DubaiSat-2 is the second Earth observation minisatellite of UAE (United Arab Emirates). EIAST (Emirates Institute for Advanced Science and Technology) started the DubaiSat-2 development in 2009 in collaboration with SI (Satrec Initiative) of Daejeon, Korea, and in continuation of the DubaiSat-1 project. EIAST engineers with various academic backgrounds participated in the DubaiSat-2 project throughout the entire development phases and they played active and crucial roles covering all technical aspects. DubaiSat-2 is technologically more advanced than its predecessor and will have considerable commercial applications.
Note: On April 18, 2015, EIAST (Emirates Institution for Advanced Science and Technology) was officially renamed to MBRSC (Mohammed Bin Rashid Space Center). 1)
• To develop a minisatellite system of less than 300 kg for Earth observation
• To provide electro-optical imagery, that can be commercialized, of the UAE and other areas with a spatial resolution of 1 m PAN (panchromatic) and 4 m MS (multispectral) from a reference orbit of 600 km altitude.
• To develop and implement new technologies, not used in DubaiSat-1, that can be used in future space programs. The new technologies are:
- High Resolution Advanced Imaging System (HiRAIS) that produces imagery of 1 m spatial resolution
- Improved internal communication system using the CAN 2.0 protocol
- Higher downlink capability of imagery with 160 Mbit/s in X-band with data compression
- Increased onboard data storage capability of 256 Gbit
- Data encryption and command authentication for TMTC and image data
- Advanced agility and spacecraft stability, with improved pointing accuracy to perform multi-strip imaging and stereo observations in a single pass
- Orbit control using an electrical propulsion system jointly developed with JAXA.
• To continue the man power training for UAE's space program.
Figure 1: Illustration of the DubaiSat-2 spacecraft (image credit: EIAST, SI)
DubaiSat-2 is a minisatellite using the SI-300 platform, an extended version of the SI-200 platform which has flight heritage from RazakSat of Malaysia and DubaiSat-1 of UAE. Its architecture is designed to accommodate an Earth observation and/or science payload (Ref. 2). 4) 5) 6) 7) 8) 9)
The SI-300 platform is hexagonal in shape with a philosophy of separating the bus from the payload. The mechanical bus consists of 2 decks and an upper sun shield. The electronics are distributed on the decks and on the side panels. Four solar panels are attached to the sides of the satellite. Longerons and rails are making the bus structure frame. On the top, CFRP (Carbon Fiber Reinforced Plastic) struts hold the sun shield at the baffle of the payload HiRAIS (High Resolution Advanced Imaging System).
HiRAIS is attached to the bus at the internal deck. The mechanical configuration of the spacecraft is 1.95 in height with a diameter of 1.5 m. The total mass of the satellite is ≤ 300 kg and a design life of 5 years.
Figure 2: Configuration of the DubaiSat-2 minisatellite (image credit: EIAST, SI)
Figure 3: Overview of DubaiSat-2 subsystems (image credit: SI, EIAST, Ref. 3)
AOCS (Attitude and Orbit Control Subsystem): The spacecraft is 3-axis stabilized. The AOCS is designed to advance the agility and stability performance of the satellite during mission operations. With a relatively high moment of inertia, the satellite is designed to support the following imaging functions:
- Single strip imaging
- Multi-strip imaging
- Single-pass stereo imaging.
The agility of the satellite supports a body-pointing maneuver of up to 60º within 90 seconds. The pointing accuracy is < 0.12º (3σ) and the stability is < 0.009º/s. The AOCS is designed to satisfy TDI (Time Delay Integration) sensor operations requirements. Actuation is provided by 5 reaction wheels which are in constant operation with 4 FOGs (Fiber Optic Gyros). Attitude sensing is provided by fine sun sensors and magnetometers, including Star Trackers for fine pointing. A HEPS (Hall Effect Propulsion System) is used to perform on-orbit maintenance services. It uses electric propulsion with Xenon gas and utilizes a microwave cathode similar to the one used for the Hayabusa ion propulsion system of JAXA.
EPS (Electrical Power Subsystem): EPS supplies and controls the required voltage levels and current that is essential for the satellite operation during its long life mission. The EPS uses a rechargeable Li-ion battery to provide power for the satellite's payload and other subsystems. The system is divided into two stages, first is the charging stage and the second is the discharging stage.
The charging stage is made of power generator (solar panels) and power regulator. DubaiSat-2 generates more than 450 W of power using four solar panels. Each solar panels contains 6 arrays and each array consists of 26 cells. The solar panels charge the batteries. The battery charging process is handled and regulated by the BCR (Battery Charging Regulator) modules. DubaiSat-2 has three BCRs in a hot redundancy configuration. The spacecraft can function normally with only two BCRs. All BCRs are referred to as BCU (Battery Charging Unit).
The second stage of the EPS is the discharging stage. In this stage, battery outputs are converted and distributed to other subsystems. The conversion process occurs in the PPCM (Primary Power Conditioning Module) and the SPCM (Secondary Power Conditioning Module), where the discharged voltage, produced from the batteries (26 V – 32 V), is converted into unregulated -15 V, -12 V, +5 V, +12 V and +15 V voltages. These voltages are distributed by the PPDM (Primary Power Distribution Module (PPDM) and SPDM (Secondary Power Distribution Module) to the relevant subsystems.
