The ASIM Mission -- A Contamination Control and Thermal Approach

Abstract

The Atmosphere-Space Interactions Monitor (ASIM) is a European Space Agency (ESA) payload developed by the ASIM industrial consortium with Terma A/S, Denmark, as prime contractor. ASIM is mounted on the exterior of the European Columbus laboratory module on the International Space Station. Launched in April 2018 on the Space-X CRS-14 this external payload is a collection of optical cameras, photometers and an X- and gamma-ray detector designed to look for electrical discharges born in stormy weather conditions that extend above thunderstorms into the upper atmosphere.

Now almost three years into nominal operations, ASIM is continuously collecting data which researchers utilise for investigation of the relationship between terrestrial gamma-ray bursts, lightning and high-altitude electric discharges across all seasons, different latitudes and different times of day and night. As part of this successful operation many new design concepts and materials choices were implemented for ASIM in order to mitigate against phenomena such as cross contamination, inorbit debris and plume due to the sensitive nature of optical sensors and radiator surfaces. There is also the need to comply with non-scientific ISS external contamination and deposition requirements during the intended operational phase.

This paper will give an overview of the ASIM mission, a brief description of the instruments and focus on the cleanliness and contamination approach , implementation of bake-out and outgassing strategies and preconditioning, contamination budgets and cleanliness mitigations during AIT as well as the use of cleanliness mitigation concepts in the design, such as decontamination heaters on sensitive optics, venting design and dust caps to protect sensitive surfaces. External ISS requirements must also be met, hence an overview of the ASIM thermal design control will be presented to consolidate and substantiate the cleanliness approach. Real in-orbit data from the mission are presented showing how contamination has affected or not its performance.