The Dark Fog is the main enemy in Dyson Sphere Program, but it can prove useful to the player. By farming the Dark Fog, it will level up and drop progressively rarer and more valuable items, some of which are used for otherwise-unobtainable Technologies.
General Overview
To effectively farm the Dark Fog, the player must construct facilities that automatically destroy Dark Fog units without harming the Planetary Bases producing them or the Relay Stations powering them. Additionally, the Dark Fog Space Hive will continually deploy more and more Relay Stations to construct new Planetary Bases, so the player must have a way to address these new bases to prevent the Dark Fog from breaking free of the farm. Signal Towers put the Dark Fog into overdrive mode to greatly increase the number of units produced, thereby increasing the farm's output. Finally, Battlefield Analysis Bases are necessary to automatically collect the Dark Fog's drops, and a system must be put in place to organize and store the drops so that the Battlefield Bases do not overflow.
Weapons and Placement
The first and most important choice to make is what weapon(s) to use to destroy the Dark Fog's units. While explosive damage from Missile Turrets and the like is fantastic for fighting through waves of Dark Fog fighters, farming requires a more delicate and precise approach. The goal is only to destroy the units, but explosive damage is liable to damage their camps, costing the base matter and energy. This means that only Gauss Turrets and Laser Turrets are suitable for farming, as they are the only turrets that deal damage to a single target at a time. Gauss Turrets are unlocked before Laser Turrets, are much cheaper to produce, and use almost 15 times less power, but Laser Turrets have the benefit of requiring no ammunition whatsoever. This dramatically cuts down on micromanagement, as only a consistent source of power is required. Laser Turrets also deal considerably more damage than Gauss Turrets, except when using Superalloy Ammunition.
Regardless of which turret is used, the placement strategy is the same. Once the Planetary Base is constructed, the Dark Fog will attempt to construct up to 3 each of Raider Camps and Plasma Sentries. These are placed in alternating order around the base, so two given Raider Camps are always separated by 120 degrees, with a spot for a Plasma Sentry between them. While the Raider Camps are the source of the Dark Fog units to farm, the Plasma Sentries throw a wrench into the works. They deal very high damage at a good range, enough to seriously damage or potentially destroy Signal Towers. Thus the best way to place turrets is such that the Planetary Base is at the very edge of their range. Make sure that the Raider Camps are not in any turret's range, but that all possible Plasma Sentry locations are within range.
Handling Items
Once the player has formed a perimeter of turrets around the Planetary Base, the next step is to handle the item drops. Battlefield Analysis Bases have a lot of storage, but it is not infinite, and slots can be taken up surprisingly quickly if farming a lot of different items. Within the Battlefield Base's inventory is a menu to set the items that the Dark Fog is allowed to drop, so deselect all items that are irrelevant so they do not take up space. Each Battlefield Base also only has nine ports, so keep this in mind when selecting how many types of items should drop. Finally, add some external storage for each desired item.
Controlling the Dark Fog
While it is relatively straightforward to corral a Planetary Base, the Dark Fog will still continuously try to expand throughout the system and establish new Planetary Bases. Left unchecked, these may launch assaults on the player's facilities and break down the confines of the farm. Once the player is satisfied with the number of Planetary Bases being farmed on a planet, they must prevent any new Planetary Bases from being built. Destroying the Hive itself may seem enticing, as this cuts off new Relays at the source. All established Planetary Bases will be too busy using their resources on new units to send any back to reconstruct the Hive, so it will effectively be out of commission permanently. However, the Hive is still a major source of energy for Planetary Bases. Without a Hive supplying them with energy, Planetary Bases will barely be able to produce any units, as the energy required to operate three Raider Camps in overdrive mode is much greater than the amount that the Relay can naturally generate.
Since destroying the Hive is not a viable option, the only way to prevent new bases from being constructed is to drive off Relays that attempt to reach the planet. At first, it will likely be worthwhile to allow Relay Stations to found new bases, as destroying these new bases is easy and allows the use of Geothermal Power Stations to generate huge amounts of energy. However, the farm will eventually reach a point where the micromanagement of destroying new bases is undesirable. There are several ways to drive off Relay Stations that are arriving at a planet, with varying requirements. Planetary Shield Generators prevent Relays from reaching their shielded areas, and with enough of them the entire planet can be permanently protected from any new Relays. Alternatively, Missile Turrets and Plasma Turrets can attack Space targets, allowing them to destroy Relays before they reach the planet. Finally, covering the entire planet with structures will leave nowhere for a Relay to establish a base, although this is the least practical of these options. To truly eliminate micromanagement, these anti-Relay measures must be put in place on every planet in the system, as the Dark Fog will attempt to settle on each of them. While systems with only a single planet are few and far between, they are the simplest systems to farm in the late game.
The only remaining thing that will require micromanagement no matter what is the production of Seeds. The Hive will inevitably produce these, as farming allows the Dark Fog to continuously harvest matter and energy. To prevent the Dark Fog from spreading to new systems, the player must eliminate Seeds whenever they appear. Alternatively, the player can try to "prune" the Hive by attacking it and partially destroying its facilities, forcing it to use its resources on reconstruction instead of Seeds. Luckily, in both cases the player will not need to check up on the system very often. Seeds travel extremely slowly through space and are completely vulnerable, so destroying them is simple as long as the player takes notice, and the Hive takes a long time to get back to the point where it may produce Seeds if it is partially destroyed.