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Summary of studies on space solar power systems of the National Space Development Agency of Japan
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Acta Astronautica 54 (2004) 337 – 345 www.elsevier.com/locate/actaastro
Summary of studies on space solar power systems of the National Space Development Agency of Japan Masahiro Moria , Hiroyuki Nagayamab , Yuka Saitob;∗ , Hiroshi Matsumotoc a National
Space Development Agency of Japan, 2-1-1Sengen, Tsukuba, Ibaraki 305-8505, Japan Research Institute, Inc., 3-6, Otemachi 2-chome Chiyoda-ku, Tokyo 100-8141, Japan c Kyoto Univ., Gokasho, Uji, Kyoto 611-0011, Japan
b Mitsubishi
Received 15 April 2002; received in revised form 19 September 2002; accepted 17 December 2002
Abstract National Space Development Agency of Japan has examined studies on Space Solar Power Systems (SSPS) since FY1998 organizing a special committee and working group. The FY 1998 studies focused on creating a life cycle cost model of the SSPS which sends energy to the Earth using microwave beams (Microwave Power Transmission; MPT). With the use of this model, technological sensitivity was analyzed to identify key research issues that must be pursued in the future. In addition, a conceptual study was conducted on the SSPS using laser power transmission, with attention paid to 8ber array lasers. The FY1999 studies examined a system concept of SSPS, and three types of con8gurations were proposed. We also proposed a draft of the engineering demonstration satellite while examining major element technology. The FY2000 studies surveyed maturity of major element technologies to exam SSPS system concept. Computer simulation of a direct solar pumping solid-state laser, 5:8 GHz microwave transmitter and receiver system and “sandwich module” integrated PV cell, microwave transmitter and antennas were examined as demonstration of element technology. c 2003 Published by Elsevier Ltd.
1. Introduction
2. FY1998
This paper presents a summary of studies on SSPS that NASDA has examined since FY 1998.
The FY 1998 studies focused on creating a life cycle cost model of SSPS which sends energy to the Earth using microwave beams (MPT) [1]. With the use of this model, technological sensitivity was analyzed to identify key research issues that must be pursued in the future. In addition, a conceptual study was conducted on the SSPS using laser power transmission, with attention paid to 8ber array lasers.
Based on paper IAF-01-R.1.04 presented at the 52nd International Astronautical Congress, 1–5 October 2001, Toulouse, France. ∗ Corresponding author. E-mail addresses: [email protected] (M. Mori), [email protected] (H. Nagayama), [email protected] (Y. Saito), [email protected] (H. Matsumoto).
c 2003 Published by Elsevier Ltd. 0094-5765/$ - see front matter doi:10.1016/S0094-5765(03)00033-X
2.1. Survey of the SSPS related projects We surveyed previous and ongoing studies related to the SSPS in Japan and other nations. Attention was
338
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
paid to the NASA Reference System, the NASA Fresh Look Study, the SSP Concept De8nition Study and the SPS 2000, as well as projects that have been worked on by the Ministry of Economy, Trade and Industry. 2.1.1. The creation of a life cycle model The life cycle model of the SSPS using MPT was created. Based on various factors related to the construction and operation of the SSPS, cost model, environmental impact model and energy balance model were created.
(1) Cost model: Calculating the total costs of power generation, based on construction and operational costs of the SSPS. (2) Environmental impact model: Calculating carbon dioxide (CO2 ) emissions caused by the construction and operation of the SSPS. (3) Energy balance model: Calculating energy payback time and energy balance, based on the relationship between energy input during operation and construction and energy delivered during operation of the SSPS.
Size of Transmission Antenna Output Power Microwave-DC conversion rate DC-Microwave conversion rate Power Distribution rate (SSP) PV Cell conversion rate Unit cost of Microwave transmitor Unit cost of Rectenna element Unit cost of PV Cell Unit cost of SSP structure Construction unit cost of Rectenna Transportation unit cost Maintenance rate of Rectenna Maintenance rate of SSP Weight of Transmission Antenna Weight of SSP Construciton Period Interest -0.6 -0.4 -0.2 0.0
0.2
0.4
0.6
0.8
1.0
1.2
Power Generation Cost CO2 Emission Energy Payback Time
Fig. 1. The result of sensitivity analysis.
