KOMPSAT-3A (Korea Multi-Purpose Satellite-3A) / Arirang-3A
KOMPSAT-3A is Korea's first Earth observation/Infrared satellite with two imaging systems on board. The main goal of the KOMPSAT-3A program of KARI (Korea Aerospace Research Institute) is to develop an Earth observation satellite to obtain IR (Infrared) and high resolution EO (Electro-Optical) images for GIS (Geographical Information Systems) applications in environmental, agricultural and oceanographic sciences as well as natural disasters.
A prime example of cooperation between the government and private sector to commercialize space technologies is the current KOMPSAT-3A project. KARI designed and built KOMPSAT-3 , an Earth observation satellite that was launched in May 2012 from Japan's Tanegashima Space Center. Now KARI is assisting Korea Aerospace Industries (KAI) and Asia-Pacific Aerospace build the KOMPSAT-3A, a near replica of the KOMPSAT-3, in an exercise that will transfer technologies to these firms and enable them to enter the satellite supplier market. The Ministry of Science, ICT and Future Planning (MSIP) is tasked by the president to conduct studies and to develop strategies for the commercialization of the space sector, but the ministry delegates most of the actual work to KARI for subsequent review by the MSIP's Space Policy Division. The MSIP has commissioned KARI's Policy and International Cooperation Division to conduct an ongoing study on the commercialization of space technologies. 1)
Figure 1: Illustration of the KOMPSAT-3A spacecraft (image credit: KARI)
The spacecraft is being built at KAI (Korea Aerospace Industries, Ltd.) with HQs at Sacheon, Korea. The KOMPSAT-3A satellite carries an optical imaging system sensitive to wavelengths in the visible and infrared range, building on the KOMPSAT-2 and -3 satellites that carried similar payloads.
KOMPSAT-3A is the sister of KOMPSAT-3, using an identical satellite bus and payload with the only difference being an added infrared capability via beamsplitter and relay optics. The satellite will expand the existing constellation and ensure data continuity after KOMPSAT-3 reaches is planned EOL (End-of-Life) date after three to five years of operation. The main purpose of the optical KOMPSAT spacecraft is to deliver high-resolution imagery for Geographical Information Systems as well as environmental, agricultural and oceanographic monitoring.
The satellite bus consists of a hexagonal platform and a cylindrical nadir module hosting the optical payload systems. Beginning in the aft, the satellite consists of a Spacecraft Adapter interfacing with the launcher, a Propulsion Module, an Equipment Module and the Nadir Module. The satellite has a mass of just under 1,100 kg measuring 2.0 m in diameter and standing 3.5 m tall. The design life is 4 years.
Figure 2: Schematic of the KOMPSAT-3A structural components (image credit: KARI)
ADCS (Attitude Determination and Control Subsystem): The spacecraft is equipped with three different attitude sensors - a series of coarse sun sensors, an IMU (Inertial Measurement Unit) and star trackers. The coarse sun sensors provide a basic sun vector direction to be used in the event of a spacecraft safe mode to keep the solar panels pointed to the sun to ensure good power generation. The star trackers use optical imaging heads and electronics units to capture imagery of the star-filled sky using a narrow field of view. The stars in that field of view are compared to a catalog of known star constellations from which the three-axis orientation of the satellite can be determined to provide very precise pointing information. Inertial measurement data is used to measure body rates used to reduce spacecraft motion to allow the star trackers to acquire star patterns which requires low body rates on the satellite.
Attitude actuation is provided by reaction wheels. The reaction wheel assembly represents a rotating mass that is driven by a motor – when accelerating or decelerating the wheel, the satellite body will move into the opposite direction as the result of induced counter torque. To allow de-spins of the wheels, the satellite uses magnetic torquers that use the Earth's magnetic field to create a force that counters that of the de-spinning wheel to desaturate the reaction wheels at regular intervals. The agile attitude control system achieves a pointing accuracy of 0.025º and can support quick slew maneuvers up to ±45 º off nadir. This satellite agility permits event monitoring. Position and velocity measurements are provided by a GPS unit.
EPS (Electrical Power Subsystem): Provision of 1.4 kW with three deployable solar panels.
