Helios class

The Helios class was a Federation space station type, a hub and research station in Starfleet and civilian service throughout the 24th century. By the 2380s, the design was considered out of date. 

History and specifications
A Helios station was mushroom-shaped. The upper decks were housed in the mushroom's cap, or saucer section, and included the bridge and officer quarters. Four to ten decks of the stalk contained additional quarters, labs, work spaces, and stowage. The station's reactor was located in a bulb at the base of the stalk. The shuttle hangar could be found just below that. Design-wise, "Every expense was spared" according to one of Engineer Nog's Starfleet Academy professors. 

A Helios-class hub appeared as a variation of the starbases, and could be changed to have a thinner stalk and a stack of three saucer sections, like Jupiter Station. 

Jupiter Station itself featured two mushrooms, with a stack of three saucer sections each, tethered together and placed in a planetary orbit. 

Scores of Helios-class hubs were constructed by the Federation when the second great age of exploration began between 2300 and the 2310s decade. They were dropped off as pickets for a fleet of newly commissioned ships to refuel and resupply.

By 2386, Nog did not think that Starfleet would still use Helios stations. The Robert Hooke Research Station was an example of continued civilian usage.