The EPS also includes PSSM (Power Safety and Separation Module) to insure the stability and reliability of EPS system. The PSSM was designed to save and maintain battery voltage level prior to spacecraft launch. Once the satellite separates from the launcher, PSSM allows the power to flow into the satellite.
Figure 4: Block diagram of the EPS (image credit: EIAST, SI)
C&DHS (Command and Data Handling Subsystem): C%DHS handles all telecommands received by the spacecraft and collects the telemetry from all subsystems. It also provides the required environment for the satellite's onboard software. Two separate CAN networks, CDH and AOCS CAN, are used to exchange data between C&DHS and the other subsystems. Each CAN network has a data rate of 500 kbit/s. The ACS CAN is dedicated to the ACS modules and the CDH CAN to all other modules. The C&DHS is shown in Figure 5, it consists of the following modules:
• TMTC (Telemetry and Telecommand)
• OBC (On-Board Computer)
• IBs (Interface Boards)
The IBs are are used to interface satellite modules with the two CAN bus networks. The IBs perform the following tasks: a) formatting the telemetry data collected into the CAN packet format, b) handle messages received and delivered from and to OBC. All interface boards do the same tasks, but each board is designed to accommodate the needs of the device it's interfacing with:
- AIB (Actuator Interface Board) controls the speed of reaction wheels and provides a speed feedback to the OBC. It also controls the current driven to the MT rods.
- GRIB (Gyro Interface Board) collects gyro's telemetries and forward them to OBC
- PPIB (Primary Power Interface Board) controls the PPMU via commands received from OBC. It also collects PPMU telemetries and forwards it to OBC
- SPIB (Secondary Power Interface Board) controls the SPMU via commands received from OBC. It also collects SPMU telemetries and forwards it to OBC
- SIB (Sensor Interface Board) collect attitude Information from different sensors (CSS, FSS, MAG, etc.) and forward it to OBC
- TCIB (Thermal Control Interface Board) takes the temperature reading from all modules and forwards them to OBC. The OBC analyzes the temperature profile and upon those commands the TCIB controls the temperature via the PPMU.
- XADE (X-band Antenna Driving Electronics) holds the circuitry that drives the X-band gimbal antenna.
- HEPS Control Interface Board (HCIB) controls the HEPS modules via commands received from OBC. It also collects HEPS telemetry and forwards it to the OBC.
Figure 5: Block diagram of the C&DHS (image credit: EIAST, SI)
Figure 6: Illustration of the C&DHS (image credit: EIAST, SI)
TMTC: The spacecraft features two TMTC modules in hot redundancy configuration. Both TMTCs share the same board. The TMTC performs all CCSDS telecommand decoding and CCSDS telemetry encoding, reducing the load on the OBC. It receives telecommands sent by the ground station through the S-band demodulator, and sends the telemetry to the ground station through an S-band modulator. The TMTC also acts as a watchdog to the DubaiSat-2 OBC. It has an autonomous reconfiguration capability, which insures normal spacecraft operation in the event that the primary OBC fails.
OBC (On-Board Computer): The OBC is the primary central processing unit of the spacecraft. It communicates with all modules through the CAN bus network. All the telemetries generated by the different subsystems go to OBC were they are recorded and processed. The OBC also handles all decoded telecommands received from the TMTC. Based on the received telecommands or the collected telemetry, the OBC decides and commands different DS-2 modules. OBC is directly connected to both C&DHS and the ACS CAN network buses. The spacecraft features two OBCs in cold redundancy configuration. The primary and redundant OBCs can be reconfigured either through a ground station command or autonomously by the TMTC.
IBs (Interface Boards): The IBs are used to interface with the spacecraft modules and to interconnect the two CAN buses. They provide the following tasks:
• Formatting of the telemetry data into the CAN packet format
• Provision of message data handling of the OBC.
FSW (Flight Software): The backbone of the FSW is the VxWorks real-time operating system. Several application tasks are running concurrently to perform satellite health monitoring, control and data logging (housekeeping task), HiRAIS management, imaging and data download operations (payload task), internal and external network management, Onboard SW management (executable task), large data handling (large data transfer task), flight attitude and orbit control (flight control task). The FSW runs on OBC that has the capacity to save data for up to 3 days. It also has the redundancy in EEPROM bootloading operation. The FSW performs memory wash operations and is also supported by EDAC hardware to detect and recover from SEU (Single Event Upset) events.
RF communications: The S-band is used for all TT&C communications. The uplink consists of an S-band receiver and a 32 kbit/s modulator. The downlink channel includes a 32 kbit/s BPSK demodulator and S-band transmitters. The receivers have a hot redundancy configuration, while the transmitters use a cold redundancy configuration.
Figure 7: Block diagram of the S-band TT&C communications system (image credit: EIAST, SI)
The payload data are transmitted in X-band at a data rate of 160 Mbit/s. The XTU (X-band Transmission Unit) receives imagery from CIB in the SSRU and downlinks it to the ground station. The XTU uses a one-axis (±90º) steerable antenna.