Orbit corrections and maintenance are supported by a hydrazine propulsion system that consists of a central hydrazine tank, a pressurization system and two thruster banks of four 4.5 N thrusters. The thrusters use the catalytic decomposition of hydrazine monopropellant over a heated catalyst bed to generate thrust.
RF communications: Use of an S-band systems for TT&C communications. A high-speed X-band system (1 Gbit/s) is used to downlink the acquired imagery from a large solid-state memory module.
Figure 3: Photo of the KOMPSAT-3A spacecraft at integration (image credit: KARI)
Figure 4: Photo of KOMPSAT-3A during assembly at Jasny (image credit: Anatoly Zak)
Launch: The KOMPSAT-3A spacecraft was launched on March 25 2015 (22:08:53 UTC) on a Dnepr-1 vehicle (RS-20) from the Jasny Dombarovsky launch site in Russia. The launch was executed by the Russian Strategic Rocket Forces of the Russian Ministry of Defense with the support of the Russian, Ukrainian and Kazakhstan organizations, which are part of the ISC (International Space Company)Kosmotras industrial team. 2) 3) 4)
After mounting tensions between Russia and the Ukraine and a continued dispute over commercial revenue, a Ukrainian-built Dnepr rocket finally lifted off from a Russian rocket silo on March 25, 2015, carrying the KOMPSAT-3A Earth Observation Satellite into orbit for South Korea (Ref. 4).
Orbit: Sun-synchronous orbit, altitude = 528 km, inclination = 97.5º, LTAN = 13:30 hours, period = 98.5 minutes, repeat cycle = 28 days.
• The KOMPSAT-3A/Arirang-3A spacecraft and its payload are operating nominally in January 2017. 5)
Figure 5: Sample KOMPSAT-3A high-resolution image of the Dubai International Airport, UAE (United Arab Emirates), acquired on December 20, 2016 (image credit: SIIS, KARI)
• October 25, 2016: A high accuracy grid of 21 cm in elevation was verified by PhotoSat for KOMPSAT-3A data. The Canadian Vancouver-based PhotoSat company invented in recent years a new technology, that generates the world's most accurate satellite surveying; the technique specializes in elevation surveying for civil engineering infrastructure projects.
PhotoSat has just published the survey data processed from the new 40 cm resolution KOMPSAT-3A satellite; this has been verified as accurate to within 21 cm in elevation. The stereo KOMPSAT-3A data was provided to PhotoSat by SIIS (SI Imaging Services) of Daejeon, Korea. SIIS is in charge of commercial marketing of the KOMPSAT satellite series that KARI (Korea Aerospace Research Institute) has developed and operates. 6) 7)
For the study, PhotoSat produced a 1m grid of elevations using their proprietary geophysical processing technology with stereo satellite images taken by KOMPSAT-3A. The resulting elevations were then compared to a 1 m LiDAR elevation grid in Southeast California, accurate to approximately 5 cm in elevation and available on the OpenTopography website. The size of the comparison area was 86 km2. The resulting 21 cm RMSE (Root Mean Square Error) elevation accuracy was measured at 6,294 survey check points.
Figure 6: Left: KOMPSAT-3A 40 cm resolution orthophoto. Right: PhotoSat 1m elevation grid showing the histogram of the elevation differences to a highly accurate LiDAR survey on the right (image credit: PhotoSat)
PhotoSat's highly accurate survey grids have been used for years by oil and gas and mining engineers as a cost -effective alternative to ground GPS and airborne LiDAR surveying. The stereo satellite photos from KOMPSAT-3A will enable PhotoSat to deliver engineering quality survey data everywhere in the world.
Legend to Figure 7: This is a former open pit diamond mine, now inactive, located in Mirny, Eastern Siberia, Russia. The mine is 525 m deep (4th in the world) and has a diameter of 1,200 m; it is one of the largest excavated holes in the world.
"The KOMPSAT -3A satellite data is the highest quality KOMPSAT satellite photo data that PhotoSat has processed," said Gerry Mitchell, President of PhotoSat. "In this test, an elevation grid extracted from stereo KOMPSAT-3A satellite photos matches a highly accurate LiDAR elevation grid to better than 21 cm in elevation. This result takes satellite elevation surveying into the engineering design and construction markets and directly competes with LiDAR and high resolution air photo surveying for applications like mine tailings monitoring."
