.. index:: Telescope thermal timescale; Characterization .. _char-telescope-thermal-timescale: **CHAR-TEL-001:** Telescope thermal timescale ============================================= .. include:: definitions.rst Parent requirement ------------------ Objective --------- Every time the telescope changes its attitude with respect to the Sun, it goes into a new thermo-optical equilibrium that affects the VIS PSF. To this end, in particular AA variations are minimized in the survey design. The typical timescale of the telescope to reach a sufficiently stable state for weak lensing after an attitude change is poorly known prior to flight. This characterization aims at determining the typical timescale. The metrics used will be the focus term obtained from the diffraction spikes, and the thermistor readings from the PLM. The latter provide an instantaneous view of the thermal state without time lags due to pixel processing. Cadence ------- Once, during PV phase. Observations ------------ Methodology / Uplink procedure ------------------------------ Targets and pointing constraints -------------------------------- Instrument configuration ------------------------ Inter-operability constraints ----------------------------- Dependencies ------------ Fulfilling ---------- Fulfilled by ------------ :ref:`calobs-block-pv-vis-thermal-timescale` Time-critical ------------- Yes. Must be executed prior to :ref:`calobs-block-pv-phase-diversity`. Validation ---------- Recovery -------- In-orbit duration ----------------- :command:`In-orbit Duration`: Processing time --------------- Processing input ---------------- :command:`Ground Processing Input Data`: :command:`Data Description`: Data volume ----------- Processing tools ---------------- Processing element ------------------ DataModel: ``_ Quality control parameters -------------------------- DataModel: ``_ Required accuracy, constraints ------------------------------ Processing method ----------------- Processing output ----------------- PSF metrics (mainly focus; but could also be ellipticity) as a function of time, and as a function of temperature of relevant opto-mechanical parts, such as M1. Ideally, determine the e-folding or half-time of these parameters. If possible, determine the typical timescale the telescope would need after a change of :math:`\Delta{\rm AA}=1` before weak lensing observations can resume. Build a correlation between the thermistor readings and the focus term. Contact person -------------- Calibration Lead Status ------ |today| - In progress. FLAG ---- Priority -------- Observation record ------------------ Comments -------- .. raw:: latex \clearpage