FITSat-1 (Fukuoka Institute of Technology CubeSat) / Niwaka
FITSat-1 (nickname: Niwaka) is a 1U CubeSat of the Fukuoka Institute of Technology (FIT), Fukuoka Prefecture, Japan. The overall objective is to demonstrate a high-speed transmission module for a small satellite and a visible light communication experiment using high power LEDs (Light-Emitting Diodes). 1) 2)
Figure 1: Photo of the FITSat-1 flight model (image credit: FIT)
FITSat-1 is a standard 1U CubeSat with a size of 10 cm x 10 cm x 10 cm and a mass of 1.33 kg. The structure is made from a square aluminum pipe. Both ends of the cut pipe are covered with aluminum plates. The surface of the body is finished with black anodic coating. The CubeSat slide rails and side panels are not separate; they are made as a single unit. The thickness of the square pipe is 3mm, but the surfaces attached by solar cells are thinned to 1.5 mm because of the weight limit. In order to make the 8.5 mm square CubeSat rails, 5.5 mm square aluminum sticks are attached to the four corners of the square pipe.
Figure 2: Illustration of the CubeSat body (image credit: FIT)
The solar cells are attached to the four sides of X and Y panel. The top (+Z panel) has a 5.8GHz patch antenna, green LEDs, and hole for the camera lens. The bottom (–Z panel) has the deployment switches, separation springs, 1.2 GHz patch antenna, red LEDs and a hole for the 430 MHz UHF-band antenna. Figure 3 shows the top panel and the bottom panel.
Figure 3: Top panel and bottom panel of FITSat-1 (image credit: FIT)
EPS (Electrical Power Subsystem): The EPS consists of solar cells, DC/DC converters, a single Li-ion (Lithium-ion) battery, three Li-ion batteries connected in series (Hitachi Maxell INR18650PB2, 1450 mAhr), battery controllers (SII S-8233BAFT, Linear Technology LTC4054-4.2), two deployment switches, and a flight pin switch. Each of these three switches controls electronic switches. Figure 4 shows the lithium ion battery pack. The single battery and three batteries in series are connected with the three electronic switches in series. So they never supply power until all three switches are turned on. Since the solar cells are also connected with two electronic switches and a physical switch in series, they never generate power until all three switches are turned on.
Figure 4: Photo of the battery assembly (image credit: FIT)
The single lithium ion battery supplies the power for communication and data handling system, except for the high speed communication system and the camera. The three batteries in series supply power for the experiments of the 5.8 GHz high speed transmission link and for the flashing LEDs.
Each side of the solar cells generates 2.3 W (4.74 V x 0.487 A) of electrical power. The generated power is extracted by the MPPT (Maximum Power Point Tracking) DC/DC converter and supplied to 5 V load, single Li-ion battery, and the three Li-ion batteries. The charging of the single Li-ion battery is controlled by a battery protection IC (Liner Technology LTC4054-4.2), and the three Li-ion batteries are controlled by a battery protection IC (SII: S-8233BAFT).
Normally, the EPS will operate at 5 V under 0.13 A. When the solar cells face to the sun, excess currents charge the single battery. When the single battery is charged enough, the three batteries are charged. When the FM transmitter (437.445 MHz, 0.8 W RF-output) operates for replying to remote commands, a discharge current (0.3-0.7 A) will be drawn for 10 minutes from the single battery.
CDHS (Communication and Data Handling Subsystem) : Figure 5 is a block diagram of the FITSat-1 CDHS. With the deployment switches turned on, the 430 MHz TX/RX controller, the main CPU (RX-CPU, TX-CPU) and the backup CPU start operating. Thirty minutes after deployment, the timer of the 430 MHz TX/RX controller turns on the switch of the servomotor for extending the 430 MHz UHF antenna (Figure 6).
Figure 5: Block diagram of the FITSat-1 CubeSat (image credit: FIT)
Figure 6: Illustration of FITSat-1 with the deployed UHF antenna (image credit: FIT)
RF communications: The communication subsystem consists of a low speed system and a high speed system. Using the low speed system, FITSAT-1 always sends a CW beacon signal at 437.250 MHz with 100 mW of power. This signal includes telemetry data such as internal voltages, currents, temperatures, timestamp, and other FITSAT-1 status data. The low speed system accepts remote commands from the ground station between beacon signal intervals. The remote commands are sent by AX.25 packets at 1.2 kbit/s from the ground station. The packet signals are received by the 430 MHz band FM receiver and decoded by the AX.25 TNC (AXELSPACE HVU-301). The RX-CPU executes the commands and outputs signals on the bus line which connects between CPUs and peripherals. The results of the remote commands are monitored by the TX-CPU and sends to the FM transmitter through the AX.25 TNC. The FM transmitter sends the AX.25 packet at 437.445MHz with 800 mW.
