The Gaia mission will create an extraordinarily precise three-dimensional map of more than one billion stars in our
Galaxy. The Gaia spacecraft, built by EADS Astrium, is part of ESA's Cosmic Vision programme and scheduled for
launch in 2013. Gaia measures the position, distance and motion of stars with an accuracy of 24 micro-arcsec using two
telescopes at a fixed mutual angle of 106.5°, named the ‘Basic Angle’. This accuracy requires ultra-high stability, which
can only be achieved by using Silicon Carbide for both the optical bench and the telescopes. TNO has developed, built
and space qualified the Silicon carbide Basic Angle Monitoring (BAM) on-board metrology system for this mission.
The BAM measures the relative motion of Gaia’s telescopes with accuracies in the range of 0.5 micro-arcsec. This is
achieved by a system of two laser interferometers able to measure Optical Path Differences (OPD) as small as 1.5
picometer rms. Following a general introduction to the Gaia mission, the Payload Module (PLM) and the use of Silicon
Carbide as base material, this presentation will address an overview of the challenges towards the key requirements,
design, integration and testing (including space-level qualification) of the Gaia BAM.