From Gineipaedia, the Legend of Galactic Heroes wiki
Inertial control is one of the primary technologies used in modern spacecraft engineering. It can be used to negate the inertial forces created by starship thrust.
Inertial control technology was developed sometime between the 27th and 28th century, and helped to usher in the Galactic Federation's golden age of exploration and colonisation alongside the other Three Graces. (Legend of Galactic Heroes Volume 1: Dawn)