The Institute of Space and Astronautical Science at Japan Aerospace Exploration Agency is actively engaged in the research and development of a cutting-edge lightweight deployable solar array paddle, called solar array membrane. This technology is specifically designed for small satellites, with a particular focus on the OPENS-0 small probe for the Saturn flyby engineering demonstration. This paper provides the current status of the development of the full-scale prototype for the 9 m2 solar array membrane

Funase, Ryu

Hori, Toshiyuki

Ito, Hiroaki

Katsuyama, Yoshihiko

Kubo, Yuki

Kurose, Minoru

Kusumoto, Tetsuya

Matsushita, Masanori

Miyazaki, Yasuyuki

Mori, Osamu

Okuizumi, Nobukatsu

Ono, Hiroyuki

Ozaki, Naoya

Satou, Yasutaka

Sugawara, Yoshiki

Sugihara, Ahmed Kiyoshi

Tabata, Minoru

Watanabe, Akihito

Yano, Hajime

Yoneda, Hiroaki

English

DigitalCommons@USU

Matsushita 1 38th Annual Small Satellite Conference SSC24-IX-06 Solar Array Membrane Prototype for the OPENS-0 Small Saturn Probe   Masanori Matsushita National Defence Academy  1-10-20 Hashirimizu, Yokosuka, Kanagawa, 239-8686, Japan ; +81-46-841-3810  matsushita@nda.ac.jp   Osamu Mori, Yasuyuki Miyazaki, Yasutaka Satou, Yuki Kubo , Ahmed Kiyoshi Sugihara, Tetsuya Kusumoto, Naoya Ozaki, Hajime Yano, Ryu Funase Japan Aerospace Exploration Agency 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, 252-5210, Japan  Nobukatsu Okuizumi Muroran Institute of Technology 27-1 Mizumoto-cho, Muroran, Hokkaido, 050-8585, Japan  Akihito Watanabe, Toshiyuki Hori, Hiroaki Ito Sakase Adtech Co., Ltd. 14-10 Shimoyasuta, Maruoka, Sakai, Fukui, 910-0363, Japan  Yoshihiko Katsuyama, Minoru Tabata, Minoru Kurose SLK LLC 10F HULIC Minatomirai, 1-1-7 Sakuragicho, Naka-ku, Yokohama, Kanagawa, 231-0062, Japan  Hiroyuki Ono cosmobloom Inc. 229 ROKUGOU BASE, 3-10-16 Minami Rokugo Ota-ku, Tokyo, 144-0045, Japan  Hiroaki Yoneda, Yoshiki Sugawara Aoyama Gakuin University 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-0206, Japan  ABSTRACT The Institute of Space and Astronautical Science at Japan Aerospace Exploration Agency is actively engaged in the research and development of a cutting-edge lightweight deployable solar array paddle, called solar array membrane. This technology is specifically designed for small satellites, with a particular focus on the OPENS-0 small probe for the Saturn flyby engineering demonstration. This paper provides the current status of the development of the full-scale prototype for the 9 m² solar array membrane. INTRODUCTION The Institute of Space and Astronautical Science (ISAS) at the Japan Aerospace Exploration Agency (JAXA) is currently exploring missions under the Outer Planet Exploration by Novel micro-Spacecraft (OPENS) program1. By launching small satellites with the Epsilon rocket, a compact launch vehicle, a working group for the OPENS aims to develop a space system capable of conducting low-cost, high-frequency deep space exploration missions, including those to outer planets. This initiative seeks to continuously achieve a variety of missions within a programmatic framework. The first engineering demonstration probe in this series, OPENS-0, is a small probe weighing approximately 200 kg with a body size of less than 1 meter. It will perform a Saturn flyby after a Venus swing-by. The mission proposal will be submitted under the ECO & FAST competitive M-class missions framework, with a budget cap of up to 12.5 billion yen and a targeted launch date as early as 2028.  In cases where it is challenging to equip spacecraft with nuclear batteries due to various constraints, solar cells become essential as a power source. When venturing into the outer planetary regions far from the Sun, irradiance decreases in proportion to the square of the solar distance, Matsushita 2 38th Annual Small Satellite Conference necessitating a larger solar cell area. For instance, at Saturn's orbit (10 au), the irradiance is reduced to 1/100 of that at Earth's orbit. To generate the same power as at Earth's orbit, ignoring temperature dependencies and other factors, one would need approximately 100 times the solar cell area. Meanwhile, when aiming to reach the Saturn region with a small rocket, there are stringent demands to reduce the spacecraft's mass.  