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TerraSAR-X Proves its Suitability for Space
TerraSAR-X, the German Earth observation satellite, has successfully demonstrated its suitability for space.
TerraSAR-X, the German Earth observation satellite, has successfully demonstrated its suitability for space.
• German satellite passes the endurance test with flying colours
• Mission opens up new perspective to Earth observation
• Radar can image one million square kilometres per day
These days ends a three-month test campaign at IABG in Ottobrunn, in which the Earth observation satellite has been thoroughly examined under space conditions. In addition to proving its performance and vacuum durability under hot and cold weather conditions, the satellite ? developed and built by EADS Space ? had to endure extreme vibrations and acoustic loads similar to those encountered during a rocket launch.
“The successful completion of the test series marks an important milestone for this mission”, gladly stated Uwe Minne, Director for Earth Observation and Science of EADS SPACE in Friedrichshafen. “Following the test results we are fully justified in saying that TerraSAR-X will be the best and most powerful ever built space radar sent into space.” Thus, for example, the satellite could image one million square kilometres of the Earth’s surface ? with a resolution of three metres ? regardless of light or cloud conditions. Minne added that it is planned to launch TerraSAR-X from the Baikonur Cosmodrome this very year.
The satellite will circle the Earth at an altitude of approximately 514 kilometres and will scan the surface of our planet with a radar beam day and night regardless of weather and cloud conditions. It will quickly and reliably deliver data for a wide range of applications, thus opening up completely new opportunities for commercial, public and scientific users. TerraSAR-X is the first national remote sensing satellite built in a Public-Private Partnership (PPP). On behalf of the German Aerospace Centre (DLR), EADS SPACE, Friedrichshafen, developed and constructed the satellite by contributing substantial company funds. Infoterra, a subsidiary of EADS SPACE, will be responsible for the marketing of data and products. TerraSAR-X is due to operate for five years, and its successor TerraSAR-X2 is already in preparation. Furthermore, it is planned to build a partner satellite, called TanDEM-X, which is to orbit the Earth together with TerraSAR-X. This tandem is planned to produce a spatial elevation model of the whole Earth with unprecedented resolution.
Commercial use requires high-quality data
The need for high-quality images of our planet has greatly increased in recent years. Whilst initially, Earth observation was primarily focussed on scientific aspects, commercial interest is becoming more and more important.
This development from pure scientific aspects to commercial and public applications has called for awarding the acquisition of Earth observation data to the private sector. In the future, it is intended to create a sustainable business area which is of benefit to all concerned. Successful commercial use is based on the availability of high-quality data – they must feature a high level of detail and allow rapid and reliable delivery.
The starting signal for TerraSAR-X was the signing of the cooperation contract on 25 March 2002. This contract, with a total volume of €102 million, was awarded by DLR to EADS SPACE to develop, build and launch the satellite. The space company contributed company funds amounting to €28 million and, in addition, financed the development of the geo-information products and their marketing. Since then, DLR has set up the ground segment for data reception and satellite commanding. Furthermore, it will perform data processing, archiving and distribution. EADS has built and tested the satellite; its subsidiary Infoterra has already won companies as marketing partners for data products and concluded initial contracts with future customers. All this indicates a successful project.
Active radar with zoom function
Following its launch on board a Russian-Ukrainian Dnepr-1 launch vehicle (former SS18 long-range rocket), TerraSAR-X will orbit the Earth in approximately 95 minutes at an altitude of about 514 kilometres. During that period, the Earth continues rotating so that the radar can access any spot on Earth within maximally four days (even within two days in 95 per cent of the cases).
The spacecraft will scan the Earth by means of the so-called “Synthetic Aperture Radar” (SAR) method. Compared to images in the visible range, the radar has the following major advantages: Firstly, the radar beam always produces its own exactly defined illumination. This is quite different for optical satellite images where the respective position of the Sun considerably influences the appearance of a landscape. Secondly, the radar operates day and night and, thirdly, it can also peer through clouds. “This is decisive, especially in regions near the equator which are often clouded”, explains Wolfgang Pitz, project manager of TerraSAR-X at EADS SPACE in Friedrichshafen.
Another special feature is the technical variant of an active radar. Active in this context means that the beam can be aligned in a slewing range of 20 to 60 degrees. This is not done by mechanically moving the antenna or the complete satellite, but by superimposing many individual radar beams. Thus, the range which can be covered by the instrument is expanded. “With a passive radar we can take a maximum of two images during a fly-over from Munich to Berlin, whilst now we can take up to twenty”, states Wolfgang Pitz.
A broad spectrum of applications is offered by the possibility of selecting three degrees of resolution and image size. In ScanSAR mode, at an image swath of 100km, this zoom function allows the observation of details down to a resolution of 16m. The resolution in Stripmap mode (30 km image swath) is 3 metres and even 1 metre in Spotlight mode (5km by 10 km).
This extremely high image resolution was only possible because EADS SPACE‘s engineers and technicians operated the radar in the so-called X-band spectrum. The radio signals emitted in this spectrum have a frequency of 9.65 Gigahertz, which corresponds to a wavelength of about 3 centimetres. Many of the former satellites operated in the C- or L-band spectrum at larger wavelengths of 5.7 or 24 centimetres respectively; thus, they delivered images with a lower resolution.
However, the requirements to be met by X-band technology concerning the properties of materials used and the processing accuracy are more demanding. In this field, EADS SPACE can look back on many years of experience which it has proven in scientific predecessor projects, such as the SIR-C/X-SAR mission in 1994 and the Shuttle Radar Topography Mission (SRTM) in 2000. “X-band technology has always been a German specialty”, states Pitz. “In this field, we are at the leading edge worldwide”.
