KazEOSat-2 (Medium Resolution Earth Observation Satellite), Kazakhstan
The Republic of Kazakhstan is leveraging the advances in small satellite Earth observation capability to create a national system which supports the government with information gathering for its policy and decision making. It will be implemented by a team comprising EADS Astrium SAS of France and SSTL (Surrey Satellite Technology Ltd ) of Guildford, UK, and will include a high resolution mapping spacecraft and a wide-swath medium resolution multispectral mapping spacecraft. The project was initiated in late 2009, and is the first collaboration between SSTL and Astrium since its ownership change (Note: in April 2008, EADS Astrium NV acquired SSTL from the University of Surrey). It highlights how small satellites can be employed in complex satellite systems to complement larger spacecraft. 1)
Figure 1: Photo of the first trainees arriving at SSTL in Surrey, UK (image credit: Ghalam, KGS)
The two KazEOSat-1 and KazEOSat-2 projects highlight, how systems from the two EADS Group companies can be deployed together to provide integrated multi-satellite space systems for a customer.
Figure 2: The architecture of the EO program for Kazakhstan to be supplied by EADS Astrium (image credit: SSTL)
Legend to Figure 2: The highlighted elements are associated with the KazEOSat-2 mission supplied by SSTL. The remaining elements are supplied by EADS Astrium as part of the HRES (KazEOSat-1) mission.
The key objectives of the KazEOSat-2 mission can be summarized as follows:
• To provide a state-of-the-art medium resolution imaging satellite and the accompanying ground segment to KGS
• To provide a 7 year operational lifetime
• To provide agile imaging modes
• To be capable of imaging up to 1,000,000 km2 per day.
In addition to the above key mission objectives, more specific details have been defined. These key mission performance parameters are summarized in Table 2.
Table 2: Summary of the key KazEOSat-2 mission performance requirements
The KazEOSat-2 spacecraft will aid the government of Kazakhstan in decision making when it comes to resource monitoring, resource management, land-use mapping and environmental monitoring.
SSTL will deliver the KazEOSat-2 satellite within a 3 year timeframe which includes a comprehensive training and development element, by building upon its heritage designs from its successful SSTL-150 class missions. This platform was first used for the DMC+4 (Beijing-1) and TopSat missions which were both launched in 2005. In addition the RapidEye constellation of 5 spacecraft (launch August 29, 2008) is based on the SSTL-150 platform. 8) 9)
The architecture of KazEOSat-2 is similar to that of the RapidEye spacecraft. The main differences are the enhanced agility enabling stereo and area imaging with the new generation Rigel-L star trackers and 100SP-M reaction wheels, increased on-board memory and downlink rate for the image data. Enhancements also include a narrow beam X-band antenna with an antenna pointing mechanism and the use of triple-junction solar cells.
The KazEOSat-2 spacecraft will provide wide-swath multispectral imagery (77 km swath, 6.5 m GSD). The KazEOSat-2 system will also incorporate advanced new technologies that have been developed for the NigeriaSat-2 satellite that include enhanced data handling and downlink capabilities.
The minisatellite bus has an envelope of 700 mm x 800 mm x 900 mm with a launch mass of ~185 kg. The agile KazEOSat-2 spacecraft is 3-axis stabilized providing an off-nadir body-pointing capability of ±35º. The existing AOCS (Attitude and Orbit Control Subsystem) of the SSTL-150 bus will be enhanced to improved spacecraft agility. The existing reaction wheels will be replaced with the next generation of SSTL wheels that allow for faster slewing as required by some of the imaging modes. Furthermore, SSTL's newest generation of star trackers will be flown: The Rigel-L star tracker. This star tracker uses a Hydra head from Sodern and an SSTL DPU (Data Processing Unit) to provide highly accurate attitude data.
RF communications: The KazEOSat-2 mission uses the SSTL-300 architecture for the payload downlink chain and hence uses HSDR (High Speed Data Recorders) to capture and compress image data (16 GB HSDR capacity). Use of the X-band downlink system at a data rate of 160 Mbit/s.
The RF subsystem includes two dual-axis APMs (Antenna Pointing Mechanisms) of NigeriaSat-2 heritage to increase the downlink performance. APM is providing a real-time imaging & downlinking capability in parallel for a range of targets close to the ground station.
Figure 3: Illustration of the Kazakhstan KazEOSat-2 satellite (image credit: SSTL)
Launch: The KazEOSat-2 minisatellite (~185 kg) was launched on June 19, 2014 (19:11:11 UTC) on a Dnepr-1 vehicle of ISC Kosmotras. The launch site was the Yasny Cosmodrome in the Dombarovsky region of Russia. 10) 11) 12) 13)
The Deimos-2 minisatellite of Deimos Imaging S.L.U., Spain, was another primary payload on this flight with a mass of ~310 kg.
