The ESA GAIA mission ; Designing in Silicon Carbide and related issues

TNO is developing the Basic Angle Monitoring Opto-Mechanical Assembly for the GAIA mission of ESA, a space telescope that will create a map of the universe including distant stars and planets. GAIA is being built by EADS Astrium and scheduled for launch in 2011. Due to its stability and hardness properties, Silicon Carbide has been chosen for the structure, payload mirrors and most components of GAIA. The Basic Angle Monitoring subsystem was developed by TNO and is a metrology system for monitoring the angle between the two GAIA telescopes. With the Basic Angle Monitoring an Optical Path Difference as small as 1.5 picometers RMS can be measured. During the design phase of the Basic Angle Monitoring subsystem, TNO also developed solutions for ultra stable mounting of non-Silicon Carbide optical components. These components have to withstand launch with preservation of the alignment and retain optical properties from ambient to 100 K in vacuum. The manufacturing of off-axis Silicon Carbide mirrors of the Basic Angle Monitoring down to nm-level represented another challenge. A comprehensive program was conducted on SiC manufacturing of freeform optics. Status: the Basic Angle Monitoring has past the Critical Design Review

Pico meter metrology for the GAIA mission

To measure the relative motions of GAIA's telescopes, the angle between the telescopes is monitored by an all Silicon Carbide Basic Angle Monitoring subsystem (BAM OMA). TNO is developing this metrology system. The stability requirements for this metrology system go into the pico meter and pico radian range. Such accuracies require extreme measures and extreme stability. Specific topics addressed are mountings of opto-mechanical components, gravity deformation, materials and tests that were necessary to prove that the requirements are feasible. Especially mounting glass components on Silicon Carbide and mastering the Silicon Carbide material proved to be a challenge. © 2009 SPIE