Geoscience Reference
In-Depth Information
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Providing a significant improvement in satellite orbit determination
and prediction. This especially applies to low-orbiting satellites. The
highly accurate gravity field will enable a better separation of the per-
turbations caused by the static gravity field and other perturbing forces
(not only the nongravitational forces caused by air drag and solar ra-
diation pressure but also perturbations caused by the solid earth and
ocean tides).
The duration of the mission is scheduled with nominally 20 months,
including a 3-month commissioning and calibration phase and two measure-
ment phases, each lasting six months and separated by a long eclipse period.
The other main mission parameters are the following:
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due for launch in 2007 from Plesetsk in Russia,
sun-synchronous orbit, inclination 96
.
5
◦
,
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measurement altitudes: approximately 250 km,
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single ground station in Kiruna, Sweden, to exchange data and com-
mands; the European Space Operations Center (ESOC) at Darmstadt
will be used for mission and satellite control.
The main payload components are the following:
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three-axis gravity gradiometer based on three pairs of electrostatic
servo-controlled accelerometers to measure gravity gradients in three
spatial orthogonal directions: the desired signal is the difference in
gravitational acceleration (between a pair of accelerometers separated
by 0.5 m) at the test mass location inside the spacecraft caused by
gravity anomalies from attracting masses of the earth;
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geodetic dual-frequency (to compensate for ionospheric delays) multi-
channel GPS receiver with codeless tracking capability to (1) determine
the orbit of the GOCE satellite and (2) derive gravity information from
this orbit (the first task is performed by satellite-to-satellite tracking
in the high-low mode: this provides knowledge of the precise position
of the [low] spacecraft relative to [high] reference satellites such as the
GPS satellites; the second task is solved by orbit perturbation analysis
yielding gravity information);
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laser retroreflector to enable tracking by ground-based laser stations;
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attitude control accomplished by actuators comprising an ion thruster
assembly, star trackers, a three-axis magnetic torquer, and some other
sensors;
length of the satellite about 5 m, cross section of 1 m
2
,weightabout
1000 kg.
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