Geoscience Reference
In-Depth Information
4.2.
Magnetic field detection: from 0.1Hz to 640 kHz
Two search coil sensors, LF-SC and DB-SC, are combined to measure AC
magnetic fields: tri-axial vector components for low frequencies (0.1 Hz-
20 kHz), and one-axial component along the spacecraft spin axis for high
frequencies (10 kHz-640 kHz). They offer excellent sensitivity (Fig. 4) and
dynamic range (
>
80 dB) that will cover all expected electromagnetic waves.
4.3.
Spacecraft potential
The PWI electric field sensors have sucient dynamic range for spacecraft
potential (
100 V) to operate at all electron densities and temperatures
expected in Mercury's magnetosphere and in the solar wind.
±
4.4.
Electron density and temperature
Continuous surveying of electron density and temperature will be performed
by SORBET, using the technique of QTN spectroscopy
8
,
9
in the frequency
range 2.5-640 kHz. The performance may be roughly summarized as follows:
The electron density will be measured from 0.1 to
6,000 cm
−
3
(with
∼
∼
1%
accuracy) and the core temperature from 0.1-100 eV (with
10% accu-
racy). SORBET will also provide a diagnostic of the suprathermal electron
population (which is ubiquitous in the solar wind).
∼
4.5.
Calibration of electric field antenna impedance
The precise antenna impedance is very important for calibration of the
observed waveform and spectrum data. Since we have two different types
of electric field antennas, we include two instruments for the onboard mea-
surement of antenna impedance. AM
2
P and EWO serve to measure the
antenna impedance of MEFISTO and WPT, respectively. Both components
feed a known source signal to the antennas. By collecting the responses of
MEFISTO and WPT, we can calculate their frequency-dependent antenna
impedances.
5. Summary
Up to now, the MMO is scheduled to be launched in 2012, and initiate
observations at Mercury from 2016. At this stage, we extensively discuss
the development of the PWI system, so that it can provide excellent science
