SAR (Synthetic Aperture Radar)-Lupe Constellation
SAR-Lupe is Germany's first satellite-based reconnaissance system, developed by OHB-System AG for the German Ministry of Defence and the Federal Office of Defence Technology and Procurement. This SAR (Synthetic Aperture Radar) project consists of five identical satellites, which are still operational after having been launched in 2006-2008 with the overall objective of providing high-resolution radar imagery to German defence forces for at least ten years.
Each of the satellites in the SAR-Lupe constellation contains an X-band SAR instrument (XSAR) which performs refined image acquisition in the X-ray spectrum through a parabolic SAR reflector antenna. XSAR is equipped for automated data reception and image processing in the two imaging modes available: stripmap and spotlight.
The spacecraft are calibrated both internally, through continuous calibration of the SAR antenna and the high power amplifier, and externally, to ensure a high image quality after the commissioning phase, as well as a nearly continuous image quality in the routine phase of the mission by re-calibration in certain time intervals. The entire constellation is monitored and controlled from a ground segment by OHB-System AG, Bremen.
The SAR antenna has dimensions 3.3 m x 2.7 m and can record images on all weather conditions, both during the day and the night. Stripmap scenes have a size of 60 km x 8 km, while the spotlight scenes are square images with a 5.5 km side, observable at a 0.5 m resolution and a centre wavelength of 31 mm. The system’s response time is less than 36 hours, with availability depending on the constellation configuration. More than 30 scenes of interest can be taken every day.
The five satellites were launched into three orbital planes, with an average altitude of about 500 km and an inclination for near-polar orbits of 98.2°. The three planes contain two, one and two spacecraft respectively.
Space and Hardware Components
Each satellite has dimensions 4 m x 3 m x 2 m and weighs approximately 770 kg, with a design life of ten years. Within the Attitude Control Subsystem, attitude is sensed by sun sensors, star sensors and gyroscopes, while the attitude control is achieved by reaction wheels and magnetic torquers. The Electric Power Subsystem features solar cells for energy collection and lithium-ion batteries for storage. The robust monopropellant hydrazine system allows for compensation of altitude decay, caused by residual air drag, and for end-of-life de-orbiting. The Satellite Management Unit is providing the service functions relevant for Onboard Data Handling, as well as power and control distribution.
Radio-frequency communication is provided in X-band for encrypted downlink transmissions, while the uplink encrypted communication is in S-band. In addition to this, an intersatellite link in S-band is provided for data product transfer.
SAR-Lupe is a SAR (Synthetic Aperture Radar) reconnaissance satellite imaging project of the German government, in particular the German Ministry of Defense (BMVg) and the Federal Office of Defense Technology and Procurement, referred to as BWB (Bundesamt für Wehrtechnik und Beschaffung - Federal Office of Defense Technology and Procurement), Koblenz, Germany (BWB manages the procurement of the ground and space segments). The overall objective is to provide high-resolution radar imagery to German defense forces over a period of ten years starting in 2006. SAR-Lupe is in fact the first dedicated reconnaissance satellite imaging project of Germany. More specific objectives are: 1) 2) 3) 4)
• To provide an event monitoring observation capability independent of weather and illumination conditions, in particular for regions of crisis or emergency situations (such as natural disaster coverage) to support the government in the assessment of intelligence information
• To assist the military to plan and to prepare operations
• To support deployed forces with frequent event-driven intelligence information.
The construction and launch contract of the five identical satellites was awarded to a consortium in Aug. 2001, with OHB-System AG of Bremen as prime contractor (signed in Dec. 2001). Some consortium partners in the SAR-Lupe project are: TAS (Thales Alenia Space) formerly Alcatel Alenia Space, Toulouse; Saab Ericsson of Göteborg, Sweden (SAR antennas); Carlo Gavazzi Space, Milan, Italy; TESAT-Spacecom GmbH, Backnang, Germany (development the high-performance amplifier); RST Radar Systemtechnik GmbH, Salem, THALES of Ulm, Germany, EADS (ground segment), DLR [LEOP (Launch and Early Orbit Phase) and operational backup function].
Background: Germany's development of this program was directly related to its experiences during the NATO action in Kosovo (1998-1999), particularly to difficulties in getting the US to share satellite intelligence of direct relevance to the protection and security of non-US allied forces. These experiences convinced Germany of the need for its own spaceborne intelligence-gathering assets to deal with crisis management. 5)
In October 2003, the BWB tasked OHB-System to conduct a second-phase study focusuing on the specifics of SAR-Lupe and Helios II operating in tandem. The study involved arriving at a detailed description of the needed technical adjustments to the SAR-Lupe ground station and the precise interfaces required, as well as a clear understanding of program costs and schedules.
