Göktürk-2 Imaging Mission, Turkey
Göktürk-2 is a high-resolution optical reconnaissance and Earth observation mission (dual use - civil and defense) of the Turkish government's Undersecretariat for the Defense Industry (SSM). In July 2009, an agreement was signed in Ankara with the Italian space systems company Telespazio (Finemeccanica/Thales) to built the Göktürk spacecraft plus training and ground facilities. Already in December 2008, the Turkish Ministry of Defense had selected the offer of Telespazio among the various bidders for Göktürk-1. — In addition to the construction and launch of the spacecraft, the Telespazio-led team has agreed to provide Turkey with one fixed and one mobile ground station to receive imagery of the Göktürk spacecraft.
The project goal is to procure a satellite system in line with technological cooperation and joint development and usage principles to meet the need for high-resolution imagery for military intelligence on a global scale.
The Göktürk satellite will also be used for monitoring civilian activities such as control of forestland, tracking illegal construction, rapid assessment of damage after natural disasters, determination of agricultural boundaries and geographical data gathering. The project also aims to furnish national industries with the capability of designing and integrating satellite systems and running tests on them here in Turkey. Turkish defense industry companies and research centers such as TAI (Turkish Aerospace Industries, Inc.), Aselsan, the Technological and Scientific Research Council of Turkey (TÜB?TAK), and TurkSat A.S. will participate in all phases of the project. The contribution of local companies in Turkey to the project will be around 22%, and the imagery obtained from the system will be sold on the international market.
Telespazio (Rome, Italy) and its sister company TAS (Thales Alenia Space) will be the prime developers of the Göktürk-1 spacecraft. The satellite will use the Proteus multimission platform. The Italian-French contractor will also deliver a satellite assembly integration and test facility to be built at Turkey's TAI A.S. company with assistance from Turksat, Turkey's national telecommunications operator. TAI A.S. is designated as the main local partner with the purpose of building Göktürk-1 in its national satellite assembly, integration and test center at Ankara.
Figure 1: Artist's rendition of the deployed Göktürk-2 spacecraft (image credit: Turkish Aerospace Inc.)
Göktürk-2 is a minisatellite built by the TUBITAK-UZAY and TAI (Turkish Aerospace Industries Inc.) consortium. The indigenously designed Göktürk-2 spacecraft was integrated and tested (bus assembly & integration, payload integration, mass properties measurement, system level functional & thermal vacuum tests) at TAI's facilities.
EPS (Electrical Power Subsystem): The design of the EPS reflects the need for autonomous operation independent of all other systems and no intervention from the ground station. To meet the system-level requirements and to achieve its purpose, GÖKTÜRK-2 power subsystem consists of main components as follows: 4)
• Solar Panels (SPs)
• Battery Charge Regulators (BCRs)
• Battery Block (BB)
• Power Conditioning & Distribution Module (PCDM)
• Electronic Separation Switch Module (ESSM)
• Pyro Driver Module (PDM).
Figure 2: Block diagram of the EPS (image credit: TUBITAK UZAY)
The solar panels are provided by STI (SpaceTech GmbH Immenstaad), Germany, consisting of: 6)
- 3 solar panels including the photovoltaic assembly
- the solar panel deployment mechanisms
- the PDM (Pyro Drive Module) electronics executing the deployment sequence of the mechanism.
Each of the three panels on the spacecraft consists of four arrays with 3 strings of 20 cells each. In addition to the cells temperature sensors for thermal control, thermistors as input to the satellite's maximum power point tracker as well as bleed resistors for controlled insulation with the spacecraft body are accommodated on each panel. Third generation Azur GaAs triple junction cells with a rated efficiency of 28 % are used to make up the photovoltaic assembly. Each cell is protected with a bypass diode and each solar string by a blocking diode (Ref. 4).
The power produced by solar panels is utilized to charge the BCRs. Each BCR module consists of four independent working battery charge regulators connected to four independent solar cell sections on each solar panel separately, where each independent solar cell section on each panel operating In MPPT (Maximum Power Point Tracking) mode or battery end of charge (EoC) mode on each BCR module. This makes twelve solar cell sections in total on three solar panels and twelve regulators in total on three BCR modules. A nominal capacity of 34.8 Ah Li-ion battery block constitutes the unregulated bus for Göktürk-2 EPS.
The unregulated bus voltage at 28±5 V is distributed to the power conditioning module and power distribution modules via ESSM (Electronic Separation Switch Module). The PCDM also converts the raw 28±5 V battery voltage level to regulated ±5 V level, which is necessary for some subsystems, payloads, and power system internal usage. The power condition part of PCDM is realized as cold redundant for high system level reliability. The PCDM and PDDMs have also an under voltage detection and reset circuitry for battery discharge protection. Each power system module has CAN (Controller Area Network) microcontrollers to provide a serial interface for telemetry and telecommands via flight computer and ground station. The on-orbit average power consumption is 164.2 W as illustrated in Figure 3.
Figure 3: Göktürk-2 power consumption profile for one typical orbit (image credit: TUBITAK UZAY)
Figure 4: Photo of the Göktürk-2 spacecraft (image credit: TAI)
RF communications: S-band for TT&C data. X-band for the payload data downlink at > 100 Mbit/s. The on-board image storage capacity is > 15 Gbit.
