UNISEC Space Takumi Conference for Practical Study of Problem Finding and Solving in Space Systems
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
Structure and Functions of CubeSat FITSAT-1 (NIWAKA)
Takushi TANAKA 1,*,†,Yoshiyuki KAWAMURA
2, Takakazu TANAKA
3
1
Department of Computer Science and Engineering, Fukuoka Inst. Tech., 2Department of Intelligent Mechanical Engineering, Fukuoka Inst. Tech.,
3-30-1 Wajiro-Higashi, Higashi-ku, Fukuoka 811-0295, Japan 3
Logical Product Corp.,
2-25-5 Nakahara-bldg., Matoba, Minami-ku, Fukuoka 811-1314, Japan
SUMMARY
FITSAT-1 (NIWAKA) is a 10 cm 1U CubeSat that was deployed from ISS on October 5, 2012. The main
mission of FITSAT-1 is to test a high speed transmitter module developed by our group (115.2 kbps, 5.8 GHz,
FSK, 2 W RF output). It can send a VGA resolution jpeg image (640x480 pixels) in 2 to 6 seconds. The second
mission is to make the satellite twinkle as an “artificial star” using high-output LEDs. This light will be observed
by binoculars and the optical signal will be detected by a telescope with a photomultiplier. These experiments are
controlled by remote commands from the ground station using 430 MHz and 1.2 GHz bands of Ham radio. We
already received more than 10 photographs from the deployed FITSAT-1. We have also started the flashing LED
experiments.
.
KEY WORDS: CubeSat; 5.8 GHz; High Speed Transmission; Flashing LEDs; FITSAT-1; NIWAKA
* Corresponding author. Professor, Member UNISEC. † E-mail: [email protected].
2 Takumi UCHUU
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
1. INTRODUCTION
FITSAT-1 (NIWAKA) is a 10 cm 1U CubeSat which was deployed from ISS/JEM on October 5, 2012. The
main mission of the FITSAT-1 is to demonstrate a high speed transmitter module developed by our group (115.2
kbps, 5.8 GHz, FSK, 2 W RF-output). It can send a VGA resolution jpeg image (640x480 pixels) in 2 to 6
seconds. The second mission is to make the satellite twinkle as an “artificial star” using high-output LEDs driven
by pulses that exceed 200 W. This light will be observed by binoculars and the optical signal will be detected by
a telescope with a photomultiplier. These experiments are controlled by remote commands from the ground
station using 430 MHz band and 1.2GHz band Ham radio communication.
2. STRUCTURE
2.1 Overview
The top of FITSAT-1 has a 5.84 GHz patch antenna, green LEDs, and a hole for camera lens (Figure 1). The
5.84 GHz patch antenna is protected by a teflon sheet and generates a right circularly polarized wave. Fifty green
LEDs are driven by pulses of over 200 W. Four sides have attached solar cells. Each of these sides has two solar
cells connected in series. The –Y side also has a hole for a flight pin and a conenctor for testing internal states.
The bottom side has a 1.26 GHz patch antenna, thirty-two red LEDs, a hole for a camera lens, and a 437 MHz
antenna which is extended 30 minutes after deployment.
Figure 1: Overview of FITSAT-1
2.2 Body
The body of FITSAT-1 is made by cutting a section of 10cm square aluminum pipe. Both ends of the cut pipe
are covered with aluminum panels as shown in Figure 2. The aluminum pipe is made of aluminum alloy A6063
and the panels are made of aluminum alloy A6061. The surface of the body is finished with black ANODIC
coating (MIL-A-8625 Type Ⅲ Class1). 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. In order to make the 8.5mm square CubeSat rails,
5.5mm square aluminum sticks (Figure 3) are attached to the four corners of the square pipe (Figure 4).
