CALBLOCK-PV-032: VIS Thermal timescale

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 CALBLOCK-PV-008: Phase Diversity Calibration. Must be executed immediately after the telescope was stabilized at a different \({\rm AA}\).

Dependencies

The spacecraft must be prepared with a stable, thermal state that is different than the one for CALBLOCK-PV-008: Phase Diversity Calibration.

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 \({\rm AA}\) 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 \({\rm AA}=-3.5\) for 3-7 days (e.g. CALBLOCK-PV-002: NISP-P and VIS Absolute Photometric Standards). 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 \({\rm AA}=-7.5\).

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 \(5--48\) 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

CHAR-TEL-001: Telescope thermal timescale

Targets and pointing constraints

Pointing: Maintain \({\rm AA}=-3.5\) for 3-7 days prior to these observations. Then switch to \({\rm AA}=-7.5\) to create a thermal imbalance. Small changes in \({\rm AA}\), such as by 0.035 degrees due to orbit progression during the maximum 3000s SCCI on-target time are permissible.

Table 67: Self-cal field CSV file

# ID

R.A.

Dec

SELFCAL-CENTER

268.812745

65.2855857

Instrument configuration

Instrument: VIS

Inter-operability constraints

NISP mechanisms must not move while VIS observes on sky.

In-orbit duration

In-orbit Duration: 7-10 days

Data volume

(15+44+40)*VS = 44748 MB

Processing input

Ground Processing Input Data: TBD

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: https://gitlab.euclid-sgs.uk/

Contact person

Calibration lead