Starfleet Command is the operating authority for the interstellar, scientific, exploration and defence agency of the United Feration of Planets. The primary control hub is located in San Francisco, on Earth, but other command facilities are located in various starbases throughout Federation space. Starfleet Command stays in touch with its starships by means of a subspace radio communications network, but even with faster than light medium, interstellar space is so vast that it was not common for ships on the frontier to be out of touch. As a result, starship captains are frequently granted broad discretionary powers to interpret Federation policy in the absence of immediate instructions from Starfleet Command.