OHB-System undertook its initial hardware tests involving a radar transmitter tube in November 2002. The company and the BWB completed the CDR (Critical Design Review) of the system during the first half of 2003. The engineering test model for the SAR-Lupe satellite was completed by 2004 in OHB-System's Bremen integration facility, which includes a radome.
In addition, a bilateral agreement with the French government was signed for data from SAR-Lupe to be provided in exchange for data from Helios.
The S/C structure has a size of about: 4 m x 3 m x 2 m with a fixed parabolic SAR/communication dual-use reflector antenna (antenna size: 3.3 m x 2.7 m). Three-axis stabilization is used.The ACS (Attitude Control Subsystem) features high performance attitude knowledge and control capabilities. Attitude is being sensed by sun sensors, star sensors and gyroscopes; attitude control is provided with reaction wheels and magnetic torquers. With the special agile bus the satellite and thus the antenna boresight can be aligned with great precision to a specific location on the ground via its three-axis stabilization.
The EPS (Electric Power Subsystem) features a solar panel of 2.4 m2 of GaAs solar cells providing 550 W of power at EOL. Use of 2 x 66 Ah Li-ion batteries for power storage (ABSL, UK).
The robust monopropellant hydrazine system allows for compensation of the altitude decay due to the residual air drag and for EOL de-orbiting.
The SMU (Satellite Management Unit) is providing the service functions relevant for OBDH (Onboard Data Handling), power and control distribution, AOCS, etc. The SMU is based on a radiation tolerant DSP processor, TSC21020. To achieve maximum integration and miniaturization, the SMU design makes extensively use of FPGA components. Various interfaces are implemented in the SMU such as standard serial lines (RS422 and IEEE1355) as well as standard ESA OBDH interfaces. Each S/C is furnished with two SMU units for redundancy.
RF communication is provided in X-band for encrypted downlink transmissions (the constellation satellites use the same antenna for image acquisition and X-band data downlink; however, each function requires exclusive antenna use). The uplink communication is in S-band (also encrypted). In addition, an intersatellite link (or cross-link) in S-band is provided for data product transfer. The satellite control data routing is selectable either via ground station and/or via an inter-satellite link.
Orbit: The five satellites are launched into three orbital planes. Average altitude of about 500 km, inclination for near-polar orbits (98.2º). Orbital plane 1 contains 2 S/C; orbital plane 2 contains 1 S/C, orbital plane 3 contains 2 S/C. The angle between orbital plane 1/2 is 64º; the angle between orbital planes 2/3 is 65.6º. The phase angles of the S/C are: Orbital plane 1 = 0º+69º; orbital plane 2 = 34.5º; orbital plane 3 = 0º+69º. The five spacecraft constellation offers very short response times and a high system redundancy.
SAR-Lupe-1 (international code: 2006-060A) has a perigee of 468 km, an apogee of 505 km, inclination = 98.2º, period= 94.3 minutes.
The 5-satellite constellation was launched in the time frame 2006-2008 (single launches in half year increments), initiating operations from 2006 onwards and full utilization of services starting in 2008. The launch provider was Cosmos International GmbH using the Cosmos 3M launch vehicle.
• A successful launch of the SAR-Lupe-1 spacecraft of the constellation took place on Dec. 19, 2006 from the Plesetsk Cosmodrome, Russia (service provider: Eurockot). Initial S/C control and monitoring services in LEOP (Launch and Early Orbit Phase), involving S/C injection/deployment, system check-out, positioning, etc., are being provided by DLR/GSOC (German Space Operations Center).
Germany and France have already agreed on cooperation regarding mutual SAR-Lupe and Helios-II data exchange services. Eventually, a European reconnaissance capability may evolve consisting of the following systems: SAR-Lupe, Helios-II, COSMO/SkyMed, Pléiades, and TerraSAR-X [also within the context of the European initiative GMES (Global Monitoring for Environment and Security)].
December 19, 2006 (Cosmos-3M launch vehicle)
July 2, 2007, launch successful, LEOP operations at DLR/GSOC
November 1, 2007, launch successful, LEOP operations at DLR/GSOC
March 27, 2008, launch successful, LEOP operations at DLR/GSOC
July 22, 2008, launch successful, LEOP operations at DLR/GSOC
Status of the SAR-Lupe Constellation
• The SAR-Lupe constellation of operational as of 2016.
