Gaia: focus, straylight and basic angle

TL;DR

The Gaia mission faces challenges from focus changes, straylight, and basic angle variations, which impact astrometric precision, but ongoing analysis and mitigation efforts aim to address these issues for improved mission stability.

Contribution

This paper provides a comprehensive review of Gaia's stability issues, their root causes, and mitigation strategies, offering valuable lessons for future space missions requiring extreme stability.

Findings

Straylight and basic angle variations were much larger than expected.

Payload decontaminations and refocusing improved image quality.

Data analysis shows strong correlation between BAM signals and astrometric solutions.

Abstract

The Gaia all-sky astrometric survey is challenged by several issues affecting the spacecraft stability. Amongst them, we find the focus evolution, straylight and basic angle variations Contrary to pre-launch expectations, the image quality is continuously evolving, during commissioning and the nominal mission. Payload decontaminations and wavefront sensor assisted refocuses have been carried out to recover optimum performance. Straylight and basic angle variations several orders of magnitude greater than foreseen were found and studied during commissioning by the Gaia scientists (payload experts). Building on their investigations, an ESA-Airbus DS working group was established during the early nominal mission and worked on a detailed root cause analysis. In parallel, Gaia scientists have also continued analysing the data, most notably comparing the BAM signal to global astrometric solutions, with remarkable agreement. In this contribution, a status review of these issues will be provided, with emphasis on the mitigation schemes and the lessons learned for future space missions where extreme stability is a key requirement.