Rising-2 is a cooperative microsatellite project of Tohoku University (Sendai) and Hokkaido University, Sapporo, Japan. The primary objective of the mission is Earth observation with a resolution of ~ 5 m. In particular, high-resolution cumulonimbus scenes will be observed using the LCTF (Liquid Tunable Multispectral Filter) technique. The secondary objective is the observation of sprite phenomena in the upper atmosphere. Sprites are so-called TLEs (Transient Luminous Events), which are rather frequent natural phenomena induced by lightning discharges. 1) 2) 3) 4) 5) 6) 7)
The Rising-2 project started in July 2009 and inherited the experiences gained in the design and development of the SpriteSat (Rising-1) spacecraft which was launched on January 23, 2009. The Rising-2 microsatellite is expected to be completed in the summer of 2013.
Figure 1: Two views of the Rising-2 microsatellite (image credit: Rising-2 partners)
The spacecraft structure is cubical with a side length of 50 cm and a launch mass of ~42 kg. The central pillar configuration is inherited from SpriteSat, using an aluminum alloy material for the central pillar and the side panels. The spacecraft is 3-axis stabilized.
ADCS (Attitude Determination and Control Subsystem): The ADCS uses star and sun sensors, gyros and magnetometers for attitude sensing (Honeywell HMC2003). Actuation is provided by a reaction wheel assembly and 3 magnetorquers (MTQs). The observation requirements call for a spacecraft pointing accuracy of < 0.1o and an angular velocity accuracy of 0.02o/s. 8) 9) 10) 11) 12)
The ADCS offers two observation modes:
· Fine pointing control mode: This is the observation mode which is used for ~ 15 minutes in the sunlit phase of the orbit and for about 15 minutes in the ecliptic phase of the orbit (use of star sensor and reaction wheels).
· Coarse control mode: In this mode, the ADCS sensors idle - the power is turned off for most of the ADCS elements to save energy for the active orbit phases. Six solar cells are being used as SAS (Coarse Sun Sensors), their output is sent to the SCU where the coarse attitude control is taking place.
Figure 2 shows the block diagram of the ADCS. The coarse attitude control system consists of the SCU (Satellite Central Unit), the GAS (Geomagnetic Aspect Sensor) and the 3-axis MTQ (Magnetic Torquers). In this system, the geomagnetic field is measured using the GAS, and the body angular velocity damps using the MTQs.
The fine attitude control system consists of ACU (Attitude Control Unit, 3-axis RW (Reaction Wheel), 3-axis Gyro (Gyroscope), 2 star sensors (HSS), and 4 sun sensors SASH (Sun Angle Sensor - High precision). In this system, the body angular velocity is measured using Gyro. The quaternion is detected using the HSS. The ACU calculates the control torque and sends the command to the RW. The ACU acquires the current time from the SCU, and sends the internal data as status data and telemetry to the SCU. The commands sent from the ground station via SCU are processed using the ACU for the changing of the target direction or the attitude control parameter.
Figure 2: Block diagram of the ADCS (image credit: Rising-2 partners)
EPS (Electrical Power Subsystem): EPS uses surface-mounted GaAs solar cells for power generation (efficiency of 24%). Four solar panels are mounted on the circumference of the spacecraft (each 8 series x 4 parallels), and one solar panel is mounted on the top side (8 series x 2 parallels). An average power of 42 W is provided. The 9-cell NiMH battery has a capacity of 3.7 Ah (10.8 V). During observations, the spacecraft requires 28.4 W of power while only 7.8 W are needed during non-observation periods. 13)
From the lessons learned of SpriteSat, the EPS has been newly designed and tested. The new design uses an idea of peak power tracking with careful understanding of the characteristics of the solar cells and NiMH batteries.
C&DH (Command and Data Handling) subsystem: The 4 controller units in the bus system are the SCU (Satellite Central Unit, ACU (Attitude Control Unit), SHU (Science Handling Unit), and the PCU (Power Control Unit). The SCU is the main unit of the C&DH subsystem. The ACU, SHU, and the PCU are connected to SCU like spokes. Each unit features an FPGA (Field Programmable Gate Array) and CPU (Figure 3). The SCU has two FPGAs (antifuse and flash) and a CPU. The peripheral units are a magnetometer (GAS), sun sensors (SAS), a GPS receiver (GPS-R), a MEMS attitude measurement unit (TAMU), a U-band receiver (URX), and a S-band transmitter (STX). The antifuse FPGA in SCU has the only reboot function of flash FPGA.
