KOMPSAT-3 (Korea Multi-Purpose Satellite-3) / Arirang-3
KOMPSAT-3 is an optical high-resolution Korean observation mission of KARI (Korea Aerospace Research Institute). The mission is funded by MEST (Ministry of Education, Science and Technology). The project was started in 2004. The objective is to provide observation continuity from the KOMPSAT-1 and KOMPSAT-2 missions to meet the nation's needs for high-resolution optical imagery required for GIS (Geographical Information Systems) and other environmental, agricultural and oceanographic monitoring applications.
A further goal is to meet the nation's satellite demand and form a technology infrastructure that will make inroads into the world space industry at a stage when the industry is improving the capability to design and develop highly advanced remote sensing satellites.
Figure 1: Illustration of the KOMPSAT-3 spacecraft (image credit: KARI)
The KOMPSAT-3 spacecraft bus design, development and integration is being led at KARI. The spacecraft is 3-axis stabilized. The agile spacecraft features a body pointing capability of ±45º into any direction (cross-track or along-track). This satellite agility permits event monitoring as well as single-pass stereoscopic observations. 1) 2) 3)
- SI provided the DM (Development Model) of power controller, and on-board computer processor module as well as six FM coarse sun sensors to KARI. Image Receiving and Processing Station and several key subsystems of Mission Control Station is currently being developed.
- SI developed OBC (On-Board Processor) module with reliable RTOS and high-end CPU. SI developed a space qualified processor module based on TSC695F CPU (ERC32).
- SI was contracted by KARI to develop PADS ( Precision Attitude Determination Software) of KOMPSAT-3. PADS is a software package which performs precision attitude determination by using precise orbit data and attitude sensor data (star trackers and gyros). This software estimates all sensitive parameters including misalignment angle between each sensor and optical bench, the drift rate error and scale factor error of each gyro and etc. PADS includes simulated sensor data generator, data analysis tools, validation tools as well as animation tools.
The KOMPSAT-3 SADM (Solar Array Deployment Mechanism) was the first flight hardware contract for SpaceTech GmbH of Immenstaad, Germany signed in 2005/2006 with Korean Airlines Ltd. The deployment mechanism is based on an earlier patented design by SpaceTech exhibiting very low friction, high torque margin and at the same time low deployment shock through a cam/spring driven system. The contract also included the delivery of stiffening mechanism for each of the solar arrays, to achieve a high eigenfrequency of the solar array wings in order to allow agile satellite operation/pointing. 6)
Table 1: Main parameters of the spacecraft
RF communications: The S-band is used for TT&C communications. The X-band is used to downlink the payload data.
Figure 2: System architecture of the KOMPSAT-3 mission (image credit: KARI)
Figure 3: Photo of the KARI KOMPSAT-3/Arirang-3 spacecraft at TNSC on May 1, 2012 (image credit: The Korea Herald)
Launch: The KOMPSAT-3 (Arirang-3) spacecraft was launched as a "co-payload" on May 17, 2012 (16:39 UTC) from the Tanegashima Space Center of JAXA, Japan on the H-IIA launch system. The primary payload on this flight was GCOM-W1 (Global Change Observation Mission - Water 1) of JAXA (nickname: Shizuku) with a launch mass of ~ 1990 kg. Launch provider: Mitsubishi Heavy Industries, Ltd. 7) 8) 9)
A contract between the launch service provider MHI (Mitsubishi Heavy Industries, Ltd.) and KARI was signed in January 2009. This represents the first satellite launch services order placed to MHI by an overseas customer. 10)
Further secondary payloads are:
• SDS-4 (Small Demonstration Satellite-4) of JAXA with a mass of ~ 48 kg
• HORYU-2, a technology demonstration satellite mission of KIT (Kyushu Institute of Technology), Fukuoka, Japan with a mass of ~ 7 kg.
Orbit: Sun-synchronous near-circular orbit, altitude = 685.1 km, inclination = 98.13º , period = 98.5 minutes, LTAN (Local Time on Ascending Node) = 13:30 hours.
