  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.
