We describe scientific objective and project status of an astronomical 6U CubeSat mission VERTECS (Visible Extragalactic background RadiaTion Exploration by CubeSat). The scientific goal of VERTECS is to reveal the star-formation history along the evolution of the universe by measuring the extragalactic background light (EBL) in the visible wavelength. Earlier observations have shown that the near-infrared EBL is several times brighter than integrated light of individual galaxies. As candidates for the excess light, first-generation stars in the early universe or low-redshift intra-halo light have been proposed. Since these objects are expected to show different emission spectra in visible wavelengths, multi-color visible observations are crucial to reveal the origin of the excess light. Since detection sensitivity of the EBL depends on the product of the telescope aperture and the field of view, it is possible to observe it with a small but wide-field telescope system that can be mounted on the limited volume of CubeSat. In VERTECS mission, we develop a 6U CubeSat equipped with a 3U-sized telescope optimized for observation of the visible EBL. The bus system composed of onboard computer, electric power system, communication subsystem, and structure is based on heritage of series of CubeSats developed at Kyushu Institute of Technology in combination with high-precision attitude control subsystem and deployable solar array paddle required for the mission. The VERTECS mission was selected for JAXA-Small Satellite Rush Program (JAXA-SMASH Program), a new program that encourages universities, private companies and JAXA to collaborate to realize small satellite missions utilizing commercial small launch opportunities, and to diversify transportation services in Japan. We started the satellite development in December 2022 and plan to launch the satellite in FY2025.
The extragalactic background light (EBL) is the integrated emission from out of our Galaxy.Its observation is crucial for revealing the history of star-formation from the early universe to the present epoch. Visible Extragalactic background RadiaTion Exploration by CubeSat (VERTECS) is a 6U astronomical satellite to observe the EBL in visible wavelength from 0.4 µm to 0.8 µm. To observe the EBL, a telescope with 11 lenses and a high-performance CMOS sensor are equipped within 3U volume. The remaining 3U comprises the bus section mainly based on the bus design previously developed at Kyushu Institute of Technology. This paper describes the design and verification processes of the structure and thermal model of the satellite to fulfill the interface and mission requirements. From a mission perspective, the precise attitude and orbit control system unit is mounted on the same interface plate as the telescope to meet stringent pointing stability requirements during observations. The purpose of the stiff design of this interface plate is to minimize structural deformation. Furthermore, integrating multiple external antennas with relatively large X-band and S-band communication units require effective routing harness management. Static stress analysis is performed under the quasistatic loading condition. In addition, modal analysis is also conducted to fulfill the strength and stiffness requirements of the launcher. A series of mechanical environmental tests (shock, random, and sinusoidal vibrations) have been conducted to verify the design and analysis results. The results showed that designed model can fundamentally withstand the launch environment.
The extragalactic background light (EBL) is the integrated emission from all objects outside of the Milky Way galaxy and is a crucial observational quantity in the broader study of the history of cosmic structures. In the nearinfrared EBL, there have been measurements of an emission component several times brighter than the cumulative light from extragalactic galaxies. This unknown radiation component has led to proposals for candidate source objects, such as first stars and galactic halo brown dwarfs. These source objects exhibit distinct radiation spectra in the visible wavelength. The VERTECS (Visible Extragalactic background RadiaTion Exploration by CubeSat) project is focused on continuously observing the visible EBL using a wide-field small telescope on a 6U CubeSat. The primary characteristic of this telescope is its high-throughput (SΩ > 10−6 m2sr). The 3U-sized optical telescope onboard this satellite consists of a lens optics with a total field of view of 6° × 6°, pixel field of view of 11” × 11”, a highly sensitive and low-noise detector module, and a baffle to eliminate stray light from the Sun and Earth. Additionally, color filters divide the wavelength range from 400 to 800 nm into four bands. Our observation strategy involves capturing 60-second exposure images while shifting the observed field by 3° increments and stacking the acquired images to perform photometry in the four bands. Thus far, most of the telescope design has met the required specifications, and the project is currently advancing towards the production of an engineering model. This project was selected in the JAXA-SMASH and is currently progressing in satellite development with a planned launch in the 2025 fiscal year. In this presentation, we will report on the strategy for observing the visible EBL, the progress in the development of the optical telescope, and the future plans.
This study focuses on optimizing the thermal performance of the Visible Extragalactic background RadiaTion Exploration by CubeSat (VERTECS), a 6U CubeSat with a 3U telescope for observing Extragalactic Background Light. Aside from dealing with satellite survivability in the space environment, the payload includes a CMOS sensor which requires operational temperatures of less than 0°C to minimize the noise due to temperature dependent dark current in observation data. The payload telescope lens optical system is designed to operate within a temperature range of -10°C to 35°C. The thermal analysis considers solar radiation, internal heat dissipation, and external factors in various orbital scenarios. The investigation identifies potential temperature fluctuations and proposes passive thermal control strategies, including enhanced coatings and radiators. By implementing tailored strategies, this research enhances the reliability and longevity of 6U CubeSat missions, advancing small satellite technology in space exploration and scientific research.
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