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TanDEM-X: “Cutting Edge” Technology at DLR
Oberpfaffenhofen
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“The successful
launch of the TanDEM-X satellite (TDX) signifies the importance of space
research as a firm building block of our technological development program of Germany” said Parliamentary State
Secretary of the Federal Ministry of Economics and Technology, Peter Hinze at
the launch of TDX.
Germany's second Earth observation satellite, TanDEM-X,
was launched as planned on 21 June 2010 at 04:14 Central European Summer Time
(CEST, at 08:14 local time) from the Baikonur Cosmodrome in Kazakhstan. Atop a Russian Dnepr
rocket, the satellite, weighing more than 1.3 tons and five metres in length,
started its journey into orbit. At 4.45 CEST first signals were received via the
ground stations Troll and O’Higgins in the Antarctic. The German Aerospace Center (Deutsches Zentrum für
Luft- und Raumfahrt; DLR) manages the TanDEM-X mission (DEM-X = Digital
Elevation Measurement using X-Band) now together with the TerraSAR (TSX) mission (first German Earth
observation mission, launched on 15. June 2007) via its ground segment, and is
responsible for mission operations and for generating and utilizing the
scientific data. "TanDEM-X is a key German project and will provide us
with a homogeneous 3D elevation model of the Earth which will be an
indispensable aid for a great many scientific and commercial avenues of
enquiry," said DLR Chairman Prof. Dr Johann-Dietrich Woerner at the launch
event held in the German Space Operations Center (GSOC) at the DLR site in
Oberpfaffenhofen. "This mission demonstrates Germany's expertise in
satellite-based radar technology and is, in particular, the outcome of a
consistent focus in the national space program. Also, TanDEM-X demonstrates a
successful public-private partnership," stressed Prof. Woerner.
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Public-private
partnership
TanDEM-X is
being run as a Public-Private Partnership (PPP) between the DLR and EADS/Astrium
GmbH, with DLR funding coming from the German Ministry of Economics and
Technology. Infoterra GmbH, a subsidiary of Astrium, is responsible for the
commercial marketing of the TanDEM-X data. Astrium GmbH in Friedrichshafen built the satellite and
is sharing the cost for its development and operation. The TanDEM-X mission
cost amount to 165 million Euros. DLR’s share is 125 million Euros and the
Astrium is contributing 40 million Euros. TanDEM-X
and its twin satellite, TerraSAR-X, will fly in formation  | Together with
its twin satellite TerraSAR-X, in space since June 2007, TanDEM-X will survey
the entire land mass of the Earth from an altitude of 514 kilometers within
three years.
"This will be the first time we will ever have had a globally standardized
3D digital elevation model of Earth, and with a measuring point density of 12
meters, it will be incredibly accurate," said Prof. Dr Alberto Moreira,
Science Director of the TanDEM-X mission and Director of the DLR Microwaves and
Radar Institute at Oberpfaffenhofen. Germany will be the first
country ever to have a digital, three dimensional elevation model of Earth,
making it a globally unique data product. This can be used in initiatives and
programmes such as the ZKI (Center for Satellite-Assisted Crisis Information at
DLR), GMES (Global Monitoring for Environment and Security) and GEOSS (Global
Earth Observation System of Systems), and may also be incorporated in
security-related cooperation treaties and agreements. |
SpaceOps News (SoN) had the opportunity to talk to Dr. Martin
Wickler (MW), Head of Satellite Mission Operations at DLR-GSOC:
SoN:
TanDEM-X was launched exactly at equinox while TerraSAR-X was launched with a
little offset to the equinox on 15. June 2007, what are the orbit
peculiarities? MW: Both
satellites fly in a dusk-dawn orbit
because of power supply considerations (optimized illumination of the solar
array) and to be able to cover the Earth repeatedly from pole to pole. The TanDEM-X satellite will be maneuvered into
very close vicinity (approx. 200 m) of TerraSAR-X to fly in formation to be able
to take 3D profiles of the Earth. These manoeuvers will be performed in Oct
2010 finally.
SoN: It is
possible for the first time to have a complete 3D model of the earth: Can new
fields of applications be expected or will the 3D model just enhance the
accuracy and the completeness? MW: The
TerraSAR-X and TanDEM-X measurements will be more accurate than those available
so far and the total landmass of the Earth will be measured. So far only the
SRTM-X/C mission provided equivalent data, however only between+-60 Deg because
of the Shuttle’s orbital constraints. The accuracy will be increased by a
factor of 5-10. New
applications are predictable, like for the DLR operated Center for Satellite-Assisted Crisis Information (ZKI) or for
providing reference data for comparison before and after catastrophic events
like floods or earthquakes.
SoN: Since
TerraSAR-X was run under a PPP arrangement already: What is the experience with
the commercial market and how is the interface with strategic demands outside
Germany, i.e., what mechanisms exist to make sure the provided information is
not “misused”? MW: TerraSAR’s
operator is GSOC, the marketing of the data is divided between DLR and the
commercial company Infoterra, Germany (ITD), a subsidiary of
EADS/Astrium. Data for scientific
purposes are distributed by DLR, data for commercial purposes is marketed by
ITD. The
operations of the satellite as well as the distribution of the data is
regulated by a German satellite data security law, the “Satelliten-Daten
Sicherheits-Gesetz” (SatDSiG). That means the
satellite operator has to make sure that all commands to the satellite can not
be corrupted by a third parties and the data distribution units are forced by
this law to make security checks on the trustworthiness of its customers. In
some cases the data can be withheld for some days before released.