If the 430 MHz receiver does not work, the ground station can send remote commands with DTMF (Dual-Tone Multi-Frequency) signals using a 1.2 GHz transmitter. The DTMF signals are received by the 1.2 GHz band receiver and sent to the DTMF decoder. The backup CPU executes the commands and outputs signals on the bus line.
FIT developed the 5.8 GHz high speed transmitter for the CubeSat. It consists of an exciter module with a 115.2 kbit/s FSK modulator and a liner amplifier which amplifies a 10 mW signal to 4 W. However, since the two modules were too big for a CubeSat, the project developed a new module (Figure 7) which combines the exciter and the liner amplifier of 2 W output. The new module can transmit a JPEG VGA image(of size 480 x 640 pixels) within 6 seconds.
Figure 7: New module of exciter and liner (image credit: FIT)
ACS (Attitude Control Subsystem): Some attitude control is provided by a permanent neodymium magnet which acts against the Earth's magnet field and orients CubeSat into the general north direction (Figure 8). The permanent magnet causes the top (+Z panel) of the body to face to the magnetic north at all times. The top panel features a 5.8 GHz patch antenna, LEDs, and a hole for the camera lens. The circle of the satellite trajectory in Figure 8 shows the directivity of 5.8 GHz patch antenna, the corner of the satellite shows the angle of the front camera and the green LED beam.
Figure 8: Schematic of the viewing conditions of FITSat-1 from the Fukuoda ground station (image credit: FIT)
Launch: FITSat-1/Niwaka was launched as a secondary payload on July 21, 2012 from Tanegashima, Japan aboard JAXA's HTV-3 (H-II Transfer Vehicle-3) ISS resupply mission. The HTV-3 module was launched by the H-IIB launch vehicle of Mitsubishi Heavy Industries. The HTV-3 module is nicknamed Kounotori-3. 3) 4)
Further CubeSats on this mission were:
• Raiko (Drum of the Thunder), a 2U CubeSat of Wakayama University, Japan
• FITSat-1 (Fukuoka Institute of Technology), Fukuoka Prefecture, Japan
• We-Wish of Meisei Electric Co., Ltd., Tokyo, Japan
• F-1 (F Space Laboratory) of FPT University, Hanoi, Vietnam.
In addition, the J-SSOD system will be delivered on this flight to the ISS and installed in JEM/Kibo. The deployment of all CubeSats is planned for Sept. 2012.
Orbit: The ISS is in a near-circular orbit in the altitude range of 350 -400 km, inclination = 51.6º.
Deployment of CubeSats from the ISS:
J-SSOD (JEM-Small Satellite Orbital Deployer) onboard of JEM/Kibo: The J-SSOD is a platform that acts as an interface between operations inside and outside the ISS. Two rectangular, spring loaded canisters accommodate up to 3 small 1U CubeSats each. The back plate or deck provides the needed attachment points for the JEM Slide Table for passage through the JEM airlock. Satellites (CubeSats) are installed in J-SSOD by crew members, attached to the MPEP (Multi-Purpose Experiment Platform) and passed through the JEM airlock for retrieval by the JEMRMS (JEM Remote Manipulator System). A JEMRMS grapple fixture supports the capture, orientation and deployment operations, including communications and power interfaces. 5) 6)
Figure 9: Artist's rendition of the CubeSat deployment from JEM/Kibo (image credit: JAXA)
The deployment from the fairly low orbit of the ISS will limit the operational life of the CubeSats to a few months due to the encounter of atmospheric drag.
Mission status of FitSat-1 / Niwaka:
• The FITSat-1 CubeSat is operating nominally in December 2012. 10)
• Nov. 26, 2012: The first experiment of the flashing LEDs was observed in Kurashiki Japan and in Daejeon Korea. The LEDs were driven in detecting faint light mode. As this picture is tracked, the line of LED-light is shortening (Ref. 10).
Figure 10: First LED flashing of FITSat-1 reported by Kazuhisa Mishima of the Kurashiki Science Center (Japan) and by Jun-Ho Oh of KAIST (Korea Advanced Institute of Science and Technology), (image credit: FIT)
• Oct. 20, 2012: The project received the first image from FITSat-1 / Niwaka via the 5.84 GHz link.
• On Oct. 6, 2012, the project received the first status information from FITSat-1 (voltages and currents stored in response to remote commands). These transmissions (437.445 MHz, AX.25 packet 1200 bit/s) were replies to remote commands (Ref. 10).
