GBT Performance

20 June 2006 Green BankGBT Performance

GBT Performance

Dana S. Balser

GBT Performance 20 June 2006 Green Bank

Telescope Structure

Surface

Focus

Pointing


Pointing Requirements

2

2El

2Az

22

2

2

GHZ

arcsec 740

2ln4exp)(

f

g

Condon (2003)

20.0 10%)( Usable

14.0 5%)( Good

s

s

f

f


Focus Requirements

2/8/)95.0( Usable

4/16/)99.0( Good

4

Axial 2ln4exp2

asa

asa

a

a

sa

yg

yg

yg

Srikanth (1990)Condon (2003)

5.03.17

mm 3.2 mm 7 :band-Q

mm/3.7Scale Plate

3/16/)99.0( Good

6

Lateral 2ln4exp

"

"

2

f

x

xg

xg

s

lsl

l

l

sl


Surface Requirements

Ruze (1966)Condon (2003)

37.04/:Usable

54.016/ :Good

area.primary geometric theis A

.efficiency aperture theis

.atmosphere for the corrected re temperatuantenna theis T

constant. sBoltzmann' isk

density.flux theisS

A

kT2S

error. surface rms theis

surface. for the efficiency aperture theis

4exp

g

a

'A

ga

'A

s

2

s

s

s


Repeatable Errors – Pointing

• Telescope misalignments:• Azimuth track tilt• Horizontal collimation• Elevation axle collimation• Encoder offsets

• Gravity: assume linear elastic structure

Cos(E)d Sin(E)b Cos(A)d Sin(A)c d E

E)Sin(A)Sin(a E)Cos(A)Sin(b

Cos(E)d Sin(E)bd Cos(E)A

0,10,11,01,00,0

1,11,1

0,10,10,0


Repeatable Errors – Focus

• Gravity: assume linear elastic structure

Sin(E) C Cos(E) B A Z

Sin(E) C Cos(E) B A Y

Sin(E) C Cos(E) B A X

zzz

yyy

xxx


Repeatable Errors – Surface

• Gravity: • Homologous design (almost)• Photogrammetry (50.3 deg) Zero-point • Finite Element Model (FEM)• Best Fit Parabola (BFP) Active Surface: 2004 Panels

2209 Actuators


Point Source Calibrators

Condon & Yin (2005)

PCALS 4.0: 7108 sourcesTwo-dimensional rms error < 0.2 arcsec

3 mm pointing calibrators


Pointing Model

Cos(E)A SeriesAzimuth E SeriesElevation

Balser et al. (2002)


Focus Model

Axial Focus

mm Sin(E) 21.86 - Cos(E) 11.18 9.56 Z

mm Sin(E) 9.96 Cos(E) 183.74 148.39- Y

mm Sin(E) 25.55 - Cos(E) 301.98 - 212.55 X

Ghigo et al. (2001)


Finite Element Model – Gain Elevation Curve

K-band (20 GHZ)


Finite Element Model – Sidelobes

O12 EL


Non-repeatable Errors – Thermal

GHz 30at 3 mm 30

2/8/)95.0( Usable

GHz 30 offrequency aat 3 mm 30

GHz 3 offrequency aat /3 mm 03

asa yg


Non-repeatable Errors – Wind

1''

12

2

11

68

2)(

sec16.0)(

smsat

windwind

arcsm

swind


Thermal Pointing and Focus Corrections

Constantikes (2003)


Data Collection and Quality

Gaussian Fits (Az, El, Focus)

Polarization (LCP – RCP)

Direction (Forward – Backward)

Jack Scan

All-sky ObservationsSingle Source Track

Up-Down at Night GravityNCP Source Temperature


Thermal Model – Focus

Constantikes (2003)

Term Coefficient Min-Max Significance Parameter

M1 1.086 13.1 14.3 SR-PriM2 -0.697 6.2 -4.3 VFA-PriM3 3.981 15.6 62.0 HFAM4 -7.326 0.9 -6.8 BUS V1M5 -0.688 12.1 -8.3 BUS V2M6 -2.576 12.1 -31.2 BUS FM7 -180.630 0.0 0.0 Offset

M8 66.189 .7 43.1 sin term

M9 196.949 0.6 110.8 cos term


Thermal Model – Azimuth

Constantikes (2003)


M1 5.5862 4.0 22.4 Alidade M2 -8.0331 2.7 21.3 HFAM3 -1.6289 2.4 3.8 BUSM4 1.3683 2.0 2.8 VFAM5 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)


Thermal Model – Elevation

Constantikes (2003)


M1 -4.6455 1.2 -5.3 BUSM2 1.7830 15.6 -27.8 HFAM3 4.4488 5.9 26.4 VFAM4 -8.4477 1.6 -14.0 AlidadeM5 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)


Performance – Blind Pointing


Pointing Data Quality – Polarization

arcsec 0.57 0.13- RCP] - [LCP


Pointing Data Quality – Direction

arcsec 3.2B] - [F

arcsec 0.89- B] - F[

El

Az


Cross-Elevation Uncertainty

arcsec 2.7 Cos(E)]A [


Elevation Uncertainty

arcsec 4.8 E][


Focus Data Quality – Polarization

mm 0.810.0019- RCP] - [LCP


Focus Uncertainty

mm 1.2][ f


Performance – Offset Pointing


Offset Pointing Uncertainty

arcsec 7.22


Offset Focus Uncertainty

mm 2.1


Performance – Tracking

arcsec 2.12 )/'10,/'2(,

)5,1(),(

)58,290(),(

mmt

El

t

Az

ElAz

ElAz

)m/'7.11,m/'8.10(t

El,

t

Az

)9.3,6.3()El,Az(

)37,99()El Az,(

Half-power in Azimuth Half-power in Elevation

)m/'4.11,m/'0.12(t

El,

t

Az

)8.3,0.4()El,Az(

)43,105()El Az,(

arcsec 2.12


Power Spectrum

Servo resonance 0.28 Hz


Servo Error


Performance – Summary

mm 2.5 focus)(

arcsec 5pointing)(1

mm 1.5 focus)(

arcsec 7.2pointing)(2

Benign Conditions: (1) Exclude 10:00 18:00 (2) Wind < 3.0 m/s

Blind Pointing: (1 point/focus)

Offset Pointing: (90 min)

Continuous Tracking: (30 min)

arcsec 12


Surface Improvements – Holography

Traditional Holography(Phase Coherent Holography)

Out-of-Focus Holography(Phase Retrieval Holography)

Maddalena

Nikolic et al. (2006)


Zernike Polynomials – Radial Terms

Zernike (1934)Wyant & Creath (1992)


Zernike Polynomials – Images

Wyant & Creath (1992)


OOF Holography – Gravity

c )Cos( b )Sin( a)(zi



Gain-Elevation Curve


FEM only

FEM + OOF


OOF Holography – Thermal Effects

m300 rms m220 rms

m220 rms

m220 rms

m330 rms

GBT Performance

Documents

Transcript of GBT Performance