A single keyframe might not do what you like. You should consider inserting a couple of extra keys to create a quick but smooth transition from moving fast to slowing down.

Also, the sphere doesn't move very fast from frames 0-120 -- at least, not as fast as a Babylon 5 ship going through a jumpgate. The duration of that section should be something much faster, around the range of 12-14 frames (approximately half a second at 24 fps).

I've attached a modified version of your file to illustrate what I've described. The timing has been adjusted, and I have removed unnecessary keyframes in the graph editor.