Streamlining new product development forces companies to make decisions on preliminary information. This paper considers this challenge within the context of project management in the aerospace sector, and in particular the development of product-service systems. The concept of knowledge maturity is explored as a means to provide practical decision support, which increases decision makers' awareness of the knowledge base and supports cross-boundary discussions on the perceived maturity of available knowledge, thereby identifying and mitigating limitations. Requirements are elicited from previous research on knowledge maturity in the aerospace industry and a knowledge maturity model is developed through five industry-based workshops.