.. index:: Darks (NISP); Calibration observations .. _calobs-block-pv-nisp-grism-rotation-center: **CALBLOCK-PV-019:** NISP Grism Centers of Rotation =================================================== .. include:: definitions.rst Observation configuration file ------------------------------ | :download:`ocf_CALBLOCK-PV-019_ALL-GRISMS.csv ` Scheduling ---------- Once, during PV phase. In case of failure, repeat at next possible opportunity. Time-critical ------------- No Objective --------- The NISP grism wheel positions a grism with an RMS of typically 0.1 degree, with occasional excursions of up to 0.5 degree of the commanded value. The jitter angle can be determined from the orientation of the spectra traces, and must be used to appropriately transform the calibrations (potentially taken with a slightly different jitter angle) to match the science spectra exposures. Due to optics chromaticity, the dispersion pattern (i.e. spectral trace and wavelength solution) does not purely rotate with rotation of the dispersing grism, but includes higher-order distortion terms. However, to first order in small jitter angle, the dispersion pattern can locally be derived from reference calibration solution as a simple rotation with respect to an ad-hoc position. To derive these first-order rotation elements, NISP shall observe an arbitrary stellar field several times for each grism setup with independent random realisations of the jitter angle. Due to the individual nonlinearities, the process must be repeated for each grism, even though all are mounted in the same grism wheel and thus have the same mechanical center of rotation. **Reduction of NI-SA heating power:** The frequent use of the GWA will generate excess heat that has a very long (many hours) decay constant in NISP. This will affect the optical quality of NISP. To minimize the thermal impact, the NI-SA heater power will be reduced by 250 mW at the beginning of the observations, and restored to nominal value at the end. The NI-SA heater is clearly identified since it is a single heater command (NISC1001, with heater ID is SA=1). Observations ------------ .. index:: Grism center of rotation At the Self-cal field, execute the following observations. .. code-block:: python :caption: NISP grism wheel center of rotation. Uses **non-standard exposure type**. Put NISP in reference configuration (RGS000, FWA closed). OPTIONAL: Reduce NI-SA heater power by 250 mW (NISC1001, heater ID SA=1). for grism in [RGS000, RGS000_rot, RGS180, RGS180_rot, BGS000]: repeat 5x: rotate GWA to OPEN position Buffer to respect GWA timing constraints before further GWA actuation rotate GWA back to previous position Take 1 non-standard spectro-MACC(4,16,4) exposure Random dither offset in a 3' box IF DONE BEFORE: Restore NI-SA heater power to nominal value. Put NISP in reference configuration (RGS000, FWA closed). Fulfilling ---------- :ref:`calobs-nisp-spec-grism-rotation-center` Targets and pointing constraints -------------------------------- :command:`Pointing`: Straylight suppression as per MOCDA-SYS-003. .. csv-table:: **Self-cal center.** :download:`CSV file ` :file: tables/targets-selfcal-center.dat Instrument configuration ------------------------ Instrument: Wide survey Uses **non-standard spectro-MACC(4,16,4)** mode. Methodology / Uplink procedure ------------------------------ :command:`Entity`: NISP :command:`Commanding Method`: NISP: Observation; **non-standard spectro-MACC(4,16,4)** :command:`Dither Sequence`: Random dithers in a 3' box In-orbit duration ----------------- :command:`In-orbit Duration`: 1.5 h ``(5*(3*18s setup + 111s exposure + 40s SCCI) + 60s dither)*5 grisms`` Data volume ----------- ``65*NP = 3835 MB`` Processing input ---------------- :command:`Data Description`: 13 NISP science images per grism Processing method ----------------- TBD Processing output ----------------- For each grism, determine the location and uncertainty of the center of rotation as a function of position in the field of view. Quality control parameters -------------------------- DataModel: ``_ Contact person -------------- NISP-S calibration scientist .. raw:: latex \clearpage