The ACU has a flash FPGA and a CPU. The peripheral units are star CCD sensors (HSS-1,2), a gyro sensor (GYRO), high-precision sun sensors (SASH-1,2,3,4) and a reaction wheel unit (RW). The image taken by HSS is processed in the embedded CPU included in the FPGA of the ACU, and the attitude can be determined. The attitude sensors except HSS are connected by a CAN bus interface. 14)
Figure 3: Block diagram of the C&DH subsystem (image credit: Rising-2 partners)
The SHU has a flash FPGA and a CPU. The peripheral units are the telescope CCD sensors (HPC-R,G,B,M) and the sprite CMOS sensors (LSI-W,N), a fish-eye CCD sensor (WFC), a bolometer array sensor (BOL), and a VLF receiver (VLF-R).
The PCU has an antifuse FPGA without a CPU. The functions are battery charge / discharge control, and peak power tracking (PPT) control for power generation of the solar cells. The control parameters can be modified by uplink commands.
All control units feature A/D (Analog-to-Digital) converters, and the house-keeping (HK) data such as voltage, current, and temperature, are measured in each unit. The status data are sent to the SCU.
Table 1: Summary of FPGA and CPU on Rising-2
RF communications: The S-band is used for downlink data transmissions at 38.4 kbit/s (max). The uplink data rate is 1.2 kbit/s in UHF. The Sendai station, located on the campus of the Tohoku University, is being used for the uplink and downlink services. Further downlink stations are located in Kiruna, Sweden and in Thailand.
Figure 4: Schematic views (CAD models) of the internal configuration of Rising-2 (image credit: Rising-2 partners)
Figure 5: Internal view of the central pillar structure (image credit: Rising-2 partners)
Figure 6: Overview of the spacecraft subsystems and their relations among themselves (image credit: Rising-2 partners)
Figure 7: The sensor complement instruments and their connection to the SHU (image credit: Rising-2 partners)
Table 2: Summary of spacecraft parameters
Launch: A launch of the Rising-2 microsatellite as a secondary payload is planned for 2014 (launch arrangements are in process).
Orbit: Sun-synchronous orbit, altitude of 628 km.
Sensor complement: (HPT, LSI-1, LSI-2, WFC, VLF antenna & receiver, BOL)
The sensor complement consists of five scientific instruments and some subsystems: two CMOS cameras with different color interference filters, a CCD camera with fish-eye lens, and a VLF radio wave receiver.
The relationship diagram of sensor complement is shown in Figure 9. Five lenses and a mirror are exposed to the outside of the spacecraft. The newly developed items are HPT and BOL. The other instruments have been already developed in SpriteSat and other previous projects.
HPT (High Precision Telescope):
The HPT is being used to collect the incoming radiation for a particular observational target region. In the case of the sunlit orbit phase, the HPT is generally pointed in the nadir direction to collect high-resolution surface imagery. During the eclipse phase of the orbit, the HPT will be pointed toward targets of opportunity. The main objective is to observe TLEs (Transient Luminous Events).
Figure 8: Illustration of the HPT device (image credit: Rising-2 partners)
The HPT instrument specifications are:
- Cassegrain reflective telescope with an aperture of 100 mm and a focal length of ~ 1 m (f/10).
- Four CCD detector arrays are employed in the spectral ranges of 400-650 nm (RGB observations) and of 650-1000 nm. The electronic LCTF (Liquid Crystal Tunable Filter) detection technique is being used for the 650-1000 nm spectral range. This LCTF detection concept, which is polarization sensitive, makes it possible to measure the optical properties of solar radiation reflected from land and sea surfaces. The LCTF can be tuned to any desired wavelength by a computer command within its spectral range.
- CCD resolution: 5 m/pixel. The IFOV generates an image size of 3.3 km x 2.5 km from an orbit of 700 km.
- Spatial resolution: 5-50 m in LCTF mode with a 10 nm band width.
- Exposure time: minimum of 1/4000 second in RGB mode
- The 4 CCD detectors of HPC-R, -G, -B, and -M (Multispectral) were already developed in the SpriteSat project. The detectors have a high sensitivity corresponding to ISO 8000. In addition, they feature an electronic shutter with an exposure time of 1/4000 second.
Figure 9: Overview of the sensor complement (image credit: Rising-2 partners)
The primary and secondary mirrors of HPT feature ZPF (Zero-expansion Pore-Free) ceramics of Nihon providing low-mass and high-strength characteristics. A new grinding technology is being used in the polishing of the mirror surfaces.
The LCTF device is modified for use on a spaceborne imager. The device is comprised of liquid crystal multi-layer plates. The wavelength is variable with narrow 5 nm bands. The central wavelength can be tuned in the range of > 300 nm with 10 ms.