The secondary payloads (35) on this Dnepr cluster mission were: 14)
• UNISat-6, a microsatellite of GAUSS at the University of Rome (La Sapienza), Italy. UniSat-6 (26 kg) includes Pico-Orbital Deployers and PEPPODs (Planted Elementary Platform for Picosatellite Orbital Deployment) systems for the release of four CubeSats from the spacecraft. These four satellites are:
- Lemur-1, a 3U CubeSat (technology demonstration and EO) of NanoSatisfi Inc., San Francisco, CA, USA
- TigriSat, a 3U CubeSat of the University of Rome (La Sapienza), Rome, Italy.
- ANTELSAT, a 2U CubeSat of UdelaR (University of the Republic), San Marino, Uruguay
- AeroCube-6, a 1U CubeSat of The Aerospace Corporation, El Segundo, CA.
• SaudiSat-4 a microsatellite (112 kg) of KACST (King Abdulaziz City for Science and Technology) with input from NASA/ARC.
• AprizeSat-9 and -10, nanosatellites (each of 12 kg) of SpaceQuest, USA. AprizeSat-10 carries an AIS (Automatic Identification System) receiver for ship tracking.
• Hodoyoshi-3 and -4, microsatellites (60 kg and 65 kg, respectively) of the University of Tokyo and JAXA/ISAS, Japan
• BRITE-CA-1 and BRITE-CA-2, two nanosatellites (7 kg each) of UTIAS/SFL (University of Toronto, Institute for Aerospace Studies), Toronto, Canada
• TabletSat-Aurora, a microsatellite (25 kg) of SPUTNIX, Russia
• BugSat-1, a microsatellite (22 kg) of Satellogic S.A., Argentina
• Perseus-M1 and M2, two identical 6U CubeSats of Canopus Systems US / Dauria Aerospace. The nanosatellites are carrying an AIS payload for ship tracking.
• QB50P1 and QB50P2, two 2U CubeSats (2 kg each) of Von Karman Institute, Brussels, Belgium. These are two precursor satellites to the QB50 project that will launch a network of 50 satellites by a team of 15 universities and institutions around the world.
• NanoSatC-Br1, a 1U CubeSat of the Southern Regional Space Research Center and of INPE, Brazil
• DTUSat-2, a 1U CubeSat of DTU (Technical University of Denmark), Lyngby, Denmark
• POPSat-HIP-1, a 3U CubeSat of Microspace Rapid Pte Ltd., Singapore
• PolyITAN-1 of KPI (Kiev Polytechnic Institute), Kiev, Ukraine
• PACE (Platform for Attitude Control Experiments), a 2U CubeSat (2 kg) of NCKU (National Cheng Kung University), Tainan City, Taiwan
• Duchifat-1, a 1U CubeSat of HSC (Herzliya Science Center), Israel
• 11 Flock-1c nanosatellites (eleven 3U CubeSats, 5 kg each) of Planet Labs, San Francisco, CA.
Orbit: Sun-synchronous orbit, nominal altitude of 630 km, inclination = 98º, LTAN (Local Time of Ascending Node) of 10:30 hours.
• July 13, 2015: The KazEOSat-2 spacecraft is commissioned, and hand-over is officially planned alongside KazEOSat-1 over the coming weeks. 15)
• April 22, 2015: The KazEOSat-2 mission is currently in the final phases of commissioning. 16)
- The in-orbit acceptance review of the mission is scheduled for late April.
- Maximum throughput scenario has been verified in orbit
- MTF and SNR measured for all channels: MTF > 16%, SNR > 100
- Agile modes tested – one pass stereo and area imaging
- Geolocation verified
- Power profiles are in line with the predictions.
- The project reported a reaction wheel failure. However, despite this failure, the mission is still compliant with the system level technical requirements due to "redundancy for full performance" design philosophy. An investigation ruled out all viable causes of the failure including SEEs (Single Event Effects) and mechanical problems. It is considered to be a random component failure.
Figure 4: KazEOSat-2 image of Astana, the capital of Kazakhstan, showing the central district with the presidential palace, Bayterek tower and Khan Shatyr (image credit: KGS, Ghalam)
Figure 5: KazEOSat-2 image of the Cairo Airport, Egypt (image credit: KGS, Ghalam)
• In a continuation of the collaboration between the two organizations, a team from SSTL has travelled to the satellite operations center in Astana to perform initial in-orbit operations alongside Kazakh engineers. Once platform commissioning in Astana is complete, SSTL and Kazakh engineers will commission and calibrate the imaging payload from SSTL's Mission Control operations center in Guildford (Ref. 13).
