Quantum key distribution from satellites becomes particularly valuable when it can be used on a large network and on-demand to provide a symmetric encryption key to any two nodes. A constellation model is described which enables QKD-derived encryption keys to be established between any two ground stations with low latency. This is achieved through the use of low earth orbit trusted-node QKD satellites which create a buffer of keys with the ground stations they pass over, and geostationary relay satellites to transfer secure combinations of the keys to the ground stations. Regional and global network models are considered and the use of inter-satellite QKD links for balancing keys is assessed.

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A miniaturized reaction wheel suitable for picosatellites (<1 kg) has been developed for Delft University of Technology's PocketQube (PQ) mission. Delfi-PQ aims to demonstrate a reliable core bus platform for PocketQubes with a form factor of 5x5x5 cm and one or more payload(s). Continuing trends in miniaturization of technology, PocketQubes hold the potential to further reduce the cost of access to space and disrupt traditional space applications by providing cost effective global coverage. Three-axis stabilization is required for advanced capabilities such as Earth observation, high data rate transfers and propulsive manoeuvres. Precise attitude control requires reaction wheels with highly accurate speed control and low vibration levels. Power and volume requirements, however, drive a simple and compact design. A reaction wheel assembly with a mass of 7 g, maximum steady state power consumption of 25 mW and size of 18x10x11.5 mm has been designed, integrated and tested. A simple flywheel is attached to a brushless electric motor and secured in a pressurised housing. The reaction wheel can provide at least a torque of 3 ∗ 10-7 Nm over its full speed range and has a (one way) momentum storage of 1.1 ∗ 10-4 Nms. This is sufficient for attitude stabilization and ground station tracking on a triple-unit PocketQube in a 360 km Low Earth Orbit. Functional, performance, environmental and micro-vibration tests have been performed. Strict power requirements led to an in-depth analysis of the power consumption of the reaction wheel assembly. A Simulink model of the motor including control electronics models was used to characterize the power consumption. Results indicate the feasibility of using reaction wheels on picosatellites with improvements to the flywheel balance and sealing efficacy of the housing required for long-term performance. A proposed three-wheel assembly design was created measuring only 31x31x22 mm including control electronics. Once completed, world's smallest reaction wheel (assembly) is expected to be launched as part of the attitude control subsystem on the Delfi-PQ mission to demonstrate and characterize its performance under true space conditions.@en