Geoscience Reference
In-Depth Information
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initial altitude of 454 km,
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designed lifetime of five years for the mission (but the life expectation
is much higher!),
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weight of 522 kg, length of 8.3 m (including a “boom” of 4 m length),
width of 1.6 m, height of 0.75 m.
This initial altitude may be regarded as a compromise between gravity
and magnetic field measurements. Considering the gravity field, a lower al-
titude would be desirable. Primarily due to atmospheric drag, the altitude
will decrease to about 300 km and even less which is important because of an
increasing sensitivity with respect to gravity field coecient determination.
The reason for the curious 4 m boom is that the magnetometry assembly
must be separated from the main body of the satellite (“magnetic cleanliness
reasons”, see http://op.gfz-potsdam.de/champ).
To achieve the mission goals, the following payload is on board of the
satellite:
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dual-frequency GPS receiver connected to a multiple antenna system
to determine the orbit of the CHAMP satellite using code and phase
pseudoranges;
•
three-axis accelerometer to measure the nongravitational accelerations
acting on the spacecraft (air drag, solar radiation pressure, albedo,
etc.);
•
laser retroreflector for backup tracking to measure two-way ranges be-
tween ground stations and the satellites with 1-2 cm accuracy; these
measurements support the precise orbit determination;
•
fluxgate magnetometer to measure the vector components of the mag-
netic field of the earth (this instrument is supported by a scalar mag-
netometer to provide a calibration capability of the fluxgate magne-
tometer);
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equipment to determine the ion density and temperature, the drift
velocity, and the electric field;
•
two advanced star trackers to provide high-precision attitude informa-
tion as required for the three-axis accelerometer, the digital ion drift
meter, but also for the attitude control of the satellite.
Typical other equipment required for a proper operation of the satellite
but with no specific relation to the scientific objectives of the mission is not
detailed here, such as the cold gas propulsion system, the thermal control
system, the power generation, the data handling, the telemetry, tracking and
command system. Furthermore, we do not list items of the control segment