Paper Format of UNISEC Space Takumi Journal 3
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
Figure 2: Cutting square pipe Figure 3: Aluminium stick
Figure 4: Corner of squre pipe
2.2 Top and bottom planes
The top plane has a 5.84 GHz patch antenna, fifty green LEDs, and a hole for the camera lens (Figure 5). The
bottom plane has 1.26 GHz patch antenna, a hole for the rear camera, and a hole for the 437 MHz antenna, and
thirty two red LEDs (Figure 6). The four corners of the bottom have deployment switches (red squares),
separation springs (red circles).
Figure 5: Top Plane (+Z) Figure 6: Bottom Plane (-Z)
4 Takumi UCHUU
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
2.3 Side planes
The solar cells are attached to four sides of the square pipe. One of the sides (-Y plane) has also a flight pin
and a connector for testing internal state (Figure 7)
Figure7: Side +X, -X, +Y Figure 8: Side -Y
3. MECHANISM
3.1 Mechanism for deployment switch
The deployment switch consists of a microswitch and a brass lever as shown in Figure 9. In the deployer,
the brass lever is pushed and the microswitch turns off. When the satellite is relesed from the deployer, the blass
lever is relesed, and the microswitch turns on.
Figure 9: Deployment switch
Paper Format of UNISEC Space Takumi Journal 5
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
3.2 Antenna extender for 430 MHz band
The antenna element for the 430 MHz band is a 4 mm width and 18 cm length phosphorus bronze strip. It is
stored inside of the body in a spiral (Figure 10). The antenna element is extended 17 cm through the antenna hole
by a small servomotor. The RF power is fed at the top of antenna extender with small impedance matching
circuit. The motor switch for antenna extender turns on 30 minutes after deployment.
Figure 10: 430 MHz band antenna extender
4. ELECTRICAL POWER SYSTEM
Electrical power system of FITSAT-1 consists of solar cells, maximum power point tracker, DCDC-
converters, single lithium ion battery, three lithium ion batteries (Hitachi Maxell INR18650PB2, 1450 mAH),
lithium ion battery controllers, two deployment switches, and a flight pin as shown in Figure 11. JAXA required
that all batteries should have three independent switches connected in series both ground side and source side.
We realized this requirement using electronic switches. As these three switches are connected in series, all of
the batteries do no supply powers until all of these switches turn on. The single battery supplies power for 5
volt roads which consist of computers and low-speed communication system. While the three batteries
connected in series supply powers for experiments of 5.8 GHz transmission and flashing LEDs.
Solar cells are attached to four sides (+X, +Y, -X, -Y) of the satellite. Each side has two solar cells
connected in series and generates 2.3 W (4.74 V x 0.487 A, maximum) of electric power. The generated power
is withdrawn by a maximum power point tracker and fed to the 5 volt load and the single lithium ion battery.
The single lithium ion battery is charged until it reached to 3.8 volt. The charging currents decrease after it
reached to the voltage, then the three batteries in series are charged. The single battery supplies the 5 volt load
through a DCDC converter in eclipse. The three batteries in series are protected from overcharging and over
discharging by a battery controller IC(SII S-8233BAFT). If the voltage of a single battery goes under 3.5 volts,
the three batteries supply power for the 5 volt load. That is, the priority of supplying 5 volt load is (1) Solar
cells, (2) single battery, (3) three batteries in series.
6 Takumi UCHUU
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
Figure 11: Power System
5. COMMUNICATIONS AND DATA HANDLING SYSTEM
The communication system consists of two uplinks and three downlinks as shown in Figure 12. The uplink is
used for remote commands. The 437 MHz band uses AX.25 packet of 1200 bps. While the 1260 MHz band uses
DTMF signals. The 1260 MHz uplink is designed for a backup system of the 437 MHz band.
As a downlink, FITSAT-1 (NIWAKA) always sends a CW beacon signal at 437.250 MHz. This signal includes
telemetry data such as voltages and currents of solar cells and batteries, temperatures, timestamp, and other
FITSAT-1 states. FITSAT-1 has another downlink, at 437.445 MHz, which transmits AX.25 packets at 1200 bps.
It is used to send stored telemetry information. FITSAT-1 also has a high speed downlink system for picture data.
