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1 ADAMS. 1974 3 TSAO AND WOLLMAN. 1976

2 CLEAVINGER AND MAYER. 1976 4 GATES AND McALOON. 197S

1 ADAMS. 1974 3 TSAO AND WOLLMAN. 1976

2 CLEAVINGER AND MAYER. 1976 4 GATES AND McALOON. 197S

Image dissectors are subject to errors from stray electric and magnetic fields. Electric and transverse magnetic field effects can be reduced by shielding. However, it is more difficult to shield against axial magnetic fields. Errors due to these effects become significant in the outer regions of a large FOV image dissector. Correction procedures to remove these effects as well as temperature effects are described in Section 7.7. Image dissectors have the advantages of high sensitivity, low noise, and relative mechanical ruggedness.

The choices of field-of-view size and star magnitude sensitivity for any star sensor generally depend on the attitude accuracy requirements. A small FOV tracker can provide more accurate star positions than can a larger FOV tracker with comparable components. However, a small FOV tracker must be sensitive to dimmer stars to ensure that enough stars are visible to it. Use of a larger FOV demands extensive prelaunch ground calibration for temperature, distortion, and magnetic effects, as well as postlaunch preprocessing of data to correct for these effects.

6.4.2 BBRC CS-103 V-Slit Star Scanner for OSO-8

As an example of a star scanning sensor we will describe the CS-103 V-slit star scanner built for OSO-8 by the Ball Brothers Research Corporation (BBRC). It is designed to provide spacecraft attitudes accurate to ±0.1 deg at a nomimal spin rate of 6± 1 rpm. The star scanner, shown in Fig. 6-40, is oriented such that as the spacecraft rotates, the scanner's FOV sweeps a 10-deg band in the sky with a half-cone angle of S3 deg about the spin axis. The scanner generates two pulses each time its FOV sweeps past a star that is brighter than the preselected level.

Attitude Xyz
Fig. 6-40. CS-103 Star Scanner. (Photo courtesy of Ball Brothers Research Corporation.)

Thus, during spacecraft rotation, the sensor generates a series of pulse pairs corresponding to the bright stars that pass through its field of view. Characteristics of the CS-103 are summarized in Table 6-7.

Table 6-7. BBRC CS-103 Star Scanner Characteristics

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