Sensor complement: (KEIS)
KEIS (Kazakh Earth Imaging System):
KEIS is a multispectral imaging system of RapidEye constellation heritage, designed and developed by JOP (Jena-Optronik GmbH), a subsidiary of the Photonics Division of Jenoptik), Jena, Germany. The instrument is also referred to as JSS-56 (Jena-Optronik Spaceborne Scanner-56) as well as MSI (Multispectral Imager) in the literature.
The collector optics utilizes a TMA (Three Mirror Anastigmatic) design - permitting generally larger FOVs (in the range of about 2-12º) than those of Cassegrain or Ritchey-Chrétien systems (FOV of about 2º max). The TMA telescope aperture diameter is 145 mm. The TMA design is based on all-aluminium telescopes. The necessary optical surface quality for applications in the visible range is achieved with ultra-precision milling and polishing techniques. The aluminium mirrors are Ni coated to achieve a suitable surface polishing quality. KEIS is a pushbroom instrument which images the Earth's surface in 5 spectral bands over a swath width of 78 km (corresponding to a FOV of ± 6.75º about nadir) at a spatial resolution of 6.5 m at nadir. The collector optics image onto five parallel linear 12 k pixel CCD detectors. Filters, placed in close proximity to each CCD line array, separate the spectral imaging bands. 17) 18) 19) 20)
Table 3: Spectral parameters of KEIS
Table 4: Overview of KEIS instrument parameters
• PIU (Payload Interface Unit) + HSDR (High Speed Data Recorder): The dedicated PIU, in close proximity to the focal plane assembly (FPA), provides support of all KEIS data handling functions. For each spectral channel, a dedicated signal chain module sends the required CCD clocks and voltages, and reads out the CCD data. It includes two analog-to-digital converters (ADC digitization) for odd and even CCD video output, one FPGA, as well as data and command interfaces. The signal chains also include gain amplification and CDS (Correlated Double Sampling). Optional pixel binning is performed in the data processing and control electronics.
After digitization, the image data pass a typical processing flow comprising data compression in COU (Compression Unit), data storage in HSDR, data formatting in DFU (Data Formatting Unit), and the downlink. KazEOSat-2 will have a lossless 2.5:1 compression. The compressed data, together with spacecraft GPS and attitude information, is stored in mass memory, which provides sufficient storage for a 5-band imaging scene length of up to 4000 km.
• Telescope and mirrors. This telescope configuration is very compact as it uses a folded optical path that has no optical obstruction so the aperture can be kept small. The telescope is an all-aluminum design that is telecentric which minimizes plate-scale changes due to residual thermal effects.
Figure 6: Layout of the telescope (image credit: JOP)
• FPM (Focal Plane Module): The focal plane used 2 CCD packages from e2v (France) where each package has 3 linear CCD lines. These CCD's are similar to those used for the Spot-5 program. As the payload only has 5 bands, only 2 CCD lines are used from one of the packages. Each CCD line has 12,000 pixels with a 6.5 µm square pixel pitch. There are 4 CCD outputs per line with a read-out rate of 6.5 MHz per line. The CCD dies are mounted directly to the ceramic substrate that is in the FPM. The bandpass filters are mounted directly in front of the CCD lines.
Figure 7: Illustration of the FPM (image credit: JOP)
Legend to Figure 7: The left photo shows the two triple-line CCDs with 3 x 12 k pixels in a ceramic plate, the right photo shows five metal oxide interference filter stripes integrated in a filter plate are mounted directly on the FPA.
• FEE (Front End Electronics): The FEE reads out each of the CCD lines and converts the analog signals to a 12 bit digital number and sends this to the PIU. There are 5 data inputs from the FEE that correspond to each band. This data goes directly into a real-time compression unit (COU) dedicated to each channel. From the compression unit, the data is moved into one of 3 MMU (Mass Memory Unit) boards.
For downlink operations, the data from the mass memory is sent to the DFU (Data Formatter Unit) which performs the CCSDS formatting, Reed-Solomon encoding, and sends the data directly to the X-band downlink transmitters. The payload operation is controlled by the CIU (Control and Interface Unit) which has a CAN interface to the bus and also a PPS interface to the GPS to allow for time synchronization.
