(;OBAN: Design of Multi-Spectral Opto-ElectronicSatellite Camera System

0. ,enguil, U.M. Leloglu, E.Tunali, M.S. Kirik, N. Ismailoglu, R. Sever, Erdem AyvazTUBITAK-UZAY

Middle East Technical University, 06531 Ankara, TURKEYPhone: +90 312 210 10 50Fax: +90 312 210 13 15

{orhan.sengul, ugur. leloglu, erol.tunali, sancay.kirik, neslin.ismailoglu, refik.sever, erdem.ayvaz }@uzay.tubitak.gov.tr

Abstract- (OBAN (an abbreviation for "Multi-spectral Differential Signalling) bus. Another payload GEZGIN isCamera" in Turkish) is a Multi-spectral earth observing capable of compressing the captured earth imagescamera system developed for BiLSAT, a 129 Kg micro- with/without loss in data. This is one of the most importantsatellite, which was launched into a 686 km sun- features of BiLSAT to improve the efficiency of thesynchronous orbit in 27 September 2003. COBAN is one maximum 2 MBits/sec S-Band downlink channel to groundof the two Turkish R&D payloads hosted by BiLSAT in station.addition to the two primary imager payloads (a 4 bandmulti-spectral 26m Ground Sampling Distance (GSD)imager and a 12m GSD panchromatic imager).The technical specification of 1:OBANcan be summarizedas follows:

* Number of spectral bands: 8H Ground Sampling Distance: 12 meter

* Image size (in pixels): 640 x 480 (KODAK KAI-0311 CCD)

* Wavelengths of the bands: 375-425 nm, 410-490nm, 460-540 nm, 510-590 nm, 560-640 nm, 610-690nm, 660-740 nm, 850-1000 nm

Aimed primarily as a tool for improving the capabilitiesfor instrument design for space, C~OBAN successfullyperformed in space. However, the most importantoutcome has been the lessons learned from mistakes d ig gaduring design, manufacturing and testing, that willhopefully help us avoiding serious failures in futuremissions.

Figure 1: COBAN view on BILSAT-1II. INTRODUCTION

High resolution multi-spectral imaging is the main aspect of IIc GENERAL ARCHITECTUREearth-observing small satellites in Low Earth Orbit (LEO).High resolution earth-observing is important for environment The basic idea of getting digital earth image from satellite isand disaster monitoring. (;OBAN which is secondary imaging as follows. Firstly, the image is captured by Charge Coupledpayload hosted by BiLSAT is cost-effective imaging system Devices (CCD). Then the captured image is converted tofor high resolution earth-observation (See Figure 1). digital signal on high speed Analog-to-Digital (ADC) and

finally the digital data is sent to other subsystems of satelliteTInCYOBANX+,-th mgs r-atre i faetp CICDTNI-1_-----Ato be prcessed r store on SSDR (oi-StateData,-IrI-

BILSAT COBAN

Adress Adress

Figure 2: OBAN Architectural Block Diagram

and converting analog image to digital signal on high speed * CAN ControllerAnalog-to-Digital converters. In the Main Board, a Field * FPGAProgrammable Gate Array (FPGA) is responsible from * Clock Drivers and Timing Circuitsgenerating the required horizontal and vertical clocks of * RAM BlocksCCD, controlling the shutter time and transferring the digital * Power Modulesdata from A/D converters to RAM Blocks and from RAMBlocks to SSDR over LVDS links. There is an 8 bitmicrocontroller which satisfies the CAN interface of thecamera and sends telemetry-telecommand requests to FPGA

interface is unregulated 8 V DC which can differentiate

need regulated 5 V DC power. CCDs need regulated 15 V and __

produced for machine vision. Mechanpicalstructure and | , ,E, ,focusing mechanism was designed in TUBITAK-BILTEN.TAI produced the main mechanical structure and varioussmall companies had chance to work in the production finemechanical parts of focusing mechanism. Thermal Cycling Figure 3: View from COBAN PCBtests were performed in TUBITAK-UZAY and vibration testswere conducted in the premises of ASELSAN. The mainstructure was produced from 7075 grade aluminum. 1. CAN Controller

It is an 8-bit microcontroller which realizes CANcommunication interfaces. Another duty of it is to send

III. MAIN BOARD ARCHITECTURE responses to telemetry and telecommands coming fromBiLSAT On-Board-Computer. It also changes the state of

Main board of GOBAN has five basic partitions (See Figure 2 FPGA and is responsible from Power-up sequence and otherand Figure 3). basic functions oftthe main board. Infenion C5e15 C type 8-bit

microcontroller is used. The main advantage of this

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microcontroller is that it has built-in CAN controller and it 3. Clock Drivers and Timing Circuitswas used on satellite modules before. A Bootloader code was To get the analog image data stored on pixels, some clocksdeveloped for startup. After initialization of the peripherals, should be driven. And also to set the exposure time andbootcode waits for new main code from CAN bus, if there is electronic shutter time, some trig pulses should be given tono new code, it jumps to main code that was previously stored the CCD. The basic clocks and pulses circuits are:on the flash. By this feature, the main CAN code can beimproved and loaded to microcontroller from ground station a. V Select:after the launch of the satellite.