According to Moongyu Kim, President & CEO of SIIS (Daejeon, Korea), the 40 cm GSD (Ground Sample Distance) of KOMPSAT-3A data is explained by the fact that SIIS is providing oversampled data products just as Airbus DS does with the Pleiades mission. The native resolution of KOMPSAT-3A data at nadir is still 54 cm. — PhotoSat has provided its surveys for other high-resolution missions as well. Examples: The Worldview-3 data of DigitalGlobe has an RMSE of 15 cm (30 cm GSD); the data of WorldView-2 provides a 35 cm RMSE in elevation for (50 cm GSD). Hence, the result of 21cm RMSE for KOMPSAT-3A fits well in terms of the resolution (40 cm GSD), valid in terms of producing the DEM (Digital Elevation Model).
• On July 5, 2016, SIIS (SI Imaging Services) initiated commercial services of the KOMPSAT-3A imagery — the satellite is part of the KARI (Korea Aerospace Research Institute) KOMPSAT Program for EO (Earth Observation) services. The earth observation satellite offers clear imagery with a resolution of < 0.5 m. This makes Korea the world's second country to enter the < 0.5 m resolution commercial satellite imagery market after the United States. 9)
- KOMPSAT-3A is the sister spacecraft of KOMPSAT-3, using the same satellite bus and payload. Its local access time is very unique at 13:30 hours, which is the same as that of KOMPSAT-3. However, since KOMPSAT-3A was put into lower orbit than KOMPSAT-3 (528 km for KOMPSAT-3A versus 675 km for KOMPSAT-3), it delivers clearer and sharper imagery. The same imaging time and similar payload with KOMPSAT-3 will amplify its capacity and help to even out the difference of the color. With KOMPSAT-3A imagery commercially available today at 0.5 m resolution at customer's service, decision makers have new and more options to consider for their needs.
- SIIS (SI Imaging Services) is a leading satellite imagery provider for Remote Sensing and Earth Observation. SIIS is the exclusive worldwide marketing and sales representative of the KOMPSAT constellation, including KOMPSAT-2, KOMPSAT-3, KOMPSAT-3A, and KOMPSAT-5. It is a unique combination of VHR(Very High Resolution)optical and SAR (Synthetic Aperture Radar) data with variable local access times from the morning to the afternoon (06:00, 10:50, 13:30, 18:00 hours). SIIS provides the satellite imagery worldwide through over 80 sales partners.
Figure 8: KOMPSAT-3A sample image of downtown New York, acquired on Nov. 4, 2015 (image credit: KARI, SIIS)
Figure 9: KOMPSAT-3A sample image of the Ferrari World, Abu Dhabi, acquired on October 26, 2015, (image credit: KARI, SIIS)
• The KOMPSAT-3A spacecraft and its payload are operating nominally in 2016. 10)
• October 2015: An optimization approach is proposed to operate KOMPSAT-3 and KOMPSAT-3A in a more efficient way. For this purpose, the project confirmed communication windows, geometrical characteristics, and contact sequences of the KGS (KARI Ground Station) with KOMPSAT-3A and KOMPSAT-3 during operation period by using the real orbit data. Also, a mitigation plan is proposed to decrease the possibility of KOMPSAT-3 and KOMPSAT-3A flying over the KGS at the same time. Finally, some issues are removed such as contact overlap time, the interference possibilities and so on. This paper contains a more representative analysis result of real satellite operation and could be a reference to setup an operational strategy for the multiple satellite operations in terms of orbit and their communication windows.11)
Table 1: Mission status of the KOMPSAT series as of September 2015
Table 2 shows the mission orbits of KOMPSAT-3A and KOMPSAT-3. Due to the same LTAN between KOMPSAT-3A and KOMPSAT-3 with different altitude, the close approach of two satellites are foreseen. For example, the difference of orbital periods makes the two satellites to be close each other every second day.
