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), 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) 5) 6) 7)
• 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].
Figure 1: Artist's rendition of the SAR-Lupe spacecraft in orbit (image credit: OHB-System AG)
The S/C structure has a size of
about: 4 m x 3 m x 2 m with a fixed parabolic SAR/communication
reflector antenna (antenna size: 3.3 m x 2.7 m). Three-axis
stabilization is used. 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 S/C has an average power consumption of 250 W (use
battery for power storage). The S/C mass is about 770 kg. The design
life is 10 years (using a redundant design concept). Orbit control is
provided with hydrazine thrusters
and a fuel capacity for 10 years. 8)
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.
Figure 2: Illustration of the SMU (image credit: Carlo Gavazzi Space)
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
Ground segment: 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.
Orbit: The five satellites
are launched into three orbital planes. Average altitude of about 500
km, inclination for near-polar orbits. 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.
Figure 3: Alternate view of the SAR-Lupe spacecraft (image credit: OHB-System AG)
Figure 4: Illustration of the three orbital planes of the SAR-Lupe constellation (image credit: OHB-System AG)
Launch: The 5-satellite constellation is planned to be 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 is 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 (Kosmos-3M launch vehicle)
July 2, 2007, launch successful, LEOP operations at DLR/GSOC
November 1, 2007, launch successful, LEOP operations at DLR/GSOC
planned for March 2008
planned for June 2008
Table 1: Overview of SAR-Lupe mission schedule
Figure 5: Several views of the SAR-Lupe spacecraft configuration (image credit: OHB-System AG)
Mission status: The SAR-Lupe-1 spacecraft and payload are operating nominally as of 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.
• SAR-Lupe-2 is operational as of mid-August 2007. 9)
Sensor complement (XSAR):
In the absence of an instrument
description (the SAR-Lupe mission is classified), some general
observational objectives/features are provided:
The XSAR (X-band SAR instrument) 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
• Parabolic SAR reflector antenna of size: 3.3 m x 2.7 m. The choice of using a reflector antenna instead
of an active beam-steering antenna represented a major cost saving in the development of the instrument. 10)
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,
• 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: << 1 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
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: 11)
- 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.
Figure 6: Illustration of the SAR-Lupe ARC in X-band (image credit: RST)
Figure 7: Block diagram of the calibration of the XSAR antenna
1) In German, the word Lupe means "magnifying glas," a reference and connotation for high-resolution imagery.
2) OHB-System brochure, "SAR-Lupe - The innovative program for satellite-based Radar Reconnaissance"
3) Information kindly provided by Fritz Merkle and Daniela Sell of OHB-System, Bremen
6) "The SAR-Lupe Program - An Industrial View," Security and Defence Aspects of Space: The Challenges for EU, Athens, Greece,
May 8-9, 2003, URL: http://ec.europa.eu/comm/space/doc_pdf/merkle.pdf
D. Koebel, C. Tobehn, B. Penné, "OHB Platforms for Constellation
Satellites," 5th IAA Symposium on Small Satellites for Earth
Observation, Berlin, Germany, April 4-8, 2005
10) 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
11) H. M. Braun, S. Kiecherer, "External Calibration for CRS-1 and SAR-Lupe," Proceedings of EUSAR 2006, Dresden, Germany, May
This description was provided by Herbert J. Kramer from his documentation of: "Observation of the
Earth and Its Environment: Survey of Missions and Sensors," - comments and corrections to this article
are welcomed by the author.