This document describes the proposed exchange file format for the pointing control angles theta and phi describing the telescope attitude. Control angles are defined as in the Pointing Reconstruction Model (PRM) document. Encoder control angles are provided by the Telescope Control System (TCS) from the reading of
the telescope encoders without any further processing (calibration)

MARIS, Michele

NOVELLI, Alessandro

SARTOR, Stefano

OA@INAF - Istituto Nazionale di Astrofisica

2022Publication Year2023-07-21T09:23:47ZAcceptance in OA@INAFSTRIP/LSPE: Telescope Raw Pointing File FormatTitleMARIS, Michele; SARTOR, Stefano; NOVELLI, AlessandroAuthorshttp://hdl.handle.net/20.500.12386/34308HandleLSPE-STRIP-SP-031NumberINAF/OATs LSPE-STRIPTITLE: LSPE-STRIP: Estimation of star tracker optimal parametersDOC. TYPE: Technical notePROJECT REF.: LSPE-STRIP-TN-023 PAGE:  I of IV, 11ISSUE/REV.: 00/01Prepared byMichele MarisMatteo PorruDate:Signature:2017 Dec 15thAgreed byDate:Signature:Approved byDate:Signature:LSPE-STRIP – titleDocument No.:Issue/Rev. No.:Date:Page:LSPE-STRIP-TN-xxx0.02017 Dec 15IIDISTRIBUTION LISTRecipient Company / Institute E-mail address SentINAF/OATsLSPE-STRIP – titleDocument No.:Issue/Rev. No.:Date:Page:LSPE-STRIP-TN-xxx0.02017 Dec 15IIICHANGE RECORDIssue Date Sheet Description of Change Release0.0 2017 dec 15 Start of document, structure prepared 0.01.0 2018 Jan 25 Number assigned, first release, plots again to beadded1.0INAF/OATsLSPE-STRIP – titleDocument No.:Issue/Rev. No.:Date:Page:LSPE-STRIP-TN-xxx0.02017 Dec 15IVTABLE OF CONTENTS1 ACRONYMS                                                                                                                                                                ..............................................................................................................................................................12 APPLICABLE AND REFERENCE DOCUMENTS                                                                                                ..............................................................................................22.1 APPLICABLE DOCUMENTS                                                                                                                                       .....................................................................................................................................2  2.2 REFERENCE DOCUMENTS                                                                                                                                        ......................................................................................................................................2  3 INTRODUCTION                                                                                                                                                        ......................................................................................................................................................34 CONCLUSIONS                                                                                                                                                          ........................................................................................................................................................4INAF/OATsLSPE-STRIP – titleDocument No.:Issue/Rev. No.:Date:Page:LSPE-STRIP-TN-xxxxxxxx1ACRONYMSAcronym MeaningTBD To be definedTBC To be confirmedSTR Star TrackerFOV Field of ViewINAF/OATsLSPE-STRIP – titleDocument No.:Issue/Rev. No.:Date:Page:LSPE-STRIP-TN-xxxxxxxx21 APPLICABLE AND REFERENCE DOCUMENTS1.1 Applicable Documents1.2 Reference DocumentsINAF/OATsLSPE-STRIP – titleDocument No.:Issue/Rev. No.:Date:Page:LSPE-STRIP-TN-xxxxxxxx32 Scope of the DocumentThis document1 describe the statistics needed to optimize the Star  Tracker (STR) design forLSPE-STRIP.A Star Tracker (STR) is a device used to determine the instantaneous pointing direction of thetelescope, by looking at stars observed in the sky.Pointing direction is the direction at which the telescope optical centre is aimed.The STR is made of three components:1. optics, aligned with the telescope optical centre (or off-setted of a known amount)2. imager, able to collect an image of the stars observed on the sky3. processor, able to process the images, store them and communicate with the telescopecontrol systemThe work presented here is aimed at the optimization of optics and camera parameters.In particular, the relevant optics and camera parameters must be optimized looking at the numberof stars observed per frame by the STR.In this run no simulation of camera electronics is carried on.In this run no atmospheric refraction is accounted for.1This