Under the current development of mid-to-large size satellites, the high reliability is mandatory to avoid failures and their development cost increases enormously to achieve the high reliability. On the other hand, several universities develop and launch micro-satellites with low cost for the purpose of education from around 2000. To generate new market for satellite utilization, low cost and fast development are key points. The balance of cost and reliability is one of the very important points to realize the markets. The theoretical research toward the balance of cost and reliability is being conducted through the governmental first program "New Space Development and Utilization Paradigm by Micro-satellites Introducing Japan-oriented Reasonable Reliable Systems Engineering". This paper presents me concept of the reasonably reliable systems engineering. The reasonably reliable systems engineering consists of two approach; process approach and product approach. In the process approach, we propose meta-process and integral quality assurance concept. The meta-process is a set of the process objectives. When we develop a system, we will follow the meta-process instead of normal process. When we perform the process, we will coordinate the contents of process based on the context and system itself. This realizes the integral quality assurance. In the product approach, we propose me effective counter measure to each failure category. Current reliability is based on the assumption that there is no miss-design and it only depends on the random failure of parts. And also in the current reliability, the recovery is only considered as part of availability. But for the customer to receive service from the satellite system, the number which shows the probability to receive service is more important. In the new approach to calculate the probability of mission continuity to provide service. As far as we can keep recover functionality, the temporally failed component can restart after the recovery operation. We show how the satellite architecture can be by the utilization of this approach. And these two approaches are interrelated. If we design the satellite with redundancy, we need more time to design the system, review the design and test the system. This is a clear example of the interrelation between two approaches.