• May 2015: The U.S. NGA (National Geospatial-Intelligence Agency) provided an absolute geolocation accuracy evaluation for KOMPSAT-3 using 25 KOMPSAT-3 images provided by SI (Satrec-Initiative Co. Ltd.), Daejeon, Korea. The outcome is as follows: 13)
Table 2: Geolocation accuracy results
The Horizontal Error 90% (HE90) is 13.3 meters.
Figure 5: KOMPSAT-3 absolute geolocation accuracy (image credit: NGA)
• The KOMPSAT-3 spacecraft and its payload are operating nominally in 2015. 14)
• The KOMPSAT-3 spacecraft and its payload are operating nominally in 2014. 15)
Table 3: Performance of KOMPSAT-3 after CVP (Cal/Val Phases) 16)
Figure 6: Geometric Cal/Val framework of KOMPSAT-3 (image credit: KARI) 17)
Legend to Figure 7: The Maracanã stadium (official name: Estádio Mário Filho, Maracanã being its neighborhood's name) in Rio de Janeiro (Brazil) is one of the biggest football stadiums in the world, and it is home of the four biggest football teams of Rio: Flamengo, Botafogo, Vasco da Gama and Fluminense.
• In July 2013, ScanEx RDC of Moscow, Russia, became the official distributor of the KOMPSAT data series in Russia and the CIS countries (Ukraine, Belarus, Moldova, Kazakhstan, Uzbekistan, Kyrgyzstan, Turkmenistan, Armenia and Azerbaijan), following the signing of an agreement with the Korean company Satrec Initiative Co., Ltd. 19)
• As of May 17, 2013, KOMPSAT-3 is 1 year on orbit. For the first year of operation, the performance of KOMPSAT-3 was validated, and the worldwide commercial service of KOMPSAT-3 imagery was started by SI (Satrec Initiative), since April 1, 2013. 20) 21)
- KOMPSAT-3 can provide sub-meter images with various imaging modes including single pass stereo. It will continue to provide sub-meter imagery to domestic and international users for the applications of public safety, resource management, environmental monitoring, location-based services, intelligence and disaster monitoring.
Figure 8: KOMPSAT-3 sample image capture of the Pentagon (image credit: Satrec Initiative, KARI)
• April 8, 2013: KARI (Korea Aerospace Research Institute) has announced the start of commercial services of KOMPSAT-3 after in-orbit validation on 29 March, 2013. Now, Satrec Initiative will distribute KOMPSAT-3 imagey on a world-wide basis. KOMPSAT-3 provides 0.7m panchromatic and 2.8m multispectral imagery. KOMPSAT-3 has a unique local access time of 13:30 hours, and the imaging capability in the afternoon will increase the chance of acquiring cloud-free images over specific targets for the end users. 22)
Figure 9: KOMPSAT-3 image ( 70 cm resolution) of San Diego, CA, USA acquired on March 2, 2013 (image credit: KARI)
• In January 2013, KOMPSAT-3 is still in the commissioning phase and should be operational soon. 23)
Figure 10: KOMSAT-3 test image of Niagara Falls, USA, Canada (image credit: KARI, Ref. 23)
• In November 2012, KARI awarded SI (Satrec Initiative)of Daejeon, Korea a contract as the 'worldwide exclusive representative' for KOMPSAT imagery sales. This applies to imagery of the KOMPSAT-2, -3 and -5 missions. KARI has chosen Satrec Initiative for its ability to develop international customers and data distribution network, as well as long experience in space industry. Satrec Initiative will deliver high quality image data to worldwide customers through collaboration with existing satellite operators, and in addition to that, building its own KOMPSAT data distribution network. 24)
Figure 11: Image of the Burj Tower of Dubai, observed by KOMPSAT-3 in the fall of 2012 (image credit: KARI)
Legend to Figure 11: With 829.8 m, the Burj Tower is he tallest man-made structure in the world. The building officially opened on January 4, 2010.