Figure 8: Photo of the X-band one-axis gimbal antenna (image credit: EIAST, SI)
Onboard data storage is provided by SSRU (Solid State Recorder Unit) consisting of 2 CIBs (Control Interface Boards), 4 SBs (Storage Boards), 2 PBs (Power Boards), and a backplane. The CIB and PB have a cold redundancy configuration. Each SB has a data capacity of 64 Gbit. The total storage capacity in SSRU is 256 Gbit, which is equivalent of storing approximately 17,000 km2 of imagery.
Figure 9: Block diagram of the XTU module (image credit: EIAST, SI)
HEPS (Hall Effect Propulsion System): HEPS is an electrical propulsion system with Xenon gas fuel and microwave cathode. It will be used for orbit correction and maintenance. The system consists of XFU (Xenon Fuel Unit), THU (Thruster Head Unit), PPU (Power Processing Unit) and the MCU (Cathode Unit). It has a force of > 7 mN with a specific impulse of > 1000 s. HEPS will be used mainly when the satellite is close to the South Pole in a descending SSO orbit, due to its high power consumption of 300 W during operations.
The XFU includes a tank at 150 bar pressure and 2 kg of Xenon gas. It also includes pressure valves and orifices to control the flow of the fuel into two small tanks, each of 3 bar, for both the anode and cathode. The THU consists of a thruster head that includes magnets for ion motion direction. The PPU distributes different power voltages for the HEPS system (such as 250, -100, 15 and 5 V). It also has the switches for the XFU control. The MCU is provided by JAXA as a cooperative project to measure its performance, since a similar unit was used for the deep space mission Hayabusa. 10)
Figure 10: Photo of the HEPS instrument (image credit: EIAST, SI)
Figure 11: EIAST engineers at the SI facility in Daejeon, Korea, inspecting the DubaiSat-2 spacecraft (image credit: EIAST)
Table 1: Overview of spacecraft parameters
Figure 12: Block diagram of the DubaiSat-2 spacecraft (image credit: SI, EIAST)
Figure 13: Photo of DubaiSat-2 at the Yasny Cosmodrome (image credit: SI, EIAST)
Launch: The DubaiSat-2 minisatellite (primary payload) was launched on November 21, 2013 (07:10:11 UTC) on a Dnepr vehicle from the Dombarovsky (Yasny Cosmodrome) launch site in Russia. The launch provider was ISC Kosmotras. The STSat-3 minisatellite of KARI, Korea (~150 kg) is another primary payload on this flight. 11) 12) 13) 14) 15)
In Feb. 2011, EIAST signed a contract with ISC Kosmotras of Moscow. The launch of this mission has been delayed several times for over a year. The reasons for the long delay remain unclear and seem to be an internal Russian matter. 16) 17) 18)
The secondary payloads on this flight were:
• SkySat-1 of Skybox Imaging Inc., Mountain View, CA, USA, a commercial remote sensing microsatellite of ~100 kg.
• WNISat-1 (Weathernews Inc. Satellite-1), a nanosatellite (10 kg) of Axelspace, Tokyo, Japan.
• BRITE-PL-1, a nanosatellite (7 kg) of SRC/PAS (Space Research Center/ Polish Academy of Sciences of Warsaw, Poland.
• AprizeSat-7 and AprizeSat-8, nanosatellites of AprizeSat. AprizeSat-7 and 8 are the ninth and tenth satellites launched as part of the AprizeSat constellation, operated by AprizeSat. The constellation, which was originally named LatinSat, was initially operated by Aprize Argentina; however ownership of the constellation was later transferred to their US parent company AprizeSat. The AprizeSat constellation is used for store-dump communications, and some satellites carry AIS (Automatic Identification System) payloads for Canadian company ExactEarth. The AprizeSat spacecraft were built by SpaceQuest Ltd. of Fairfax, VA, USA, and each has a mass of 12 kg. 19)
• UniSat-5, a microsatellite of the University of Rome (Universita di Roma "La Sapienza", Scuola di Ingegneria Aerospaziale). The microsatellite has a mass of 28 kg and a size of 50 cm x 50 cm x 50 cm. When on orbit, UniSat-5 will deploy the following satellites with 2 PEPPODs (Planted Elementary Platform for Picosatellite Orbital Deployer) of GAUSS:
- PEPPOD 1: ICube-1, a CubeSat of PIST (Pakistan Institute of Space Technology), Islamabad, Pakistan; HumSat-D (Humanitarian Satellite Network-Demonstrator), a CubeSat of the University of Vigo, Spain; PUCPSat-1 (Pontificia Universidad Católica del Perú-Satellite), a 1U CubeSat of INRAS (Institute for Radio Astronomy), Lima, Peru; Note: PUCPSat-1 intends to subsequently release a further satellite Pocket-PUCP) when deployed on orbit. 20)
- PEPPOD 2: Dove-4, a 3U CubeSat of Planet Labs Inc. (formerly Cosmogia Inc.), San Francisco, CA, USA
MRFOD (Morehead-Roma FemtoSat Orbital Deployer) of MSU (Morehead State University) is a further deployer system on UniSat-5 which will deploy the following femtosats:
- Eagle-1 (BeakerSat), a 1.5U PocketQube, and Eagle-2 ($50SAT) a 2.5U PocketQube, these are two FemtoSats of MSU (Morehead State University) and Kentucky Space; Wren, a FemoSat (1U PocketQube) of StaDoKo UG, Aachen, Germany; and QBSout-1S, a 2.5U PocketQube (400 g) of the University of Maryland testing a finely pointing sun sensor.