For vertical clocks, three voltage levels are required.Circuit designed by TS902 operational amplifier is used to

The basic telemetry functions are generate these three voltage levels.* Temperature of the sensors* Shutter timing value of CCD's* Mean value of data of the CCD images b.V1 Drive and V2 Drive:* Minimum value of data of the CCD images* Maximum value of data ofthe CCD images To shift the data stored in pixels vertically, two vertical

clocks are generated by FPGA. Because CCD's clockinputs are capacitive, emitter follower buffers are used to

The basic telecommand functions are uncharged the capacitance.* SSDR LVDS data out for trial* GEZGIN LVDS data out for trial

* SelfTest ~~~~~~~c.VSUB1 andVSUB2:* Self Test* CAN Bus Change (Primary to secondary) These circuits are used to set the electronic shutter time of* LVDS and CCD clocks prescalers the CCD. The change in the voltage about 37 V starts the* Shutter timing setting value for CCD imaging operation in CCD's.* VGA gain value setting for ADC

d.H Drive2. FPGA and Clock Drivers

To shift the data stored in pixels horizontally, oneA Field Programmable Gate Array (FPGA) performs horizontal clock is generated by FPGA. Because CCD'scomputationally intensive tasks of C,OBAN (see Figure 4 for clock inputs are capacitive, emitter follower buffers areFPGA PCB layout). ACTEL A54SX32A 32.000 gate anti- used to uncharged the capacitance.fuse FPGA is used in here for robustness against SingleEvents Upsets (SEUs). Basically, the FPGA generates thehorizontal and vertical clock pulses to drive CCD, fills the 4. RAM BlocksRAM block with digital image data coming from ADCs andsends them from RAM to SSDR (Solid State Data Recorder) The RAM blocks are used for temporarily recording thevia LVDS links. The LVDS links have 25 MBits/sec digital image data coming from AD converters. They have thebandwidth. The calculation of integration time and generation capacity of 524,288-Word by 16-Bit / 1,048,576 Word by 8of some signals for ADCs are also among the functions Of bit. The I/O pins are protected from high currents by usingFPGA. The FPGA receives commands from CAN Controller 74LCX2244 Low Voltage Buffer/Line Driver. There are pull-via SPI interface and has JTAG interface for self test. up resistors that shut down the buffers and RAM blocks at

start-up.

5. Power Modules

I ! l_ In BiLSAT, two power sources are available. One isunregulated +28 V power source from batteries and the otheris regulated +5 V power source from PCM (Power Control

-1 1 < 1xModule).In (;OBAN, needed voltage levels were 15 V and +5 V.+28 V unregulated line is entered High Reliability HybridEMI filter. This filter is used for eliminating the noise coming

r _ _ ~~~~~~~~fromsatellite power system. Then, connecting the output ofEMI filters to High Reliability Hybrid DC-DC converters,+28 V is converted to +15 V (which has max. 40 W power-

Figure:Viewfrom COANPCB1,87A current) and +5 V (which has max. 30 W power and 6A current). The output of this structure is connected to other

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filters which are called Common Mode Choke Arrays. These The optics used in the imager was COTS optics, designed andhave the same job with High Reliability Hybrid EMI filters produced for machine vision. The brand and type of the lenswhich are responsible for common mode filtering. Some were COSMICAR/PENTAX C-5028-M, 50mm focal lengthcapacitors are used with parallel to Common Mode filters. For machine vision lens produced for 2/3 size CCD cameras.high and low frequency noise, these are used as Low-Pass, They were analyzed and found to be suitable for KAI-0311and High-Pass Filters. CCD. In order to make them capable of surviving in space

some modifications were made to lenses. The lensesdismantled, all kind of lubricants have been removed fromfocusing and iris mechanism and cleaned using ultrasoundbath. In order to avoid from closed chambers in the lens, inwhich air can be trapped, small holes have been drilled to

This board generates the analog image data from Kodak KAI- appropriate places. Iris mechanism and focusing mechanisms0311 CCD (Charge Coupled Device) and converts it to digital have been fixed using space-grade adhesive. Optical tests andimage data by using high speed analog-to-digital converters. alignment of lenses have been made using in house

capabilities.Sensor board has two basic partitions.

* CCD and Lenses* A/D Converters

Figure 6: An example mechanical part: CCD Holder

2. A/D Converters

8-Bit high-speed Analog-to-Digital Converters are used todgitize te analog image daa taen fom each pixel.

Figure 5: Various views Lenses from COBAN's flight ModelV. CONCLUSIONS

1. CCD and Lenses In this paper, a Multi-spectral earth-observing camera isintroduced with its design approach. C,OBAN had been the

The CCD used in C,uOBAN is KODAK KAI 311 CCD. It has first camera system fully designed and built in Turkey andVGA (640X480) resolution with 5.83x4.36 mm sensor size operated in space. It made our institute gain experience and(See Figure 6). The CCD has a spectral range from 300 nm to confidence in space system and camera design and1000 nm, so in ,fOBAN,all channels have same CCD and production. For the next micro satellite camera project, newarchitecture with different filters over the lens system to imaging systems will be developed over the experiences ofcover the required spectral bands. COBAN.

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