The 1.9.1 update cycle brought several graphical and functional upgrades to the core game that enhanced the DLC experience:
Planets and moons now feature unique geological anomalies such as cryovolcanoes, craters, and meteors. Kerbal Space Program 1.9.1 DLC
A powerful tool that lets players create, edit, and share their own custom missions with specific objectives, constraints, and unexpected events. Kerbal Space Program 1.9.1 DLC
Kerbals can now set up modular science experiments on the ground—such as seismometers and weather stations—that collect data over time and transmit it back to Kerbin. Making History DLC (Expansion) Kerbal Space Program 1.9.1 DLC
A set of missions inspired by the early days of human spaceflight, challenging players to recreate iconic historical milestones. Base Game Improvements in 1.9.x