Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.naic.edu/alfa/ealfa/meeting2/handouts/ao_handout.ps Дата изменения: Sat May 13 00:11:07 2006 Дата индексирования: Sun Dec 23 03:02:23 2007 Кодировка: Поисковые слова: http astrokuban.info astrokuban

Table 1: Basic Information on the AO Site and the 305-m Telescope
Site
Longitude (Geodetic) 66 ф 45 0 11.1 00 W
Latitude 18 ф 20 0 36.6 00 N
Elevation of re ector center of curvature 497 m (1630 ft) above MSL
Telescope
Primary Re ector
Diameter of Spherical cap 305 m (1000 ft)
Radius of Curvature 265 m (870 ft)
Illuminated Area (at zenith):
Gregorian Feeds 213  237 m (700  776 ft)
430-MHz Line Feed 305 m (1000 ft)
Surface Accuracy 2 mm (rms)
Frequency range 300 MHz <  < 10 GHz (Gregorian)
Wavelength range 1 m <  < 3 cm (Gregorian)
Slew Rates:
Azimuth 25 ф /min
Zenith Angle 2 ф .5/min
Pointing Limits:
Azimuth 0 ф {720 ф
Zenith Angle 0 ф {19 ф .7
Declination range 1 ф 20 0 < Dec < +38 ф 02 0
Pointing Accuracy 5 00 (rms)
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2.1 The Telescope Optics and Pointing
The main re ector of the telescope is is a fixed spherical cap, 305 m (1000 ft) in diameter,
and 51 m (167 ft) deep. Its surface consists of 38,778 perforated doubly-curved aluminum
panels, each measuring about 3 ft  6 ft, supported by a network of steel cables strung
across an underlying karst sinkhole.
Suspended 137 m (450 ft) above the re ector is a 900-ton triangular platform, supported
by 18 cables strung from 3 reinforced concrete towers. Each tower is back-guyed to ground
anchors with 7  3.25 inch diameter steel cables. Another system, consisting of 3 pairs of
cables, runs from each corner of the platform to large concrete blocks under the re ector.
These \tie-downs" are attached to giant jacks which allow adjustment of the height of each
platform corner with millimeter precision, retaining the optimum focus and pointing despite
changes in the ambient temperature.
Just below the triangular frame of the platform is a circular track on which the azimuth
arm turns. The azimuth arm is a bow-shaped structure 100 m (328 ft) long, whose curved
lower girders carry a second track, on opposite sides of which a carriage house and a geodetic
(Gregorian) dome can be independently positioned anywhere up to  20 ф from the vertical.
Electric motors drive the azimuth arm, the Gregorian dome and the carriage house to point
to and track any requested celestial position with millimeter precision (3 mm  5 arcsec).
Celestial tracking duration (rise to set) is given in Table 2. Tracking accuracy is about 5 arcsec
(rms) at night. The pointing corrections needed to achieve this include individual osets
for each feed, as well as analytic and tabular corrections for measured errors. Coordinate
conversion from B1950, J2000 and current coordinates to telescope azimuth and zenith angle
is provided.
Table 2: Tracking Time
Declination Tracking Time
(deg) (h:mm)
{1 ф 0:30
0 ф 0:58
5 ф 2:18
10 ф 2:27
15 ф 2:42
20 ф 2:46
25 ф 2:40
30 ф 2:20
35 ф 1:35
38 ф 0:10
Two methods are used to correct the spherical aberration inherent in the use of a spherical
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