December 3-4, Green Bank GBT PTCS In Progress Review Thermal Focus and Pointing Corrections K. Constantikes

GBT PTCS In Progress Review – December 3-4, 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” 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 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)

GBT PTCS In Progress Review – December 3-4, 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

GBT PTCS In Progress Review – December 3-4, Structural Temperature

GBT PTCS In Progress Review – December 3-4, Structural Temperature

GBT PTCS In Progress Review – December 3-4, 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

GBT PTCS In Progress Review – December 3-4, Focus Model TermCoefficientMin-MaxSignificanceParameter M1M SR-Pri M2M VFA-Pri M3M HFA M4M BUS V1 M5M BUS V2 M6M BUS F M7M Offset M8M sin term M9M cos term

GBT PTCS In Progress Review – December 3-4, Focus Model Estimation

GBT PTCS In Progress Review – December 3-4, Focus Model Tests Wind < 2.5 m/s 15° < elevation < 85° 9/5 is NCP 11/20 is all-sky Excludes Graphs show thermal contributions only

GBT PTCS In Progress Review – December 3-4, Focus Model Tests

GBT PTCS In Progress Review – December 3-4, Elevation Model TermCoefficientMin-MaxSignificanceParameter M1M BUS M2M HFA M3M VFA M4M Alidade M5M IE,d(0,0) M6M HZCZ,b(0,1) M7M HZSZ,d(0,1) M8M AW,c(1,0) M9M AN,d(1,0)

GBT PTCS In Progress Review – December 3-4, Elevation Model Estimation  = 3.6

GBT PTCS In Progress Review – December 3-4, Elevation Model Test

GBT PTCS In Progress Review – December 3-4, Elevation Model Test

GBT PTCS In Progress Review – December 3-4, Azimuth Model TermCoefficientMin-MaxSignificanceParameter M1M Alidade M2M HFA M3M BUS M4M VFA M5M CA, d(0,0) M6M NPAE, b(0,1) M7M IA, d(0,1) M8M AW, b(1,1) M9M AN, a(1,1)

GBT PTCS In Progress Review – December 3-4, Azimuth Model Estimation  = 3.9

GBT PTCS In Progress Review – December 3-4, Azimuth Model Test

GBT PTCS In Progress Review – December 3-4, Azimuth Model Test

GBT PTCS In Progress Review – December 3-4, 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?

GBT PTCS In Progress Review – December 3-4, 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

GBT PTCS In Progress Review – December 3-4, The Details….

GBT PTCS In Progress Review – December 3-4, Previous Focus Tracking Curves

GBT PTCS In Progress Review – December 3-4, Previous Focus Tracking Curves

GBT PTCS In Progress Review – December 3-4, Temperature Sensor Locations T SR T F1 T F4 T F5 T F3 T F2 T H2 T H3 T B2 T B1 T B3 T B5 T B4 T E1 T E2 T A3 T A1 T A2 T A4

GBT PTCS In Progress Review – December 3-4, Focus Model Gravity SR-Primary VFA-Primary HFA BUS

GBT PTCS In Progress Review – December 3-4, Elevation Model Gravity BUS HFA VFA Alidade

GBT PTCS In Progress Review – December 3-4, Azimuth Model Gravity Alidade HFA BUS VFA

GBT PTCS In Progress Review – December 3-4, Optimization Focus optimization using pseudo-inverse for LSE solution Coupled Az and El gravity models (AN, AW constraint) –Gradient descent