• Delfi-n3Xt, a nanosatellite (3.5 kg) of TU Delft (Delft University of Technology), The Netherlands.
• Triton-1 nanosatellite (3U CubeSat) of ISIS-BV, The Netherlands
• CINEMA-2 (KHUSat-1) and CINEMA-3 (KHUSat-2), nanosatellites (4 kg each) developed by KHU (Kyung Hee University), Seoul, Korea for the TRIO-CINEMA constellation. TRIO-CINEMA is a collaboration of UCB (University of California, Berkeley) and KHU.
• GOMX-1, a 2U CubeSat of GomSpace ApS of Aalborg, Denmark
• NEE-02 Krysaor, a CubeSat of EXA (Ecuadorian Civilian Space Agency)
• FUNCube-1, a CubeSat of AMSAT UK.
• HiNCube (Hogskolen i Narvik CubeSat), a CubeSat of NUC (Narvik University College), Narvik, Norway.
• ZACUBE-1 (South Africa CubeSat-1), a 1U CubeSat (1.2 kg) of CPUT (Cape Peninsula University of Technology), Cape Town, South Africa.
• UWE-3, a CubeSat of the University of Würzburg, Germany. Test of an active ADCS for CubeSats.
• First-MOVE (Munich Orbital Verification Experiment), a CubeSat of TUM (Technische Universität München), Germany.
• Velox-P2, a 1U CubeSat of NTU (Nanyang Technological University), Singapore.
• OPTOS (Optical nanosatellite), a 3U CubeSat of INTA (Instituto Nacional de Tecnica Aerospacial), the Spanish Space Agency, Madrid.
• Dove-3, a 3U CubeSat of Planet Labs Inc. (formerly Cosmogia Inc.), San Francisco, CA, USA
• CubeBug-2, a 2U amateur radio CubeSat of Argentina (sponsored by the Argentinian Ministry of Science, Technology and Productive Innovation) which will serve as a demonstrator for a new CubeSat platform design.
• BPA-3 (Blok Perspektivnoy Avioniki-3) — or Advanced Avionics Unit-3) of Hartron-Arkos, Ukraine.
Orbit: Sun-synchronous near-circular orbit of the primary payloads (DubaiSat-2 and STSat-3), altitude = 600 km, inclination = 97.1º, LTDN (Local Time on Descending Node) = 10:30 hours. The effective revisit time of DubaiSat-2 is < 8 days for any ground location with a body-pointing capability of the spacecraft (up to ±45º roll tilt, ±30º pitch tilt).
Due to the large number of satellites on the mission, the Dnepr used a modified fairing which has been split into two platforms. DubaiSat-2 and STSAT-3, the primary payloads, were mounted on the upper platform, with the remaining satellites and the CubeSat dispensers mounted to the lower platform. The gas dynamic shield sits atop the upper platform.
Deployment of CubeSats: Use of 9 ISIPODs of ISIS, 3 XPODs of UTIAS/SFL, 2 PEPPODs of GAUSS, and 1 MRFOD of MSU.
Figure 14: Integration photo of the primary payloads into the upper platform of the Dnepr fairing (image credit: ISC Kosmotras)
• May 2016: DubaiSat is fully operational, receiving requests from end users locally and internationally. The satellite is fully operated and controlled through MBRSC's (Mohammed Bin Rashid Space Center) Ground Station which is based in Dubai. KSAT (Kongsberg Satellite Services AS) provides ground station support services in case of emergency or contingency support. 21)
- The image data received from DubaiSat-2 are widely used by end users to: update basemaps, urban planning change detection, and environmental applications.
Figure 15: DubaiSat-2 image of Jebal Ali Port, Dubai, acquired on February 11, 2016 (image credit: MBRSC)
• October 2014: EIAST (Emirates Institution for Advanced Science and Technology) and Elecnor Deimos have set up a unique, transnational PPP (Public Private Partnership) to operate the satellites, DubaiSat-2 and Deimos-2 as a constellation, to jointly commercialize the imagery of both satellites, and interchange technical and operational information to increase the efficiency of both systems. 22)
The constellation operations are based on four ground stations: Al Khawaneej (Dubai), Puertollano (Spain), Kiruna (Sweden) and Inuvik (Canada), which assure at least a contact per orbit with each satellite. The constellation functionalities of the ground segment were developed by EIAST and Elecnor Deimos in cooperation, in order to provide a product which is exactly the same, independently of which satellite acquired the image.