It uses 115.2 kbps FSK at 5.840 GHz. It can send a VGA (640 x 480 pixels) jpeg image within 2 to 6 seconds.
The Table 1 summarizes the NIWAKA radio modules.
Figure 12: Up-links and down-links
G ND
Photovoltaic cells 1
Photovoltaic cells 2
Photovoltaic cells 3
Photovoltaic cells 4
A
solarV.2moni.
solarV.3moni.
solarV.1moni.
solarV.4moni.
solarCur.moni.
MPPTcontroled +5V convert.
G ND
G ND
1 cell Li-ionBattery chargingcotrol
1 c
ell
Li-
ion
3.8
V 1
400m
Ah
G ND
A
Batt.1 Cur.moni .
Batt.1 V.moni.
G ND
1cel l Batt. voltagedetector
Voltagetripler circuit
input×3
G ND
G ND
+5Vstep up DC-DCconvertor
G ND
+5Vstepdown DC-DCconvertor
+5V m
ain
power line
G ND
3 cell Li-ionBattery chargingcotrol
3 c
ell
Li-
ion
11.4
V 1
400m
Ah
G ND
A
Batt.3 Cur.moni .
Batt.3 Vmoni .
MPU
G ND
Main system
G ND
ReferenceVoltage +2.5V
Green LEDswitchingcircu it
+11V
Pow
er
line
G ND
Red LEDswitchingcircu it
G ND
G ND
G ND
50×3W LED
28×3W LED
FrontCameraCamera
RearCamera
MPU
Memory
5.8GHzOSC
FSKMod. PA
5.8GHz Ant.
CAMERA & 5.8GHz TX
G ND
Temp. sensors
Control
Switched +5V Line
G ND
moni.
430MHz TX&RX
430MHzBeacon TX
430MHz Data TX
430MHzCommand RX
430Mhz Ant
TNC
1.2GHz Ant.
Mot
or
Ant
.driv
e
G ND
G ND
1.2GHzCommand RX
DTMFDecorder
1.2GHz Back up RX
Power Line Block diagram of Fit-sat.(NIWAKA)
Paper Format of UNISEC Space Takumi Journal 7
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
Table 1: Radio Module
Receiver Freq. Signal
430RX 436-438MHz 1200bps packet (AFSK), DTMF
1.2GTX 1260-1270MHz DTMF
Transmitter Freq. Signal Power
430CWTX 437.250MHz CW 100mW
430FMTX 437.445MHz 1200bps packet (AFSK) 800mW
5.8GTX 5.840GHz 115.2kbps (FSK) 2W
Figure 13 shows the relationship between the communication and data handling systems. Remote commands
are sent by AX.25 packets at 1200 bps using the 437 MHz band from the ground station. The packet signals are
received by the 437 MHz band FM receiver and decoded by the TNC. The RX-CPU executes the commands and
outputs signals on the command bus line which connects between CPUs and peripherals. The results of the
remote commands are monitored by the TX-CPU. The TX-CPU samples and stores the sensor data according to
the received commands, and sent to the FM transmitter through the AX.25 TNC. The FM transmitter sends the
AX.25 packet at 437.445 MHz with 800 mW output. The 1.26 GHz band RX also receives remote commands by
DTMF signal. These signals are decoded by a DTMF decoder and sent to the backup-CPU. The backup-CPU
executes the command, and outputs signals on the command bus line.
The camera-CPU receives the signal on the command bus line and executes the command. The shutter
command takes 20 photographs and stores them in memory. The transmission command reads 20 photographs
from memory and transmits the data over the 5.84 GHz transmitter.
Figure 13: Communication and data handling system
8 Takumi UCHUU
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
6. MISSION EQUIPMENT
6.1 High speed transmitter and camera
The 5.8 GHz high speed transmitter module used was developed by our group (Figure 14). The module
generates a 2 W RF output from a 15 W DC input. It can send digital signals at 115.2 kbps. A simple FSK
modulation is used. Although its frequency deviation is ±50kHz, 99% of the energy is spread over 415 kHz
(Figure 15). The 90% energy band may be less than 300 kHz.
