A simple representation of the Space Pirate HQ in the mission briefing.
The Space Pirate HQ was the unseen base of operations for the Space Pirates on the planet Talvania and possibly the Bermuda System in Metroid Prime: Federation Force. The facility was constructed underneath a massive underground Talvania Gas pocket, as the gas does not affect any of the Pirate personnel, but will keep the Federation Force out.
Intelligence information gathered on the facility indicated that it is of a massive size, housing perhaps hundreds or thousand of Pirates. As the facility is not directly accessible to the Galactic Federation, even with the new Mech technology due to the gas pocket, an alternative plan has been devised to destroy this complex.
The Galactic Federation deploys a massive energy Drill on the surface above the base to dig a direct access shaft to it and then drop a bomb through the shaft to destroy the complex. When the Space Pirates become aware of the Galactic Federation's attempt to dig directly towards their base, they deploy various troops, as well as well possibly salvaged Talvanian equipment such as Hover Bots and RB133 Auricrushers, to destroy the Drill. All these attacks are fended off by the Federation Force that stands guard over the Drill while it is active.
The actual interior of the complex is never shown during the mission in which it is destroyed, M18: Hightower.