Figure 1: Concept Art for OPENS-0 Misson  Figure 2: OPENS-0 Probe To enable the realization of small deep-space probes, we are researching and developing the Solar Array Membrane (SAM), a solar array paddle (SAP) that is lighter than conventional lightweight deployable SAPs. SAMs are lightweight deployable solar array paddles featuring thin-film solar cells mounted on thin membranes or fabrics, deployed using lightweight booms. ISAS has previously demonstrated the small solar power sail demonstrator IKAROS2 and has proposed the solar power sail probe OKEANOS3. By applying the spin-type solar power sail technology to the boom-type SAP, we are developing a SAM. This paper reports on the prototype developed in 2022. The SAM under development is a 9m²-class unit, targeting a lightweight goal of 200 W/kg (without gimbal), intended for small satellites. Despite its small area, it surpasses the estimated 150 W/kg of the lightest conventional SAP, making it a challenging endeavor. The OPENS-0 mission becomes feasible by equipping the probe with two wings of this 9m²-class SAM with single-axis gimbals. As the on-orbit demonstration of SAM's key technologies for OPENS-0, we developed the multifunctional membrane HELIOS4, which featured solar cells and two types of antennas on the membrane. It was launched on the Epsilon-6 rocket in 2022 but failed to reach orbit. HELIOS-R5, the follow-up mission, is scheduled for launch on the Epsilon rocket in fiscal year 2025. PROTOTYPE DESIGN AND DEVELOPMENT The specifications for the SAM required for OPENS-0 are shown in Table 1. Although these values are still under consideration and subject to change, they serve as the basis for the design and study of the SAM. Each of the two SAM wings is equipped with a single-axis gimbal mechanism to address the issue of solar radiation pressure torque caused by the membrane becoming non-planar, which can disturb attitude control. The gimbal mechanisms help to avoid wasting the propellant used for attitude control. The temperature of the SAM’s solar cells will reach its highest near Venus and drop to its lowest (-175 °C) near Saturn. During operations near Venus, it is required to tilt the membrane at least 45° away from the direction of the Sun to avoid high temperatures above 120 °C on the SAM. Table 1: Requirements of SAM for OPENS-0 Item Value Power Generation 50 W (at 9 au, 25 °C, and BOL) Area 9 ㎡ Size 350 x   288 x 225 mm3 (Stowed) 4567 x 3985 x 225 mm3 (Deployed) Mass (without gimbals) 24 kg Mass of gimbals 1.95 kg × 2 Solar Array Output Voltage 23.5 to 49 V  (at -150 to +120 °C, 0.7 to 9 au) Matsushita 3 38th Annual Small Satellite Conference Figure 3 shows the housing design of the SAM prototype. The housing is divided into a membrane storage section and a boom extension mechanism section that drives the membrane deployment. It includes two launch locks and a single-axis gimbal. Figure 4 shows the appearance of the stowed SAM prototype. The prototype does not include launch locks, and the gimbal mechanism is replaced with a step motor. The dimensions are 350 mm x 288 mm x 225 mm. In this prototype, the side panels are fixed with electrical release tape (ERT). Applying voltage to the ERT reduces its adhesive strength, causing the ERT to break. This triggers the deployment of the side panels, releasing the membrane. The membrane is then extended by boom extension. However, since ERT occasionally failed to operate normally in a vacuum, the actual deployment is planned to use a Frangibolt® actuator or similar to hold and release the side panels. Figure 5 shows the appearance of the deployed 9 m² SAM prototype. The membrane is constructed from CFRP triaxial woven fabrics connected with tape. Dummy thin-film solar