- The new constellation is referred to as the PanGeo Alliance, the first global alliance of Earth Observation satellites operators. The alliance was announced at the annual summit on Earth Observation Business, in its sixth edition, in Paris, France (Sept. 11-12, 2014). The PanGeo Alliance currently federates 4 satellite operator entities from around the world: Dauria Aerospace (USA/Russia), EIAST (UAE), Elecnor Deimos (Spain) and Beijing Space Eye Innovation Technology (China). 23) 24) 25)
The PanGeo fleet is composed of 9 satellites currently in orbit: Perseus-M1, Perseus-M2, Dauria-DX-1, DubaiSat-1, DubaiSat-2, Deimos-1, Deimos-2, TH-1-01 and TH-1-02. This fleet will be expanded to more than 30 satellites in the next years with the launch of KhalifaSat, of the Perseus-O and Auriga constellations, and with the expansion of the TH-1 constellation, plus satellites brought into the alliance by prospective new members that may join in the future.
The PanGeo fleet provides multispectral imagery in a wide range of resolutions (from 20 m to 75 cm/ pixel), with a daily global imaging capability. Moreover, it provides AIS data for ship identification and maritime traffic control. All PanGeo Alliance members can provide access to the full satellite fleet and product portfolio from all members.
• On April 14, 2014, EIAST announced that the commissioning phase of DubaiSat-2 was successfully completed and that the satellite is now fully operational. EIAST has also signed an agreement with SI (Satrec Initiative) of Korea for worldwide promotion and distribution of DubaiSat-2's products and services to global customers. 26) 27)
• In early March 2014, DubaiSat-2 is still in the commissioning phase, expected to last into April (Ref. 28).
• The firing test of HEPS was performed at the beginning of the second calibration and validation phase with the participation of the JAXA engineers. The operations team found the optimal firing condition from this test, which was applied to the satellite for automatic firing operation.
• The in-orbit calibration and validation (Cal/Val) was performed in two phases. In the first phase, the team used star images from HiRAIS and star sensors for the MTF measurement, focus adjustment of the HiRAIS telescope, and refinement of sensor-to-sensor alignment, measured MTF and SNR values from ground targets, tuned radiometric non-uniformity correction (NUC) parameters, and checked line rates, TDI steps, and video signal gains. In the second phase, the team performed the following activities (Ref. 3):
- Optimization of attitude control parameters
- Validation of the image dynamic range
- Refinement of NUC parameters
- Calibration and validation of band-to-band and overlap-zone registration accuracies
- Calibration and validation of targeting and geo-location accuracies
- Measurement of MTF and SNR values using ground targets
- Derivation of the MTF correction (MTFC) kernel
The operations team completed the Cal/Val phase at the start of March 2014 with the conclusion that all system specifications were satisfied and commissioned the normal operation of the DubaiSat-2 system. From launch vehicle separation to commissioning, the team performed about 461 imaging operations of different modes not including star imaging operations.
Figure 16: Image of Dubai International Airport, acquired with DubaiSat-2 in February 2014 (image credit: MBRSC, former EIAST)
Figure 17: DubaiSat-2 image of Downtown Dubai with the Burj Khalifa (upper half center with the longest shadow to the north-east corner), the Burj Khalifa is the tallest building in the world with 828 m and more than 160 stories. The 1 m resolution image was acquired just before National Day on December 1, 2013 (image credit: MBRSC, former EIAST)
Legend to Figure 17: The Dubai Fountain is located in the center of the image next to the Burj Khalifa. The large blue building complex to the lower right is Dubai Mall, one of the largest shopping centers in the world.
• LEOP (Launch and Early Operations Phase) lasted for about seven days during which the project team checked the state of health of spacecraft bus and mission payload, calibrated attitude sensors such as the star sensors and gyros, and verified the system functions and performance including the main MCS and IRPS.
Figure 18: First image from DubaiSat-2 of the Water Refinery at Al Ruwais, UAE ( image credit: MBRSC, former EIAST)
• First contact with DubaiSat-2 was established in Norway (Svalbard Satellite Station) about 90 minutes after launch. The project downloaded the first images 24 hours after launch and it was form Abu Dhabi.
Sensor complement: (HiRAIS)
HiRAIS (High Resolution Advanced Imaging System):
HiRAIS is an optical payload developed for the DubaiSat-2 mission and an improved version of DMAC (Dubai Medium Aperture Camera) flown on DubaiSat-1. HiRAIS offers a major improvement in image quality, implementing a larger payload optical design with a larger mirror diameter, resulting in a resolution of 1m for the PAN band and 4 m for the 4 MS (Multispectral) detectors. The detectors used are TDI CCDs which improve the SNR of the imagery. 30) 31)
The HiRAIS instrument was designed and developed at SI (Satrec Initiative) in cooperation with EIAST. HiRAIS consists of three elements:
• EOS (Electro-Optical Subsystem)
• SSRU (Solid-State Recorder Unit)
• ITU (Image Transmission Unit).