• The SAR-Lupe constellation is operational in 2015. 9)
• In July 2013, OHB System AG of Bremen, Germany signed a contract with Germany's defense procurement agency (BAAINBw) to develop the SARah (Satellite-based Radar Reconnaissance System). The plans call for an operation of the system in late 2019. The second generation satellite constellation of three spacecraft, two provided by OHB System AG and one by Airbus DS (former Astrium GmbH), will replace the current SAR-Lupe constellation of five spacecraft, and will be delivered to orbit by two Falcon 9 rockets of SpaceX in 2018 and 2019. 10) 11) 12) 13)
- SARah aims to provide an enhanced follow-on to Germany's five-satellite SAR-Lupe constellation, which became fully operational in 2008. Built by OHB System AG, SAR-Lupe, which utilizes one ground station, is slated to retire after November 2017.
- Comprising just three satellites and supported by two ground stations, SARah is slated to enter full operational service by the end of 2019. Two of the three spacecraft will be based on reflector technology proved on SAR-Lupe and enhanced for SARah. A third satellite will feature phased-array technology developed by Airbus DS GmbH, and which is currently flying on Germany's TerraSAR-X and Tandem-X civil radar satellites.
• The complete SAR-Lupe constellation of 5 spacecraft is operating nominally in 2013. 14)
• The complete SAR-Lupe constellation of 5 spacecraft is operating nominally in 2012. The on orbit spacecraft service time has accumulated to more than 20 years of flawless uninterrupted operations for the constellation.
• In Sept. 2011, OHB completed a System definition study of a SAR-Lupe Follow-On (BWB, BMVg) constellation.
• The complete SAR-Lupe constellation of 5 spacecraft is operating nominally in 2011. 15)
• The complete SAR-Lupe constellation of 5 spacecraft is operating nominally in 2010.
• In 2009, the SAR-Lupe constellation experienced more than 800 close encounters with orbital junk or other operating satellites, including 32 passes at less than 1 km from another SAR-Lupe spacecraft, and one that required a collision-avoidance maneuver. Due to these collision concers, Germany inaugurated in 2009 the GSSAC (German Space Situational Awareness Center), located in Uedem, which is near Kleve in North Rhine-Westphalia, Germany. - In addition, Germany's defense forces, in a rare move, have invested cash in an ESA-led program to design a European space surveillance system starting with ground-based radars already existing in Germany and France.
• On December 4, 2008, the SAR-Lupe radar reconnaissance system was officially handed over to the German Bundeswehr. 17)
• The commissioning phase of SAR-Lupe-5 was completed and declared as "operational" in Oct. 2008 (launch of SAR-Lupe-5 on July 22, 2008). Hence, the project commenced the phase of full operational service provision in Oct. 2008 which is expected to last until the end of 2017. 18)
• In early July 2008, the SAR-Lupe-4 commissioning phase was completed and the spacecraft was integrated into the operational constellation. Operations of the full constellation (5 spacecraft) is expected to start in October 2008.
• On April 3, 2008, the FQR (Flight Qualification Review) took place for SAR-Lupe-3, thus ending the commissioning phase - the spacecraft was declared "operational" as of April 3, 2008. There are now 3 operational spacecraft in the constellation.
• In early December 2007, the German Bundeswehr accepted officially the current SAR-Lupe-System as an operational user. With two fully functional spacecraft of the projected five S/C constellation in service, a certain operational base level can be maintained. After a period of intensive tests, the BWB (Koblenz) confirmed the required performance and high quality of the SAR imagery of the two spacecraft. Hence, with a current response time of 24 hours, the system was declared as "operational" - starting in turn the projected 10-year service period (design life) of the constellation as specified by the prime contractor. 19)
• SAR-Lupe-2 was declared operational in mid-August 2007.
• The commissioning phase of SAR-Lupe-1 ended on January 19, 2007. While the cross-link capability couldn't been tested (only one spacecraft has been launched so far), the first images produced are as good as expected.
In the absence of an instrument description (the SAR-Lupe mission is classified), some general observational objectives/features are provided:
XSAR (X-band SAR Instrument)
XSAR of SAR-Lupe is observing in X-band (center frequency of 9.65 GHz corresponding to a wavelength of 3.1 cm).
