green bank telescope performance

July 2007 Pune, NCRAGBT Performance

Green Bank Telescope Performance

Dana S. Balser

GBT Performance July 2007 Pune, NCRA

Telescope Structure


Unblocked Aperture


Frequency Coverage


Telescope Control

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

0.20 f 10%) s

( Usable

GHz 20at 0.22 f 1sm6sat''8

wind1

2)wind(2

arcsec

2

1sm

s16.0)wind(

1


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

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

Zernike (1934)Maeda (2003)


OOF Holography – Gravity

c

Cos(E) b

Sin(E) a)E(zi



Gain-Elevation Curve


FEM only

FEM + OOF


OOF Holography – Thermal Effects

m300 rms m220 rms

m220 rms

m220 rms

m330 rms


Summary Surface Performance

green bank telescope performance

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