Space instrumentation

Abstract:

Methane (CH4) on Mars is of high scientific importance, particularly for its generation and destruction mechanisms. With an estimated photochemical lifetime of approximately 300 years, sporadic methane plumes observed on Mars by orbital, landed missions, and Earth-based telescopes suggest the presence of unknown destruction processes. Here, we present an experiment to examine CH4 destruction through heterogeneous electrochemistry (HEC) triggered by Martian dust activities. We performed a series of mid-strength electrostatic discharge (ESD) experiments in mixtures of CO2 and CH4 under conditions relevant to the Martian near-surface atmosphere. We characterized (1) the free radicals produced from the breakdown of CH4 and CO2; (2) the gaseous and solid products of CH4 and CO2 decomposition; and (3) the half-life of CH4 in this experiment. Based on a newly reported mission observation of electric discharge during a dust devil (DD) on Mars, we extrapolated the experimentally derived half-life to an approximate dust-devil-effective half-life of CH4 on Mars, with uncertainties spanning orders of magnitude. The result demonstrates that dust-driven HEC can cause CH4 destruction at rates hundreds to thousands of times faster than photochemistry. In future missions to Mars, if the knowledge gaps in the E-properties of dust activity are filled through regular measurements, this experimental finding may imply that Martian dust activity could be the primary factor reducing methane's lifetime, thereby contributing to understanding methane loss in the Martian atmosphere.

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:

ESA’s Ariel space telescope is due to launch in 2029 and aims to measure broadband (0.5 – 7.8 µm) spectra from ∼1000 known transiting exoplanets. For optimum stability the payload uses an all aluminium telescope with an extremely narrow (30 ′′) field of view. Prior to integration with the spacecraft, the Ariel payload will undergo a TVAC campaign to check that the telescope and instruments are capable of achieving the mission’s scientific goals. During these tests the payload will be illuminated by a quarter aperture test beam generated by a highly stable and adaptable cryogenic optical system – the payload optical ground support equipment (OGSE). This OGSE is required to output a 275 mm x 183 mm elliptical collimated beam with an RMS wavefront error (WFE) of < 214 nm to enable diffraction limited imaging in Ariel’s instruments. Furthermore this must be achieved after the collimation and beam expansion optics are cooled to an operating temperature of 70 K. In this proceeding, the optical design, specifications and simulations of the OGSE cryogenic optical system are presented. This system is designed to be athermal between room temperature and 70 K while also producing a low WFE output by using a combination of glass and aluminium mirrors. To prevent stressing and deforming the optics during cooldown, a selection of low distortion and minimally constraining mounts have been designed and simulated. The alignment and verification philosophy of the optical system is also presented. Emphasis is placed on precision mechanical alignment with only a minimal number of adjustable degrees of freedom required to focus and optimise the system. Following alignment, the end-to-end optical quality of the OGSE is verified in a single-pass configuration with a Shack-Hartmann based metrology system.

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.