Table 2: Mission orbits of KOMPSAT-3A and KOMPSAT-3
• The nominal operations phase of the KOMPSAT-3A mission was started after the Cal/Val completion in September 2015. 12)
• As of April 2015, KARI is in the process to provide initial operations of the KOMPSAT-3A mission. 13)
- First high-resolution images (55 cm) of KOMPSAT-3A were released on April 1, 2015, showing the Dubai Palm Jumeurak island and the Burj Al Arab hotel area. In addition, an infrared image (5.5 m) of the Han River in Korea is provided. 14)
Figure 10: A test image of the KOMPSAT-3A AEISS-A instrument, acquired on April 1, 2015 showing the Dubai Palm Jumeurak island (image credit: KARI)
Figure 11: AEISS-A instrument test image (55 cm) of KOMPSAT-3A, acquired on April 1, 2015 showing the Burj Al Arab, UAE (image credit: KARI, SIIS)
Figure 12: KOMPSAT-3A daytime infrared imagery of the IIS (5.5 m resolution), acquired on April 1, 2015, showing a portion of the Han River in Seoul, Korea (image credit: KARI, SIIS)
Legend to Figure 12: The lower temperatures (forest region) are coded in blue while the warmer ares are coded in lighter colors.
• March 27, 2015: KOMPSAT-3A acquired its first image a day after launch. This was possible because the bus initial activation and normal mode transition were finished in a day which had been done in three days for previous satellite programs (Ref. 12).
Figure 13: Comparison of KOMPSAT-3A and KOMPSAT-3 images. The image on the left is the KOMPSAT-3A image acquired on March 27, 2015.On the right side is the KOMPSAT-3 image. The KOMPSAT-3A is image shows high quality even before calibration (image credit: KARI)
• The KOMPSAT-3A Earth observation satellite, launched on March. 25 2015, has successfully been deployed in orbit and all systems have been tested and verified.
• The KOMPSAT-3A was sent on its way under 15 minutes after liftoff, deployed into the expected orbit of 528 km altitude, according to Russian press reports. KOMPSAT-3A was programmed to complete its initial steps shortly after separation, deploying its three solar panels, acquiring a stable orientation and switching on its transponders to begin sending data.
Some background on the KOMPSAT imagery distribution: In November 2012, Satrec Initiative (SI) of Daejeon, Korea announced an agreement with KARI (Korea Aerospace Research Institute) for "Worldwide Marketing and Sales Representative of KOMPSAT-2, -3, -3A and -5 image data." KARI assigned Satrec Initiative as the ‘worldwide exclusive representative' for KOMPSAT imagery sales. 15)
In response, the SI (Satrec Initiative Group) started a new company, SIIS (SI Imaging Services).The SIIS facilities are located at KARI. SIIS is the satellite imagery provider for Remote Sensing and Earth Observation. SIIS is the exclusive worldwide marketing and sales representative of the KOMPSAT series which is KOMPSAT-2, -3, -3A, -5 and DubaiSat-2. The DubaiSat-2 spacecraft was developed by SI in cooperation with MBRSC (Mohammed Bin Rashid Space Center), Dubai, UAE (United Arib Emirates), formerly EIAST (Emirates Institution for Advanced Science and Technology). On April 18, 2015, EIAST was officially renamed to MBRSC. 16)
Sensor complement: (AEISS-A, IIS)
The high-resolution electronic optical camera AEISS-A features 55cm class optical photography, which is the highest resolution among cameras mounted on domestic satellites. The IR sensor, which is capable of detecting heat on the ground, is used to observe fires, volcanic activity and urban thermal islands during day- and nighttime. Arirang-3A operates in the sun's synchronous orbit at an altitude of 528 km and passes over Korea twice (day and night), photographing the Korean Peninsula for up to 50 minutes each day.
AEISS-A (Advanced Earth Imaging Sensor System-A)
The AEISS-A instrument is similar to that of the KOMPSAT-3 spacecraft and was developed by KARI with technical support from Airbus Defence and Space (former EADS Astrium) and DLR (German Aerospace Center) that developed the FPA (Focal Plane Assembly) and the main CEU (Camera Electronics Unit).