• FEE Power Convertors
• Payload supports
Figure 8: Illustration of the KEIS (JSS-56) instrument (image credit: JOP)
Figure 9: Schematic of the TMA telescope design accommodated on RapidEye (image credit: JOP)
The KazEOSat-2 spacecraft provides the following imaging modes :
• Image strip : An image strip is composed of individual image ‘scenes' that are 77 km x 77 km in size which can be used for applications such as mapping. The maximum length of an image strip is 4000 km and it can be captured at roll angles of up to 35º from nadir.
• Stereo mode : The stereo mode is used to capture the two stereo images of an area of interest which can provide height information of the target area. Each stereo image comprises a pair of images taken of the same location but at different view angles. These two fully overlapping image scenes are captured at pitch angles of 30º, with the first scene captured before the spacecraft reaches the target and the second image taken after the satellite has passed overhead.
Figure 10: KazEOSat-2 stereo imaging showing capture of first image (1) followed by capture of second image (2), image credit: SSTL
• Mosaic mode : Mosaic mode is used to capture wide swath imagery and comprises of two adjacent image scenes. The mode operates in a very similar way to the stereo mode. The only difference is that the scenes imaged are adjacent and not fully overlapping.
Figure 11: KazEOSat-2 mosaic imaging: images 2 & 3 are combined to make the mosaic image (image credit: SSTL)
The ground segment will be a part of the National Space Center of the Republic of Kazakhstan being created by the national company KGS (Kazakhstan Gharysh Sapary) in the city of Astana. This center is to be created for the purpose of setting up the integrated technology process intended to allow Kazakhstan to accomplish space projects from designing, manufacturing and testing up to launch, and further operation of space systems and complexes (Ref. 1).
The KazEOSat-2 ground segment is designed to operate independently from the KazEOSat-2 ground segment. However, they will both be co-located in Astana and are cross-strapped to provide redundancy. In addition, they will share common functionality in nominal operations (antenna scheduling, user office and image processing facilities). The cross-strapping (Figure 12) allows both spacecraft to be controlled and payload data to be downlinked form either ground segment.
Figure 12: Overview of the KazEOSat-2 (former MRES, highlighted) and KazEOSat-1 (former HRES) ground segment architectures (image credit: SSTL)
Legend to Figure 12: The MRES supplied elements are highlighted green. Red lines are for TM/TC (Telemetry and Telecommand ), green lines for image requests and scheduling, blue lines for payload data (dotted lines represent cross-strapping with the HRES ground segment).
The ground segment of the KazEOSat-2 mission is comprised of the following elements:
• Ground station (S-band and X-band)
• GCC (Ground Control Complex)
• IEC (Information and Extraction Center)
• DPC (Data Processing Center).
The ground station will be located in Astana and will be housed inside a radome to protect for adverse weather conditions. The antenna is dual frequency to support platform operations (S-band) and to downlink payload data (X-band).
The GCC facility contains the MCS (Mission Control Suite), a set of computers that are used for spacecraft TT&C operations. The MCS permits the customer to command and monitor the KazEOSat-2 satellite. The uplink command instructions are generated using SSTL's standard suite of satellite control software for transmission to the satellite. The downlink telemetry is decoded and displayed using Windows PC-based software.
The IEC is used for creating imaging schedules which are then uploaded to the satellite via the GCC. The core of this functionality is supplied by the SSTL MPS (Mission Planning System). This heritage software manages scheduling, resource conflicts, ground station availability, pass availability, power constraints etc. It is interfaced directly to the user office where the main planning activities occur in nominal operations. However, it does include a user interface to be operated independently if needed.
The DPC is used for processing of the downlinked payload data, cataloging and short-term archiving. The software used will allow radiometric correction of these images to SPOT level 1A (Landsat level - L0R). In addition, the DPC includes software to assist with geo-rectification tests within the KazEOSat-2 ground segment. For the KazEOSat-2 ground segment test purposes, it will be able to process images to SPOT level 3A (Landsat level - L1T).
In nominal operations, the Astrium supplied Image Processing Facility will be responsible for producing products higher than SPOT level 1A (L0R).
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4) Information provided by Alexander Mostovoy, Chief Manager of the International Cooperation Office of KGS
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11) William Graham, "Russian Dnepr rocket lofts record haul of 37 satellites," NASA Spaceflight.com, June 19, 2014, URL: http://www.nasaspaceflight.com/2014/06/russian-dnepr-rocket-record-launch-37-satellites/
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14) Patrick Blau, "Dnepr - 2014 Cluster Launch," Spaceflight 101, June 10, 2014, URL: http://www.spaceflight101.com/dnepr-launch-updates---2014-cluster-launch.html
15) Information provided by Alex da Silva Curiel of SSTL, Surrey, UK.
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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).