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Copernicus (OAO-3)
The Copernicus satellite was launched into a nearly circular 7123 km radius
orbit, inclined at 35 degrees, on 21 August 1972. The main experiment was an
ultraviolet telescope. However, it also contained a cosmic X-ray experiment
provided by University College London/MSSL. The main body of Copernicus
measured 3 x 2 meters. The solar pannels were fixed at an angle of 34 degrees
to the observing axis, and were kept within 30 degrees of the Sun. This
restriction resulted in certain parts of the sky being visible only at certain
parts of the year. The astronomical instruments were co-aligned, with the UV
telescope residing in the central cylinder of the satellite and the X-ray
experiment in one of the bays surrounding it. While the UV telescope was
observing, the X-ray detectors primarily took background measurements.
Occasionally, the X-ray detector observed an X-ray source in the field of view
of the UV target. It operated till February 1981.
The X-ray experiment
There were 4 X-ray detectors in the UCL/MSSL experiment. The main detector
was a proportional counter sensitive to the energy range 2.5-10.0 keV (1-3
Å). It had a simple collimation tube with a 2.5 x 3.5 degree FWHM field
of view. The effective area was 17.8 cm2 with a sensitivity of about
3 mCrab. The others were two proportional counters and a channeltron, at the
foci of grazing incidence telescopes. The channeltron suffered from high UV
background and was not scientifically productive. The proportional counters
covered the energy range 0.7-1.5 keV and 1.4-4.2 keV (6-18 Å and 3-9
Å). By the clever use of stops at the foci, the fields of view and the
effective areas could be set to 10´ (12.3 cm2), 3´ (11.3
cm2), or 1´ (7.6 cm2) and 10´ (3.7 cm2), 6´ (2.4 cm2), or 2´ (1.0 cm2) for the high
and low energy systems, respectively. These 2 systems became inoperable in July
1973 due to a failure of a background shutter.
The basic accumulation time was 62.5 seconds, followed by 24 seconds of
dead time. Thus, effectively, there was an 86.509 second sampling interval.
There was a way to force better time resolution (to multiples of 1.62 s, this
mode was named J20), which was used occasionally for observing bright sources,
searching for bursts, etc. However this mode was used only on a few occasions
and was not scientifically useful.
A six channel Pulse Height Analyzer could be connected to any one of the 3
proportional counters and used to gather spectral information.
The UV Experiment
Description and data for the Princeton experiment are available at the
STScI archive.
[Copernicus Home]
[About Copernicus]
[Archive]
[Software]
[Gallery]
[Publications]
Page authors: Lorella Angelini Jesse Allen
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Last modified: Tuesday, 07-Oct-2003 11:27:52 EDT
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