• FITSAT-1 was deployed from the ISS at 15:44 (UTC) on October, 4, 2012.
Figure 11: Deployment image of the rear camera of Niwaka, showing the ISS, the image was transmitted on Oct. 27, 2012 via the 5.84 GHz link (image credit: FIT)
Figure 12: Deployment images from the ISS of the second pod release of FITSat-1, F-1 and TechEdSat (image credit: NASA)
5.8 GHz high speed transmission:
The high speed radio system uses the 5.8 GHz amateur radio band (5 cm wavelength). The transmitter sends a VGA image data (640 x 480 pixels) at 115.2 kbit/s FSK modulated in 5 to 6 seconds to the ground station. The bandwidth is 300 kHz. The transmitter generates 2 W RF power from the 15 W DC input. The patch antenna generates the right circularly polarized wave.
The camera of FITSat-1 is C1098 (Silent System) shown in Figure 13. FITSat-1 features two JPEG cameras; up to 20 pictures can be stored at a time. The image data is packed and transmitted in blocks of 128 bytes. It takes about 3 minutes to transmit all the image data to the ground station. Immediately after FITSat-1 is deployed, 20 photographs are taken every 10 seconds, and stored. All commands can be set up with delay time, so it is possible to take pictures anywhere on the orbit.
Figure 13: Photo of the JPEG camera (image credit: FIT)
Flashing LEDs (Light-Emitting Diodes):
A total of 50 green LEDs are attached on the top (+Z panel) of the CubeSat body, and 32 red LEDs are attached on the bottom (-Z panel) of the CubeSat body. The flashing of the 50 green LEDs is shown in Figure 14.
Figure 14: Illustration of the green LED flashing action (image credit: FIT)
There are two modes to the flashing LEDs. One is on duty 30% of the time with a 10 Hz signal which is also modulated with a 30% duty cycle on a 5 kHz signal. Hence, the average input power will be 220 W x 0.3 x 0.3 = 20 W. In order to detect the faint light on the ground, a 5 kHz filter might be useful. The flashing time is selected in 2 minute or 4 minute periods by commanding.
Another mode is flashing by Morse code. The Morse code is modulated with a duty cycle of 15% on a 1 kHz signal. So, the signal can directly drive a speaker with an AF amplifier to be able to listen to the Morse sound. The dot of the Morse code is 0.2 s, and a dash is 0.6 s in length. With a delayed command execution, the LEDs can also flash anywhere on orbit. Since the attitude of the CubeSat is based on a magnet, the flashing green LEDs can be observed in the northern Hemisphere, while the flashing red LEDs may be observed in the southern Hemisphere.
2) Kenta Tanaka, Takushi Tanaka, Yoshiyuki Kawamura, “Development of The Cubesat FITSAT-1,” Proceedings of the UN/Japan Workshop and The 4th Nanosatellite Symposium (NSS), Nagoya, Japan, Oct. 10-13, 2012, paper: NSS-04-0111, URL: http://www.fit.ac.jp/~tanaka/FITSAT/Kenta.pdf
3) “Launch of the H-II Transfer Vehicle "KOUNOTORI3" (HTV3) Aboard the H-IIB Launch Vehicle No. 3,” JAXA Press Release, March 21, 2012, URL: http://www.jaxa.jp/press/2012/03/20120321_h2bf3_e.html
4) “Cube Satellite Launches to International Space Station,” SJSU, URL: http://blogs.sjsu.edu/today/2012/cube-satellite-launches-to-international-space-station/
5) “JEM Small Satellite Orbital Deployer (J-SSOD),” NASA, Nov. 01, 2012, URL: http://www1.nasa.gov/mission_pages/station/research/experiments/J-SSOD.html
6) Kazuya Suzuki, Yusuke Matsumura, Shinobu Doi, “Introduction of the Small Satellite Deployment Opportunity from JEM,” Proceedings of the 3rd Nanosatellite Symposium, Kitakyushu, Japan, December 12-14, 2011, URL: http://www.nanosat.jp/images/3rd/pdf/%5BNSS-03-0107%5D_Introduction_of_the_Small_Satellite.pdf
7) “Small Satellites Deployment from Kibo were success,” JAXA, Oct. 5, 2012, URL: http://iss.jaxa.jp/en/kiboexp/news/small_satellites_deployment_fr.html
9) Ann Marie Trotta, Rachel Hoover, “NASA's TechEdSat Launches from International Space Station,” NASA News, Oct. 4, 2012, URL: http://www.nasa.gov/centers/ames/news/releases/2012/12-72AR.html
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.