JX Crystals

Sunbeams from Space Mirrors in dawn-dusk Polar Orbit feeding Solar fields on the ground for Low Cost Electricity

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A Space Power Satellite capable of providing solar electric power economically for 24 hours per day has been a dream for decades. However, the SPS concept is very complex since it assumes multiple energy conversion steps and includes specially constructed ground microwave receiver stations. The 5 km by 15 km Integrated Symmetric Concentrator SPS concept employs light weight mirrors in a GEO orbit. Herein, it is proposed to use a constellation of 10 km diameter mirror arrays in a much lower sun synchronous orbit at an altitude of 1000 km deflecting sunbeams down to terrestrial solar power fields at dawn and dusk. The key is that larger and larger terrestrial solar fields, photovoltaic or trough concentrated solar power, are already being built all around the world. Mirrors deflecting sunbeams down to earth is a much simpler concept. A surprising convergence of two technologies under development is now possible, i.e. lower cost access to space and the ongoing construction of numerous larger solar power fields. The novelty here is the idea of a constellation of mirrors in a sun-synchronous dawn dusk orbit in combination with future multiple 5-GW solar farms distributed around the world. In this scenario, the projected payback time for the mirror constellation given the additional revenues from the multiple solar fields is approximately 2 years. The key to the attractive economics for this concept is that the mirror constellation is used continuously over a 24 hour period by multiple terrestrial fields as each field comes into view at dawn or dusk. However, while this idea is very intriguing, the magnitude of its implementation is daunting. Nevertheless, the idea is intriguing enough to proceed with an initial design for the required mirror satellites. A mirror satellite design is presented here. It builds from mirror technology for solar sails as well as technology developed for the International Space Station. It appears that the technology is available to implement this mirror satellite design and at least go to a detailed design and test stage. Given all of the above, there is still another non-technical difference between this dawn dusk space mirror concept and the initial SPS concept and that difference is in perspective. The dawn dusk space mirror concept requires a global perspective and international cooperation whereas the SPS concept is based on a traditional national perspective. In this regard, the International Space Station does provide hope for future international cooperation.

Introduction

The Solar Power Satellite ('SPS') concept, a proposed method of generating solar electricity for 24 hours per day in space and transmitting it to earth to solve the energy needs of the Earth with a clean, zero-emissions energy source has been a dream since the 1970s [1]. The proposals to do this mostly focus on microwave transmission as the means to deliver the power to Earth. Due to the fundamental physics of diffraction- limited beam spread, such transmission requires apertures and receivers that are on the scale of kilometres, and hence require exceptionally large systems in space. For example, a NASA design concept, the Integrated Symmetrical Concentrator Solar Power Satellite (ISC SPS) is shown in Fig. 1. It is 5 x 15 km in size, and requires a ground station 8 km in diameter [2]. The size, mass, and power levels of this orbital system makes the proposed SPS extremely expensive.

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