INTRODUCTION The Fourth ISAS (Institute of Space and Astronautical Science) Space Energy Symposium was held on 12 February 1985. Twenty-one papers were presented on the subjects of electrical power for spacecraft, energy experiments on board the space station and solar power satellites. These subjects are the same as for the previous symposium, whose proceedings were published as a special issue of the Space Solar Power Review.* For this symposium, the ISAS published just abstracts of papers, and the speakers were encouraged to contribute their papers to the Space Solar Power Review. As a result, eight papers have been submitted and included in this issue. The formality and language peculiar to publication may be a reason why the paper number is fewer than that of the presentations, since the meeting was held in a rather casual atmosphere. As for the special issue for the previous symposium, Professor Freeman, who had invited us to write the papers, took trouble to read all the manuscripts to correct the English. Representing all of the authors, I would like to express our appreciations to Professor Freeman. A special feature of this meeting was the study of the economic aspects of large- scale space power systems, which were discussed for the first time in this symposium. Fortunately the papers are included here. On the other hand, some authors reserved publication intending to refine their concepts for presentation at such overseas conferences as the Congress of International Astronautical Federation. I hope also that they will appear in a future issue of the Space Solar Power Review. For readers who have an interest in the roots of such future articles, a bilingual abstract (in Japanese and English) can be obtained by writing to me: Professor Makoto Nagatomo Space Power System Section Institute of Space and Astronautical Science 4-6-1 Komaba, Meguro-ku, Tokyo 153, Japan ★Space Solar Power Review, Vol. 5 No. 2, 1985.
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