1. April 8/9, 2003 Green Bank GBT PTCS Conceptual Design Review Richard Prestage, Kim Constantikes, Dana Balser, Jim Condon The GBT Precision Telescope Control System

2. URSI – Jan 5-8, 2004 2 How to make a 100m telescope work at 50GHz (…with plans for 115GHz) Overview of GBT and the PTCS project Thermal Effects and their compensation Measurement of wind and servo effects

3. URSI – Jan 5-8, 2004 3 The GBT is large….

4. URSI – Jan 5-8, 2004 4 Telescope Structure and Optics

5. URSI – Jan 5-8, 2004 5 Telescope Structure and Optics

6. URSI – Jan 5-8, 2004 6 Telescope Structure and Optics

7. URSI – Jan 5-8, 2004 7 Telescope Structure and Optics

8. URSI – Jan 5-8, 2004 8 Scientific Requirements

9. URSI – Jan 5-8, 2004 9 PTCS Project Aim of the project is to deliver 3mm operation. Includes instrumentation, servos (existing), algorithm and control system design, implementation. As delivered antenna => 15GHz operation (Fall 2001) Active surface and initial pointing/focus tracking model => 26GHz operation (Spring 2003) PTCS project initiated November 2002: –50GHz operation:Fall 2003 (November) –90GHz operation:Winter 2004/05 –Full 115GHz:Winter 2005/06

10. URSI – Jan 5-8, 2004 10 Gravity/Temperature Effects - Focus Temperature Effect Gravitational Effect Measure focus over short time periodNCP source 0117+8928

11. URSI – Jan 5-8, 2004 11 Gravity/Temperature Effects - Pointing

12. URSI – Jan 5-8, 2004 12 Structural Temperatures

13. URSI – Jan 5-8, 2004 13 Structural Temperatures

14. URSI – Jan 5-8, 2004 14 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 coefficients Estimate coefficients using 9/11, 10/2, 11/10 data Test models using 9/5, 11/20 data

15. URSI – Jan 5-8, 2004 15 Focus Model TermCoefficientMin-MaxSignificanceParameter M1M1 1.08613.114.3 SR-Pri M2M2 -0.6976.2-4.3 VFA-Pri M3M3 3.98115.662.0 HFA M4M4 -7.3260.9-6.8 BUS V1 M5M5 -0.68812.1-8.3 BUS V2 M6M6 -2.57612.1-31.2 BUS F M7M7 -180.6300.0 Offset M8M8 66.189.743.1 sin term M9M9 196.9490.6110.8 cos term

16. URSI – Jan 5-8, 2004 16 Focus Model Estimation

17. URSI – Jan 5-8, 2004 17 Focus Model Test

18. URSI – Jan 5-8, 2004 18 Elevation Model TermCoefficientMin-MaxSignificanceParameter M1M1 -4.64551.2-5.3 BUS M2M2 1.783015.6-27.8 HFA M3M3 4.44885.926.4 VFA M4M4 -8.44771.6-14.0 Alidade M5M5 62.22180.0+0.000 -IE,d(0,0) M6M6 -55.86240.7-62.792 HZCZ,b(0,1) M7M7 -22.82680.9-38.216 HZSZ,d(0,1) M8M8 2.49602.0+2.169 -AW,c(1,0) M9M9 -1.33602.0-1.750 AN,d(1,0)

19. URSI – Jan 5-8, 2004 19 Elevation Model Estimation

20. URSI – Jan 5-8, 2004 20 Elevation Model Test

21. URSI – Jan 5-8, 2004 21 Thermal Compensation Results Significantly improved “static” gravity models. Focus peformance ~< 3 mm (excludes midday) during ~30 mm thermal focus shift. Elevation performance ~<3” 1 , <1”/hour (excludes midday) during ~ 30” thermal pointing shift. Azimuth performance ~<3” 1 , <1”/hour (excludes midday). Unanticipated dominance of horizontal feed arm influence.

22. URSI – Jan 5-8, 2004 22 Tracking Stability: Servo and Wind Thermal effects important on timescales ~ 0.5 hours Short term tracking stability dominated by: –Wind –Servo disturbances We are starting to characterize the effects Possibility of compensation looks promising

23. URSI – Jan 5-8, 2004 23 14GHz half-power track

24. URSI – Jan 5-8, 2004 24 14GHz half-power track

25. URSI – Jan 5-8, 2004 25 14GHz half-power track

26. URSI – Jan 5-8, 2004 26 Servo effects

27. URSI – Jan 5-8, 2004 27 Effects of wind

28. URSI – Jan 5-8, 2004 28 Effects of Wind

29. URSI – Jan 5-8, 2004 29 Future Developments New InstrumentationExisting Instrumentation/Techniques Instrument/ Technique InclinometersStar TrackerPenn Array Receiver Temperature Sensors (struct. / air) Quadrant Detector Holography (trad. / oof) Laser Rangefinders Algorithms/ Development Track irregularities Wind lift/drag Vibration Test 1” differential capability Substructure rotations, e.g., primary Rapid beam maps Surface improvements Quadrant Detector path LRF GRI Thermal imaging Add sensors Residuals, stability Wind Vibration Extend over grav, temp, wind Improve FEM Surface Peak-up Beam expand Pointing Diode replacement Surface / collimation improvements Enable W-Band Performance Under Benign Conditions and Q-Band Performance Under Normal Conditions Prototyping, Commissioning Experiments and Transition to Production Capabilities

30. URSI – Jan 5-8, 2004 30 Conclusions Blind Pointing: (1 point/focus) Offset Pointing: (90 min) Continuous Tracking: (30 min) GBT is capable of 50GHz operation under benign conditions:

31. URSI – Jan 5-8, 2004 31 Conclusions Largest “non-repeatable” effects are thermal and wind. Thermal compensation works well apart from around mid-day; may be extended to all conditions. Next development: inclinometers: –Az-track irregularities –Confirmation of alidade thermal pointing effects –Wind compensation on ~10s timescales Servo disturbances are clearly visible - good chance that we will be able to compensate for these.

32. URSI – Jan 5-8, 2004 32 Acknowledgements Joe Brandt, Ray Creager, Jeff Cromer, Paul Marganian, J.D. Nelson, Jason Ray. PTCS Project Team.