The features mentioned above also explain the satellite‘s name: Earth observation (Terra) with Synthetic Aperture Radar (SAR) in X-band (X).
A variety of applications
Radar data contain a lot of information tailored to meet the needs of every potential user. Commercial areas as well as authorities and scientific institutions will benefit from TerraSAR-X. Infoterra GmbH, a wholly owned subsidiary of EADS SPACE, is responsible for commercial data marketing. DLR, as the Federal government‘s representative, remains the owner of the data and coordinates their scientific use.
Future users may choose one of two variants: Direct Access Partner (DAP) and Direct Access Customer (DAC). They conclude a contract with Infoterra under which they may receive data with their own station. Other commercial users buy the processed data from Infoterra via a secure Internet portal or via telephone. Scientists can obtain data records for selected research projects from DLR.
TerraSAR-X opens up a broad range of applications. Thus, the cloud-independent operation enables rapid and current mapping of large areas, in particular, of extensive wooded and mountain regions. There is a great demand in many countries, also for determining the forest stands and the forestry biomass. Furthermore, the TerraSAR-X data can be used as a national contribution to “Global Monitoring for Environment and Security” (GMES). This is a European action plan combining the data of terrestrial, maritime and space-based measuring systems.
Reconnaissance is one of the fields of application for TerraSAR-X data: Intelligence services, reconnaissance aircraft and emergency relief organisations benefit from systems offering not only an extremely high resolution but also on-time data acquisition. Today, these organisations generally draw on data of optical sensors. This may require longer waiting times. The near real-time data acquisition enabled by TerraSAR-X provides these organisations with unprecedented possibilities of using satellite data in time-critical situations.
Authorities will also benefit from TerraSAR-X data in the future. Surveyor‘s offices, for example, will regularly be able to record constructional or other changes in their municipalities or, after a storm, to capture wind throw areas in a rapid and cost-efficient way. In addition, following natural disasters, precise and current maps facilitate the coordination of humanitarian aid projects and reconstruction measures at any place on Earth. Finally, radar maps can also be used for strategic reconnaissance and deployment of soldiers in crisis areas. “In the first year of operation, we will gain a lot of experience and encounter applications we do not even consider at the moment”, says Jörg Herrmann, CEO of Infoterra GmbH. New commercial applications will presumably develop from scientific projects which are supported by DLR.
Novel applications are enabled by another specialty of TerraSAR-X: the “Dual Receive Antenna Mode”. In this mode, two parts of the antenna are operated like two eyes. This allows the detection of motion on the ground. This feature will be used for measuring the speed of cars on motorways. The long-term objective of such a technology could be a space-based multi-satellite system for the monitoring and guidance of traffic flows.
In addition to the radar instrument onboard of TerraSAR-X a technology demonstrator will make it into orbit. LCT will be used for in-orbit verification of rapid optical data transfer in space. With the instrument, financed by DLR and built by the EADS SPACE subsidiary Tesat Spacecom, a link is to be established between TerraSAR-X and a ground station. Later on, by means of this new type of laser system large quantities of data can be transferred to the ground. A corresponding station on a second satellite would allow a satellite-to-satellite link, enabling a rapid data exchange via relay stations around the world.
The future has already begun: TerraSAR-X2 and TanDEM-X
Sustainability is the avowed objective of the TerraSAR-X project. It is not based on a single Earth exploration but on continuous monitoring. The radar in space shall become a regular, operational system similar to the weather satellites that have been operating in space for many years. Thus, the course is set for the successor TerraSAR-X2 which is to be financed from the gain achieved by Infoterra with the TerraSAR-X images. Its launch is scheduled for 2011.
But the development does not stop and TerraSAR-X technology can be used for further applications. Therefore, EADS SPACE will implement the TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement) project on behalf of DLR. It consists of a further satellite, which is similar to TerraSAR-X and is to fly at a distance of between 500 metres and two kilometres from TerraSAR-X. Similar to the human eyes’ spatial view, TanDEM-X could capture a three-dimensional elevation model of the Earth. Motions, such as ocean currents, could also be detected. TanDEM-X will also be funded in a PPP model. It could be launched in March 2009.
About EADS SPACE
EADS SPACE is Europe‘s leading satellite specialist. Its activities cover complete civil and military telecommunications and Earth observation systems, science and navigation programmes, and all spacecraft avionics and equipment. In 2005, EADS SPACE had a turnover of 2.7 billion euros and about 11,000 employees in France, Germany, the United Kingdom and Spain.
EADS is a global leader in aerospace, defence and related services. In 2005, EADS generated revenues of approximately 34.2 billion euros and employed a workforce of more than 113,000.
Infoterra GmbH was launched in 2001 for the purpose of exclusively pursuing the commercial exploitation of TerraSAR-X data and derived geo-information products and services. Infoterra GmbH has a workforce of 30 employees in Friedrichshafen and is part of the European Infoterra Group with a total workforce of 300 employees in Germany, the U.K. and France.
Mathias Pikelj : +49 (0) 7545 8 91 23
Mareike Doepke: +49 (0) 7545 8 39 24
TerraSAR-X at a glance
Height: 4,88 m
Launch mass: 1,230kg of which payload: approx. 472kg
Resolution: 1m, 3m, 16m (depending on image size)
Launcher: Dnepr-1 (former SS18)
Orbit height: 514km on the equator
Tilt angle towards equator: 97.4° (Sun-synchronous)
Life time: 5 years
(Source Infoterra GmbH)