Hi Mahmood.
Try this lot !

http://www.redrok.com/electron.htm#led3

Also, re Andy's contribution: Perhaps DON'T hunt if the integrated output from the detector array is less than (some site limit)

Or, Look up "Equatorial mount" for telescopes. Then one axis is driven at constant rate.

Also, put in lots of hysteresis, so you only slew the array occasionally (should save power)

Steve