Some planets lack any non-restricted terrain. For example, Hoth only has glacier and mountain terrain. Given that facilities only up to 5x5 can be built on such terrain, and a shield projector is a 7x7 facility, does this mean that it is impossible to set up any planetary shields on such planets?

It would be impossible to project a shield over any entity in orbit of the planet, yes. Shield generators are 3x3 and would thus be able to be built.

There is a Shield "Generator" that is a 3x3. But Orph is referring to the Shield "Projector" that is 7x7. So, do you need both to have a shield, or not?

“impossible to set up any planetary shields

- The Great and Powerful Orph
 ”

Shield generators create planetary shields. I'm assuming that he had a brain fart (because I know he's built plenty of shield generators) and for some reason thought you needed a shield projector to have planetary shields. To answer your question, no, you do not need to have both, you need only a shield generator. Shield projectors are not currently coded, but as far as I know they will work like the Endor shield generator, boosting the shield levels of a space station or something similar in orbit.

"It would be impossible to project a shield over any entity in orbit of the planet"

^ What a shield projector does.

"Shield generators are 3x3 and would thus be able to be built."

^ What creates a planetary shield.