ON THE INITIATION OF SPS DEVELOPMENT KYOICHI KURIKI Institute of Space and Astronautical Science Komaba Meguro-ku Tokyo 153, Japan Abstract — The concept of finite time availability, a new idea of thermodynamics, is applied to decisions on when the development of the solar power satellite (SPS) should be initiated and how long a lead time should be taken. Admitting the errors in estimation of parameters, an earlier start is concluded to be much safer than a delayed start. INTRODUCTION No phrase can describe more clearly the thermodynamics of finite time availability than “Strike while the iron is hot.” The thermodynamic concept of availability or Gibbs free energy has been frequently applied to economics assessment (1). According to the thermodynamics in equilibrium, the most efficient work can be obtained if the process is quasi-steady. However, the available power tends to zero if the process time becomes indefinitely long and practically the human activities are completed in finite time (2). On the other hand, if the process is too fast, the equilibrium state is totally lost and the available power diminishes, as in the case of a short-circuited battery. The theorem of finite time availability can be precisely applied to macroprojects in deciding the time of their initiation. The solar power satellite (SPS) is an example of macroprojects to be applied. It is apparent that its start in the late 1970s might have been premature considering the technology readiness. In addition, the driverat that lime was the politically-posed energy crisis. In order to prepare for the real crisis in the future, we have to be armed with a methodology for SPS development. The present paper proposes a scheme with reference to the finite time availability. PROCEDURE EOR INITIATION The following is the procedure proposed for the initiation of SPS development. Although the SPS is discussed as the topic in this paper, the following methodology can be generalized. 1. Define the temporal variation of energy costs for terrestrial resources and SPS. *Presented at the Fourth ISAS Space Energy Symposium, al ISAS, Tokyo, 1 March 1985.
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