Gaia Proximity Electronics : eyes to the stars

January 15th 2025 marks the end of ESA Gaia spacecraft scientific observations. This groundbreaking spacecraft's mission: to create the most precise 3D map of our galaxy, providing unprecedented insights into the structure, composition, formation and evolution of the Milky Way, as well as the fundamental laws of physics that govern the universe. This was made possible by Gaia’s ability to measure the distances and velocities of stars with remarkable precision, thanks to the astrometric and radial velocity spectrometer instruments. Other stars characteristics, such as chemical compositions, their temperatures and masses, were provided by the photometric instrument, which breaks down the light from the stars into its component wavelengths.

These three instruments in Gaia use common telescopes and share a single focal plane, which allows them to work together. Gaia's focal plane is the largest ever developed, comprising 106 pairs of Charge-Coupled Devices (CCDs) and Proximity Electronics Modules (PEMs), totaling 1 Gigapixel and measuring 0.5x1 m; each pair of CCD and PEM can be thought of as an extremely sensitive camera. The CCDs are arranged in a grid, with distinct functions assigned to separate columns. We developed, built, and tested the 106 Proximity Electronics Modules (PEMs) for Gaia's Focal Plane Assembly.

Each PEM handles CCD operation, video processing, sequencing, and power supply distribution. A versatile PEM design accommodates all focal plane functions by adjusting sequencing, biasing, video bandwidth and gain for each instrument. These functions and capabilities are integrated into a compact module weighing just 162 grams.

The realization of these objectives proved to be no small task. The team responsible for the PEM faced a multitude of challenges during the development, production and testing phases of over 100 flight units and numerous development models. Surmounting these obstacles required the team to use innovate technical solutions, develop new analysis methods, implementation of ISO 5 clean room facilities, incorporate Commercial-Off-The-Shelf (COTS) components and automate the acceptance testing of multiple units simultaneously. Nevertheless, the outcome justified the effort, as the 106 PEMs on board the Gaia spacecraft have been operating tirelessly for nearly twice as long as their original design life of 6 years, having completed 11 years in total.

During this period, the advancements achieved in PEM designs, methods and techniques have been extensively utilized in various space missions, albeit not directed towards the stars but our own planet. Numerous Earth observation missions, such as the Copernicus Sentinel-2 and EarthCARE, have already integrated these developments for both ESA and national programs. Moreover, future missions, including Sentinel 5, MicroCarb, FLEX and TRISHNA, are slated to employ them as well. Although the electronics capabilities and performance in the PEM have been surpassed by our? new generation of Front-End Electronics for CMOS detectors, such as those for the Land Surface Temperature Monitoring (LSTM) Copernicus Expansion mission, its origins can still be traced back to the Gaia spacecraft's electronics.

What is the next chapter in our video electronics products? We are now developing a modular solution targeted at image sensors with digital image outputs. This novel approach for video electronics serves a dual purpose: not only does it minimize development risks and shorten the development timeline, therefore reducing overall costs, but it also provides unparalleled processing capabilities in the immediate vicinity of the image sensor. This is made possible by the very nature of the modular design, which allows for greater flexibility, adaptability and ease of integration.

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