I believe the default setting for scan is "V" which I assume can be changed in Key Bindings. But you are correct, it does not show in your powers list for placement on the hotkey bar. As long as you can set it in Key Bindings, you shouldn't need it. I leave Full Impulse and the Shield Redistrubution buttons off the hotkey bar as well, since their default key bindings work just as well. Frees up 6 or so button spaces for more useful abilities.