Figure 12: Image of San Francisco acquired by KOMPSAT-3 on August 10, 2012 prior to Cal/Val (image credit: KARI)
• On June 15, 2012, KARI released the first image obtained by KOMPSAT-3 (Figure 13). A check-up of the condition, attitude control systems, and on-board equipment has confirmed that the KOMPSAT-3 is functioning normally. KOMPSAT-3 will be scheduled to start its full operation in September after further inspection of the satellite and its payloads. 25)
Figure 13: Comparison of an image scene observed by AEISS on KOMPSAT-3 (right) and observed by MSC on KOMPSAT-2 (left), image credit: KARI
Legend to Figure 13: The image scene is of Jeodong Port on Ulleungdo Island, Korea. The KOMPSAT-3 image (right) clearly shows the roofs of the buildings, cars on the road, and the ships and tide breakers along the shore.
• After the separation of KOMPSAT-3 spacecraft at 16 minutes into the flight, the GCOM-W1 spacecraft separated from the launch vehicle 23 minutes after launch (Ref. 12).
Sensor complement: (AEISS)
AEISS (Advanced Earth Imaging Sensor System)
AEISS is a high-resolution pushbroom imager (Pan and MS) for land applications of cartography and disaster monitoring. The prime instrument of the mission is being developed by KARI with technical support from EADS Astrium GmbH, Friedrichshafen. In turn, DLR was subcontracted by Astrium for the development of the FPA (Focal Plane Assembly) and CEU (Camera Electronics Unit). 26) 27) 28) 29)
There are two major subsystems to AEISS: EOS and the OM (Optical Module) with the telescope.
Figure 14: Schematic view of the EOS configuration (image credit: KARI)
EOS (Electro-Optical Subsystem):
The EOS architecture of AEISS is comprised of the following modules: OM (Optical Module) and CEU which in turn consists of the CEUP (CEU Power supply), CC (Camera Controller), and FPA (Figure 14). The CEUP and CC modules are actually part of the spacecraft bus, while the FPA is integrated with OM to constitute EOS.
The FPA design features a modular and scalable architecture; it has a total of six independent FPMs (Focal Plane Modules) in a stacking configuration, 2 are dedicated for the Pan bands and 4 are used for the MS bands. One Pan module operates as primary while and the other is used as a cold redundant module. Each FPM consists of a CCD module and spectral filters and FPE (Focal Plane Electronics).
Figure 15: Stacking configuration of the six FPMs (image credit: KARI, DLR)
EOS features also a focus mechanism for the best focusing and combined active/passive thermal control mechanism to take images at the best temperature condition. The focusing control is performed using the displacement of the heater ring attached on the upper and lower side of the telescope by heating one of two rings, thereby expecting downward or upward movement of the corresponding secondary mirror.
The imagery generated in EOS are transferred to the PDTS (Payload Data Transmission Subsystem) to be downlinked to Ground Station (GS) after compression, encryption, etc.
Figure 16: Photo of the FPA (view from the sensor/baffle side), image credit: DLR 30)
Table 4: Performance parameters of the AEISS instrument
CEU (Camera Electronics Unit): The CEU manages the overall operation of EOS; hence, it defines the functionality and operational capabilities of EOS which implies also the performance of the FPA. The CEU architecture is shown in Figure 17. The CC (Camera Control) unit of CEU communicates with the spacecraft OBC via a MIL-STD-1553B interface.
Figure 17: Logical block diagram of the CEU architecture (image credit: DLR, KARI)
Optical design of the Korsch-type telescope:
The large telescope of AEISS features a CFRP (Carbon Fiber Reinforced Plastic) envelope material to achieve the required low-mass structure with high stiffness and dimensional stability. Throughout the launch phase and under variable on-orbit conditions, the instrument has to keep the following optical elements in place within tolerances of a few µm and µrad (Table 6): 5 mirrors, the FPA (Focal Plane Assembly) with 1 panchromatic and 4 multispectral bands, and two Star Trackers.
