The inside is molded into two cylindrical chambers joined by a tunnel. The larger chamber holds a precipitant solution which is usually more concentrated than that in the smaller chamber. The two chambers are joined by a plug filled with a porous material to control the rate of diffusion. The plug material is selected to be compatible with the protein solution, and its properties are set to match the rate at which the crystals are to grow. The DCAM has no mechanical system.
Diffusion starts on Earth, as soon as the chambers are filled.
However, the rate is so slow that no appreciable change occurs before the samples reach orbit one or two or even several days later. This also allows protein samples to stay aboard the shuttle in case of a launch delay. In other hardware, many samples must be replaced in the event of a postponement. Such an apparatus is ideally suited for long duration mission such as the International Space Station and Mir. Upon arrival at Mir, the DCAMs will be transferred to one of Mir's modules and mounted in a quiet area where crystallization will take place.