The SDF-3's Space Fold Generators. (Robotech II: The Sentinels: Good Morning)
Space Fold Generators were technology which allowed for Hyperspace Fold jumps. They were often added to Starships, but their use could be limited by low-levels of Protoculture. Low levels of protoculture, damage, and even the Generators disappearing entirely have all been reasons that have limited space travel in the past.