1.4
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
Each model is created using parameters regarding the SSPS, rectenna (receiving antenna), launch and maintenance. 2.1.2. Evaluation of model validity A model of the SSPS beaming down the electrical power on the order of 1 GW uses such independent variables as the cost per kilowatt-hour, CO2 emissions and payback time. According to sensitivity analysis (Fig. 1) conducted using these variables, improving microwave-to-DC conversion eJciency is most important in order to reduce cost per kilowatt-hour. Another important issue is not only improving eJciency of DC-to-microwave conversion and solar power conversion, but also reducing launch costs. Similar results were reached with CO2 emissions and payback time, indicating that a key is to increase the transmission power and the diameter of the transmitting antenna. This suggestion is likely attributed to the fact that optimal diameter of the transmitting antennae was set at about 1 km. Conclusively, research and development must be conducted to improve microwave-DC/DC-microwave conversion eJciency. In addition, there must be an increase in the availability of inexpensive space transportation systems. The cost per kilowatt-hour for existing terrestrial power stations is half as much as the amount estimated using the model. However, the energy-supply system using fossil fuel combustion is anticipated to be charged for CO2 emissions in order to prevent detrimental changes to the Earth’s environment. It is also assumed that costs required for processing nuclear fuels and decommissioning reactors will be included in the electricity costs of nuclear power stations. Hence, the present unit cost per kilowatthour will not necessarily be maintained in the future. CO2 emissions from the SSPS are one order of magnitude below those from fossil fuels, such as coal, oil and liquid natural gas (LNG). The SSPS emits less CO2 than terrestrial solar power stations, but slightly more than nuclear power plants. Energy payback time of power generated by combusting coal, oil, LNG and nuclear power is shorter than that of the SSPS, which is as long as 5 years. However, the SSPS achieves a higher payback ratio
339
than various terrestrial solar power stations that require an oMset period of 6 –11 years. Coal, oil, LNG and nuclear power produce a balance of energy, including fuels, on the order of 30%. However, the SSPS delivers 6 times as much energy as was initially input. This suggests that it will be possible to construct another SSPS using energy generated by one SSPS once the space solar power system is deployed into orbit. 2.2. Survey of the energy market We surveyed and summarized domestic and international energy policies prepared since the Third Conference of Parties to the UN Framework Convention on Climate Change (COP 3), and the transitions in the US electrical industry. The global energy marketplace is thought to be of importance when conceiving the SSPS project.
3. FY1999 The FY 1999 studies presented a concept of the SSPS while examining major element technology. In addition, a draft of the engineering demonstration satellite was prepared [2]. 3.1. Study on the overall system We 8rst summarized the historical background and recent trends of studies conducted on the SSPS in the US. Subsequently, the system architecture of the SSPS was examined, and the following three con8gurations were proposed: 3.1.1. Con8guration A Features (see Fig. 2): • Altitude control using gravity gradient; • modularizing solar cells to be replaceable; • attaching solar modules alternately in pairs in order to increase received sunlight; • using C60-type solar cell modules; • enabling an increase in power generation by adding solar modules.
340
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
3.1.3. Con8guration C Features (see Fig. 4): C60-type solar cell module
• • • • •
Major characteristics:
Power distribution system
• • • • Transmitting antenna
Fig. 2. Con8guration A.
Major characteristics: • • • • •
Output power (to user): 250 MW; microwave frequency: 5:8 GHz; diameter of transmitting antenna: 2:6 km; diameter of solar collector: 50 –60 m; total length: 15 km.
3.1.2. Con8guration B Features (see Fig. 3): • Using concentrating mirrors to maximize solar collection; • integrating solar cells and a power transmitter into a ‘sandwich’ structure; • reducing weight using an inQatable structure. Major characteristics: • • • •
Output power (to user): 1 GW; microwave frequency: 5:8 GHz; diameter of transmitting antenna: 2:6 km; diameter of concentrating mirror: 4 –6 km.
Maintaining the structure using centrifugal force; using multiple collection and distribution systems; modularizing solar cells to be replaceable; installing thin-8lm lenses on solar cells; C60-type Earth-oriented phased array with microwave transmitter.
Output power (to user): 1 GW; microwave frequency: 5:8 GHz; diameter of transmitting antenna: 2:6 km; diameter of concentrating mirror: 5 km.
