Be careful about semantics when discussing solar rotation related matters.

Solar Feature Tracking is controlled by the on-board software and can move the OPS pointing DURING a raster in order to compensate for solar rotation. The pitfalls of this are discussed in CDS software note #45 ( PostScript - 54 Kb).

The other related technique, which is more widely used, and for almost all cases is preferable, is to reposition the OPS at the BEGINNING of each raster within a series of rasters to a location which takes account of the feature's movement during the time elapsed between rasters. These offsets can be calculated automatically in the planning routine mk_plan.

In the interests of clarity, if not brevity, these two modes should be referred to as

1) Solar Feature Tracking

2) Solar Rotation Compensation.

Note that there is also a further refinement possible on the 'Rotation Compensation'. Normally, the OPS is used to reposition CDS, but this is inherently inaccurate at the few arcseconds level. If, viewed from the original position, the raster when centred at the new required position is still within the internal CDS field of view (4'x4'), then the movement to the new location can take place using the scan mirror rather than the OPS. The scan mirror movement has negligible errors.

Contact the operations staff to discuss this if you require very precise relocation between rasters.