The development, manufacturing and testing under various load conditions (including thermal cycling) of the HSTS (High Stability Telescope Structure) was done and verified by EADS Astrium. 31)
Figure 18: Illustration of the AEISS telescope with EOS and star trackers (image credit: KARI, EADS Astrium)
Table 5: Main requirements for HSTS
SESO (Société Européenne de Systèmes Optiques) of Aix en Provence, France was awarded a subcontract for the manufacturing of the whole set of telescope mirrors (5 mirrors, 2 flight models). SESO activities did also include the mechanical design, manufacturing and mounting of the attachment flexures between the mirrors, the integration on the CFRP (Carbon Fiber Reinforced Plastics) baseplates, and the environment tests of the 5 mirrors. 32)
The optical design features a Korsch-type telescope with 5 mirrors, as presented in Figure 19. It includes:
• An on-axis Cassegrain telescope with a primary mirror (M1 concave) and a secondary mirror (M2 convex)
• A tertiary off-axis mirror (M3 concave off-axis)
• An on-axis M4 aspherical concave mirror
• A folding flat mirror (M5), for reasons of overall volume limitations.
Figure 19: Cross-section of the optical system (image credit: SESO)
Table 6: In-orbit stability requirements of HSTS
The use of CFRP, especially the selection of UHM (Ultra High Modulus) carbon fiber compounds, offer the possibility to build up laminates with CTE (Coefficient of Thermal Expansion) characteristics close to zero or even with a negative CTE. A CTE of zero fits well with mirrors made of Zerodur, so that the telescope becomes insensitive not only against temperature changes, but also against temperature gradients.
Figure 20: Configuration of the AEISS optical system (image credit: KARI, EADS Astrium)
Figure 21: Alternate view of the AEISS optical system (image credit: KARI, EADS Astrium)
AEISS pre-flight calibration: A LUIS (Large Uniform Light Source) was used for the electro-optical tests of the payload such as signal to noise ratio, linearity, saturation and uniformity of radiometric response. The uniform light source provides known radiance levels with absolute accuracy traceable to the NIST (National Institute of Standards and Technologies) or equivalent primary standards of radiance scale. 33)
Table 7: Performance parameters of the KOMPSAT missions 34)
Figure 22: KOMPSAT series comparison (image credit: KARI)
The ground segment at KARI site comprises two elements:
1) MCE (Mission and Control Element). The MCE provides the mission planning and satellite command, control functions that allow the operators to perform the mission, and maintain the health of the satellite. The MCE provides the S-band command and telemetry communications interface to the satellite and the necessary functions to operate the satellite.
2) IRPE (Image Reception and Processing Element). The IRPE provides the capability to receive and store KOMPSAT-3 data, support to collection planning, generate standard and value added imagery products, and distribute imagery products to users. The IRPE provides the X-band reception interface from the satellite.
SI developed the IRPS (Image Reception and Processing Station). The IRPS consists of four subsystems;
• UIS (User Interface Subsystem)
• ICPS (Image Collection Planning Subsystem)
• DIS (Direct Ingestion Subsystem)
• PMS (Product Management Subsystem).
The UIS is to process ‘Product Order' of the External User. It virtualizes a convenient operator interface to manage orders from the end-users and the end-user interface such as catalog searching, order placing, order status monitoring and product download.
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22) "Commercial sales of KOMPSAT-3 has started," Satrec Initiative, April 8, 2013, URL: https://www.satreci.com/eng/ds1_1.html?tno=100&db=pr_board&no=25
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24) "Satrec Initiative Announces Agreement with Korea Aerospace Research Institute," Satrec Initiative, Nov. 15, 2012, URL: https://www.satreci.com/eng/ds1_1.html?tno=100&db=pr_board&no=22
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32) Hélène Ducollet, Christian du Jeu, Seung-Hoon Lee, "Manufacturing of the Spaceborne Camera Mirrors for KARI's LEO Satellite," ICSO 2010 (International Conference on Space Optics), Rhodes Island, Greece, Oct. 4-8, 2010
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34) Sang-Ryool Lee, Joo-Jin Lee, "The History of the Korea Multi-Purpose Satellite Program," Proceedings of the 60th IAC (International Astronautical Congress), Daejeon, Korea, Oct. 12-16, 2009, IAC-09.E4.3.3
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 (email@example.com).