The article concerns the optimization and cost reduction when designing clean rooms exploited in rocket technology. There are shown general directions of optimization and cost reduction both for the stage of project development and exploi ting process. We propose the new architectural planning solution for clean room arrangement in the assembly and testing building (ATB). The advantages of mobile clean chamber application for the assembly of the orbital module (OM) are next: mobility, the possibility of transportation and deployment in the rooms of ATB; possibility of air purification system cutoff during the interlaunch period; compact placement in ATB; the standard lifting equipment (bridge cranes) is not used inside ATB; the transfer chamber is used as a part of OM assembly hall during technological operations for module assembly; the schedule of the temperature-humidity condition system operation in a clean chamber of OM assembly is simpler (its partial shutdown is possible); the staff working in a clean chamber provided for one-off uniform, which makes laundry unnecessary; maintenance cost minimization in inter-launch periods when the chamber can be folded and packaged in containers. The listed advantages of the mobile clean chamber prove the advisability of its application in the assembly of OM. The developed planning solution is an alternative to prior designed premises. Notice, that the concept of the mobile clean chamber design matches the current directions of the progress of ground complexes and complies with the requirements of mobility, economy, and clearance.