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Thermal Focus and Pointing Corrections

Thermal Focus and Pointing Corrections. K. Constantikes. Status. New thermal model, new gravity model parameters Uses 19 structural temperature sensors Linear thermal, tradional gravity Focus peformance ~< 3 mm (excludes midday) during ~30 mm thermal focus shift

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Thermal Focus and Pointing Corrections

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  1. Thermal Focus and Pointing Corrections K. Constantikes

  2. Status • New thermal model, new gravity model parameters • Uses 19 structural temperature sensors • Linear thermal, tradional gravity • Focus peformance ~< 3 mm (excludes midday) during ~30 mm thermal focus shift • Elevation performance ~<3” 1s , <1”/hour (excludes midday) during ~ 30” thermal pointing shift • Azimuth performance ~<3” 1s , <1”/hour (excludes midday) • Unanticipated dominance of horizontal feed arm influence • PTCS/PN/25 “Thermally-Neutral Traditional Pointing Models and Thermal Corrections to Pointing and Focus” • Test of real-time focus corrections (Balser and Prestage,11/20/03)

  3. Structural Temperature • 19 locations, 0.2C interchangeable accuracy, 0.01C resolution, 1Hz, range –35 to 40C. (actual accuracy is ~0.1C, temp control of conversion elex) • Design documentation: • PTCS Wiki (AntennaInstrumentation) • PTCS Project Note PTCS/PN12 • Accuracy tested in lab: • Solar/convective loading • Selected unit-to-unit accuracy, repeatability • Electronics temperature range • RFI mitigated, ESD protected • Two thermistor failures, forensics with YSI • Integrated into M&C • First cut pointing, focus predictive algorithms tested

  4. Structural Temperature

  5. Structural Temperature

  6. Algorithms • Use existing GBT gravity pointing and focus models • Structure is linear: Thermal effects superpose • Temperature effect on focus, pointing assumed linear in temperatures • No dependence on air or bulk temps, just differences • Simultaneously estimate gravity and temperature model coefs • Estimate coefs using 9/11, 10/2, 11/10 data • Test models using 9/5, 11/20 data

  7. Term Coefficient Min-Max Significance Parameter M1 1.086 13.1 14.3 SR-Pri M2 -0.697 6.2 -4.3 VFA-Pri M3 3.981 15.6 62.0 HFA M4 -7.326 0.9 -6.8 BUS V1 M5 -0.688 12.1 -8.3 BUS V2 M6 -2.576 12.1 -31.2 BUS F M7 -180.630 0.0 0.0 Offset M8 66.189 .7 43.1 sin term M9 196.949 0.6 110.8 cos term Focus Model

  8. Focus Model Estimation

  9. Focus Model Tests • Wind < 2.5 m/s • 15° < elevation < 85° • 9/5 is NCP • 11/20 is all-sky • Excludes 1000-1800 • Graphs show thermal contributions only

  10. Focus Model Tests

  11. Term Coefficient Min-Max Significance Parameter M1 -4.6455 1.2 -5.3 BUS M2 1.7830 15.6 -27.8 HFA M3 4.4488 5.9 26.4 VFA M4 -8.4477 1.6 -14.0 Alidade M5 62.2218 0.0 +0.000 -IE,d(0,0) M6 -55.8624 0.7 -62.792 HZCZ,b(0,1) M7 -22.8268 0.9 -38.216 HZSZ,d(0,1) M8 2.4960 2.0 +2.169 -AW,c(1,0) M9 -1.3360 2.0 -1.750 AN,d(1,0) Elevation Model

  12. Elevation Model Estimation s = 3.6

  13. Elevation Model Test

  14. Elevation Model Test

  15. Term Coefficient Min-Max Significance Parameter M1 5.5862 4.0 22.4 Alidade M2 -8.0331 2.7 21.3 HFA M3 -1.6289 2.4 3.8 BUS M4 1.3683 2.0 2.8 VFA M5 3.4124 0.0 0.0 CA, d(0,0) M6 1.3223 0.7 1.0 NPAE, b(0,1) M7 3.5152 0.9 3.0 IA, d(0,1) M8 -2.4960 1.9 4.8 AW, b(1,1) M9 -1.3360 1.8 2.5 AN, a(1,1) Azimuth Model

  16. Azimuth Model Estimation s = 3.9

  17. Azimuth Model Test

  18. Azimuth Model Test

  19. Why does it work? • Didn’t for 140’ (von Hoerner), why should GBT? • Thermal diffusivity? • Time constants? • Characteristic length of perturbations? • Surface area of structural supports? • Better temperature measurement technology ! • Better homology?

  20. Conclusions • Focus and elevation greatly improved with thermally-neutral traditional model and temperature corrections • Azimuth performance improvement marginal (but it’s already pretty good) • Use of thermal imaging to improve locations • Add sensors to HFA, BUS • Work on graceful degradations • Production implementation • Further tests for confidence • Thermal stability model

  21. The Details….

  22. Previous Focus Tracking Curves

  23. Previous Focus Tracking Curves

  24. Temperature Sensor Locations TF1 TF5 TSR TF3 TF4 TF2 TH3 TB2 TH2 TE2 TB1 TB3 TB4 TB5 TE1 TA4 TA2 TA3 TA1

  25. Focus Model • Gravity • SR-Primary • VFA-Primary • HFA • BUS

  26. Elevation Model • Gravity • BUS • HFA • VFA • Alidade

  27. Azimuth Model • Gravity • Alidade • HFA • BUS • VFA

  28. Optimization • Focus optimization using pseudo-inverse for LSE solution • Coupled Az and El gravity models (AN, AW constraint) • Gradient descent

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