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Stray light detected in Euclid’s VIS instrument at particular angles
Euclid is located at Lagrange point 2 in a unique orbit ‘behind’ Earth. Here, Euclid has its ‘back’ to the Sun, so all the sensitive parts of its telescope are protected from sunlight by a dedicated sunshield. However, it was known that a thruster bracket lay outside the shadow of the sunshield and would receive direct sunlight.
It seems a small amount of sunlight is reflecting off the bracket towards the VIS instrument that is protected by many layers of insulation. However, because of the extreme sensitivity of the VIS instrument, the current theory is that enough light is still getting through this insulation, with stray light being detected in test observations when VIS is turned at specific angles.
The majority of VIS’s observations showed no significant stray light interference, but at particular angles, about 10% of observations were affected. Science, engineering and industrial teams spent weeks deciphering which angles let too much of this unwanted light in and have re-designed and optimised Euclid’s survey to constrain each pointing’s orientation in the sky. While this will not affect Euclid’s ability to take the precise images required, it could impact the efficiency of the survey – something that is still under investigation.