• Global observation coverage capability
• Use of a parabolic SAR reflector antenna of size: 3.3 m x 2.7 m. The choice of using a single beam offset reflector antenna instead of an active beam-steering antenna represented a major cost saving in the development of the instrument. SAR-Lupe uses a single beam offset reflector antenna and a TWT (Travelling Wave Tube) based transmitter, illuminated by a feed horn on a deployable boom. The highly efficient TWT and a low-loss high-gain antenna are providing good power potential for radar with efficient DC power utilization. 20) 21)
Prior to an image acquisition, the satellite rolls in an appropriate position and stabilizes its attitude. Then, the SAR image is acquired. After that, the satellite rolls back into its standby attitude and continues to load its batteries preparing itself for the next SAR image acquisition.
• Number of scenes of area of interest: ≥ 30/day
• System response time: < 36 hours
• System availability: 95%
• Automated monitoring and control of the constellation via a ground control station
• Automated data reception and image processing
• LEOP (Launch and Early Orbit Phase) support is provided by DLR/GSOC
• The mean response time of the system is in the range of 10 hours. System availability is provided by the distribution of the satellites in their orbital planes.
• The modular interface design of the ground segment permits also future integration into an international reconnaissance network (mutual utilization of the system, etc.).
• SAR imaging modes provided: stripmap and spotlight. Stripmap imaging involves antenna pointing into a fixed direction (normally in cross-track). Internally, these modes are referred to as "Strip-SAR" and "Slip-SAR." Strip-SAR observations are conducted in the nadir direction. In Slip-SAR mode, the entire spacecraft is rotated into the direction of the target to increase the integration time and therefore the in-track resolution.
• Spatial resolution of SAR data: 0.5 m in spotlight mode for a scene of about 5.5 km x 5.5 km in size; a stripmap scene has a size of 60 km x 8 km.
• Satellite operations permit "spotlight imaging" of a scene. This involves rotation of the entire S/C about a target area to increase the integration time of the scene (the SAR beacon is pointable). In SAR-Lupe terminology, spotlight imaging is referred to as "Slip-SAR."
• An onboard image storage capability of 128 Gbit (EOL) is provided.
• The main image products are: 1) stripmap scenes of size 60 km x 8 km, and 2) square scenes of 5.5 km x 5.5 km in size.
• The following additional products can also be generated: a) elevation models from multipass interferometric products, b) multipass stereo products, c) change detection products, d) products with enhanced radiometric resolution.
The calibration concept of the SAR instrument consists of two parts: 1) internal calibration and 2) external or end-to-end calibration. The internal calibration feature is used for continuous calibration of the SAR antenna and the high power amplifier. External calibration is employed for two purposes: 22)
- Ensure a high image quality after the commissioning phase
- To ensure nearly continuous image quality in the routine phase of the mission by re-calibration in certain time intervals (e.g. every year).
The calibration is using new developments on Active Radar Calibration (ARC) targets in X-band and L-band specially developed for that purpose.
The SAR-Lupe constellation is being monitored and controlled (TT&C function) by OHB-System AG, Bremen. The user ground segment services, including payload data reception, processing and archiving, and user interface, are provided at a service center located in Gelsdorf, near Bonn. 23)
As part of the bi-national collaboration between France and Germany in the area of satelliteborne reconnaissance, OHB-System AG has implemented a further SAR-Lupe ground station in France, allowing the French army to directly access the reconnaissance information collected by the German SAR-Lupe radar satellite system. On April 1, 2010, the German Federal Office of Defense Technology and Procurement [BWB (Bundesamt für Wehrtechnik und Beschaffung), Koblenz] awarded OHB a contract to operate this ground station for a period of 5 years. 24) 25)
The ground stations permit the French and German military forces access to each other's optical and radar satellite systems. The contracts are part of a bilateral French-German program called E-SGA (Europäisierung der satellitengestützten Aufklärung - or Europeanization of Satellite-aided Reconnaissance) and are an example of progress made among European nations to harness space-based assets that were financed and built separately into a system usable by several nations. 26)
The partnership will provide Germany with access to the two French Helios-2 optical and infrared imaging satellites, while French forces will be able to use Germany's constellation of five SAR-Lupe radar spacecraft. OHB is the contractor and for implementing the E-SGA program. The main tasks are: (Ref. 24)
- to modify the national SAR-Lupe ground segment so that it can function as a multinational ground segment which can be addressed by partner nations requesting or providing image data
- to develop, supply and operate a partner ground segment for France, referred to as FSLGS (French SAR-Lupe Ground Segment)
- to connect the German HELIOS-2 ground segment, called CPHD (Centre Principale HELIOS Germany), to the multinational SAR-Lupe ground segment. In addition, OHB will be operating the CPHD.