3.2. Studies on element technology 3.2.1. Microwave transmission system We examined systems to transmit and receive microwaves with the aim of reducing the diameter of the rectenna, focusing on transmission patterns and frequencies. Consequently, it was determined optimal to set the transmission frequency at 5:8 GHz, the diameter of the transmitting antenna at 2:6 km and the diameter of the rectenna at 1:9 km. Using these values, the rectenna eJciency is 89.91% and the receiving power density at the periphery of the rectenna is 0:96 mW=cm2 . 3.2.2. Fiber array laser A solid-state laser was examined as one candidate for the photovoltaic laser. The principle of the system is as follows. First, Fresnel lenses and the like are used to magnify the energy density of solar power one thousand times, then the energy is radiated to a concentration and transmission unit (clad). The clad contains optical 8bers doped with rare earth (Nd, Cr, Yb) having diameter of 10 mm. The proposed solid-state laser excites single-mode laser beams using power radiated to optical 8bers (see Fig. 5). 3.2.3. Photovoltaic array system We examined types of solar cells applicable to the SSPS and sandwich module integrating solar collectors and transmitting antennas (see Fig. 6). In principle, the power collected by a
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
341
Fig. 3. Con8guration B.
Fig. 4. Con8guration C.
solar cell-faced module is converted into a microwave beam through a self-contained microwave transmitter. The microwave is then beamed down from a transmitting antenna at the rear face of the module.
Each module is a replaceable structure on a honeycomb frame. Except for control signals, each module is structured independently so that malfunctions of one module do not aMect other modules.
342
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
Sun light
‚
‚
‚Q
‚
‚R
‚P
Clad
Fig. 5. Fiber array laser and clad.
Solar cell
Microwave transmitter
Transmitting antenna
Honeycomb frame
3.2.5. Transportation system Taking the cost per kilowatt-hour into account, we examined the requirements of the transportation system to deploy the SSPS into low Earth orbit (LEO). Consequently, it was required to reduce current launch costs to one-tenth or less and to realize a short turnaround time, similar to commercial aircraft. We also examined velocity increments and duration requirements for transition into geostationary orbit (GEO) from LEO, assuming that an electrical propulsion system is used. 3.2.6. Operational orbit GEO is the optimal orbit for operating the SSPS. Considering a GEO altitude of about 36; 000 km, the orbit is not necessarily appropriate for an initial small-scale SSPS project. Equatorial orbit lower than GEO is imaginable, but it is not appropriate for power transmission to Japan. Hence, we examined Molniya orbit.
Fig. 6. Sandwich module integrating solar cell, microwave transmitter and transmitting antennas.
3.2.4. Orbit and attitude control We estimated the amount of propellant required for stationkeeping of the SSPS.
3.2.7. Robotics We surveyed a robot that the CMU has examined for use in the assembly and maintenance of the SSPS. 3.2.8. Evaluation of cost and operation We examined the relationship between construction costs and availability, and cost per kilowatt-hour. We also examined the eMects of the SSPS on existing terrestrial electrical systems.
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
3.3. Examinations of technological demonstration A conceptual study was conducted on an engineering demonstration satellite for transmitting power from space to ground receiving systems. Based on the concept developed during the ETS-VII
343
project, we examined con8gurations of a reusable bus module (Mother satellite) and a reusable mission module (Kid satellite) in space. The Mother satellite transmits power wirelessly and communicates with the Kid satellite using lasers or microwaves.
Fig. 7. Concept of the space environment utilization mission.
Fig. 8. Concept of Earth observation mission.
344
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
Figs. 7 and 8 illustrate concepts of the space environment utilization mission and Earth observation mission. 4. FY2000
Fig. 9. SPRITZ.
Since it is not necessary to mount solar panels on the Kid satellite, the acceleration conditions can be improved to 10−6 G or less. The Kid satellite is optimal for a space environment utilization mission that can provide a high quality of microgravity. Experimental instruments can be replaced during the mission. In addition, the satellite can obtain high resolution data of disasters and the like in a timely manner when the altitude is lowered to the minimum. Furthermore, it is possible to use the Kid satellite as a testbed for orbital demonstration missions, during which many experiments are conducted.
