If i'm not mistaken, it's kept in an armed state and in case of the failure of both AC power busses it will deploy without intervention. There is also a manual button for manual deployment and testing.

> In case of total loss of all main generators, the RAT is automatically
> extended and drives the emergency generator via a hydraulic motor. The
> EMER GEN supplies the AC ESS BUS and the DC ESS BUS via the ESS TR.
> The ECAM WD remains powered, with associated procedures presented.
> Alternate law is operative through ELAC 1 and SEC 1

> ([Source][1])

As more the mechanical aspects, I'd quite sure that it's be spring loaded. You'd want it to be as simple as possible. Have a look at the video below around 0:20. The slow upwards motion might suggest that it's having to restore the spring at 1:20. The doors are attached mechanically. 

http://www.youtube.com/watch?v=67pBrUVPAO8

  [1]: http://www.smartcockpit.com/download.php?path=docs/&file=A319-320-321_Flight_Deck_and_Systems_Briefing_for_Pilots.pdf