Motivation is a Premium option that allows players to pay with Credits in order to increase the speed of ships on a particular Flight. The increase in speed is active for the current Flight only. By motivation the player can reduce flight time by up to 50%. If two Alliances have a War policy, flights between them can be motivated to reduce flight time by up to 70%.
The Speed motivation drop-down menu can be found just after choosing the ships for the current flight on the 5th row under "Speed" and above "Distance" information.