Structure and Functions of CubeSat FITSAT-1 (NIWAKA)tanaka/FITSAT/Space_takumi_Niwaka.pdf · 2-25-5 Nakahara-bldg., Matoba, Minami-ku, Fukuoka 811-1314, Japan SUMMARY FITSAT-1 (NIWAKA)

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


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


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


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



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


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

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Power Line Block diagram of Fit-sat.(NIWAKA)



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


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



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)

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10 Takumi UCHUU


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.



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

Documents

Structure and Functions of CubeSat FITSAT-1 (NIWAKA)tanaka/FITSAT/Space_takumi_Niwaka.pdf · 2-25-5 Nakahara-bldg., Matoba, Minami-ku, Fukuoka 811-1314, Japan SUMMARY FITSAT-1 (NIWAKA)