A.C.U stands for Ant Containment Unit, but that is not the only purpose for this object. The design is meant for the Mars missions or any other long duration mission. It has been proposed that when we go to Mars the Orion or a vessel like it will attach to a larger unit. If that happens there will most likely be a rotating section that will make some sort of artificial gravity. This model of the A.C.U will be ideal for this type of environment but will work just fine without gravity. The way the A.C.U works is it is basically a place to put the food that the astronauts do not eat. Ants will decompose it and it will become a place to get fertile dirt for growing plants. The worker ants usually eat 1 to 2 milligrams a day and live from 1 to 3 years. That is about 2,160 milligrams per ant for duration of three years. This model is just meant for the worker ants but would easily be able to be modified to accommodate the whole colony of ants.