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Basic GBT Info – Quick Technical Facts

LocationGreen Bank, West Virginia, USA
CoordinatesLongitude: 79°50’23.406″ West (NAD83)
Latitude: 38°25’59.236″ North (NAD83)
Track Elevation: 807.43 m (NAVD88)
Optics110 m x 100 m unblocked section of a 208 m parent paraboloid
Offaxis feed arm
Telescope Diameter100 m (effective)
Available FociPrime and Gregorian
f/D (prime) = 0.29 (referred to 208 m parent parabola)
f/D (prime) = 0.6 (referred to 100 m effective parabola)
f/D (Gregorian) = 1.9 (referred to 100 m effective aperture)
Receiver mountsPrime: Retractable boom with Focus-Rotation Mount
Gregorian: Rotating turret with 8 receiver bays
Subreflector8-m reflector with Stewart Platform (6 degrees of freedom)
Main reflector2004 actuated panels (2209 actuators)
Average intra-panel RMS 68 μm
FWHM BeamwidthGregorian Feed: ~ 12.60/fGHz arcmin
Prime Focus: ~ 13.01/fGHz arcmin (see Section 4.1.1 of the Observer’s Handbook)
Elevation LimitsLower limit: 5 degrees
Upper limit: ~ 90 degrees
Declination RangeLower limit: ~−46 degrees
Upper limit: 90 degrees
Slew RatesAzimuth: 35.2 degrees/min
Elevation: 17.6 degrees/min
Surface RMSPassive surface: 450μm at 45° elevation, worse elsewhere
Active surface: ~250μm, under benign night-time conditions
Pointing accuracy1σ values from 2-D data
5″ blind
2.2″ offset