There is a growing realization in education than didactic, lecture-based modes of instruction are less effective than more learner-centered models in which learners, frequently in collaboration with peers, are engaged in problem solving and inquiry. Predicated on constructivist and situated notions of what it means to know and learn, many educators are suggesting the creation of learning environments that support the natural complexity of content, avoid over-simplification, engage students in knowledge construction, and present instruction in real-world contexts. Rather than presenting instructional treatments, the goal is to establish rich learning environments where learners engage in domain-related practices to carry out socially negotiated tasks. In this paper, the authors argue that a new model based on designing tools for learners, not just users, is needed. Learner-centered design focuses on creating an interface that is easy to use and facilitates the development of domain understanding. This approach can overcome the learner's lack of domain knowledge and skills so that a novice can accomplish meaningful tasks within a relatively short period of time. Application of learner-centered design in the domain of a satellite orbital control simulation system is discussed.