Hodoyoshi-1 (Remote Sensing Microsatellite)
In 2010, the University of Tokyo started the research and development initiative "New Paradigm Space Development and Utilization Opened by Micro- Nanosatellites - introducing the 'Reasonably Reliable Systems' (Hodoyoshi in Japanese) concept." Funding is provided by JSPS (Japan Society for the Promotion of Science) in the FIRST (Funding Program for World-Leading Innovative R&D on Science and Technology) program , initiated by CSTP (Council for Science and Technology Policy) of Cabinet Office, Government of Japan. 1)
The project aims to accelerate the technology development and practical utilization of micro/nano-satellites. Micro/nano-satellites are expected to reduce the cost of satellite development by an order(s) of magnitude which may in turn open new ways of satellite utilization by the introduction of satellite constellations. The following research goals are to be pursued in the project period of 2010-2015 through collaboration of several leading universities and small industries in Japan.
1) Conceptualization and demonstration of novel reliability concept "Reasonable Reliable Systems ("Hodoyoshi" in Japanese)" suitable for micro/nano-satellites.
2) Research and development of all the required components for micro/nanosatellites with advanced concept and technologies, aiming for the world top level "performance per size".
3) Innovation of satellite development process including standardization of interfaces and software, ways of ground test, etc, to further reduce the development cost and period.
4) Construction of all-Japan consortium for R&D, supply chain network, creation of international user communities, and capacity building.
As part of the Hodoyoshi project, four micro/nanosatellites are under development and Hodoyoshi-1, the first one, has been designed and developed by AxelSpace Corporation of Kashiwa City, Japan. 2) 3) 4) 5) 6)
The four satellites to be developed by Japanese institutions are:
• Hodoyoshi-1 :The University of Tokyo and NESTRA (Next Generation Space System Technology Association)
• ChubuSat-1 : Nagoya University and Daido University
• Tsubame : Tokyo Institute of Technology, Tokyo University of Science and JAXA
• QSAT-EOS : Kyushu University.
Figure 1: Photo of the HodoYoshi-1 microsatellite (image credit: Axelspace)
Hodoyoshi-1 is a microsatellite with the aim to provide fairly high-resolution imagery of Earth's surface. The spacecraft cubic structure has a size of 60 cm on a side, the mass of the spacecraft is ~60 kg and the average power is ~50 W. The satellite is equipped with an onboard computer (FPGA), a reaction wheel, a star sensor, a MEMS gyro, a GPS receiver, thrusters, and an optical sensor. The satellite is capable of accurate 3-axis attitude control and orbital control using hydrogen peroxide water thrusters.
Figure 2: Illustration of the Hodoyoshi-1 microsatellite (image credit: University of Tokyo)
RF communications: Payload data communications in X-band at data rates of 10-20 Mbit/s.
JAXA developed a novel communications system for 320 Mbit/s downlink with 16 QAM for small satellites in the 50 kg class. 12)
Figure 3: Young engineers with their Hodoyoshi-1 microsatellite (image credit: Axelspace)
Launch: The Hodoyoshi-1 microsatellite was launched as a secondary payload on November 6, 2014 (07:35:49 UTC) on a Dnepr-1 vehicle from the Yasny Cosmodrome, Russia. The primary payload on this flight was the ASNARO minisatellite of USEF, Japan.
Orbit: Sun-synchronous orbit, altitude of 504 km, inclination = 97.4º, LTDN (Local Time on Descending Node) = 11:00 hours.
The secondary payloads on this mission were:
• ChubuSat-1, a microsatellite (50 kg) of Nagoya University and Daido University, Japan.
• Hodoyoshi-1, a microsatellite (60 kg) of the University of Tokyo and NESTRA (Next Generation Space System Technology Association)
• QSat-EOS, a microsatellite (49 kg) Kyushu University (KU), Fukuoka, Japan.
• Tsubame, a microsatellite (49 kg) of Tokyo Institute of Technology, Tokyo University of Science and JAXA.
• August 2018: Hodoyoshi-1 is a Japanese small satellite that was launched on November 6, 2014 and it has successfully observed the Earth's surface with a 6.7 m ground sampling distance (GSD) for almost three years. Hodoyoshi-1 has pushbroom multi-band sensors that cover blue, green, red and near-infrared bands (band B, G, R, and IR). From the successful operation, Axelspace Corporation has released Hodoyoshi-1's images on their website as "image of the week". 14) Because of weight and cost limitations, the Hodoyoshi-1 is not equipped with any onboard calibration instruments. 15)
- Well calibrated satellite images are not just images, but scientific data that can be used for many applications such as evaluating the land surface environment, monitoring land use changes, predicting crop growth, assessing hazard damage. However, due to the harsh environment in space, an optical sensor inevitably experiences temporal variation of its sensitivity, which may cause incorrect brightness changes in data if we do not correct the variation. Therefore, radiometric calibration in space is essential to maintain the reliability of observed brightness, which is required to provide accurate measurement.
