Phase Centre Calibration of the Galileo Satellite Navigation Antenna

Phase Centre Calibration of the Galileo Satellite Navigation Antenna IGS workshop 2017, Paris (France) Antennas & Biases Session F. Gonzalez (ESA) M. Söllner (Airbus) E. Schönemann (ESA) F. Dilssner (ESA) 05/07/2017 ESA UNCLASSIFIED - For Official Use

Summary 1. Introduction 2. Metadata information to correct phase measurements Antenna Phase Centre Offset (PCO) Antenna Phase Centre Variation (PCV) Antenna Reference Point (ARP) Centre of Mass (CoM) User direction (attitude) 3. Galileo Metadata and IGS 4. Conclusions ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 2

Introduction Metadata for NAVANT correction (θ,φ) Phase Centre Variation (E1, E5a, E5b, E5, E6) Phase Centre Offset (E1, E5a, E5b, E5, E6) Static Antenna Reference Point Centre of Mass Dynamic ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 3

Antenna - types Two antenna types GSAT01xx - EADS CASA GSAT02xx - Thales Alenia ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 4

Antenna chamber calibration Individual for each navigation antenna by manufacturer Directional in azimuth (Φ) and nadir (θ) Each single frequency bands (E1, E5a, E5b, E5, E6) ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 5

Antenna Phase Centre offset (PCO) Farfield Sphere Segment with Radius r around MRP C MRP (a) from measurements in constant distance from MRP Delay pattern C FF on farfield sphere in distance r around MRP: C a, r = C a ( ) ( ) r FF MRP + R(a 1 ) R(a) PCO d r MRP R(a 2 ) - C dx = - C dy = C dz = MRP MRP ( q, j) 2 2 sin q cos j MRP ( q, j) sinq cosj sinq sinj 2 2 sin q sin j ( q, j) cosq - C ( q, j) MRP 2 2 ( cos q - cosq ) cosq Range from PCO to sphere around MRP: " R a = r - d! rˆ a ( ) ( ) PCO: Find d, where R(q) is most similar to C FF (q,r) Minimize!! 2! ( d ) = ( C ( ) ( ) 2 PCO a, d - CPCO a, d " " ( a, d ) = C ( a ) + d! rˆ ( a ) ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 6 with res C PCO MRP < > (weighted) averaging over a (field of view) Note, a represents the observation direction (off-axis angle q and azimuth angle j)

Antenna Phase Center Variation (PCV) Azimuthal values [0,360 ] Zenith values from 0 to 14 (GSAT01) and 20 (GSAT02) All 5 single frequencies GALILEO-1 E11 E101 2011-060A TYPE / SERIAL NO CHAMBER ESA 1 09-FEB-12 METH / BY / # / DATE 2.0 DAZI 0.0 14.0 1.0 ZEN1 / ZEN2 / DZEN 5 # OF FREQUENCIES GALILEO-2 E18 E201 2014-050A TYPE / SERIAL NO CHAMBER ESA 1 12-FEB-16 METH / BY / # / DATE 5.0 DAZI 0.0 20.0 0.5 ZEN1 / ZEN2 / DZEN 5 # OF FREQUENCIES ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 7

Antenna Phase Center Variation (PCV) Azimuthal values [0,360 ] Zenith values from 0 to 14 (GSAT01) and 20 (GSAT02) All 5 single frequencies 4 2 GSAT0101 (IOV) GSAT0201 (FOC) 0 [millimetres] 2 4 6 8 0 2 4 6 8 10 12 14 16 18 20 ESA UNCLASSIFIED - For Official Use Nadir angle [deg] ESA 05/07/2017 Slide 8

Antenna - PCV Azimuthal components ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 9

Antenna Reference Point Antenna integrated on body frame Physical point on the satellite [mm] ESA UNCLASSIFIED - For Official Use X Y Z GSAT0 1 1375.5 600.0 1100.5 GSAT0 2 140.0 0.0 1215.0 ESA 05/07/2017 Slide 10

Centre of Mass dry measurement in stow ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 11

Centre of Mass tank filling ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 12

Centre of Mass Solar array deployment ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 13

Centre of Mass - Values Dynamic information, with value after any maneuver sent to ILRS Agreement between S/C well below 1 cm +X [mm] GSAT01 1206,0 1205,8 1205,6 1205,4 1205,2 1205,0 695 696 697 698 Mass [Kg] +X [mm] 320 310 300 290 280 270-01 -02 GSAT02 260 650 660 670 680 690 700 710 720 Mass [Kg] ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 14

