.. index:: VIS thermal stabilization timescale .. _calobs-block-pv-vis-thermal-timescale: **CALBLOCK-PV-032:** VIS Thermal timescale ========================================== .. include:: definitions.rst Observation configuration file ------------------------------ Not applicable Scheduling ---------- Once, during PV phase. At the beginning, the telescope must be in a stable thermal state that is different from the thermal state realised here. In case of failure of a single VIS image, do not repeat, just continue with the plan. In case of multiple failures we likely have a more general problem. Time-critical ------------- Yes. Must be executed immediately prior to :ref:`calobs-block-pv-phase-diversity`. Must be executed immediately after the telescope was stabilized at a different :math:`{\rm AA}`. Dependencies ------------ The spacecraft must be prepared with a stable, thermal state that is different than the one for :ref:`calobs-block-pv-phase-diversity`. Objective --------- Every time the telescope changes its attitude with respect to the Sun, it goes into a new thermal equilibrium that affects the VIS PSF. To this end, in particular :math:`{\rm 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, and must be determined prior to the beginning of the routine survey operations. Observations ------------ Prepare a stable thermal state by keeping Euclid at :math:`{\rm AA}=-3.5` for 3-7 days (e.g. :ref:`calobs-block-pv-absolute-standards-imaging`). After 40 hours we expect the PLM to be in the exponentially decaying regime of the thermal state change. The e-folding time from thermistor readings during the TVac tests is about 20 hours. Create a thermal pulse by switching to :math:`{\rm AA}=-7.5`. Take continuous VIS images with decreasing cadence, as the on-ground STOP analysis predicts the strongest and fastest optical response to a thermal state change at the beginning: 1. Take 1 standard VIS science image every 20 minutes, for 5 hours. 2. Take 1 VIS image per hour in the period :math:`5--48` h after start. 3. Take 1 VIS image every 3 hours after 48 h onward, until the available thermal stabilization time is used up (ideally, 7 days or more). Fulfilling ---------- :ref:`char-telescope-thermal-timescale` Targets and pointing constraints -------------------------------- :command:`Pointing`: Maintain :math:`{\rm AA}=-3.5` for 3-7 days prior to these observations. Then switch to :math:`{\rm AA}=-7.5` to create a thermal imbalance. Small changes in :math:`{\rm AA}`, such as by 0.035 degrees due to orbit progression during the maximum 3000s SCCI on-target time are permissible. .. csv-table:: **Self-cal field** :download:`CSV file ` :file: tables/targets-selfcal-center.dat Instrument configuration ------------------------ Instrument: VIS Methodology / Uplink procedure ------------------------------ :command:`Entity`: VIS :command:`Commanding Method`: :command:`Dither Sequence`: None. Single image at the current attitude. Inter-operability constraints ----------------------------- NISP mechanisms must not move while VIS observes on sky. In-orbit duration ----------------- :command:`In-orbit Duration`: 7-10 days Data volume ----------- ``(15+44+40)*VS = 44748 MB`` Processing input ---------------- :command:`Ground Processing Input Data`: TBD :command:`Data Description`: Single VIS images. Processing method ----------------- Focus term obtained from the diffraction-spikes in single VIS images. One needs to link the stability of higher-order Zernikes to that of the focus term. Processing output ----------------- The focus term is obtained from the diffraction spikes and as a function of time. It shall be linked to various thermistor readings in the PLM, such that - if possible - the latter can be used to assess whether the telescope is truly stable for science observations. Processing tools ---------------- OU-SHE tools to measure diffraction spikes. Quality control parameters -------------------------- DataModel: ``_ Contact person -------------- Calibration lead .. raw:: latex \clearpage