Military operational use of the integrated system is expected to commence in mid-2010.
1) In German, the word Lupe means "magnifying glas," a reference and connotation for high-resolution imagery.
3) Information was provided by Fritz Merkle, Danela Sell, Ingo Engeln, and Steffen Leuthold of OHB-System, Bremen
4) "The SAR-Lupe Program - An Industrial View," Security and Defence Aspects of Space: The Challenges for EU, Athens, Greece, May 8-9, 2003
6) David Koebel, Carsten Tobehn, Boris Penné, "OHB Platforms for Constellation Satellites," 5th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 4-8, 2005, URL: http://www.dlr.de/iaa.symp/Portaldata/49/Resources/dokumente/archiv5/0304_Koebel.pdf
7) R Spurrett , N Simmons, C Pearson, "Advanced Batteries Based on Commercial Cell Technology: From Imagination to Reality," Proceedings of the 59th IAC (International Astronautical Congress), Glasgow, Scotland, UK, Sept. 29 to Oct. 3, 2008, IAC-08.C3.3.5
8) "SAR-Lupe, Germany's first satellite-based reconnaissance system, now completed," DLR, July 22, 2008, URL: http://www.dlr.de/en/desktopdefault.aspx/tabid-6214/10201_read-13077/
9) "SAR-Lupe - The innovative program for satellite-based radar reconnaissance," 2015, URL: https://www.ohb-system.de/tl_files/system/images/mediathek/downloads/pdf/OHB_System_SAR-Lupe_2015.pdf
10) Peter B. de Selding, "OHB Signs Contract for Germany's Next-gen Radar Satellites," Space News, July 02, 2013, URL: http://www.spacenews.com/article/military-space/36091ohb-signs-contract-for-germany%E2%80%99s-next-gen-radar-satellites
11) Doug Meiser, "SpaceX Adds to Growing Launch Backlog with German Radar Satellites Contract," Aug. 8, 2013, URL: http://www.parabolicarc.com/2013/08/08/spacex-adds-growing-launch-backlog-german-radar-satellites-contract/
12) "Nine-month report 2013 for the period from January 1 to September 30," OHB. URL: http://www.ohb.de/tl_files/ohb/pdf/finanzberichte_hauptversammlung/2013/2013_9M-Q3_OHB_E.pdf
14) Information provided by Steffen Leuthold of OHB, Bremen, Germany
15) Information provided bei Reiner Knauer of OHB, Bremen, Germany
16) Frank Döngi, "Earth Observation from Space - The European Landscape in the Second Decade," Proceedings of SPIE, Remote Sensing 2011, Vol. 8181, Prague, Czech Republic, Sept. 19-22, 2011, URL: http://spie.org/Documents/AboutSPIE/PDF/ERS11-plenary-Doengi.pdf
17) "OHB-System AG: SAR-Lupe now officially handed over to Strategic Reconnaissance Command," Dec. 4. 2008, URL: http://www.ohb.de/press-releases-details/items/ohb-pr_sl_%C3%BCbergabe.html
18) Information provided by Ingo Engeln of OHB-System, Bremen, Germany
19) "10-year operation period of the SAR-Lupe system for the German Federal Armed Forces now to commence," Dec. 3, 2007, URL: http://www.ohb-technology.de/press-releases-details/items/id-10-jaehriger-betrieb-des-sar-lupe-systems-fuer-die-bundeswehr-beginnt.html
20) H. M. Braun, P. E. Knobloch, "SAR on Small Satellites- Shown on the SAR-Lupe Example," Proceedings of the International Radar Symposium 2007 (IRS 2007), Cologne, Germany, Sept. 5-7, 2007
21) J. Zemann, et al., "The Deployable Boom Assembly for SAR-Lupe," 28th ESA Antenna Workshop, June 2005, Estec Noordwijk, The Netherlands.
22) H. M. Braun, S. Kiecherer, "External Calibration for CRS-1 and SAR-Lupe," Proceedings of EUSAR 2006, Dresden, Germany, May 15-18, 2006
25) "OHB-System awarded contracts for the operation of the French SAR-Lupe ground station and the German HELIOS II ground station," May 4, 2010, URL: https://www.ohb-system.de/press-releases-details/items/ohb-system-awarded-contracts-for-the-operation-of-the-french
26) Peter B. de Selding, "OHB To Support Franco-German Imagery Partnership," Space News, May 4, 2010, URL: http://www.spacenews.com/military/100504-ohb-imagery-partnership.html
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).