K. Brieß’s research while affiliated with Technische Universität Berlin and other places

This paper proposes high-accuracy and reliable attitude measurement methods exclusive for CubeSat with restrictions of low cost, limited space, and low power consumption. The attitude measurement unit is equipped with Commercial Off-The-Shelf (COTS) components including Micro-Electro-Mechanical System (MEMS) gyro and two simultaneously operating star trackers (STR) to enhance the measurement accuracy. The Multiplicative Extended Kalman Filter (MEKF) is used to estimate the attitude of CubeSat, and four kinds of attitude estimation layouts are put forward according to the idea of weighted average of two quaternions from two STR and different architectures of information fusion. Using the proposed methods, the attitude measurement unit can continuously provide accurate and reliable attitude knowledge for attitude control unit when the CubeSat is running in orbit. Numerical simulation is performed to verify the effectiveness of the proposed methods, and it offers a reference for CubeSat developers from the perspective of engineering application.

Satellite networks are inevitable for the ubiquitous connectivity of M2M (machine to machine) and IoT (internet of things) devices. Advances in the miniaturization of satellite technology make networks in LEO (Low Earth Orbit) predestined to serve as a backhaul for narrow-band M2M communication. To reduce latency and increase network responsivity, intersatellite link capability among nodes is a key component in satellite design. The miniaturization of nodes to enable the economical deployment of large networks is also crucial. Thus, this article addresses these key issues and presents a design methodology and implementation of an adaptive network architecture considering highly limited resources, as is the case in a nanosatellite (≈10 kg) network. Potentially applicable multiple access techniques are evaluated. The results show that a time division duplex scheme with session-oriented P2P (point to point) protocols in the data link layer is more suitable for limited resources. Furthermore, an applicable layer model is defined and a protocol implementation is outlined. To demonstrate the technical feasibility of a nanosatellite-based communication network, the S-NET (S band network with nanosatellites) mission has been developed, which consists of four nanosatellites, to demonstrate multi-point crosslink with 100 kbps data rates over distances up to 400 km and optimized communication protocols, pushing the technological boundaries of nanosatellites. The flight results of S-NET prove the feasibility of these nanosatellites as a space-based M2M backhaul.

Since 1991, Technische Universität Berlin has developed and operated 21 small satellites with an accumulated launch mass of over 300 kg. Most of the university's early spacecraft were microsatellites with launch masses above 30 kg. However, after the launch of LAPAN-TUBSAT in 2007, the university concentrated on the development of single-unit CubeSats to explore new technology trends and implement consistent miniaturization. Taking into account the experiences gained within the picosatellite development, Technische Universität Berlin recently designed the TUBiX20 platform to support future microsatellite missions. In July 2017, TechnoSat was launched to a 600 km Sun-synchronous low-Earth orbit. With a mass of 20 kg the in-orbit demonstration satellite that carries seven technology payloads is the first spacecraft based on the TUBiX20 platform. The subsequent TUBiX20 mission is TUBIN that will demonstrate wildfire detection using microbolometer technology and is scheduled for launch in 2020. QUEEN is another TUBiX20 mission that is currently in the preliminary design phase while FACIS is an early study for a TUBiX20 based formation flight mission in cooperation with the University of Stuttgart. Within this paper, the TUBiX20 platform is introduced, focusing on its modular architecture and how it enables scalability. Subsequently, TUBiX20 based satellite missions are briefly described. Concluding the paper, current and future developments are introduced that will shape the future of the platform.

To meet the need of high performance thermal management materials in the field of space application, thermal interfaces made out of copper composite materials reinforced with carbon nanotube (CNT) have been prepared via powder metallurgy combined with hot extrusion. The CNT content was controlled between 3 and 25 vol.%. The distribution of CNT in the composite powder was realized with ultrasonic supported mixing. The mixed powders were consolidated with Spark Plasma Sintering (SPS) to a density above 70 %. Afterwards, hot extrusion compacted the composite materials to a density close to 100 % and introduced a CNT alignment parallel to the extrusion direction. After machining and etching the CNT are standing free one the thermal interface. The performance under inert and vacuum conditions regarding the effective thermal conductivity across the interfaces was measured with flash method after machining and etching under the same contact pressure.