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4.7.7 Error on the SRP Determination

The errors on the SRP derive from the sun sensor accuracy, sun sensors mounting, spin axis tilt, and computation accuracy. The errors associated with the computation inside the data handling subsystem have been minimized by using high precision arithmetic. In general the sun datations are 16 bit words, and all multiplication is carried out with full precision. An error transmission analysis shows that with the datation accuracy of 1/2048 seconds the maximum error on the SRP is +1 ms with a mean value of .5 ms.

The errors associated with the hardware are:

• Principal axis tilt, 0.1 deg., single crossing only
• Sensor accuracy, worst case 0.02 deg
• Aging effect, 0.018/sin (solar aspect angle)
• Random error, 0.001 deg
• Calibration accuracy, 0.044 deg

Figures 4.55 and 4.56 show the errors for double and single crossing. For double crossing the specification is met for all solar aspect angles. With the single crossing the specification is met for solar aspect angles greater than 5 degrees.

Figure 4.55 Error of SRP, double crossing

Figure 4.56 Error of SRP, single crossing

Next: 4.8 Calibrations

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