SoN: A
recent SpaceNews (Vol. 21, issue 24) issue is postulating a conflict between
France and Germany with respect to technology developments of high-resolution
optical Earth observation satellites (a French domain) and radar imaging
satellites (a German domain) and a possible fusion of optical and radar
pictures. Any comments from a TerraSAR-X, TanDEM-X point of view? MW: This
conflict is not relevant for TSX and TDX since both satellites deliver radar data
for scientific and commercial purposes only.
SoN: How
efficiency driven is the private/institutional interface between DLR and EADS?
What are the contractual arrangements? MW: The
financial contribution shares of ITD are regulated in a memorandum for the execution
of the project, the so called “Durchführungs-Vereinbarung”. The
financial amounts IDT has to transfer to DLR depend on the quality, volume and
timeliness of the data.
SoN: Any
indications with respect to customer satisfaction from the TerraSAR-X
experience so far? MW: The total
production chain from ordering of a data product, the mission
planning/commanding efficiency of the satellite, the actual data taking and the
data processing and delivery was recently investigated and evaluated by the National
Geospatial-Intelligence Agency (NGA) in comparison with the performance of the Cosmo-Skymed
and RadarSat satellites. TerraSAR-X was rated best. The quality
of the products as well as the service of the ground segment is decisive also
for ITD: In specific urgent cases the system response time between ordering and
delivery of a certain data take can be reduced to 3 hrs. In
conclusion it could be said that the scientific users as well as the commercial
clientèl is very satisfied with the provided quality and service. The current
planning of IDT is to finance the follow-on mission TSX-2 (planned for 2015) using
the accumulated profit.
SoN: DLR
has the unique advantage that the radar technology development group within the
DLR Microwaves and Radar Institute as well as the image processing team (DLR-DFD)
is on location – does this improve the operations efficiency as well? MW: As
mentioned before to have the end-to-end production chain on the premises is a
unique feature. For operating the satellite it is very convenient to have the
support of the instrument experts available on your fingertips. Especially
during emergency situations a quick recovery can be guaranteed.
SoN: What
kind of operational back-up provisions exist to guarantee continuous customer
service? MW: We have
established different kinds of backups. All critical elements are one- or
two-failure tolerant like data lines, antennas, command system, mission
planning etc., each position of the operations team is covered by at least 4 resident
experts and a catastrophic loss of the control center facility at Oberpfaffenhofen
would be covered by a physically separate control center located at our antenna
site at Weilheim, 50 km south of Oberpfaffenhofen.
SoN: If one
of the two satellites would fail prematurely - does the project have a Plan-B? MW: No, we
expect both satellites to work during the entire mission period.
SoN: The German Ministry of Economics and Technology promised in a press
release after the TanDEM-X launch that it would support the national satellite
radar research program without any financial reductions despite it might be
forced to reduce or freeze the ESA contributions because of the global
financial crisis. What is the next development step to stay ahead of the technological and
economic competition? MW:
There are a couple of activities which will be followed up in the future. For
the commercial sector ITD has the obligation to continue the TerraSAR-X
satellite series using its own revenue in case the radar market proves to be commercially
successful (TSX-2) according to the PPP agreements. The
next generation of radar satellites will implement a technological quantum leap:
The key word is HRWS (High Resolution, Wide Swath), i.e., the combination of
highest possible resolution with a wider swath by applying the concept of
“digital beam-forming”. Those activities are driven by the DLR-Agency. A
further improvement idea is move TanDEM-X to the L-Band (TanDEM-L). To discuss
the possible advantages and applications realizing this idea would be outside
the scope of this interview. The biggest challenge would be the spacecraft
design (large antennas) and the handling of the enormous data volume. With this
concept the total landmass could be charted within one week, while TanDEM-X
needs approximately one year.
SoN: In conclusion could you tell us what the
challenges for GSOC are to operate TerraSAR-X and TanDEM-X satellites? MW: We have to face three challenges. Naturally the
biggest challenge is flying the two spacecraft in the desired formation side by
side with only 200 m apart which has never been realized before. The design
features we have implemented onboard the spacecraft side and on the ground will
allow us to complete the various formations within three years. Another
challenge is mission planning. To explain the situation: Only 10% of the time
within a certain formation can be used for data takes, because this is the only
time within a helix (i.e., within the intertwined orbits) where both satellites
are flying right-looking side by side. The rest of the time will be used to
take separate measurements, i.e., two separate missions for two satellites have
to be planned, where each satellite can perform up to 500 data takes per
day. Both
missions are operated at GSOC within the so called multi-mission-environment,
i.e., all Earth observation missions are operated by the same operations
personnel. This concept yields very good financial synergies, however requires a
very high flexibility within the team, vast relevant operational know-how and absolute
dedication to the job of each team member.
As a result of this, the first
TanDEM-X picture could be taken in record time on 24. June 2010 as verification of the
instrumentation (picture see below), the first 3D pictures using TerraSAR and
TanDEM-X data will be generated in October 2010 as part of the commissioning
phase.
Madagaskar as seen from space Even the ups and downs of the waves in the Indian Ocean – coloured pale
yellow on the image – are charted by TanDEM-X as it flies over at a speed of
seven kilometres per second. The change in the waves at the entrance to the
Diego Suarez Bay is clearly visible. The water in the bay itself, on the shore
of which the provincial capital, Antsiranana, can be recognised, is very flat –
in contrast to the undulating ocean – and reflects the radar signals from
TanDEM-X more uniformly. The area of valleys to the south drains the volcanic
cone of Ambre-Bobaomby into the Indian Ocean. Dr.
Wickler, SpaceOps News wants to thank you for providing this inside information
for the space operations community on this very successful project and good
luck for the future projects TSX-2 and TanDEM-L .Joachim J. Kehr (joachimkehr@aol.com) Editor SpaceOpsNews
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