MEMOIR is the special track of the Reactor Core ~=ENCODE=~ mission. It's a Nearly Impossible track that takes place in the virtual-reality plane that E.N.T.I.T.Y. created while eating the world (which is also the place where the Bloontonium Lab was built upon later to cover the distorted void.) You can only place the towers on the gears. The other parts of the track is counted as Outer Space.