The attitude control system uses momentum wheels, magnetic torquers, and control-moment gyros as the actuators. As the attitude sensors, two sun sensors and a star tracker, as well as geomagnetic sensors, are available for determining the spacecraft pointing relative to the direction of the sun and to the ecliptic plane, respectfully. An inertial reference unit comprising four gyros detects changes of attitude with time. HXA??
Four gyros are present on the Yohkoh spacecraft, one each in X, Y and Z and the fourth one in a 45 degree skew position. The IRU values are used by the IDL software to create the attitude (ATT) database.
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Used to define spacecraft roll. Tracks star Canopus. Eclipses...
What are these??
The HXT aspect sensor (HXA) consists of two 1-dimensional CCD arrays located in a cross, 90 degrees to each other. The cross is rotated approximately 45 degrees relative to the SXT and HXT coordinate system. The HXA values are used by the IDL software which creates the attitude (ATT) database. There are fiducial marks which can reduce the resolution of the HXA results if the limb coincides with the fiducial mark.
The attitude determination software (ADS) runs on the FACOM mainframe at ISAS and has been found to have noise problems (probably due to the TFSS). The ATT IDL database was created to replace the ADS results, which uses the HXA and IRU raw data. The ATT database does copy the ADS roll results into the database.
Table of values
Due for movement of filter wheel.
In Sep-93, it was decided to switch to the X, Y and skew gyros (instead of X, Y, and Z) because of the high drift rate of the Y gyro. Stil believed to be functional??
The two dimensional fine sun sensor had a noise problem shortly after launch and it's usefulness was greatly reduced.
Loss of spacecraft Roll... See appendix ?? for list of dates...
Summery of paper by Wuelser et al. (1998)
Ranging. ORB and FEM files.