It's the Sun. -Fairly- important.

Distance from Sol: 0AU

The handful of constructed settlements on this dense belt of Sun-blasted asteroids orbiting between Sol and Mercury are deep underground, dug out by automated systems and dedicated to the most top-secret and sensitive research, storage and disposal operations conducted by the CSA. A perimeter is patrolled regularly by heavily shielded naval vessels and trespassing on the Vulcanoids tends to be dealt with terminally. Rumours suggest that at least a handful of the Vulcanoids are also dedicated computer processing stacks used by Sol for decryption, file cracking and crypto-currency mining.

A dense chain of heavily shielded automated stations are clustered around the Sun, serving as an 'energy mining' operation that converts solar energy into a usable form, then shunts it to other portions of the system either by coordinated masers or huge shipments of batteries. Human presence on these stations is minimal and generally restricted to shifts of workers who are only woken from cryogenic storage for emergency maintenance tasks; positions on the ring are extremely taxing and correspondingly extremely well-paid.