers, link up with organizations, monitor job openings or stay abreast of breaking news, deadlines and upcoming conferences. Using this platform, prospective students will be able to discover space academia and related opportunities, and current and former students can leverage their education by promoting their course of study or joining alumni networks. Lastly, the platform s thematic boards and dedicated project areas will ensure that game-changing ideas are readily visible to the entire community.