EOS is comprised of the following elements: telescope, ACM (Auxiliary Camera Module), and FPA (Focal Plane Assembly). EOS is a pushbroom type camera with 1 m GSD (Ground Sampling Distance) for a panchromatic imagery and 4 m GSD in four MS (Multispectral) bands (red, green, blue and NIR). The swath width of the generated image is 12 km.
Figure 19: Overview of the HiRAIS optical design (image credit: SI, EIAST)
EOS features a Korsch telescope with 5 mirrors. The optical design includes the main mirror (M1) of 415 mm diameter, 3 mirrors to increase the focal length up to 5.7 m, and a flat mirror to reflect light rays onto FPA. Light-weighted Zerodur is used for the mirrors, while CFRP material was used to design the main optomechanical structure of HiRAIS. The temperature balance of the mirror surfaces, the distances between the mirrors and the FPA are all actively controlled by a feedback heating system, which includes thermostats and heaters. Also passive cooling with heat dissipative materials.
Figure 20: Illustration of the EOS structure and components (image credit: SI, EIAST)
Table 2: Some parameters of the HiRAIS instrument
The ACM is a power-conditioning unit, which provides the necessary voltage levels for FPA. It also includes the CAN interface to control the FPA imaging operation and to provide the EOS telemetry to the OBC. The FPA includes the pushbroom CCD TDI sensor, which collects light from the telescope and converts it into an analog signal. It then converts these analog signals into a 10 bit digital data stream and sends it to SSRU.
Figure 21: EOS electronics modules (image credit: SI, EIAST)
• Two ACMs are used interfaced with FPA1 and FPA2. ACM regulates +28 V and converts it into different voltage levels that are essential for FPA operation by using DC/DC convertors and linear regulators. Switching circuits are provided in ACM to control the power tp each FPA. ACM is interfaced with two bus channels: PPS bus for the synchronization of the FPAs, and a CAN bus for commands and telemetries.
• The FPAs feature a PB (Processing Board) and a SB (Sensor Board). FPA-PB contains FPA digital parts, slow driver circuits, power regulation circuits and video signals processors while FPA-SB handles the sensor, low noise amplifiers and fast switching circuits. FPA-SB utilizes the CCD detectors with the TDI (Time Delay and Integration) function to take accurate image data at high speed.
• SSRU (Solid State Recorder Unit): SSRU handles the processing, storage and maintenance of image data. In total, it consists of 9 PCBs: 2 CIB (Control and Interface Boards), 4 SB (Storage Boards), 2 PB (Power Boards) and a BP (Backplane Board). All boards in SSRU are connected through the BP. The SSRU is capable of storing raw image data received from FPA during the image mode. SSR is also capable of compressing, encrypting and encoding the image data before sending it to the ITU (Image Transmission Unit) during downloading mode. SSRU has a storage capacity of 256 Gbit arranged in 4 identical SB.
The function of the SSRU is to receive, process, store and transmit the image data. The two CIB (Control and Interface Boards) of SSRU are used in cold redundancy. The CIB include a 8051 microcontroller (implemented in ACTEL's RT ProAsic3 FPGA) responsible for the overall management and operation of SSRU. It communicates with OBC through the CAN bus. The CIB receives the imagery from the FPA and bypasses the data to the dedicated memory location in SB (Storage Board). Moreover, CIB also handles the real-time compression, encryption and CCSDS formatting of image data before sending it to the XTU (X-band Transmitter Unit).
ITU (Image Transmission Unit): ITU provides X-band data transmission at a rate of 160 Mbit/s. ITU is divided into two main components: XTU (X-band Transmitter Unit) and high gain XANT (X-band Antenna). XTU provides the RF data signal to the antenna using XMOD (X-band Modulator), XLO (X-band Local Oscillator), and X-band power. XMOD modulates the image data signal from SSRU using the QPSK modulation scheme.
Table 3: Comparison of DubaiSat-1 and DubaiSat-2 payload instrument parameters
The nominal mission operations are as follows:
• Strip imaging
• Multi-target imaging
• Single-pass stereo-imaging
• Consecutive imaging and download
• Data download (day & night time).
The ground segment includes the main ground station and other supporting stations. The DubaiSat-2 ground system consists of MCS (Mission Control Station), the Subsidiary MCS, the Main IRPS (Image Receiving and Processing Station), the Customer IRPS, and the antenna system. 32)
• The Main MCS monitors and controls the satellite. It is located at EIAST's ground station in Dubai, UAE. The Main MCS performs satellite operation planning, which includes imaging and download scenarios, mission timeline, and orbit maintenance operation. It has direct interface with the Subsidiary MCS, Main IRPS, and EIAST's ground station antenna system. All imaging and downloading requests are received from Main IRPS.
Figure 22: Overview of the DubaiSat-2 system operation context (image credit: EIAST)
• The Subsidiary MCS is located in ground stations other than EIAST's ground station. It is connected directly to the Main MCS and the antenna system of the ground station where it is located. The Subsidiary MCS relays telecommands and telemetries between Main MCS and DubaiSat-2 via TCP/IP links (Internet). The Subsidiary MCS does not perform any satellite operation planning tasks. The main purpose of the Subsidiary MCS is to utilize the satellite when it is not over Dubai.
