Operational Description Werner Magnes Institut fr Weltraumforschung IWF

Operational Description Werner Magnes Institut für Weltraumforschung (IWF) Austrian Academy of Sciences FGM peer CDR Op Description - 1 Berlin, April 6, 2004

FGM Block Diagram FGM peer CDR Op Description - 2 Berlin, April 6, 2004

FGM Signal Flow (F 20) FGM signal flow 2 x Boxcar filter amplitude response phase response N. . . number of accumulated samples T. . . sampling period (1/(4 F 0) or 128 Hz) FGM peer CDR Op Description - 3 Berlin, April 6, 2004

Frequency Response (F 20) FGM raw data amplitude response of the 128 Hz raw data FGM peer CDR Op Description - 4 phase response of the 128 Hz raw data Berlin, April 6, 2004

Filter Modes (F 20) FGM filter modes Filter mode 1: • only data decimation (D) • 4 Hz data with 5. 7 x higher noise • huge aliasing • no de-spinning problems Nf. . . number of accumulated samples in table Tr. . . raw data rate (1/128) Filter mode 2: • filter calc. down to 16 Hz (Nf) • decimation from 16 to 4 Hz • 4 Hz data with 2 x higher noise • less aliasing • little de-spinning problems Filter mode 3: • filter calc. down to 4 Hz • little aliasing Number of data decimation (D) and accumulation (Nf) according to the selected filter mode • de-spinning problems FGM peer CDR Op Description - 5 Berlin, April 6, 2004

Frequency Response (F 20) FGM TML data Amplitude characteristics of the 128 Hz raw data as well as the 64 Hz and 32 Hz output data (filter mode 2 and 3) FGM peer CDR Amplitude characteristics of the 16 (filter mode 2 and 3), 8 and 4 Hz (filter mode 3) output data Op Description - 6 Berlin, April 6, 2004

AC-Field Distortion Spin tone distortion (1) B-field data measured by magnetometer on spinning S/C (4) Box car filter causes amplitude attenuation and phase shift (2) Assumed AC field (Bx=By=0) (3) Mag components with left- and right-hand polarized terms FGM peer CDR (5) Final de-spinning Op Description - 7 Berlin, April 6, 2004

Frequency Response Frequency response around spin-frequency amplitude response FGM peer CDR phase response Op Description - 8 Berlin, April 6, 2004

AC-Field Distortion Spin tone distortion spin period = 3 sec; Bz = 1 n. T; fz = 0. 4 Hz; By = 0 n. T; filter mode 3: 4 Hz FGM peer CDR spin period = 3 sec; Bz = 1 n. T; fz = 0. 4 Hz; By = 0 n. T; filter mode 3: 16 / 8 / 4 Hz Op Description - 9 Berlin, April 6, 2004

AC-Field Distortion Spin tone distortion spin period = 3 s; Bz = 1 n. T; fz = 1 Hz; By = 0 n. T; filter mode 3: 4 Hz FGM peer CDR spin period = 3 s; Bz = 1 n. T; fz = 1 Hz; By = 0 n. T; filter mode 3: 16 / 8 / 4 Hz Op Description - 10 Berlin, April 6, 2004

Large Fields (F 4) Large field feedback (VEX-MAG) ± 900 n. T; 3 Hz; 128 Hz FB update max. FB step of 130 n. T; STD residuum: 54 p. T STD noise: 48 p. T (0. 5. . 64 Hz) ± 900 n. T; 0. 3 Hz; 128 Hz FB update max. FB step of 13 n. T; STD residuum: 53 p. T (0. 1. . 64 Hz) ± 900 n. T; 0. 03 Hz; 128 Hz FB update; max. FB step of 1. 3 n. T; STD residuum: 56 p. T (0. 04. . 64 Hz) FGM peer CDR Op Description - 11 Berlin, April 6, 2004

DAC Linearity Check (F 3) DAC linearity check • National Instruments 16 -bit ADC card with digital I/O • 12 -bit DAC under test stepped through all 4096 output voltages • 100 measurements per step; mean value and standard deviation • Comparison with nominal value for integral non-linearity • Comparison of real with ideal voltage step for differential non-linearity Block diagram DAC linearitiy test FGM peer CDR Op Description - 12 Berlin, April 6, 2004

DAC Linearity Check (F 3, F 19) DAC linearity check FGM peer CDR Op Description - 13 Berlin, April 6, 2004

DAC Linearity Check (F 3, F 19) DAC differential and integral non-linearity … and a bad one. A good … FGM peer CDR Op Description - 14 Berlin, April 6, 2004

FGM Ranges (F 3, F 19) Consequences of DAC non-linearity on measurement accuracy • • • Dynamic range of ± 32, 768 n. T (24 bits) Digital resolution of approx. 4 p. T Fine (12 bits) and course (6 bits) feedback DAC • • • Dynamic range of fine DAC is ± 512 n. T with 0. 25 n. T resolution Maximum error due to DNL in fine (‚science‘) range of 58 p. T Digital resolution of 14 bits in fine range • • • Dynamic range of course DAC is ± 32, 768 n. T with 1024 n. T resolution Maximum error due to DNL in course range of 7. 8 n. T (13 bits) Digital resolution of 13 bits in course range FGM peer CDR Op Description - 15 Berlin, April 6, 2004

Operation FGM turn-on • At least Start command from Data Control Board • Default values for phase, sampling, K-values, offsets and averaging mode stored in FPGA • Start of data acquisition with one second sync • No in-flight configuration storage FGE standard mode • Field calculation: k 1*ADC+k 2*DAC+Offset (@ 128 Hz) • 24 bits per axis (LSB ~ 4 p. T - 32, 000 n. T range) • TML output: 4 Hz data in filter mode 2 IDPU tasks • Auto ranging by taking only 16 bits per axis • Calculation of spin-average data (Slow Survey Modes) FGM peer CDR Op Description - 16 Berlin, April 6, 2004

Operation FGM operation during all science phases • • Slow Survey: 1 vector / spin Fast Survey: 4 vectors / sec Particle Burst: 32 vectors / sec Wave Burst 1/2: 128 vectors / sec FGM operation during boom deployment • Check of the magnetic moment of the S/C FGM operation during complete checkout phase • Survey of DC and AC magnetic disturbances FGM peer CDR Op Description - 17 Berlin, April 6, 2004

Operation FGM operation during special mission phases • • Change of orbit Eclipse Special use of FGM data • • • S/C attitude control in perigee Knowledge of FGS axes to spin axis orientation During perigee knowledge of FGS axes relative to a geophysical reference system with 0. 1 degree accuracy (request for a 56 n. T accuracy in course feedback range) FGM peer CDR Op Description - 18 Berlin, April 6, 2004