RAL Space has an extensive suite of clean rooms, both on the Main site and in the new R100 building. On the Main RAL site, the Large Space Test Chamber is housed in a large clean room and the access areas at each end of the chamber are effectively assembly and integration clean rooms in their own right. Similarly, the access areas for the smaller thermal vacuum chambers are also clean rooms. In addition to these areas, there are two dedicated instrument level build facilities available. Operated and maintained to ISO14644 these clean rooms are used for the assembly, integration and test of spacecraft instruments and sub-systems. The rooms are fully conditioned for temperature, humidity and pressure and benefit from the addition of carbon filtration to limit the transmission of airborne hydrocarbons into the facilities. New facilities will be available in the NSTF in due course. NSTF facilities and the existing R100 facilities , may be used by external companies subject to availability and appropriate commercial arrangements.