Figure 10: Observation scenario of SpriteSat/Rising-2 (image credit: Tohoku University)
LSI-1 (Lightning Spectrum Imager-1):
The objective is to detect lighting flashes. The camera features a CMOS detector with a format of 512 x 512 pixels. Observations are being made in the spectral band of 744-826 nm. LSI-1 and LSI-2 have a square FOV of 29o corresponding to a ground surface side length of 342 km (Figure 10).
LSI-2 (Lightning Spectrum Imager-2):
The objective is to detect sprites. The camera features a CMOS detector with a format of 512 x 512 pixels.. Observations are made in the spectral band at 762 nm.
Figure 11: Instrument photos of the LSI-1, -2 (left) and WFC (right), image credit: Tohoku University)
WFC (Wide Field-of-view Camera):
The camera is being used to determine the location of lightning flash which is relating to the TGF (Terrestrial Gamma-ray Flashes) event. This high sensitivity panchromatic CCD camera with a fish-eye lens covers a FOV of 140o.
VLFR (Very Low Frequency Receiver):
The objective of (VLF-ANT, VLFR) is to detect TLEs (Transient Luminous Events).
BOL (Bolometer array camera):
The BOL detector array offers observations in the spectral region of 8-14 m, corresponding to the MWIR (Midwave Infrared) and the TIR (Thermal Infrared) regions. At the 700 km altitude, the spatial resolution is ~ 1 km, which corresponds to 0.076o/pixel. Temperature distribution imagery of such targets as: a cumulonimbus region, a ground surface scene, and a region of the sea surface can be generated.
The following three phenomena can be recognized:
- From the temperature of the top of cumulonimbus, the altitude can be estimated. With the simultaneous observations by LSI and WFC, the relationship of transient luminous events and cumulonimbus is analyzed.
- Observing the temperature distribution of the ground surface, buildings, and the sea, the generation of cumulonimbus can be monitored, which is a resource for determining heavy rain.
- Natural disasters such as wildfires and volcano eruptions will be observed; the objective is to check the applicability of this observation method for rapid detection results.
The commercial bolometer camera is being slightly modified for space observations. The instrument has a power consumption of 8.4 W and a mass of 0.554 kg. During a BOL observation mode, the satellite is rotated in such a way as to avoid solar radiation entering the BOL optics. In the rotation period of the satellite, the power of BOL is turned on, and deep space imagery is taken for calibration purposes. After the attitude has been stabilized and the instruments are pointing into target region on Earth's surface, observations may be started.
Figure 12: Photo of the MWIR/TIR bolometer array (image credit: Tohoku University)
Figure 13: Photo of the commercial BOL camera (image credit: Tohoku University)
The observation modes of the spacecraft are being conducted in 15 minute periods, where one period is in the sunlit phase of the orbit and the second observation period is in the eclipse phase of the orbit. One of the following 7 modes is being selected and completed in < 15 minutes. In the EPS, the sensor power is defined as 3 W on average. This requires some adjustment of the time for Mode-1 and Mode-5 to avoid a battery degradation.
1) Mode-1: Sprite observation mode (LSI-1,-2, and VLFR), 3.8 W, only in the eclipse phase
2) Mode-2: Lightning observation mode (WFC, and VLFR), 2.8 W, only in the eclipse phase
3) Mode 3: LSI mode (LSI-2), 1.0 W, for cumulonimbus, ground, and sea, generally in the sunlit phase
4) Mode 4: WFC mode (WFC), 1.0 W, for aurora, ground, and sea
5) Mode 5: BOL mode (BOL), 7.8 W, for cumulonimbus, ground, and sea
6) Mode-6: RGB telescope mode (HPC-R, -G, -B), 3.0 W, for cumulonimbus, ground, moon, and planets
7) Multispectral telescope mode (HPC-M, LCTF), 2.0 W, for cumulonimbus, ground, moon, and planets.
The Tohoku University ground station will be used as the primary station for spacecraft operations. In addition, the ground stations in Kiruna (Sweden) and in Thailand will be used as receiving stations only. The three stations will provide a daily contact time with the spacecraft for ~ 165 minutes.
