ROSETTA
FLIGHT REPORTS
of RPC-MAG
RO-IGEP-TR0013
Issue:1 Revision:0
November 10, 2004
Mission Commissioning Results Review
MCRR
Andrea Diedrich
Karl-Heinz Glassmeier
Ingo Richter
Institut f�r Geophysik und extraterrestrische Physik
Technische Universit�t Braunschweig
Mendelssohnstra�e 3, 38106 Braunschweig
Germany
1. Introduction
This document describes the results of the
commissioning and interference campaign concerning the
RPC MAG experiment. The tests were executed from
March 17. - October 14, 2004.
Details and an overview of the measured data can be
found in:
RO--IGEP--TR0006: Report of the Commissioning
PART 1, March 17. -- March 19, 2004
RO--IGEP--TR0008: Report of the Commissioning
PART 2, May 05. -- May 10, 2004
RO--IGEP--TR0010: Report of the Commissioning
PART 3, September 6. -- September 10, 2004
RO--IGEP--TR0011: Report of the Interference
Campaign, September 20. -- October 14, 2004
RO--IGEP--TR0012: Investigation of the impact of
ROSETTA's Reaction wheels on the Magnetic Field
measurements.
These documents can be found on :
ftp-server: ftp.geophys.nat.tu-bs.de
user: anonymous
directory: /pub/rosetta/docs
A copy is also available on the RPC server at the
Imperial College.
2. Activities during CVP
2.1 Functional Tests
* RPCMAG could be switched on successfully every
time and worked as expected.
* RPCMAG was tested in all modes successfully.
* Both RPCMAG sensors are working nominally.
* Sensor temperatures: - 120�C ... -45�C
2.2 Boom Deployment
The MAG Boom deployment was successfully performed
on March 19th, 2004.
* The s/c generated Residual field before Deployment
was
~200 nT at the IB sensor
~740 nT at the OB sensor
* The s/c generated Residual field after Deployment
was
~ 250 nT at the IB sensor
~100 nT at the OB sensor
* The noise level after the boom deployment was
about a factor of ten lower than before the
deployment.
All measurements were taken at a sensor temperature of
about T = -88�C.
Figure 1:The magnetic Field at the IB sensor during the
boom deployment
Figure 2: The magnetic Field at the IB sensor during the
boom deployment
3. Cognitions from CVP
3.1 DC Analysis - Temperature Behaviour
* S/C generated Residual field after Deployment
~ 250 nT @ IB ~100 nT @ OB
* RPCMAG readings vary with temperature
* Temperature dependence of RPCMAG offset
deviates from GND CAL results.
The most likely reason for this is that the ground
calibration was only be performed down to -60�C,
the observed temperatures in space, however, are
going down to -125 �C.
==> A New temperature model has to be applied
3.1.1 The old Temperature Model
The quality of the ground calibration based temperature
model of the sensors was checked using the following
Procedure:
* Long term investigation: May - September 2004
All available commissioning data were taken
* Averages were built on a 10 minute base
Result:
Figure 3: 600s average OB Magnetometer readings,
calibrated with ground calibration results, versus sensor
temperature.
It is obvious that a strong correlation between the sensor
temperature and the MAG sensor readings occurs.
Therefore, a better temperature model has to be
developed.
3.1.2 The new Temperature Model
To get an idea of the real dependence between the MAG
sensor readings and the sensor temperature the 10 minute
averaged MAG data were plotted versus the temperature.
Refer to Figure 4. As a result it turned out, that a cubic
Temperature model (solid line) like
Bi*(t) =Bi(t) - P3i(T(t))
Describes the sensor behaviour in a convenient was. The
original ground based model was just a pure linear
model.
The successful application of the new model to the data
can be seen in Figure 5.
Figure 4: 600s average OB Magnetometer readings
versus sensor temperature.
Figure 5: 600s average OB Magnetometer readings,
calibrated with the new temperature model, versus sensor
temperature.
3.2 AC-Analysis: Impact of the Reaction wheels
The signal analysis revealed that
* there is always a sinusoidal disturbance in the order
of 1nTpp with slow varying frequencies.
* The observed frequencies of the disturbers are
different for different modes. ==> Aliasing effect
* Disturbance can be seen on OB, IB & ROMAP
This behaviour is displayed on the following diagrams.
3.2.1 Typical Timeseries
Figure 6: Typical timeseries of OB burst mode data.
Data were zoomed in a 1 minute interval. The DC level is
quite stable, the noise is in the order of 0.7 nTpp.
3.2.2 Typical Powerspectra
The power spectra reveal discrete, monofrequent signals
in the order of a few Hertz if the MAG signal is sampled
with 20 Hz.
Figure 7: Typical Power spectra. Data of the OB sensor
in Burst mode. X and Y component in s/c coordinates is
plotted.
3.2.3 Typical Dynamical Spectra
Figure 8: Typical Dynamic spectra. Data of the OB
sensor in Burst mode (20 Hz sampling) in s/c coordinates
is plotted.
