Euclid Data Release 1 (DR1): Spacecraft performance in the L2 environment

The Euclid mission was designed around the need for thermo-optical and mechanical stability, stray-light suppression, low outgassing, and precise guiding. After three years in space, a wealth of data is available to assess the performance in these areas. We review the L2 halo-orbit design and consumables budget. Solar stray-light gradually increases by 14\% per year and is consistent with meteoroid puncturing, but remains low overall. Data loss from high solar activity has declined notably since the maximum of the 25th Solar cycle passed. The thermodynamical response of the optical elements to a thermal step impulse follows sigmoidal growth curves, entering the asymptotic equilibration regime after 21--46 hours. Water-ice contamination has affected data from both instruments and requires continued monitoring; we review detection and decontamination methods, and Euclid's contamination history. High-precision measurements of the zodiacal background reveal, at eight sigma significance, the subtle modulation caused by the changing perspective on the dust distribution due to the L2 halo-orbit libration. These data also show that conservative pre-launch estimates overestimated the out-of-field stray-light by factors of 4 (H band) to 27 (I band). Telemetry data demonstrate excellent guiding, and enable highly significant detections of solar radiation pressure and of thermal-emission recoil from Euclid's unilluminated dark sides. Lastly, we present a list of 34 meteoroid impacts, discuss their mechanical and optical signatures, and derive a minimum detectable impactor mass of 5e-7 g.