In the AOCS Framework, data that are passed through several consecutive
stages of processing will be said to go through a sequential data processing
chain. As an example of a sequential data processing chain consider the
processing of the raw data collected by a sensor:
· conversion from raw data to engineering units ;
· correction for sensor misalignments;
· bias correction;
· transformation from sensor to satellite reference frame
In another example, an attitude controller processes the raw attitude
measurement as follows:
· filtering of raw data to remove the measurement noise;
· filtering to cut off frequencies that might excite solar panel
oscillations;
· passage through a controller to compute the control torque.
Once again, each bullet can be seen as representing a processing stage
in a sequential data processing chain. In the previous examples, each processing
stage was single-input-single-output. However, a processing chain can also
include multi-input-multi-output stages.
In considering the implementation of sequential processing chains, a trade-off must be made between generality and complexity: the most general implementation is also the most complex and the simplest implementation cannot cover all cases of processing chains. In the framework, they are implemented using the Control Channels concept. Control channels are based on the composite pattern and cover the most general case of multi-input-multi-output processing stages linked in any arbitrary manner.
A sequential processing chain is made up of inter-connected and nested processing blocks. The term control channel block (or simply block) is used to designate a processing block that cannot be further decomposed into lower level processing blocks. Blocks chains can be nested within higher-level blocks called superblocks. Superblocks and blocks can be freely mixed in processing chains as in the example in the figure in the next page.
The implementation of sequential data processing chains in the AOCS
Framework is discussed in greater detail in a dedicated
technical note.