The Figure 16 shows the block diagram of the 5.8 GHz transmission system. Two cameras (C1098 and Silent
System) are connected to this radio module. The MPU PIC16F886 not only controls the transmitter PLL but also
controls these two cameras. These two cameras take photographs every 5 seconds alternatively by commands
from the MPU and 20 photographs are stored in flash memory as jpeg images. The microcontroller also reads the
photographs from the memory in response to a transmit command, and sends the 20 photographs to the FSK
modulator.
Figure 14: 5.8 GHz transmitter module
Figure 15: Spectrum of 5.8 GHz signal
Paper Format of UNISEC Space Takumi Journal 9
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
Figure 16: 5.8 GHz transmission system
A jpeg image is transmitted using 128-byte packets. Figure 17 shows the format of the data. The first 4 bytes
and the last 2 bytes do not hold jpeg data. Thus the data size of all the packets except the last is 122 bytes. A jpeg
image starts with "FFD8" and ends with "FFD9". A jpeg image is reconstructed by connecting the data parts of
each packet, which is acquired by removing the first 4 bytes and the last 2 bytes. Twenty VGA images are sent at
a time. It takes 2 to 6 seconds to send each image. Packets are sent at 8 ms intervals to read the 122 byte from the
memory and there is a 5 second interval between images to prevent heat buildup.
(e.g.) 00 00 7A 00 FF D8 FF E0 ...
01 00 7A 00 09 0A 16 17 ...
...
12 34 56 00 ..... FF D9 ...
Figure 17: Picture Data Packet
☆FITSAT-1 5.84GHz TX Block Diagram (TX ,Mod & cont)
~0
90
TX part ofMAX2828
TXPA
osc
Loo
p Filt
er
CP PLL Logic Cont.
Serial I/Oref.f.in
VCTCXO
f=20MHz
mod
.
cont.
LPF
Butterworth -12dB/oct.
bias adj.
Gain&c.F.adj.
BALAN LPF
Fc=6GHz
5.8GHz driver amp
VMMK2503
Ga=14dB
1.5dBm 0dBm
BPF
Fc=5.8GHz
+14dBm +12dBm3dB Att.Pad.
5.84GHz PA
GaAs MM ICTMD5872-2
+9dBm +34.5dBm
LPF
Fc=6GHz
+33dBm
-bias
+10V
5.8GHz Patch Ant.
Gain≒1.5dBi
Pch-FET
cont.SW.
Biasdrive. bias timing
Charge pumpVoltage Inv. -10V
TC7660S
control data from MPU
TX +3.3V
TX
+5V
+3.3V Regu.for OSC & Mod.
Pch-FET
cont.SW.TX stage
mod data
+10V
BP Low loss
L4940D2T10+10V Reg.
Pch-FET
cont.SW.bias timing
Final stagePow. ON cotrol
from
3ce
ll Bat
t
+TX
PA
Camera Unit
Front Camera
Camera Unit
Rear Camera
Pch-FET
Pow.SW.Camera
C1098-SS
C1098-SS
VGA
VGA
Jpeg
Jpeg
from TX+3.3V
Camera dataselect SW.
MPU PIC16F886
from +5V TX pow.
7.37MHzWatch dogResettimer
+11V
Flash Memory
M25P32-VMW6G
115.2kbps
115.2kbps
busycommands infrom +3.3V pow line.
+3.3V - 5V Logic Level shift. ICs.
DC/DC Power.hold
hold
Low Volt.detect
busy
XC6209A332
10 Takumi UCHUU
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
6.2 High output LEDs
The top panel (+Z plane) has fifty green 3 W LEDs (Figure 5). Two green LEDs are connected in series, and
twenty five of these series LED pairs are connected in parallel (Figure 17). A current of almost 20 A is applied
and the LEDs are driven with more than 200 W. While the bottom panel (-Z plane) has thirty two red 3 W LEDs
(Figure 6). Four red LEDs are connected in series, and eight of these sets of series LEDs are connected in
parallel. A current of 5 to 6 A is applied and the LEDs are driven with about 60W (Figure 18).
