We introduce a refined formulation of the Fragmentation Environmental Index (FEI), designed to assess changes in the Low Earth Orbit (LEO) environment resulting from the fragmentation of a specific mass. The index quantifies this impact by comparing overall LEO criticalities before and after the fragmentation event. To highlight the contribution of smaller debris, we enhance the index by incorporating weighting factors tailored to optical and radar surveillance networks. Testing of the upgraded FEI on a series of simulated fragmentation events shows that it can characterize both the perturbation to the LEO environment and its temporal evolution, providing a more accurate quantification of the short- and medium-term impact of debris clouds compared to the original formulation.

Single-charge pumps are the main candidates for quantum-based standards of the unit ampere because they can generate accurate and quantized electric currents. In order to approach the metrological requirements in terms of both accuracy and speed of operation, in the past decade there has been a focus on semiconductor-based devices. The use of a variety of semiconductor materials enables the universality of charge pump devices to be tested, a highly desirable demonstration for metrology, with GaAs and Si pumps at the forefront of these tests. Here, we show that pumping can be achieved in a yet unexplored semiconductor, i.e. germanium. We realise a single-hole pump with a tunable-barrier quantum dot electrostatically defined at a Ge/SiGe heterostructure interface. We observe quantized current plateaux by driving the system with a single sinusoidal drive up to a frequency of 100 MHz. The operation of the prototype was affected by accidental formation of multiple dots, probably due to disorder potential, and random charge fluctuations. We suggest straightforward refinements of the fabrication process to improve pump characteristics in future experiments 2021 The Author(s). Published by IOP Publishing Ltd.