Some good comments but let me try to add.<br /><br />Yes, they spend a fair amount of time training. Some is generic (e.g., 'shuttle' or 'ISS') and some is specific (particular mission or increment when assigned). However, when no preparing for a mission, they do a lot of technical roles. They help the flight control team develop displays, procedures and flight rules, and they check and verify many of the items. They will also support design reviews for software or hardware - anything they touch. Some will help astronauts train (for example the EVA office has a number assigned to help train others). They also act as capcoms. They are also support astronauts - for example when someone is on ISS for an extended stay, the Crew Support Astronaut (CSA) is that person's proxy on the ground for all things, as well as an interface to the family. They are generally pretty busy.<br /><br />As to capcoms - yes, as I have said we don't have enough to man the ISS capcom console 24/7. However, when not available we use Training Leads or flight directors, not flight controllers. The controllers are only put ont eh horn for special discussions where a middle man makes it too hard.