cell sheets (PET) are mounted on the membrane, with only two sheets being actual thin-film solar cell sheets. The tips of the two CFRP bistable booms (Figure 6) and the corners of the membrane are connected with Kevlar thread, expanding the membrane by boom deployment. Figure 7 illustrates the boom extension mechanism. A motor with a worm gear rotates sprockets, extending the two perforated booms synchronously. The thin-film solar cell sheet is the film-type Space Solar Sheet (SSS) with 31 % efficiency at BOL (Figure 8). Considering handling and the dimensions of the stowed state, each sheet contains six solar cells. Grommets are used to attach the SSS to the membrane. Flexible printed circuits (FPC) are used for wiring to the thin-film solar cell sheets.     Figure 3: Deployable housing Design     Figure 4: Solar Array Membrane Prototype (Stowed) Matsushita 4 38th Annual Small Satellite Conference  Figure 5: Solar Array Membrane Prototype (Deployed)   Figure 6: Bistable boom   Figure 7: Boom Extension Mechanism   Figure 8: Space Solar Sheet (Film Type).  This prototype was specially designed with a thinner base film. Deployment testing Figures 9 and 10 show the deployment tests conducted on the ground. By applying voltage to the ERT for approximately one minute, both the front panel and the side panel are deployed. Subsequently, the booms are Matsushita 5 38th Annual Small Satellite Conference extended to 4.6 meters, deploying the membrane. In the ground test, the deployment is carried out on a sloped floor to compensate for gravity. The intermediate shape of the membrane during this deployment shows a characteristic where the central part of the membrane deploys later. This characteristic has also been confirmed in numerical simulations that simulate zero-gravity conditions (Figure 11).  Figure 9: Front and Side Panel Deployment testing  Figure 10: Membrane Deployment with Boom Extension testing  Figure 11: Simulation of Membrane Deformation during Deployment Vibration testing A vibration test was conducted on this prototype to evaluate whether cracks would form in the actual solar cells (Figure 12). The vibration levels were based on those experienced by the onboard component of a 100 kg-class satellite launched by the Epsilon rocket. Electroluminescence testing before and after the vibration test indicated that no additional cracks formed, suggesting that the solar cells could withstand the launch vibrations (Figure 13).  Figure 12: Vibration testing  Figure 13: Electroluminescence testing before and after vibration testing CONCLUSION ISAS is currently developing the SAM, a key technology for the small Saturn probe OPENS-0. The SAM prototype underwent deployment and vibration tests to assess its feasibility. Further development will continue to enhance the technology readiness level. References  1. Funase, R., et al. “JAXA's Solar System Exploration Program with Small Satellites: From PROCYON and EQUULEUS to Outer Solar System Exploration,”  38th Annual Small Satellite Conference, Utah, USA, August 7, 2024. 2. Tsuda, Y., et al. “Achievement of IKAROS—Japanese deep space solar sail demonstration Matsushita 6 38th Annual Small Satellite Conference mission,” Acta Astronautica Vol.82, No. 2, pp. 183-188, 2013. 3. Mori, O., et al. “Solar power sail mission of OKEANOS,” Astrodynamics, vol. 4, pp. 233-248, 2020. 4. Kusumoto, T., et al. “Development of a Multifunctional Lightweight Membrane with a High Specific Power Generation Capacity,” 35th Small Satellite Conference, SSC21-WKIV-01, Utah, USA, 2021. 5. Nakagawa, Y., et al., “Development of Multifunctional Lightweight Membrane Structure for Antennas and Power Generation on Small Satellites,” 38th Annual Small Satellite Conference, SSC24-WVIII-02 , Utah, USA, 2024. 

Solar Array Membrane Prototype for the OPENS-0 Small Saturn Probe

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Solar Array Membrane Prototype for the OPENS-0 Small Saturn Probe

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