Although early and thorough assessment of requirements prior to design is a beneficial goal, our current experience in assessing embedded, real-time architectures is that such an approach is rarely completed satisfactorily. Given this situation, the Realtime Embedded Architecture-Centric Testbed (REACT) was developed to assess contractor-developed, object-oriented software architectures during their evolution in order to reduce technical and programmatic risks. This paper presents some results in applying REACT's aspect-oriented assessment approach to large space systems. The approach was highly effective in diagnosing architectural problems of complex, evolving, and often handicapped, real-time embedded systems.