impact of slr tracking on galileo _galileo.pdf · galileo orbit constellation walker 27/3/1 plus 3...
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ESOC Navigation Support Office ILRS GNSS Workshop 2009
Metsovo, Greece
Impact of SLR Tracking on Galileo
T.A. Springer, D. Navarro-Reyes, D. Escobar, R. Zandbergen
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• Prime design criteria Avoid “station keeping” orbital maneuvers during the spacecraft
lifetime Avoid the “deep 1:2 resonance“ from the GPS satellites
• Constellation Features So called “Walker 27/3/1” constellation Almost circular orbit
Orbit Radius ~29'600 km (above GLONASS and GPS) Orbit repeat period 10 days
17 revolutions in 10 days, ~14 hour per revolution Inclination 56 degrees Three equally spaced orbital planes Nine operational satellites, equally spaced in each plane
Plus one spare satellite in each plane
Galileo Orbit Constellation
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Galileo Orbit Constellation
Walker 27/3/1 plus 3 in-orbit spares (1/plane)
orbit radius ~29600 km
inclination 56 deg
period: ~ 14 h./4 min./42s 17 revs in ~10 days
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• Dimensions – 2.5 x 1.2 x 1.1 m
• Length (Y-axis) 19 m with deployed solar arrays • Spacecraft weight: ~700kg • Power: ~ 1.5 kW • Navigation payload: ~130kg • Power consumption: 900 W • Launcher options
– Ariane-5 – Proton – Soyuz (from Kourou) – Zenit.
The Galileo Satellites
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Galileo IOV LRA
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• Support to Galileo for early phases – With low number of GSS and few IGS Galileo
stations GNSS based orbits of Galileo will be of medium accuracy
– Addition of SLR observation will offer a significant accuracy improvement
• Calibration of Spacecraft Dynamics – The Y-bias as present on most GNSS satellites has
a long term effect on the satellite position. – The accurate determination of the Y-bias for each
Galileo satellite will be of prime importance to fulfill the “once in a lifetime“ station keeping manoeuvre requirement
• Alignment of GTRF to ITRF
Galileo SLR Scenario
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IOV LRA
Size of Array ~0.35 x 0.35 m = 0.12 m2
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Conner Cube Reflectors
• 84 Corner Cube Reflectors (CCR) doped fused silica glass tetrahedron no metallic coating aperture face is included in a circle of 43 mm diameter height of the tetrahedron is 23.3 mm Iso-static mounting to plate N = 1.46, critical angle16.9 deg
which covers the entire LRR operating range (Earth radius of 12.44°) no coating, total reflection is obtained without any loss
Velocity aberration compensation 24 µrad CCR are randomly oriented LRA Centre of Phase TBD after Qualification Tests
• This information will be published in an update to “Specification of Galileo and GIVOVE Space Segment Properties Relevant for Satellite Laser Ranging” (ESA-EUING-TN-10206) and in the “Mission Support Request Form”
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SLR-relevant Data Flow
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• Support to Galileo for early phases – Support for satellite “fine positioning“ – Support for Galileo operational POD
• Completely independent validation • Calibration and validation of spacecraft dynamics • Alignment of GTRF to ITRF • Maintain and improve the ITRF • Ensure the position of Galileo • Position Galileo as „best“ GNSS system
– No SLR LRA's on GPS – „split“ LRA's on GLONASS
• Ensure GNSS interoperability through a common independent measurement technique
Summary of SLR Tracking Benefits