• The Main IRPS is located only at EIAST's ground station in Dubai, UAE. It has direct interface with Main MCS, Customer IRPS, and the end users. The Main IRPS generates schedule requests, which includes imaging and download schedules. It also archives image and ancillary data for product generation and distribution. The ancillary data consists of attitude and ephemeris data.
The Main IRPS receives imaging requests from the Customer IRPS and imaging orders from end users. It prioritizes and schedules the received requests and orders accordingly, then generates and transmits the schedule request to the Main MCS for satellite operation planning.
• The Customer IRPS is located at any ground station, other than EIAST's ground station, that desires to receive images data directly from DubaiSat-2. It has a direct interface only with the Main IRPS and the ground station's end users. The Customer IRPS archives imagery and ancillary data for product generation and distribution. It receives imaging orders from end users and sends imaging requests to the Main IRPS. An image request is generated based on the received imaging orders. When a Customer IRPS is to be installed, the geographical location of the customer's facility is taken into consideration to avoid overlap with other ground stations.
The Main MCS and Main IRPS share the same antenna system. The primary antenna used for the DubaiSat-2 mission operation is an 11.28 m S/X-band antenna located at EIAST's main facility in Dubai, UAE.
Figure 23: Photo of the EIAST ground station antenna (image credit: EIAST)
Some background of the DubaiSat program:
The DubaiSat program has played an important role in the establishment and development of the Space Industry in the UAE. The program was set forth as a result of a shift in strategy and economic structure. The collaboration with SI (Satrec Initiative) of Korea proved to be a successful partnership in the ability of a space-developing nation who has been empowered to empower others by making knowledge and technology accessible. Moreover, the impact of the satellites is felt across various sectors in the country aiding and contributing to the development of the nation. 33) 34)
EIAST (Emirates Institution for Advanced Science and Technology ) is a Government of Dubai organization, established in 2006, working towards the vision of Dubai and the UAE (United Arab Emirates) to transform the knowledge-based economy. EIAST's vision is to be recognized globally as a major contributor to the Space Industry. To accomplish this ambitious goal, the organization is developing the capabilities of the UAE Space sector by empowering the country with the necessary skills, environment and infrastructure to sustain the industry in the long run. EIAST moved towards acquiring such capabilities and competencies by means of a hands-on approach in the form of designing, manufacturing and operating DubaiSat-1 and DubaiSat-2 Earth Observation satellites. EIAST has sparked an interest within the country to continue to develop the Space Industry and to continue the path of developing the Advanced Science and Technology (AST) sector in the UAE. Last but not least, EIAST will provide its experience in establishing a Space industry as a model to other countries in the developing world. The knowledge and experience gained throughout the last six years could be passed along to other countries willing to venture into the final frontier.
DubaiSat-1 was developed and manufactured by EIAST's partners, Satrec Initiative, as part of the know-how and technology transfer program. The program included eight UAE engineers who worked alongside the SI engineers to gain know-how into the development of the various satellite subsystems. The engineers were involved in the design, manufacturing and testing of various parts and modules. DubaiSat-1 was successfully launched on July 29, 2009 on-board a Dnepr launch vehicle. EIAST engineers were fully involved in the launch and early operation of the satellite. Currently the satellite is operated from the ground station at EIAST's premises in Dubai, with the image processing and product development being done entirely by the UAE engineers based in Dubai.
The launch of DubaiSat-1 marked the beginning of the direct contribution of the DubaiSat program into the various sector of the economy. DubaiSat-1 images aided the infrastructure development projects in Dubai by providing up-to-date images of the various projects throughout the phases of development. Using those images, different image processing tools were applied to provide the key personnel with a Space view of each project and the completion of all the phases. In addition, DubaiSat-1 images were able to prove that the claims made on the sinking of the World Islands in Dubai were false. DubaiSat-1 provided the various government entities with images of the UAE to aid in urban planning and development projects across the country. In addition, engineers at EIAST have used the images to study environmental factors such as the quality of water around desalination plants, fog detection and red tide detection. EIAST has supported students in the academic sector by providing images from DubaiSat-1 to include them in their projects sand by guiding them on using different image processing techniques. On the international level, DubaiSat-1 images were provided during the flooding that occurred in Pakistan and to aid in disaster relief after the 2011 earthquake and tsunami in Japan.
DubaiSat-2 marked a new chapter for EIAST and for SI as the project was a new endeavor for both entities where the development of an entirely new satellite with new specifications was underway. The project started in 2008 with planned completion by the fourth quarter of 2012. DubaiSat-2 saw a shift in the role of EIAST's engineers who started working side-by-side with their Korean counterparts to develop different parts of the satellite system. The technology and know-how program continued with a greater contribution by the engineers into system, subsystem and modules designs. Moreover, the engineers had a bigger involvement in the integration and testing of the whole system. DubaiSat-2 will continue alongside DubaiSat-1 to provide images with better resolutions to all the sectors within the UAE to aid in development.