Figure 14: Overview of the ground station network for Rising-2 operations support (image credit: Tohoku University)
1) Yuji Sakamoto, Yukihiro Takahashi, Kazuya Yoshida, Kazufumi Fukuda, Toshihiko Nakano, Steve Battazzo, Tetsuya Fukuhara, Junichi Kurihara, "Development of the microsatellite RISING-2 by Tohoku University and Hokkaido University," Proceedings of the 61st IAC (International Astronautical Congress), Prague, Czech Republic, Sept. 27-Oct. 1, 2010, IAC-10-B4.2.12
2) Kazuya Yoshida, Yuji Sakamoto, Toshinori Kuwahara, Yukihiro Takahashi, "A Series of 50 kg-Class Micro-Satellites for Advanced Science Missions," 8th IAA (International Academy of Astronautics) Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 4-8, 2011
3) Toshinori Kuwahara, Yuji Sakamoto, Kazuya Yoshida, YukihiroTakahashi, Tetsuya Fukuhara, Junichi Kurihara, "Mission and System of the Earth Observation Microsatellite RISING?2," 8th IAA (International Academy of Astronautics) Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 4-8, 2011, URL: http://media.dlr.de:8080/erez4/erez?cmd=get&src=os/IAA/archiv8/Presentations/IAA-B8-1404.pdf
4) Yuji Sakamoto, Yukihiro Takahashi, Kazuya Yoshida, "Development of the microsatellite RISING-2 by Tohoku University and Hokkaido University," Japan Geoscience Union Meeting 2010, Makuhari, Chiba, Japan, May 23-28, 2010
6) Yuji Sakamoto, Toshinori Kuwahara, Yukihiro Takahashi, Kazuya Yoshida, "Progress Report of the Development of microsatellite RISING-2 for cumulonimbus and sprite observation by multi-spectrum," Japan GeoScience Union Meeting 2012, Makuhari, Chiba, Japan, May 20-25, 2012, URL: http://www2.jpgu.org/meeting/2012/html5/PDF/M-SD05/MSD05-11_e.pdf
7) Yoshihiro Tomioka, Yuji Sakamoto, Toshinori Kuwahara, Kazufumi Fukuda, Nobuo Sugimura, Kazuya Yoshida, "Lessons Learned on Structural Design of 50kg Micro-satellites based on Three Real-life Micro-satellite Projects," Proceedings of the UN/Japan Workshop and The 4th Nanosatellite Symposium (NSS), Nagoya, Japan, Oct. 10-13, 2012, paper: NSS-04-0411
8) Kazufumi Fukuda, Toshihiko Nakano, Yuji Sakamoto, Toshinori Kuwahara, Kazuya Yoshida, Yukihiro Takahashi, "Attitude control system of micro satellite RISING-2," 8th IAA (International Academy of Astronautics) Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 4-8, 2011
9) Toshinori Kuwahara, Steve Battazzo, Yoshihiro Tomioka, Yuji Sakamoto, Kazuya Yoshida, "System Integration of a Star Sensor for the Small Earth Observation Satellite RISING-2," Proceedings of the 28th ISTS (International Symposium on Space Technology and Science), Okinawa, Japan, June 5-12, 2011, paper: 2011-d-11
10) Yuji Sakamoto, Toshinori Kuwahara, Kazufumi Fukuda, Kazuya Yoshida, Tetsuya Fukuhara, Junichi Kurihara, Yukihiro Takahashi, "Development Status and Operation Plan of 50-kg Microsatellite RISING-2 for Earth Observations by Multi-Spectrum Instruments," Proceedings of the 28th ISTS (International Symposium on Space Technology and Science), Okinawa, Japan, June 5-12, 2011, paper: 2011-f-25
11) Yoshihiro Tomioka, Toshinori Kuwahara, Yuji Sakamoto, Hironori Fukuchi, Yuta Tanabe, Kazuya Yoshida, "Micro-satellite structure system for cost-effective and rapid development," Proceedings of the 3rd Nanosatellite Symposium, Kitakyushu, Japan, December 12-14, 2011, paper: NSS-03-0411
12) Nobuo Sugimura, Kazufumi Fukuda, Masato Fukuyama, Yoshihiro Tomioka, Toshinori Kuwahara, Yuji Sakamoto, Kazuya Yoshida, Yukihiro Takahashi, "Attitude Control for Earth Observation Microsatellite RISING-2," Proceedings of the 9th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 8-12, 2013, paper: IAA-B9-0603
13) Yuji Sakamoto, Toshinori Kuwahara, Yoshihiro Tomioka, Kazufumi Fukuda, Kazuya Yoshida, "Evaluation of Power Control System for Micro and Nano Satellites by Hardware-in-the-Loop Simulator," Proceedings of the 26th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 13-16, 2012, paper: SSC12-X-8
14) Yuji Sakamoto, Toshinori Kuwahara, Steve Battazzo, Kazufumi Fukuda, Yoshihiro Tomioka, Kazuya Yoshida, "Development Method of Command and Data Handling System for Micro and Nano Satellites," Proceedings of the 3rd Nanosatellite Symposium, Kitakyushu, Japan, December 12-14, 2011, paper: NSS-03-0412
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.