mines (and the only exception still bears a similarity to Trader ships), but they are all unshielded, have heavier armor, often have their armament switched to autocannons, and are heavily customised with spikes and stylized holographic "Jolly Rogers". Rebellion also has voiced responses for pirate units (which can often found in the service of TEC Rebels). Sins of a Solar Empire: Diplomacy expands upon the Diplomacy mechanic. The relations system is more visible, and players can give missions to each other, as opposed to the original's NPC-only mission issuing. Diplomatic envoy cruisers can be used to further improve relations, and the researchable pacts can significantly strengthen both sides of the alliance. The expansion also sees a noticeable increase in pirates' strength, and their bases are now outfitted with mines and TEC-issue repair platforms and strike craft hangars. Tech tree and artifacts In the base game, each faction has two technology trees, divided between military and civic improvements. These two trees in turn branch off into three race-specific categories. The Military tree contains upgrades to armor, shields, and weapons and unlocks units and defensive structures. The Civic tree contains upgrades to resource gathering and unlocks civic buildings, PSIDAR (Phase Signature IDentification And Ranging, which allows incoming enemy ships to be detected), planetary upgrades, diplomacy upgrades, and terraforming. In Entrenchment, several elements of both trees, as well as new elements such as starbase-related technology, are merged into the Defense tree. In Diplomacy, the diplomatic elements from the civic tree, as well as new technology that focuses on upgrading the race's diplomatic Envoy cruiser and various other bonuses, are merged into the Diplomacy tree. The Rebellion expansion grants additional unique technologies to each sub-faction of the three races. There are many different hidden artifacts that can be found by exploring colonized planets. There are a total of nine (twelve in Entrenchment) artifacts, each giving the owner a unique and powerful bonus. For example, an alien artificial intelligence can increase economic efficiency across the player's empire, while an ion field technology can fortify planets against attack. When an artifact is discovered, all other players are notified of its location but not its type. Units There are five main categories of ships in the base game: capital ships, strike craft, cruisers, frigates and civilian ships. Capital ships are large, powerful vessels and the cornerstones of any fleet; they can gain experience in combat and "level