gps iif yaw attitude control during eclipse seasonacc.igs.org/orbits/yaw-iif_esoc_agu11.pdf ·...
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![Page 1: GPS IIF yaw attitude control during eclipse seasonacc.igs.org/orbits/yaw-IIF_ESOC_agu11.pdf · 2015-11-02 · GPS IIF yaw attitude control during eclipse season | Dilssner et al](https://reader033.vdocuments.net/reader033/viewer/2022042909/5f39f7c94f94b572e3769db1/html5/thumbnails/1.jpg)
GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 1
GPS IIF yaw attitude control
during eclipse season
F. Dilssner, T. Springer, W. Enderle European Space Operations Centre (ESOC), Darmstadt, Germany
AGU Fall Meeting, San Francisco Dec 9, 2011
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 2
Sun-nadir-steering (1/2)
– L-band antenna needs to be pointed toward geocenter; solar panels have to be perpendicular to Sun direction
– Orientation (“attitude”) needs to be continuously adjusted through yaw and pitch control
– ADCS provides sensors (Earth, Sun, Gyro) and effectors (reaction wheels, torque rods)
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 3
Sun-nadir-steering (2/2)
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 4
Today’s focus
– Shadow-crossing maneuvers: How does GPS Block IIF S/C control its yaw attitude when solar sensors’ view of the Sun is obstructed by the Earth / the Moon?
– Noon-turn maneuver: How does S/C perform its noon-turn to keep +X side facing the Sun?
Yaw angle is crucial for precise satellite antenna phase centre and clock modeling
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 5
Estimated GPS IIF satellite antenna PCVs
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 6
Evidence for GPS IIF yaw attitude modeling issues
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 7
Epoch-wise yaw angle estimation
– 30-sec code & phase measurements from global IGS tracking network
– 1st step: IGS-like GNSS analysis
– 2nd step: Resolving satellite clocks & phase centre positions epoch-by-epoch (“reverse kinematic point positioning”)
– “Nominal” yaw attitude model employed
– Yaw error reflected in horizontal PCOs
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 8
Midnight-turn regime (1/2)
– Linear drift in yaw angle estimates as soon as S/C enters umbra
– S/C is rotating around its z-axis with nearly constant rate (here: ≈ 0.06º/s)
– S/C keeps “natural” sense of rotation due to yaw bias which is set to have the same sign as β-angle
– Yaw angle upon shadow exit may be off from “nominal” value forcing S/C to perform short post-shadow recovery maneuver (< 5 min)
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 9
Midnight-turn regime (1/2)
– Linear drift in yaw angle estimates as soon as S/C enters umbra
– S/C is rotating around its z-axis with nearly constant rate (here: ≈ 0.06º/s)
– S/C keeps “natural” sense of rotation due to yaw bias which is set to have the same sign as β-angle
– Yaw angle upon shadow exit may be off from “nominal” value forcing S/C to perform short post-shadow recovery maneuver (< 5 min)
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 10
Midnight-turn yaw-rate estimates (1/2)
– Yaw-rate estimates for 228 eclipse events (SVN-62: #176, SVN-63: #52)
– Yaw-rate varies through the eclipse season; the lower the β-angle, the higher the rate
– Estimates for β > 0° closely match thereoretical expectations; values for β < 0° tend to be higher as expected
– Difference between high rate (β < 0°) and low rate (β > 0°) values of 0.005°/s
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 11
Midnight-turn yaw-rate estimates (1/2)
– Yaw-rate estimates for 228 eclipse events (SVN-62: #176, SVN-63: #52)
– Yaw-rate varies through the eclipse season; the lower the β-angle, the higher the rate
– Estimates for β > 0° closely match thereoretical expectations; values for β < 0° tend to be higher as expected
– Difference between high rate (β < 0°) and low rate (β > 0°) values of 0.005°/s
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 12
Midnight-turn yaw-rate estimates (2/2)
– Yaw-rate parameter can be well described by two “block-specific” 2nd order polynomials
– De-trended rate estimates exhibit RMS of ±0.0014°/s
– Yaw rate uncertainty translates into uncertainty in yaw angle of ±5° at the end of a 55-min eclipse event