User direction - Attitude Azimuthal correction requires Satellite yaw modeling Orientation accuracy better than ground antennas 1 1 Source: F.Dilssner, Galileo IOV Spacecraft Metadata and Its Impact on Precise Orbit Determination, EGU2017 ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 15

Metadata versus IGS Dynamic Static Phase Centre Variation Ionosphere-free (E1-E5a) Static (θ) (θ,φ) Phase Centre Offset (E1, E5a, E5b, E5, E6) Antenna Reference Point Phase Centre Variation (E1, E5a, E5b, E5, E6) Static Centre of Mass Dynamic ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 16

Metadata versus IGS Galileo (GSAT_wwww.atx) IGS (IGS14.atx) Source Measured on ground Estimated in space Types Frequencies Static data Per single Satellite Single Frequency (E1,E5a,E5b,E5,E6) PCV PCO (θ,φ) PCO - ARP ARP - SRF per family (IOV,FOC-L3,FOC) Ionosphere-free (E1-E5a) PCV PCO (θ) =0 Dynamic data CoM - SRF PCO CoM Frame Satellite Reference Frame Antex Attitude Normal + Modified Normal ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 17

Metadata versus IGS Estimated in Space using NAPEOS versus measured on ground Accuracy of estimated in space affected by models accuracy (e.g. SRP) 0,035 0,2 0,03 0,15 0,025 0,1 0,02 0,05 Metre 0,015 0,01 0,005 0-0,005-0,01 101 102 103 201 202 203 204 205 206 207 208 X Y Metre 0-0,05-0,1-0,15-0,2-0,25 101 102 103 201 202 203 204 205 206 207 208 Z ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 18

Summary and conclusions Metadata for Galileo antenna phase center corrections Antenna Phase Centre Offset (PCO), Variation (PCV) and Reference Point (ARP) Satellite Centre of Mass (CoM) and Attitude (user direction) Benefit Tie GNSS phase measurements consistently to the spacecraft CoM Especially relevant for GNSS-based realization of terrestrial scale, independent of SLR/VLBI Galileo is the first GNSS disclosing the full range of metadata for each antenna and carrier frequency Radial antenna offsets for other GNSS become accessible without the need to adopt any external scale Status GSAT01 released during Initial Service Declaration (Dec-2016) GSAT02 under release process. Recommendation ANTEX format update to handle COM / ARP Location https://www.gsc-europa.eu/support-to-developers/galileo-iov-satellite-metadata#2 https://ilrs.cddis.eosdis.nasa.gov/missions/satellite_missions/current_missions/ga01_com.html ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 19

THANKS for your attention ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 20

BACK-UP slides BA ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 21

Introduction - request by IGS Requested by Scientific community Galileo scientific advisory committee (GSAC) International GNSS Service (IGS) ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 22

Antenna - PCV Azimuthal components GSAT01 ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 23

Antenna - PCV Azimuthal components GSAT02 ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 24

ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 25

Antenna chamber calibration ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 26

ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 27

Antenna correction information from Galileo Four components Five frequencies Ground calibrated Phase Centre Variation (E1, E5a, E5b, E5, E6) Antenna Phase Centre (E1, E5a, E5b, E5, E6) Static Antenna Reference Point Centre of Mass Dynamic ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 28

Antenna correction information in IGS Two components Iono-free Phase Centre Variation Computed from POD Iono-free (E1, E5a) Static Antenna Phase Centre Iono-free (E1, E5a) Centre of Mass Dynamic ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 29

Antenna correction information from Galileo (θ,φ) Phase Centre Variation (E1, E5a, E5b, E5, E6) Phase Centre Offset (E1, E5a, E5b, E5, E6) Static Antenna Reference Point Centre of Mass Dynamic ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 30

Metadata content Requested by Galileo scientific advisory committee (GSAC) International GNSS Service (IGS) Status Galileo IOV Satellite Metadata released during Initial Service Declaration (Dec-2016). Galileo FOC metadata to be released (Q3,2017). Content Attitude Law Mass and Centre Of Mass evolution Navigation Antenna Phase Centre Corrections Geometry and optical properties Laser Retro Reflector Location Satellite Group Delay ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 31

Metadata location https://www.gsc-europa.eu/support-to-developers/galileo-iov-satellite-metadata#2 https://ilrs.cddis.eosdis.nasa.gov/missions/satellite_missions/current_missions/ga01_com.html ESA UNCLASSIFIED - For Official Use ESA 05/07/2017 Slide 32