- Considering the increasing number of small satellites, a standardized calibration method is required for comparing data obtained by different satellites that have equal radiometric accuracy. On the other hand, physical constraints on the acceptable payload and limitations of their operation and cost restrict the functionality of these small satellites. Due to these constraints and limitations, there are few satellites that have instruments for onboard calibration. A reliable and low-cost calibration method would be useful for any small satellite mission.
- "Lunar calibration" is a reasonable candidate for conducting radiometric calibration for a small satellite, in which we utilize the Moon as a calibration target in space. First, because the photometric properties of the Moon have been investigated well and its brightness models have been established based on several Moon exploration missions and projects, we can consider the Moon as a well-known brightness target. Secondly, because the lunar calibration can be done simply by observing the Moon with the optical sensor to be calibrated, it does not require any special onboard instrument or special activity on the ground.
- Hodoyoshi-1, which is operated by Axelspace Corporation, observed the Moon with its visible and near-infrared multi-band sensors for the first time on August 16, 2016, and since then, it has observed the Moon almost every month for about one year.
- Figure 4 shows examples of raw Moon images from the first two observations taken in band G. It should be noted that because coefficients to convert the digital count to a value with a physical unit, such as radiance (W m-2 sr-1 µm-1), have not been published yet for Hodoyoshi-1's images, we used the digital count as an indicator that is linearly related to the target brightness.
Figure 4: Examples of raw Moon images obtained in band G (520-600 nm) on (a) August 16, 2016 and (b) August 19, 2016. Measured over sampling factors were approximately 1.3 for both (a) and (b), image credit: Hodoyoshi Study Team
- Since the scan rate for a Moon observation is different from that of Hodoyoshi-1's regular operation (i.e. observing the Earth's surface), the Moon shape in an image tends to be an ellipse as shown in Figure 4. In the Hodoyoshi-1 case, the length of the Moon in the scan direction (vertical direction in the image frame) is longer than the cross-track direction (horizontal). In this case, a region of the Moon surface oversampled by a factor based on the scan speed and the length of one-pixel field of view. This factor is called the over sampling factor.
- Figure 5 shows eight observations of the Moon conducted by Hodoyoshi-1 whose oversampling effects were corrected. Before correction of the oversampling effect, we subtracted the offset value of the image of the Moon, which was obtained from deep space where brightness should be 0, from the Moon brightness value at each pixel.
- Note that we found that the over sampling factor varied from 1.3 to 1.6 in the Hodoyoshi-1 observations. In addition, we found that the over sampling rate was slightly different at different lines during one observation, resulting in a distorted circular shape of the Moon after correcting the over sampling effect with a constant over sampling factor (for example, the length of the southern hemisphere is slightly shorter than that of the northern hemisphere in the scan direction).
- In summary, Hodoyoshi-1 has conducted Moon observations for radiometric calibration of its sensors since August 2016. The target phase angle was around 10° to have a stable lunar brightness among observations. The sensor sensitivity variations of band G and R were investigated with eight Moon observations by comparing the observed brightness and simulated Moon brightness based on the SP (Spectral Profiler -onboard SELENE) model. In both bands, G and R, the sensor sensitivity degradations whose magnitudes were even less than 1 %, were successfully identified. In other words, by utilizing a lunar calibration method, we may detect a sensor sensitivity variation with an accuracy of more than 1 %. Since Hodoyoshi-1 will continue lunar observations, more detailed sensor sensitivity variation will be investigated. — Lunar calibration can be applied without any special instruments other than optical sensors if thermal balance and attitude control of the satellite allows it to observe the Moon. Therefore, the lunar calibration can be a candidate for a common radiometric calibration method for a huge number of small satellites, which usually have strict weight and cost restrictions.
