GAIA SCANNING LAW - FULL OPERATIONAL MISSION PERIOD

    The Gaia scanning law pointings for the data collection period underlying Gaia (E)DR3 are available from the Gaia ESA Archive in a table named "gaiadr3.commanded_scan_law". Here we provide an additional and complementary data set, namely the commanded scanning law pointings over the full mission interval (from 2014-07-25 10:31:26 TCB to 2025-06-30 23:59:56 TCB), including the Ecliptic Pole Scanning at the beginning of the mission. As in the case of the Gaia (E)DR3 table, the data presented here contains the attitude as commanded in the past and as currently planned to be commanded in the future. The actually realised attitude of the spacecraft could deviate from it by up to about 30 arcsec. The time interval, in particular the end date in summer 2025, is excepted to contain the full operational mission period. Obviously, the precise end of spacecraft operations is not yet defined.

     

    SCANNING LAW DATA

    Please connect with an FTP client of your choice to ftp.cosmos.esa.int and navigate to the folder GAIA_PUBLIC_DATA/GaiaScanningLaw. The data file is named commanded_scan_law.csv.gz (2.5 GB).

     

    SAMPLING

    The scanning law has been sampled at a 10 second interval, in which the satellite rotates about 10 arcminutes (the target spin rate is actually 59.9641857803 arcsec/sec). Note that this is several times shorter than a typical field-of-view transit and the scan position angle will be practically constant during this interval. The sampling does not reckon with (known) operational outages. Not all pointings contained in this data set will therefore have observational data associated to them.

     

    COLUMNS

    The columns in the output file are:

    1. jd_time = Time [Julian Date in TCB at Gaia - 2455197.5]
    2. bjd_fov1: Time [Julian Date in TCB at barycentre for FOV1 - 2455197.5]
    3. bjd_fov2: Time [Julian Date in TCB at barycentre for FOV2 - 2455197.5]
    4. ra_fov1: Right Ascension of FOV1 centre [deg]
    5. dec_fov1: Declination of FOV1 centre [deg]
    6. heal_pix_fov1: FOV1 HEALPix level 12
    7. scan_angle_fov1: Scan position angle of FOV1 [deg]
    8. parallax_factor_al_fov1: FOV1 parallax factor AL
    9. parallax_factor_ac_fov1: FOV1 parallax factor AC
    10. ra_fov2: Right ascension of FOV2 centre [deg]
    11. dec_fov2: Declination of FOV2 centre [deg]
    12. heal_pix_fov2: FOV2 HEALPix level 12
    13. scan_angle_fov2: Scan position angle of FOV2 [deg]
    14. parallax_factor_al_fov2: FOV2 parallax factor AL
    15. parallax_factor_ac_fov2: FOV2 parallax factor AC
    16. solution_id: Solution Identifier

     

    NOTES

    • The times in columns 1, 2, and 3 are in Julian days in TCB with time origin 2010-01-01T00:00 (JD 2455197.5), following the time coordinate convention used in the Gaia ESA Archive. TCB stands for Barycentric Coordinate Time and is the time standard used in Gaia processing, equivalent to the proper time experienced by a clock at rest in a coordinate frame co-moving with the barycentre of the Solar system but outside its gravity well, therefore not influenced by the gravitational time dilation caused by the Sun and the rest of the Solar system.
    • Column 1 is the reference time for the spacecraft attitude, while columns 2 and 3 give the times with the (relativistic) corrections applied for the light-travel time to the Solar system barycentre, corresponding to an infinitely distant source at the RA, DEC at the centres of FOV1 and FOV2, respectively.
    • FOV1 and FOV2 correspond to the preceding (PFOV) and following (FFOV) fields-of-view, respectively.
    • The centres of the field of views (FOVs) are separated by the basic angle of 106.5 deg, see Fig. 2 of Lindegren et al. (2012). Their origin in the focal plane is illustrated in Fig. 3 of the same paper: both originate in the astrometric field (AF) 7, with FOV1 in row 3 and FOV2 in row 5.
    • The scan angle, theta, is the position angle of the direction in which the FOV is moving (also called 'along-scan' direction), and is defined in the usual astronomical sense: theta=0 when the FoV is moving towards local North, and theta=90 deg towards local East.

     

    Published 31 October 2023