The FY2000 studies surveyed maturity of major element technologies to exam SSPS system concept. Computer simulation of a direct solar pumping solid-state laser, 5:8 GHz microwave transmitter and receiver system and “sandwich module” integrated PV cell, microwave transmitter and antennas were examined as demonstration of element technology [3]. 4.1. Solar power radio integrated transmitter (SPRITZ) NASDA and Kyoto Univ. developed a system to test technology by which electricity generated in space using light from the sun is converted into microwaves and transmitted to Earth. (see Fig. 9). The prototype includes a 3-m-high, hexagon-shaped device, consisting of a solar panel, through which sunlight is converted into electricity, and an additional device, through which electricity is converted into microwaves.
Fig. 10. Concept of 10 MW class demonstration system on ISS co-orbit.
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
When the transmitting device was exposed to halogen light, bundles of microwave beams, 20 cm in diameter, were generated from the antenna at the bottom of the device and transmitted downward. The direction of the beam’s transmission was able to be changed. The fact that light-emitting diodes on the equipment’s base turned on proved that the microwave beams had reached their intended destination. By combining a number of hexagon-shaped pieces, a huge power station could be created in space. NASDA plans to put the system into practical use around 2020. Speci8cations: • Sizes(in mm) ◦ 2000D × 2300W × 2850H ; • Solar simulator ◦ 133 × 75 W halogen lamps; • Solar cells ◦ Output ¿ 166 W (eJciency : about 15%); • Solid-state microwave transmitter ◦ Frequency 5:770 GHz; ◦ Output 25 W; ◦ Active phased array antenna; (10 × 10 elements) ◦ Phase control 3 bits;
345
• Power receiving antenna ◦ 1848 rectennas and LED. 5. Study plan of FY2001 The FY2001 studies will survey the technological subject, demonstration scenario, safety and eJciency of SSPS on the basis of the study about maturity of element technologies which was investigated in FY2000. We will also propose a research and development road map for SSPS and a study plan in the future. In addition, the concept study on 10MW class demonstration system on ISS co-orbit will be conducted. (see Fig. 10). References [1] Study on space solar power systems, NASDA Contractor Report, 1998. [2] Study on space solar power systems, NASDA Contractor Report, 1999. [3] Study on space solar power systems, NASDA Contractor Report, 2000.
Acta Astronautica 54 (2004) 337 – 345 www.elsevier.com/locate/actaastro
Summary of studies on space solar power systems of the National Space Development Agency of Japan Masahiro Moria , Hiroyuki Nagayamab , Yuka Saitob;∗ , Hiroshi Matsumotoc a National
Space Development Agency of Japan, 2-1-1Sengen, Tsukuba, Ibaraki 305-8505, Japan Research Institute, Inc., 3-6, Otemachi 2-chome Chiyoda-ku, Tokyo 100-8141, Japan c Kyoto Univ., Gokasho, Uji, Kyoto 611-0011, Japan
b Mitsubishi
Received 15 April 2002; received in revised form 19 September 2002; accepted 17 December 2002
Abstract National Space Development Agency of Japan has examined studies on Space Solar Power Systems (SSPS) since FY1998 organizing a special committee and working group. The FY 1998 studies focused on creating a life cycle cost model of the SSPS which sends energy to the Earth using microwave beams (Microwave Power Transmission; MPT). With the use of this model, technological sensitivity was analyzed to identify key research issues that must be pursued in the future. In addition, a conceptual study was conducted on the SSPS using laser power transmission, with attention paid to 8ber array lasers. The FY1999 studies examined a system concept of SSPS, and three types of con8gurations were proposed. We also proposed a draft of the engineering demonstration satellite while examining major element technology. The FY2000 studies surveyed maturity of major element technologies to exam SSPS system concept. Computer simulation of a direct solar pumping solid-state laser, 5:8 GHz microwave transmitter and receiver system and “sandwich module” integrated PV cell, microwave transmitter and antennas were examined as demonstration of element technology. c 2003 Published by Elsevier Ltd.
1. Introduction
2. FY1998
This paper presents a summary of studies on SSPS that NASDA has examined since FY 1998.
The FY 1998 studies focused on creating a life cycle cost model of SSPS which sends energy to the Earth using microwave beams (MPT) [1]. With the use of this model, technological sensitivity was analyzed to identify key research issues that must be pursued in the future. In addition, a conceptual study was conducted on the SSPS using laser power transmission, with attention paid to 8ber array lasers.
