How can I access my time capsule through ssh?
You would need to forward TCP port 548, which is AFP (Apple Filing Protocol). This is the storage protocol used by Time Machine to access content on a Time Capsule.

Note: This will not necessarily make it possible for your remote systems to auto detect the Time Capsule - as any DNS information (Bonjour) you forward would probably be incorrect as it needs to be translated (i.e. a different IP-address).

Connect to the Time Capsule directly using the IP instead. From Finder select Go => Connect to Server and then enter: afp://123.123.123.123/ 

Substitute your own IP ofcourse!