There are two LED drive modes. In one mode, the LEDs flash Morse code patterns. Since the Morse code is
modulated with a 1 kHz signal, if the light is observed on the ground and converted to an electrical signal, Morse
code audio can be generated simply by connecting it to an audio amplifier and speaker. The duty of the 1 kHz
pulse is 15 %, so average power of green LEDs is 200 x 0.15 = 30 W and that of the red LEDs is 60 x 0.15 = 9
W.
The other mode is the faint light detection mode. In this mode, the LED drive current is modulated with both
a 10 Hz signal and a 5 kHz signal. The light is received by a photo-multiplier equipped telescope aligned with a
5.84 GHz parabolic antenna. Since both the 10 Hz and 5 kHz signal have duty ratio of 30 %, the average power
of the green LEDs will be almost 220 x 0.3 x 0.3 = 20 W and that of the red LEDs will be 5 to 6 W.
Figure 17: Green LED panel
Figure 18: Red LED panel
7. POSTURE CONTROL SYSTEM
The trajectory of the ISS is inclined 51.6 degrees from the equator and as a result FITSAT-1 will travel
between 51.6 degrees south latitude and 51.6 degrees north latitude. Since a permanent magnet is mounted in
FITSAT-1, the top plane (+Z plane) of the body will always face magnetic north like a compass (Figure 19). The
top plane has a 5.8 GHz patch antenna, LEDs, and a hole for the camera lens. When FITSAT-1 rises above the
horizon, it will be to the south of the Fukuoka ground station, and both the 5.84 GHz antenna and the LEDs will
be aimed accurately enough by the magnet aligning itself and the satellite with the earth's magnetic field that the
Fukuoka ground station will be within the main beams. The circle of the satellite in the figure shows the
directivity of 5.8 GHz patch antenna, the corner of the satellite shows the angle of front camera and green LED
beam.
Paper Format of UNISEC Space Takumi Journal 11
Copyright © 2011 UNISEC UNISEC Space Takumi Conference Paper
Figure 19: Posture on the orbit
8. CONCLUSIONS
FITSAT-1 is now in orbit. We have received more than 500 signal and telemetry reports from all over the
world in these two months, and all reports show FITSAT-1 is operating as designed. We have received more than
10 photographs that were taken at deployment. The 5.8 GHz signal reception experiment has been carried out not
only in Japan, but also in Vermont, USA, and Bochum, Germany, successfully. We have just started the flashing
LED experiment. The first signal was observed and photographed by the Kurashiki Science Center and the
Korea Advanced Institute of Science and Technology.
ACKNOWLEDGEMENT
I would like to thank Mr. Ryuichi Hirata, who made the body of FITSAT-1 in our machinery center, our
undergraduate student, Mr. Toshiki Otsuka, who made the 437 MHz antenna extender, and our graduate student,
Mr. Kenta Tanaka, who developed most of the software. I would like to thank the people of Logical Product
Corp., who developed the circuits of FITSAT-1. I would like to thank the people of JAXA who gave us important
advice for FITSAT-1 development.
REFERENCES
[1] Takushi Tanaka and Takakazu Tanaka, 5.8 GHz-Band High Speed Radio Module for Small Artificial Satellites,
Fukuoka Institute of Technology, Information Science Research Institute Bulletin 20, pp.1-6, 2009.
[2] Yoshiyuki Kawamura, Takushi Tanaka: Emission of LEDs from a ultra small satellite,
The 418th Topical Meeting of the Laser Society of Japan, 2012.
[3] Takushi Tanaka, Yoshiyuki Kawamura, Takakazu Tanaka: Overview of FITSAT-1 (NIWAKA) developed at
Fukuoka Institute of Technology, The 53rd Symposium on Space Science and Technology in Japan, 2012.
[4] http://www.fit.ac.jp/~tanaka/fitsat.shtml