Figure 9: Typical Dynamic spectra. Data of the IB sensor
in Burst mode (1Hz sampling) in s/c coordinates is
plotted.
The dynamic spectra show various spectral lines beside
the "real magnetic field data". These line vary slowly
with the time and show specific structures. The shape of
these disturbance lines is specific to the sampling
frequency of the MAG sensosrs. All these criteria lead to
the guess, that the disturbance might be an Aliasing effect
and might be dependent of ROSETTAs four reaction
wheels.
3.2.4 The Reaction Wheels
The next figure show the speeds of the reaction wheels in
rpm. The data are taken from the DDS. The panels show
the timeseries of the parameters
* NAAD60014
* NAAD6024
* NAAD6034
* NAAD6044
The parameters have been calibrated using the DDS
calibration value 0.50813.
Figure 12 shows the same data but in the unit of Hertz
rather than Rpm.
Figure 10: Revolutions of all 4 Rosetta Reaction wheels
in rpm.
Figure 11: Revolutions of all 4 Rosetta Reaction wheels
in Hertz.
3.2.5 Reaction Wheels - Seen from the MAG sensors
Figure 12: Magnetic signature of the 4 Reaction wheels
seen by a sensor which is sampled with 20 Hertz.
Figure 13: Magnetic signature of the 4 Reaction wheels
seen by a sensor which is sampled with 1 Hertz.
To get an idea how the "high frequent" reation wheel speeds
would appear on sensor which is only sampled with 20 Hz or
1Hz the wheel data have been shifted and folded down to the
Nyquist frequency interval according the sampling theorem.
The result can be seen in Figures 13 and 14.
3.2.6 AC-ANALYSIS : Results
* RPCMAG clearly identifies the signatures of the 4
Reaction wheels
The comparison of the dynamic spectra of the
magnetic field data and the reaction wheel frequencies
from the DDS parameters reveals a nearly perfect
accordance.
==> Dynamic frequency reduction model to be developed
to get rid of the reaction wheel impact
* Spin -Off:
Analysis of OB, IB and - independently - ROMAP
revealed a slightly wrong reaction wheel calibration
factor (1.00335 ~ 4 rpm)
==> DDS HK Calibration Parameters to be updated.
3.3 Comparison with ROMAP
3.3.1 Power Spectra
Figure 14: Power Spectra of the RPC_MAG OB sensor.
1 s average data in s/c coordinates.
Figure 15: Power Spectra of the RPC_MAG IB sensor.
1 s average data in s/c coordinates.
Figure 16: Power Spectra of the ROMAP sensor.
1 s average data in s/c coordinates.
The Figures 15 - 17 show the Power spectra for of the
RPCMAG OB, RPCMAG IB, and the Lander
Magnetometer ROMAP. Data were taken in a 1 Hz
mode.
As result it can be stated, that all three sensors have quasi
the same dynamic properties. The noise level of the
RPCMAG sensors seem to be slightly better in the higher
freuquent part of the spectrum.
3.3.2 Dynamic Spectra
As a last point of the investigation also the dynamic
spectra for RPCMAG and ROMAP are shown in Figures
18 - 20. All there sensor sho the impact ot the reaction
wheels. The slightly different pictures are caused by
different sampling modes.
* RPCMAG OB was sampled with 20 Hz. The data were
averaged later to 1s mean values.
* RPCMAG IB was sampled with 1Hz. No additional
averaging was done. The "low activity" areas in the
spectrum are caused by a mode switching to a low
smapling mode on the IB sensor.
* ROMAP was sampled with 1Hz. No additional
averaging was done.
Therefore, these data show different behaviour
concerning the response of the reaction wheel speeds.
Figure 17: Dynamic Spectra of the RPC-MAG OB
sensor. 1 s average data in s/c coordinates.
Figure 18: Dynamic Spectra of the RPC-MAG IB sensor.
1 s average data in s/c coordinates.
Figure 19: Dynamic Spectra of the ROMAP sensor.
1 s average data in s/c coordinates.
4. Interference Campaign
The analysis of the interference campaign did not show
remarkable interference effects rather than the reaction
wheels. A detailed analysis could be performed if a
detailed list of activities on the s/c (Time, event) would
be available. A coarse overall first view analysis,
however, did not show any further problems.
5. Instrument Status
RPCMAG is fully operable!
6. Archiving S/W Status
For the archiving of the data an IDL s/w package called
DDS2PDS has been developed. This is a day based
Data processing tool which
* gets data from the ftp sever
* converts binary to ASCII data
* calibrates the data
* generates plots and PDS compliant files
This s/w is working but always under improvement.
Improvements:
* New Temperature model already implemented
* Dynamic frequency elimination to be implemented
According to this, the RPCMAG EAICD is kept up to
date.
Reference
:
RO-IGEP-TR0013
Issue
:
1
Rev.
:
0
:
0.9
Date
:
November 10, 2004
, 2002
, 2002
Page
:
29
0.9
Draft
Rev.
:
0