Ulysses HISCALE Pages
The Spin Reference Pulse (SRP) is defined as a pulse issued when the sun crosses the positive XZ reference plane of the spacecraft. During the Ulysses mission the spacecraft will see the sun at very low Solar Aspect Angle, and using conventional methods for the generation of the SRP the error will be too high and unacceptable for both the attitude control of the spacecraft and the scientific payload. The solution adopted consisted of:
*special selection of sensor field of view.
*new electronics which provide the leading and trailing edges of the sun crossings.
*use of a digital filter to estimate the sun crossing time.
With this approach the required SRP accuracy of 0.28 degrees, referenced to the center of the sun, for solar aspect angles greater than 2.5 degrees is met.
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Updated 4/21/09, T. Hunt-Ward