Reconstructed tilt (wobble) angles between the satellite body frame and the principal axis frame. Vertical blue lines mark the boundaries of operational years, and the dashed black line indicates day 540 after launch, when the thermal control on the LFI radiometer electronics box assembly (REBA) was adjusted. Top: first tilt angle, ψ₁, which corresponds to a rotation about the satellite axis just 5° off the focal plane centre. Observed changes in ψ₁ have only a small effect on the focal plane line-of-sight. Bottom: second tilt angle, ψ₂, which is perpendicular to a plane defined by the nominal spin axis and the telescope line of sight. Rotation in ψ₂ immediately impacts the opening angle and thus the cross-scan position of the focal plane. We also plot a scaled and translated version of the Solar distance that correlates well with ψ₂ until the reconstructed angles became compromised about 1000 days after launch.