The spacecraft has a launch mass of ~ 450 kg (dry mass of 408 kg), the design life is 5 years (with a goal of 7 years).
Gokturk-2 is Turkey's second Earth observation satellite, following the RASAT EO microsatellite, launched on August 17, 2011 aboard a Dnepr vehicle from the Yasny/Dombarovsky launch site located in the Orenburg Region, Russia.
Figure 5: Photo of the Göktürk-2 minisatellite during integration tests (image credit: TAI)
Orbit: Sun-synchronous orbit, mean altitude of 680 km, inclination = 98.1º, period = 98.3 minutes, LTAN (Local Time on Ascending Node) = 10.30 hours.
Note: The Göktürk-1 spacecraft is still under development. A launch of of the Göktürk-1 mission is planned for the timeframe 2015.
• The Göktürk-2 satellite and its payload are operating nominally in 2013. 11)
• In January 2013, Nihat Ergün, Minister of Science, Industry and Technology of Turkey, announced that the project began receiving initial imagery from the satellite ten days ago. According to Ergün, the Air Forces Command will primarily benefit from the imagery obtained by the observation satellite and will have the capabilities of acquiring and processing the imagery on their own land station. 12)
Figure 6: Sample image of Antalya, a city on the Mediterranean coast of southwestern Turkey, acquired by Göktürk-2 (image credit: Sabah)
• On December 26, 2012, the GökTürk-2 project team is reporting that it received the temperature, current, regression data and camera images from the spacecraft for the past four days. 13)
• The first signal from Göktürk-2 was received at 17:39 UTC in the Tromsø Satellite Station, northern Norway.
Sensor complement: (EOS-C)
EOS-C (Earth Observation Satellite - Camera)
EOS-C is a multispectral pushbroom imager. The data requirements call for civil and defense applications: disaster and emergency response, environment, mapping, urban planning, landcover, geology, coastal zone monitoring, ecosystem, and water resource management.
The EOS-C instrument was built by SI (Satrec Initiative) of Daejeon, Korea for TUBITAK/UZAY. The instrument is based on the EOS-C version 3.0 (of DubaiSat-1 heritage).
Table 1: Parameters of the EOS-C instrument
Figure 7: Photo of the EOS-C instrument (image credit: SI)
1) “Turkey gives go-ahead to Göktürk satellite project,” July 18, 2009, URL: http://www.todayszaman.com/tz-web/news-181288-turkey-gives-go-ahead-to-gokturk-satellite-project.html
2) Tamer Özalp, “The Status of Turkish National Earth Observation Missions.” GSCB (Ground Segment Coordination Body) Workshop, June 6-7, 2009, ESA/ESRIN, Frascati, Italy, URL: http://earth.esa.int/gscb/papers/2012/30-Turkish_EO_missions_status.pdf
3) Peter B. De Selding, “Turkey Expecting Satellite Deal To Spark Homegrown Space Industry,” Space News July 27, 2009, p 1 and 4.
4) Hasan Özkaya, Emrah Akku?, F. Ercan Karagöz, Ba?ak Gonca Özdemir, “Power Subsystem of Göktürk-2 Flight Model,” Proceedings of the 6th International Conference on Recent Advances in Space Technologies (RAST), Istanbul, Turkey, June 12-14, 2013
7) “China closes 2012 with 19th successful Orbital Launch,” Spaceflight 101, Dec. 18, 2012, URL: http://www.spaceflight101.com/long-march-2d-gokturk-2.html
8) Stephen Clark, “Turkish imaging satellite lifted to orbit by China,” Spaceflight Now, Dec. 18, 2012, URL: http://www.spaceflightnow.com/news/n1212/18longmarch/#.UNGZJ5GQk9Y
9) “Second Turkish EO Satellite Launch Successful,” Earth Imaging Express, Dec. 27, 2012, Vol. 2, No 40, URL: http://eijournal.com/industry-insights-trends/second-turkish-eo-satellite-launch-successful?utm_source=EIX+Subscribers&utm_campaign=436bea6fc9-Group_312_27_2012&utm_medium=email
10) “Göktürk-2 is in Space,” TUBITAK-UZAY, URL: http://www.uzay.tubitak.gov.tr/tubitakUzay/en/newsArchive/gk-2.php
11) Enes Koytak, “Recent Space Activities in Turkey,” 56th Session of UNCOPUOS (UN Committee on the Peaceful Uses of Outer Space), Vienna, Austria, June 12-21, 2013, URL: http://www.oosa.unvienna.org/pdf/pres/copuos2013/tech-10.pdf
12) “Turkey receives initial Göktürk-2 satellite images,” Sabah, Jan. 9, 2013, URL: http://english.sabah.com.tr/economy/2013/01/09/turkey-receives-initial-gokturk-2-satellite-images-631569259770
13) “First images received from Gokturk-2 satellite,” TurkishPress.com, Dec. 26, 2012, URL: http://www.turkishpress.com/news.asp?id=383031#.UN_ncoapKTw
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.