Benefits of the DubaiSat program to various sectors in UAE:
The direct contribution of an EO satellite on the different sectors of the country is realized upon the launch of the satellite and its full commissioning. The images proved to be of great value across all sectors within the UAE and internationally. There is no doubt that any country who owns an EO satellite benefits from it directly as it provides the highest frequency of imaging at the lowest costs in order to aid in the development and planning of key sectors.
The vision of this small satellite program was beyond the images; its impact expanded beyond the direct tangible products supplied to various sectors. The DubaiSat programs provided and are continuing to provide the economy and the community with intangible assets, and that is the knowledge and know-how. The real contribution of DubaiSat-2 to the UAE economy is the growth of the intellectual capital of the economy due to the hands-on training of EIAST's engineers in the various stages of development of the satellite. Through the DubaiSat-2 project, the country for the first time owned and developed its own intellectual property for space technology. The end of this project marks the beginning of the development of the UAE's space industry by passing on the leadership of satellite manufacturing and systems development to the UAE. In addition to the full input of the UAE engineers to the future projects, the infrastructure development to host the projects will commence, bringing back to the UAE the knowledge and technology transferred to the engineers during the DubaiSat-1 and DubaiSat-2 projects at SI in Korea.
EIAST's space program focused around all levels of satellite development, manufacturing, integration and application utilization to provide the organization with the ability to establish a complete Space Industry within the UAE. With that, the depth of knowledge was expanded and truly tested to clearly establish strong-holds within various fields of engineering in the context of Small satellite development.
The next phase of EIAST's journey is the development of the infrastructure for the industry. Moreover, EIAST is entrusting the Engineers with the leadership to be able to test their abilities by allowing them to develop systems independent of other entities. EIAST will continue to invest in human capital development with an increased emphasis on applied research and development within the scope of the Space Industry. Following this, the future holds an infrastructure development in the UAE to be able to host capabilities of small satellite development, design, testing, assembly and manufacturing. The beginning of the development of satellites in the UAE will see a definite spill over of technology into other sectors of the economy, as the cluster industries start forming. Moreover, EIAST will move towards developing and nurturing other manufacturing sectors in the UAE to become ready to develop Space ready components. Allowing the future knowledge-based economy to sustain itself by placing the groundwork to utilize the knowledge gained across all sectors in the economy.
In addition, EIAST will move towards providing students at various education levels with hands-on experience in the space industry through joint research projects with academia. This will enable a shift in the mindset and prepare the future generations for the coming of the knowledge-based economy.
The current space sector in the UAE is comprised of various private companies and two government organizations that serve various purposes in the industry. The Government sector consists of the Dubai-based EIAST and the UAE Space Reconnaissance Centre, which is under the UAE military. Thuraya and YahSat are privately owned companies involved in the Satellite Communication sector.
1) Information provided by Adnan Al Rais of MBRSC (Mohammed Bin Rashid Space Center), Dubai,UAE (United Arab Emirats).
2) "DubaiSat-2 Technical Overview," EIAST document, June 2, 2011, the information was provided by Salem Al Marri of EIAST.
3) Ee-Eul Kim, Amer Al Sayegh, "Early Operation Result of DubaiSat-2, a 1-m Resolution Small Satellite," Proceedings of the 4S (Small Satellites Systems and Services) Symposium, Port Petro, Majorca Island, Spain, May 26-30, 2014
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7) Salem Al Marri, DubaiSat-1 Mission & DubaiSat Future Programs," Proceedings of the 9th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 8-12, 2013
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16) Information provided by Salem H. Al Marri of EIAST, Dubai.
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21) Information provided by Fatma Ali AlSumatti (Officer, Business Development & External Relations) of MBRSC (Mohammed Bin Rashid Space Center), Dubai.
22) Fabrizio Pirondini, Salem Al Marri," The DubaiSat-2/Deimos-2 Constellation: Public Private Cooperation between Emirates and Spain," Proceedings of the 65th International Astronautical Congress (IAC 2014), Toronto, Canada, Sept. 29-Oct. 3, 2014, paper: IAC-14,B1,1.8
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28) Information provided by Salem Al Marri, Assistant Director General for Scientific and Technical Affairs, EIAST, Dubai.
29) "EIAST Releases first images of DubaiSat-2," Space Daily, Dec. 12, 2013, URL: http://www.spacedaily.com/reports/EIAST_Releases_first_images_of_DubaiSat_2_999.html
30) Suhail AlDhafri, Hamad AlJaziri, Khalid Zowayed, Jiho Yun, Sanjin Park, "DubaiSat-2 High Resolution Advanced Imaging System (HiRAIS)," Proceedings of the 63rd IAC (International Astronautical Congress), Naples, Italy, Oct. 1-5, 2012, paper: IAC-12.B4.6A.6
31) "DubaiSat-2 mission payload – HiRAIS," EIAST News, Nov. 26, 2012, URL:
32) "DubaiSat-2 Ground Segment," URL:
33) Ahmed AlMansoori, Sarah Amiri, Omran Sharaf, "UAE & the Space Industry - through the lens of DubaiSat," Proceedings of the 63rd IAC (International Astronautical Congress), Naples, Italy, Oct. 1-5, 2012, paper: IAC-12- B4.1.2
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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 (firstname.lastname@example.org).