Based on paper IAF-01-R.1.04 presented at the 52nd International Astronautical Congress, 1–5 October 2001, Toulouse, France. ∗ Corresponding author. E-mail addresses: [email protected] (M. Mori), [email protected] (H. Nagayama), [email protected] (Y. Saito), [email protected] (H. Matsumoto).
c 2003 Published by Elsevier Ltd. 0094-5765/$ - see front matter doi:10.1016/S0094-5765(03)00033-X
2.1. Survey of the SSPS related projects We surveyed previous and ongoing studies related to the SSPS in Japan and other nations. Attention was
338
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
paid to the NASA Reference System, the NASA Fresh Look Study, the SSP Concept De8nition Study and the SPS 2000, as well as projects that have been worked on by the Ministry of Economy, Trade and Industry. 2.1.1. The creation of a life cycle model The life cycle model of the SSPS using MPT was created. Based on various factors related to the construction and operation of the SSPS, cost model, environmental impact model and energy balance model were created.
(1) Cost model: Calculating the total costs of power generation, based on construction and operational costs of the SSPS. (2) Environmental impact model: Calculating carbon dioxide (CO2 ) emissions caused by the construction and operation of the SSPS. (3) Energy balance model: Calculating energy payback time and energy balance, based on the relationship between energy input during operation and construction and energy delivered during operation of the SSPS.
Size of Transmission Antenna Output Power Microwave-DC conversion rate DC-Microwave conversion rate Power Distribution rate (SSP) PV Cell conversion rate Unit cost of Microwave transmitor Unit cost of Rectenna element Unit cost of PV Cell Unit cost of SSP structure Construction unit cost of Rectenna Transportation unit cost Maintenance rate of Rectenna Maintenance rate of SSP Weight of Transmission Antenna Weight of SSP Construciton Period Interest -0.6 -0.4 -0.2 0.0
0.2
0.4
0.6
0.8
1.0
1.2
Power Generation Cost CO2 Emission Energy Payback Time
Fig. 1. The result of sensitivity analysis.
1.4
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
Each model is created using parameters regarding the SSPS, rectenna (receiving antenna), launch and maintenance. 2.1.2. Evaluation of model validity A model of the SSPS beaming down the electrical power on the order of 1 GW uses such independent variables as the cost per kilowatt-hour, CO2 emissions and payback time. According to sensitivity analysis (Fig. 1) conducted using these variables, improving microwave-to-DC conversion eJciency is most important in order to reduce cost per kilowatt-hour. Another important issue is not only improving eJciency of DC-to-microwave conversion and solar power conversion, but also reducing launch costs. Similar results were reached with CO2 emissions and payback time, indicating that a key is to increase the transmission power and the diameter of the transmitting antenna. This suggestion is likely attributed to the fact that optimal diameter of the transmitting antennae was set at about 1 km. Conclusively, research and development must be conducted to improve microwave-DC/DC-microwave conversion eJciency. In addition, there must be an increase in the availability of inexpensive space transportation systems. The cost per kilowatt-hour for existing terrestrial power stations is half as much as the amount estimated using the model. However, the energy-supply system using fossil fuel combustion is anticipated to be charged for CO2 emissions in order to prevent detrimental changes to the Earth’s environment. It is also assumed that costs required for processing nuclear fuels and decommissioning reactors will be included in the electricity costs of nuclear power stations. Hence, the present unit cost per kilowatthour will not necessarily be maintained in the future. CO2 emissions from the SSPS are one order of magnitude below those from fossil fuels, such as coal, oil and liquid natural gas (LNG). The SSPS emits less CO2 than terrestrial solar power stations, but slightly more than nuclear power plants. Energy payback time of power generated by combusting coal, oil, LNG and nuclear power is shorter than that of the SSPS, which is as long as 5 years. However, the SSPS achieves a higher payback ratio
339
than various terrestrial solar power stations that require an oMset period of 6 –11 years. Coal, oil, LNG and nuclear power produce a balance of energy, including fuels, on the order of 30%. However, the SSPS delivers 6 times as much energy as was initially input. This suggests that it will be possible to construct another SSPS using energy generated by one SSPS once the space solar power system is deployed into orbit. 2.2. Survey of the energy market We surveyed and summarized domestic and international energy policies prepared since the Third Conference of Parties to the UN Framework Convention on Climate Change (COP 3), and the transitions in the US electrical industry. The global energy marketplace is thought to be of importance when conceiving the SSPS project.
