Do not know about starbases however on ships the ability to shoot missiles into other hexes is an icon on the ship/fleet picture in the lower left of the main screen, know starbases have this pop-up just never looked for the missile launch option as that I did not know they had. Comes from my own not paying attention to them after I build them.  

I thought you might be not noticing the icon that allows you to use the ability, so I used the console to allow me to quickly build a starbase and add the module.  I then saw the next two modules, so I added them also.

Notice that all 3 claim to add a Harpoon Salvo, so that is probably wrong.

I then checked the starbase for an indication that at least one type of ranged missile attack was available, like is shown for this ship.

Nothing like that was shown.

I think you found another bug.

EDIT

And I'm so slow that 2 comments were added before I could finish this.

The beam and kinetic weapons don't claim to have ranged attack.  I checked anyway and found they don't have any indication of ranged attack when they are added to a starbase.  I'm convinced this is correct.