AEISS-A consists of an Optical Module and CEU which itself is comprised of a power supply, a camera controller and the FPA (Focal Plane Assembly). The electronics interface with the onboard computer via a 1553 data bus to exchange commands and housekeeping data. The Optical Module is cylindrical in shape, enclosed in a CFRP (Carbon Fiber Reinforced Plastic) structure that provides a high thermal stability and structural stability, which is also provided by support struts to ensure the telescope structure remains in place with tolerances of a few micrometers. The two star trackers of the spacecraft are installed on the aft segment of the cylindrical optical unit. The optical unit measures 1.3 m x 2.0 m and has a mass of around 80 kg (Ref. 4).
The telescope uses a Korsch combination with three aspheric mirrors and two folding mirrors, using an aperture diameter of 80 cm. This design was chosen because of its simplicity and compact size – fitting within the small spacecraft platform. An entrance baffle is used for stray light rejection. Light entering the instrument passes through a Cassegrain-arrangement with an on-axis system of the concave M1 primary mirror and an on-axis convex M2 secondary mirror. The light then passes to an off-axis M3 mirror (concave) reflecting the light to an on-axis M4 aspherical concave mirror passing it on to the M5 folding mirror focusing the radiation onto the FPA. The additional M3 and M4 mirrors create a focal length of 8.6 m.
The telescope mirrors are installed on a CFRP structure while the mirrors themselves consist of Zerodur that provides an extremely high thermal stability with low thermal gradients throughout the structure.
Figure 14: Photo of the optical module (image credit: KARI, Airbus DS)
Figure 15: Photo of the FPA (image credit: KARI, DLR)
The FPA of the AEISS instrument features a stacked architecture - with two Focal Plane Modules dedicated to the panchromatic band covering a wavelength range of 450 - 900 nm. The two PAN modules are operated in cold redundancy with one module active at a given time. The remaining four Focal Plane Modules are covering the four multispectral channels of AEISS-A, - a blue channel (450-520 nm), green (520-600 nm), red (630-690 nm) and near infrared (760-900 nm).
The panchromatic line array detector consists of 12,000 pixels per module using a TDI (Time Delay Integration) in four stages creating a raw data rate of 3.84 Gbit/s. The multispectral channels use 6,000 pixel line array detectors with TDI employing pixel binning and delivering data at 240 Mbit/s per channel. The optical payload uses anti-blooming techniques and a 14 bit data quantization. After going through onboard processing and compression, data is stored in a solid-state memory for downlink via a high-speed X-band system.
The FPA includes an active focus control system that uses heater rings on the lower and upper side of the telescope attachment. Heating the rings leads to a thermal expansion that allows for a slight displacement of the secondary mirror.
Overall, the AEISS-A instrument achieves a resolution of around 0.5 m for panchromatic imagery and 2.0 m for multispectral MWIR images, covering a ground swath of around 12 km.
Figure 16: Cross-section of the optical system (image credit: Thales/SESO)
Table 3: Performance parameters of the AEISS-A instrument
IIS (Infrared Imaging System)
The IIS instrument was built by AIM (AIM Infrarot-Module GmbH), Heilbronn, Germany. The overall objective is to capture geospatial, environmental and agricultural information by scanning the earth's surface in a pushbroom mode. According to KARI, temperature-sensitive infrared sensors onboard KompSat-3A can be especially useful for monitoring forest fires, volcanic activity and other natural disasters around the world.
IIS operates within the MWIR (Mid-Wavelength Infrared) region of 3 - 5 µm at high spatial and thermal resolution. The sensing array is made of MCT (Mercury Cadmium Telluride) and hybridized with the ROIC (Read-Out-Integrated-Circuit) forming the FPA (Focal Plane Array). With a total heat load of 800 mW, the KOMPSAT-3A MWIR MCT detector is to be operated at 80 K. For those given conditions, the AIM SF400 compressor was chosen in conjunction with a ½" pulse-tube cold finger. Overall, the infrared imaging payload acquires imagery at a ground resolution of 5.5 m on a swath of 12 km. 17)
Figure 17: SF400 standard compressor housing (left), space modified housing (right), image credit: AIM
Figure 18: Photo of the pulse-tube coldfinger and the flexure bearing compressor (image credit: AIM)
KOMPSAT-3A imaging modes:
Strip imaging is a scanning method which the scan direction is aligned with satellite velocity. The satellite is fixed in LVLH coordinate and yaw steering maneuver is automatically performed to eliminate the effect of the earth rotation. Single pass stereo imaging is a scanning method which the scan direction is the same as strip imaging, but the satellite takes two images of the same target in the same pass. The first image is taken at positive pitch tilt angle, and the second image is taken at negative tilt angle. Therefore the two image of different view point can be utilized to generate 3D image. Multi-point imaging is a scanning method which the satellite takes an image and quickly rotates the body to the next position to take several images in different location. While scanning, the satellite body is fixed in LVLH coordinate. Wide arbitrary imaging is a scanning method which the scan direction is different from the satellite velocity. Therefore, the ground track can be arbitrary direction such as direct north direction, east direction, or west direction.