3. FY1999 The FY 1999 studies presented a concept of the SSPS while examining major element technology. In addition, a draft of the engineering demonstration satellite was prepared [2]. 3.1. Study on the overall system We 8rst summarized the historical background and recent trends of studies conducted on the SSPS in the US. Subsequently, the system architecture of the SSPS was examined, and the following three con8gurations were proposed: 3.1.1. Con8guration A Features (see Fig. 2): • Altitude control using gravity gradient; • modularizing solar cells to be replaceable; • attaching solar modules alternately in pairs in order to increase received sunlight; • using C60-type solar cell modules; • enabling an increase in power generation by adding solar modules.
340
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
3.1.3. Con8guration C Features (see Fig. 4): C60-type solar cell module
• • • • •
Major characteristics:
Power distribution system
• • • • Transmitting antenna
Fig. 2. Con8guration A.
Major characteristics: • • • • •
Output power (to user): 250 MW; microwave frequency: 5:8 GHz; diameter of transmitting antenna: 2:6 km; diameter of solar collector: 50 –60 m; total length: 15 km.
3.1.2. Con8guration B Features (see Fig. 3): • Using concentrating mirrors to maximize solar collection; • integrating solar cells and a power transmitter into a ‘sandwich’ structure; • reducing weight using an inQatable structure. Major characteristics: • • • •
Output power (to user): 1 GW; microwave frequency: 5:8 GHz; diameter of transmitting antenna: 2:6 km; diameter of concentrating mirror: 4 –6 km.
Maintaining the structure using centrifugal force; using multiple collection and distribution systems; modularizing solar cells to be replaceable; installing thin-8lm lenses on solar cells; C60-type Earth-oriented phased array with microwave transmitter.
Output power (to user): 1 GW; microwave frequency: 5:8 GHz; diameter of transmitting antenna: 2:6 km; diameter of concentrating mirror: 5 km.
3.2. Studies on element technology 3.2.1. Microwave transmission system We examined systems to transmit and receive microwaves with the aim of reducing the diameter of the rectenna, focusing on transmission patterns and frequencies. Consequently, it was determined optimal to set the transmission frequency at 5:8 GHz, the diameter of the transmitting antenna at 2:6 km and the diameter of the rectenna at 1:9 km. Using these values, the rectenna eJciency is 89.91% and the receiving power density at the periphery of the rectenna is 0:96 mW=cm2 . 3.2.2. Fiber array laser A solid-state laser was examined as one candidate for the photovoltaic laser. The principle of the system is as follows. First, Fresnel lenses and the like are used to magnify the energy density of solar power one thousand times, then the energy is radiated to a concentration and transmission unit (clad). The clad contains optical 8bers doped with rare earth (Nd, Cr, Yb) having diameter of 10 mm. The proposed solid-state laser excites single-mode laser beams using power radiated to optical 8bers (see Fig. 5). 3.2.3. Photovoltaic array system We examined types of solar cells applicable to the SSPS and sandwich module integrating solar collectors and transmitting antennas (see Fig. 6). In principle, the power collected by a
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
341
Fig. 3. Con8guration B.
Fig. 4. Con8guration C.
solar cell-faced module is converted into a microwave beam through a self-contained microwave transmitter. The microwave is then beamed down from a transmitting antenna at the rear face of the module.
Each module is a replaceable structure on a honeycomb frame. Except for control signals, each module is structured independently so that malfunctions of one module do not aMect other modules.
342
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
Sun light
‚
‚
‚Q
‚
‚R
‚P
Clad
Fig. 5. Fiber array laser and clad.
Solar cell
Microwave transmitter
Transmitting antenna
Honeycomb frame
3.2.5. Transportation system Taking the cost per kilowatt-hour into account, we examined the requirements of the transportation system to deploy the SSPS into low Earth orbit (LEO). Consequently, it was required to reduce current launch costs to one-tenth or less and to realize a short turnaround time, similar to commercial aircraft. We also examined velocity increments and duration requirements for transition into geostationary orbit (GEO) from LEO, assuming that an electrical propulsion system is used. 3.2.6. Operational orbit GEO is the optimal orbit for operating the SSPS. Considering a GEO altitude of about 36; 000 km, the orbit is not necessarily appropriate for an initial small-scale SSPS project. Equatorial orbit lower than GEO is imaginable, but it is not appropriate for power transmission to Japan. Hence, we examined Molniya orbit.
