Starstrike1 if you make it unmanned then it has to be programmed. And that programming has to be maintained by some type of link. If it is being maintained by some type of link on the planet it can be eavesdropped from space. It can also be hacked and that would be a bad thing in my humble opion.
Duh
It remains a cost saving measure. If it's unmanned, it doesn't need an artificial intelligence (it'd need "programming" anyways), it only needs a radio link to a ground control center. Eavesdropping and hacking would be concerns with such a setup... reliability ALWAYS is an issue with a remote controlled machine. Nothing in there would make that setup more expensive than manning a station. The costs saved on supplies, life support, and crew more than make up for any measures that need to be taken to ensure the security of the station.
Besides, the encryption technology of an interstellar civilisation would be nothing to sneeze at.
Duh, the bottom line here is that a nearly immobile orbiting defense station, manned or unmanned, is always, ALWAYS going to be cheaper to maintain and operate than it's warp capable, space faring counterpart.
@Iamcatfu
The idea being thrown around here is basically just allowing ships to be built without engines... they'd become like orbiting defense stations because they couldn't leave the planet, and the space they'd save on engines, life support, and sensors would give them a combat edge.