The issues of quantitative assessment of functional efficiency, which are solved at the development stage, are considered on the example of life support systems, which are one of the key ones in a manned spacecraft. The definition of the functional efficiency of the life support systems of the manned spacecraft is given. Formalized private complex indicators of functional efficiency are singled out, such as an indicator of functionality, functional safety, functional reliability, cost, as well as a generalized complex indicator of the functional efficiency of life support systems. An approach based on the principles of qualimetry and the Data Envelopment Analysis method of data shell analysis is proposed for the formalization of partial complex indicators and a generalized complex indicator of the functional efficiency of the life support systems of the spacecraft, taking into account the "weight" of these indicators. This approach makes it possible to intensify the process of development of life support systems for spacecraft by determining the optimal configuration of the system at the early stages of design.