Fig. 6. Sandwich module integrating solar cell, microwave transmitter and transmitting antennas.
3.2.4. Orbit and attitude control We estimated the amount of propellant required for stationkeeping of the SSPS.
3.2.7. Robotics We surveyed a robot that the CMU has examined for use in the assembly and maintenance of the SSPS. 3.2.8. Evaluation of cost and operation We examined the relationship between construction costs and availability, and cost per kilowatt-hour. We also examined the eMects of the SSPS on existing terrestrial electrical systems.
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
3.3. Examinations of technological demonstration A conceptual study was conducted on an engineering demonstration satellite for transmitting power from space to ground receiving systems. Based on the concept developed during the ETS-VII
343
project, we examined con8gurations of a reusable bus module (Mother satellite) and a reusable mission module (Kid satellite) in space. The Mother satellite transmits power wirelessly and communicates with the Kid satellite using lasers or microwaves.
Fig. 7. Concept of the space environment utilization mission.
Fig. 8. Concept of Earth observation mission.
344
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
Figs. 7 and 8 illustrate concepts of the space environment utilization mission and Earth observation mission. 4. FY2000
Fig. 9. SPRITZ.
Since it is not necessary to mount solar panels on the Kid satellite, the acceleration conditions can be improved to 10−6 G or less. The Kid satellite is optimal for a space environment utilization mission that can provide a high quality of microgravity. Experimental instruments can be replaced during the mission. In addition, the satellite can obtain high resolution data of disasters and the like in a timely manner when the altitude is lowered to the minimum. Furthermore, it is possible to use the Kid satellite as a testbed for orbital demonstration missions, during which many experiments are conducted.
The FY2000 studies surveyed maturity of major element technologies to exam SSPS system concept. Computer simulation of a direct solar pumping solid-state laser, 5:8 GHz microwave transmitter and receiver system and “sandwich module” integrated PV cell, microwave transmitter and antennas were examined as demonstration of element technology [3]. 4.1. Solar power radio integrated transmitter (SPRITZ) NASDA and Kyoto Univ. developed a system to test technology by which electricity generated in space using light from the sun is converted into microwaves and transmitted to Earth. (see Fig. 9). The prototype includes a 3-m-high, hexagon-shaped device, consisting of a solar panel, through which sunlight is converted into electricity, and an additional device, through which electricity is converted into microwaves.
Fig. 10. Concept of 10 MW class demonstration system on ISS co-orbit.
M. Mori et al. / Acta Astronautica 54 (2004) 337 – 345
When the transmitting device was exposed to halogen light, bundles of microwave beams, 20 cm in diameter, were generated from the antenna at the bottom of the device and transmitted downward. The direction of the beam’s transmission was able to be changed. The fact that light-emitting diodes on the equipment’s base turned on proved that the microwave beams had reached their intended destination. By combining a number of hexagon-shaped pieces, a huge power station could be created in space. NASDA plans to put the system into practical use around 2020. Speci8cations: • Sizes(in mm) ◦ 2000D × 2300W × 2850H ; • Solar simulator ◦ 133 × 75 W halogen lamps; • Solar cells ◦ Output ¿ 166 W (eJciency : about 15%); • Solid-state microwave transmitter ◦ Frequency 5:770 GHz; ◦ Output 25 W; ◦ Active phased array antenna; (10 × 10 elements) ◦ Phase control 3 bits;
345
• Power receiving antenna ◦ 1848 rectennas and LED. 5. Study plan of FY2001 The FY2001 studies will survey the technological subject, demonstration scenario, safety and eJciency of SSPS on the basis of the study about maturity of element technologies which was investigated in FY2000. We will also propose a research and development road map for SSPS and a study plan in the future. In addition, the concept study on 10MW class demonstration system on ISS co-orbit will be conducted. (see Fig. 10). References [1] Study on space solar power systems, NASDA Contractor Report, 1998. [2] Study on space solar power systems, NASDA Contractor Report, 1999. [3] Study on space solar power systems, NASDA Contractor Report, 2000.