Liam McSherry IEng MIET

Abstract:

The modern world is increasingly computerised and, as more functionality is shifted to the edges of systems in bids to reduce latency or energy consumption, the Internet of Things (IoT) increasingly includes safety-critical systems. A typical such system is 'functionally dense,' with a time-shared processing element (PE) carrying out many tasks; we believe that they should instead be functionally sparse, with many small PEs dedicated to single tasks. We present case studies of this design approach and introduce FUNK, our effort to build the tools that will support the development of hard real-time, functionally safe systems that follow this approach.

Abstract:

This paper presents developments in the thermal design and testing of the optical ground support equipment (OGSE) used to characterise the optical performance of the Ariel space telescope at payload level. As part of ESA’s Cosmic Vision programme, Ariel will carry out transit spectroscopy on approximately 1,000 exoplanets over four years of operation. To simulate a flight-like thermal environment during payload level testing, the payload is enclosed in the cryogenic test rig which provides a 35K radiative environment. The payload is illuminated by the OGSE, which comprises an illumination module that illuminates the payload and a periscope module that steers the test beam into the payload line of sight. To enable verification of the dark current requirement in the payload’s detectors (< 1 e− pix−1 s−1), both the periscope and illumination module must be kept at 70 K. The illumination module has a two-stage thermal design consisting of a thermally isolated optical bench and a radiative shroud constructed from low-emissivity MIRO-27 sheeting. The optical bench and radiative shield are cooled using a pair of cryocoolers connected to flexible, high-conductivity copper straps. To de-risk the thermal design, a thermal breadboard of the illumination module has been constructed. Here, we present the thermal designs of the periscope and illumination module as well as the results of the thermal breadboarding activities. In particular, the cryocooler performance was found to be consistent with the manufacturer’s specifications. The thermal performance of the flexible copper straps was characterised, and the influence of thermal interface materials on interface conductance was quantified, with 40 μm graphite foil providing approximately twice the interface conductance of direct metal-to-metal contact for heaters operating at approximately 100 ◦C. The dominant thermal loads acting on the illumination module shroud were identified, and the effective emissivity of a MIRO-27-based shroud was determined to be 3.5 %. Furthermore, the periscope thermal design was experimentally verified at its operational temperature of approximately 70 K, and several critical aspects of the periscope thermal design were de-risked.

Abstract:

In 2018, the European Space Agency (ESA) asked the scientific community for proposals for a new ‘Fast class’ of missions: faster, lower cost, and allowing more experimentation than flagship programs. The selected mission would be a payload of opportunity sharing a launch with the medium class ARIEL exoplanet telescope to the Earth-Sun L2 Lagrange point, around1.5m kilometers from the Earth.