Figure 19: KOMPSAT-3A imaging modes (image credit: KARI, Ref. 12)
1) Daniel A. Pinkston, "Joining the Asia Space Race: South Korea's Space Program," Korea Economic Institute of America, 2014, URL: http://www.keia.org/sites/default/files/publications/kei_aps_2014_pinkston.pdf
3) Anatoly Zak, "Dnepr launches KompSat-3A," March 25, 2015, URL: http://www.russianspaceweb.com/dnepr-kompsat-3a-arirang-3a.html
4) Patrick Blau, "Silo-Launched Dnepr Rocket delivers KOMPSAT-3A to Orbit," Spaceflight 101, March 25, 2015, URL: http://www.spaceflight101.com/dnepr---kompsat-3a-launch-updates.html
5) Information provided by Moongyu Kim, President & CEO of SIIS (SI Imaging Services), Daejeon, Korea
6) "PhotoSat verifies the accuracy of survey data from the new KOMPSAT-3A satellite to 21cm in elevation," KOMPSAT -3A News Release, PhotoSat, SIIS, October 34, 2016, URL: http://www.photosat.ca/wp-content/uploads/2016/10/KOMPSAT-3A-survey-accuracy-PhotoSat-SIIS-jpegs-24oct2016-.pdf
7) "PhotoSat verifies accuracy of survey data from new KOMPSAT-3A satellite," Geospatial World, October 25, 2016, URL: https://www.geospatialworld.net/news-posts/photosat-verifies-accuracy-survey-data-new-kompsat-3a-satellite/
8) Information provided by Moongyu Kim of SIIS, Daejeon, Korea.
9) "SI Imaging Services started KOMPSAT-3A commercial services," SIIS News, July 7, 2016, URL: http://www.si-imaging.com/ds6_1_1.html?db=new_bbs&no=104&c=view&page=1&SK=&SN=&kind3=&idx=
10) Information provided by Daewon Chung, head of the KARI Ground Systems Development Department, Daejeon, Korea.
11) Hwayeong Kim, Okchul Jung, Hyeonjeong Yim, Sang Il Ahn, "Analysis on the Minimization of Contact Overlap Time between KOMPSAT-3 and KOMPSAT-3A," Proceedings of the 25th International Symposium on Space Flight Dynamics, Munich, Germany, Oct. 19-23, 2015, URL: http://issfd.org/2015/files/downloads/papers/086_Kim.pdf
12) Moon-Jin Jeon, Sang-Rok Lee, Eunghyun Kim, Seong-Bin Lim, Seok-Weon Choi, "Launch and Early Operation Results of KOMPSAT-3A," Proceedings of the 14th International Conference on Space Operations (SpaceOps 2016), Daejeon, Korea, May 16-20, 2016, paper: AIAA 2016-2394, URL: http://arc.aiaa.org/doi/pdf/10.2514/6.2016-2394
14) SIIS (SI Imaging Services), April 14, 2015, URL: http://kompsat.satreci.com/ds6_1_1.html?db=new_bbs&no=44&c=view&page=1&SK=&SN=&kind3=&idx=
15) "Satrec Initiative Announces Agreement with Korea Aerospace Research Institute," SI, Nov. 15, 2012, URL: http://www.satreci.com/eng/ds1_1.html?tno=100&db=pr_board&no=22
17) M. Mai, I. Rühlich, A. Schreiter, S. Zehner, "AIM-Space Cryocooler Programs," URL: https://smartech.gatech.edu/bitstream/handle/1853/38766/018.pdf
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).