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 13
Midnight-turn yaw-rate estimates (2/2)
– Yaw-rate parameter can be well described by two “block-specific” 2nd order polynomials
– De-trended rate estimates exhibit RMS of ±0.0014°/s
– Yaw rate uncertainty translates into uncertainty in yaw angle of ±5° at the end of a 55-min eclipse event
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 14
Midnight-turn yaw-rate estimates (2/2)
– Yaw-rate parameter can be well described by two “block-specific” 2nd order polynomials
– De-trended rate estimates exhibit RMS of ±0.0014°/s
– Yaw rate uncertainty translates into uncertainty in yaw angle of ±5° at the end of a 55-min eclipse event
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 15
“Nominal” attitude model vs. new attitude model
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 16
Noon-turn regime
– S/C cannot keep up with required yaw rate, if |β| < 4.5°
– Estimated and “nominal” yaw angle diverge under small negative β-angle (-0.9° < β < 0°); ∆ψ adds up to 360°
– Linear drift in IGS clock solutions in the range of 0.4 ns (0.12 m) due to phase wind-up mismodeling
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 17
Noon-turn regime
– S/C cannot keep up with required yaw rate, if |β| < 4.5°
– Estimated and “nominal” yaw angle diverge under small negative β-angle (-0.9° < β < 0°); ∆ψ adds up to 360°
– Linear drift in IGS clock solutions in the range of 0.4 ns (0.12 m) due to phase wind-up mismodeling
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 18
Noon-turn regime
– S/C cannot keep up with required yaw rate, if |β| < 4.5°
– Estimated and “nominal” yaw angle diverge under small negative β-angle (-0.9° < β < 0°); ∆ψ adds up to 360°
– Linear drift in IGS clock solutions in the range of 0.4 ns (0.12 m) due to phase wind-up mismodeling
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 19
Noon-turn yaw-rate estimates
– Yaw-rate estimates for 81 noon-turn events (SVN-62: #63, SVN-63: #18)
– S/C yaws about twice as fast as during shadow crossing
– Discontinuity at β = -0.9°; difference between high and low rate values of 0.01°/s
– Estimates vary by 5%; repeatability four times worse than midnight rates
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 20
Moon eclipse
– Analysis of eight partial Moon eclipses
– No yaw anomalies detected, except for 40-min eclipse event on Aug 9, 2010
– S/C reached darkest point on its eclipse passage at 21:58 UTC; angle between S/C-Moon and S/C-Sun is 0.07°
– S/C starts yawing with -0.08°/s; yaw reversal after 20 min; rotation at full rate until “nominal” attitude is resumed
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 21
Moon eclipse
– Analysis of eight partial Moon eclipses
– No yaw anomalies detected, except for 40-min eclipse event on Aug 9, 2010
– S/C reached darkest point on its eclipse passage at 21:58 UTC; angle between S/C-Moon and S/C-Sun is 0.07°
– S/C starts yawing with -0.08°/s; yaw reversal after 20 min; rotation at full rate until “nominal” attitude is resumed
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 22
Moon eclipse
– Analysis of eight partial Moon eclipses
– No yaw anomalies detected, except for 40-min eclipse event on Aug 9, 2010
– S/C reached darkest point on its eclipse passage at 21:58 UTC; angle between S/C-Moon and S/C-Sun is 0.07°
– S/C starts yawing with -0.08°/s; yaw reversal after 20 min; rotation at full rate until “nominal” attitude is resumed
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GPS IIF yaw attitude control during eclipse season | Dilssner et al. | Pag. 23
Conclusions
– Block IIF satellites follow a completely different yaw attitude scheme, when passing through the Earth's shadow, as the Block IIA and IIR S/C
– Midnight-turn yaw rate is kept constant to the value needed to get the S/C near to its nominal attitude when leaving the Earth's shadow
– S/C crossing shadow during middle of the eclipse season (β = 0°) needs to yaw almost two times faster as towards the edges of the eclipse season
– Yaw angle can be precisely modeled using 2nd order yaw rate polynomial; model reduces phase residual RMS from up to ±7 cm down to ±1 cm
– Noon-turn model still under development
– Moon eclipses rarely affect attitude control