work is partially based on the work of Matteo Porru for his “Tirocinio” as an undergraduate studentat the Trieste University Physics Department, hosted at Trieste Astronomical Observatory from October15th to December 15th 2017.INAF/OATsLSPE-STRIP – titleDocument No.:Issue/Rev. No.:Date:Page:LSPE-STRIP-TN-xxxxxxxx43 Method and validationThe simulation is based on a model of the sky with its diurnal and seasonal variation. The telescope is assumed to scan during the night the sky according to a predefined scanningstrategy. The sky is framed either in rings of constant zenith angles and constant widths or in framescorresponding to the STR Field of View (FOV). Stars in each ring or frame are counted. To validate the code the observed star counts was simulated against a model sky containing auniform distribution of stars. In this hypothesis Na v g=N sin (i n c )2F OV . This was verified usinga uniform HEALpix distribution of 196000 stars, calculating results in the range 10° - 40° ofinclination and 2°, 4°, 8° of FOV.INAF/OATsLSPE-STRIP – titleDocument No.:Issue/Rev. No.:Date:Page:LSPE-STRIP-TN-xxxxxxxx54 Results and Conclusions1. The goal of the simulations was to estimate the number of stars present in each frame as afunction of the limit magnitude. As an intermediate step, a simple star count per ring wasgenerated for each scan.2. The  simulation  assumes  a  simple  scanning  strategy,  with  the  telescope  rotating  at  1R.P.M. around the zenithal axis, and with fixed angular distance between the zenith andthe center of the FOV of the STR, Z. In this way, the STR scans a circular ring around thezenith, which from now on we will refer to as ring.3. Stars  for  the  simulation  are  derived  from  Star  catalog  Tycho-2  (http://vizier.u-strasbg.fr/cgi-bin/VizieR-3?-source=I/259/tyc2) truncated at the 10th magnitude.4. Simulations are done for FOV=3° and 6° and for Z=15°, 20°, 25°, from 2018 August 1stto  2019  August  1st,  for  the  Teide  National  Observatory  site  (neglecting  atmosphericrefraction).5. The nominal use case is FOV=6° and Z=20°.6. In the nominal case we have, for limiting magnitude (m_lim) equal to 6, a minimum of40 stars per ring and a maximum of 128 stars per ring, with 78 as an yearly nocturnalaverage.7. This  translates  into  3.804  stars  per  frame  on  average,  which  is  consistent  with  theexpected  value  of  3.801,  obtained  with  simple  geometrical  considerations  from  theaverage per ring.8. More relevant to the scope of our observations is the number of frames containing 0, 1, 2,3 or more stars, i.e. the sky coverage. At the 6th limit magnitude, the fraction of framescontaining 3 or more stars fluctuates between 55% in August and 73% in February. Thefraction of empty frames is around 3%.9. Increasing the limiting magnitude to 7 yields significantly better results: the number ofstars per ring fluctuates in the interval [134, 357], with an average of 245.10. The average number of stars per frame increases to 11.943, which is consistent with theexpected value of  11.939.11. With m_lim=7, the fraction of frames with 3+ stars varies between 97% and 99.7%, withno empty frames.12. In the worst-case scenario of m_lim=5 the number of stars per ring varies in the interval[10, 46], with 24 as average. This means only 1.17 stars in each frame, on average.13. Only 8-18% of the frames contain 3 or more stars, and 30-40% of the frames are empty.INAF/OATsLSPE-STRIP – titleDocument No.:Issue/Rev. No.:Date:Page:LSPE-STRIP-TN-xxxxxxxx614. A change  in  FOV from 6 deg  down to  3  deg  has  a  significant  effect.  From planargeometry, we expect the number of stars per ring to halve, while the number of stars perframe should reduce of a factor four. Simulations show an agreement within 3%. Thedifferences are due to the non-uniform distribution of stars in the sky and to projectionerrors. In order to get the same level of sky coverage obtained with FOV=6 deg andm_lim=6  it  is  necessary  to  increase  m_lim  to  a  value  between  the  7th and  the  8thmagnitude. 15. A change in Z in the range [15°, 25°] does not affect the previous results in a significantmanner. There is not a systematic change in the fractions of frames with 0, 1, 2, 3, 3 ormore stars varying Z. the mean number of stars per frame changes at most of about tenpercent.16. Our findings about star counts can be summarized by the following formula:log10 ⟨n ⟩=A mlim+C log10 (FOV3° )+DWhere A=0.5, C=0.963, D=-1.49 for counts per ring,  while in the case of counts perframe we have A=0.505, C=1.927, D=-3.1.INAF/OATs

STRIP/LSPE: Telescope Raw Pointing File Format

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STRIP/LSPE: Telescope Raw Pointing File Format

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