• January 2018: Hong Kong has developed through free economy: high competition among domestic and foreign companies makes it one of the world's best business cities. The city is vibrant, day and night. 16)
Figure 6: Hodoyoshi-1 image of Hong Kong, China, caputred on 11 January 2018 at 03.46 UTC (image credit: Axelspace Corporation CC BY-SA 4.0)
• In January 2015, AxelSpace opened the Hodoyoshi-1 image gallery. The gallery shows a collection of photos taken during the initial operation phase of Hodoyoshi-1. 18)
- Hodoyoshi-1 is being regularly operated. Currently, the project is tuning a few final parameters that will make it possible to receive image requests from the end-users.
Legend to Figure 8: Dammam is the capital of the Eastern Province of Saudi Arabia with a population of >1 million (metropolitan area population is more than 4 million).
Sensor complement: (Camera)
The satellite will observe the Earth using an optical pushbroom imager (line scanner) with a GSD (Ground Sample Distance) of 6.7 m on a swath width of ~28 km. The camera was developed by Genesia Corporation, Tokyo, Japan. The design employs a refractive telescope and lenses providing a wide field of view.
Figure 10: Photo of the pushbroom imager (image credit: Axelspace)
Table 1: Specification of the camera system
The medium-resolution imagery is expected to be used in a wide range of applications including agriculture, forestry, fishery, map-making, GIS (geographic information system) and disaster monitoring.
1) Shinichi Nakasuka,"The University of Tokyo FIRST Program," Sept. 30, 2011, URL:
2) Shinichi Nakasuka, Rei Kawashima, "Micro/Nano-satellite Activities by Japanese Universities and Vision towards International Contribution," Proceedings of UN COPUOS (Committee on the Peaceful Uses of Outer Space), UNOOSA, Vienna, Austria, June 6-15, 2012, URL:
3) Tokyo University, May 16, 2012, URL: http://www.t.u-tokyo.ac.jp/etpage/release/2012/2012051601.html
4) Hiroyuki Koizumi, Junichi Aoyama, Koji Yamaguchi, "Engineering Model Development of a Miniature Ion Propulsion System," Proceedings of the UN/Japan Workshop and The 4th Nanosatellite Symposium (NSS), Nagoya, Japan, Oct. 10-13, 2012, paper: NSS-04-0125
5) Shinichi Nakasuka, "Opening Remarks at the 4th Nano-satellite Symposium," Proceedings of the UN/Japan Workshop and The 4th Nanosatellite Symposium (NSS), Nagoya, Japan, Oct. 10-13, 2012, URL: http://www.nanosat.jp/4th/pdf/Day1-1_OpeningSession1_Nakasuka/Opeining_Prof.Nakasuka.pdf
6) Hironori Sahara, "Systems Engineering for Microsatellite," 6th International Workshop on Remote Sensing and Environmental Innovations in Mongolia, June 10-11, 2013, URL:
9) "Micro-Satellite for Earth Remote Sensing, Hodoyoshi-1, Axelspace, Jan. , 2014, URL: http://www.axelspace.com/wp-content/docs/Hodoyoshi-1_Flyer_EN.pdf
10) Shinichi Nakasuka, "Current Status and Future Vision of Hodoyoshi Microsatellites – Systems for Quick and Affordable Space Utilizations," 2013, URL: http://www.nanosat.jp/images/report/pdf/nanosat_201311.pdf
11) Seiji Yoshimoto, et al., "Environment Monitoring of Fukushima and Chernobyl Areas using a Constellation of Earth Observation Microsatellites," Nov. 20, 2013, URL: http://www.nanosat.jp/images/report/pdf/NSS-05-0104.pdf
12) Hirobumi Saito, Naohiko Iwakiri , Atsushi Tomiki, Takahide Mizuno, Hiromi Watanabe, Tomoya Fukami, Osamu Shigeta, Hitoshi Nunomura, Yasuaki Kanda , Kaname Kojima, Takahiro Shinke, Toshiki Kumazawa, "High-Speed Downlink Communications with Hundreds Mbps from 50kg Class Small Satellites," Proceedings of the 63rd IAC (International Astronautical Congress), Naples, Italy, Oct. 1-5, 2012, paper: IAC-12-B2.3.1
15) Toru Kouyama, Ryosuke Nakamura, Soushi Kato, Naoki Miyashita, "One-year lunar calibration result of Hodoyoshi-1, Moon as an ideal target for small satellite radiometric calibration," Proceedings of the 32nd Annual AIAA/USU Conference on Small Satellites, Logan UT, USA, Aug. 4-9, 2018, paper: SSC18-III-04, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=4080&context=smallsat
16) "Hong Kong, China," Axelglobe, January 2018, URL: https://www.axelglobe.com/en/axelspace-images/hong-kong-china/
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).