Status of standard pipeline pointing products: ground-based improvements (SPG 13.0 and beyond)

Scope of applicability

This page refers to the improved pointing information provided in products created in SPG 13.0 and later, derived from gyro-reconstructed attitude data. For data products created with SPG versions before 13.0, please refer to the page on improved pointing information from "simple" ground-based processing.

Background information

The accuracy of the Herschel's attitude measurements was notably improved along the operational phase of the mission, and further improved on-ground (see the pointing calibration sections in this web), but the attitude measurements derived on-board and down-linked (the so-called filtered attitude) were too heavily filtered and therefore resulted in a poor estimation of the high-frequency changes in the spacecraft attitude (the spacecraft pointing jitter/stability). The "gyro-based attitude reconstruction" method was devised to overcome this limitation. It combines the star tracker attitude measurements with the output from the Inertial Reference Unit (gyroscopes).

As the name implies, this method places much greater weight on the measurements made by the gyros, using attitude measurements constructed from star tracker data to provide an absolute reference and to account for gyro drifts. Although it has been demonstrated that this method is able to successfully reduce the high-frequency components of the Absolute Measurement Error (AME) it neverthess suffers from a couple of drawbacks (when compared with a conventional attitude estimator) related to limitations in the calibration of gyro biases and drift rates.

Software based on the gyro-based attitude reconstruction method was developed initially at the PACS ICC. The design and first prototype was implemented by H. Feuchtgruber in IDL and ported to Jython and integrated as toolbox package in HIPE 12.0, by B. Vandenbussche.

-- MiguelSanchez - 08 Apr 2015

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Topic revision: r3 - 2015-04-09 - MiguelSanchez
 
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