Concept information
Preferred term
VFM
Definition
- VFM is the prime instrument of the Swarm mission developed at DTU Space. The objective is to measure the magnetic field vector, on the boom, together with the star tracker for precise attitude measurement. The boom mounted Swarm vector magnetometer instrument consist of a triple star sensor block and a CSC (Compact Spherical Coil) vector magnetometer sensor, mounted on a stable optical bench (Figure 8). Each satellite contains the optical bench with one CSC and three CHU (Camera Head Unit). The three star sensor units are arranged with the boresights 90º from each other so as to ensure that only one CHU may be affected by Sun or Moon intrusion at any given time. Hereby an attitude solution accurate in all three degrees of freedom can be delivered to the CSC throughout the entire mission. The CSC sensor and the triple star sensor block are mounted on either end of a highly stable mechanical structure. The CSC vector sensor is supported by a zero CTE (Coefficient of Thermal Expansion) CFRP (Carbon Fiber Reinforced Polymer) adapter that on the one end matches the zero CTE CFRP tube, used to displace the CSC sensor from the star sensor heads (CHU), and on the other end matches the 32 ppm CTE CSC sensor, by means of a finger section. The rotational symmetry of this design ensures an excellent angular stability. The other end of the CFRP tube is attached to a CSiC bracket holding the three CHUs. The CSiC exhibit a heat distribution capacity second to none, minimizing thermal biases of this section, from the inevitable thermal gradient induced when the sun happens to illuminate any of the three CHUs. Because the CSiC is weakly magnetic, this material can only be used at distances larger than 20 cm from the CSC sensor. Each CHU is fitted with a straylight suppression system that is thermally decoupled from the optical bench. This separation minimizes thermal excursions from the time varying sun impingement over an orbit to less than a few degrees C. The straylight suppression system is mechanically mounted on an external thermal CFRP shroud, which also provides for thermal control of the entire optical bench. The material selection for all thermal protection has been performed to suppress soft or hard magnetic parts as well as parts that can generate magnetic fields under thermal gradients. VFM instrument: The VFM (fluxgate type) is based on the fluxgate transducer using a ringcore with amorphous magnetic material, which has a very low noise (10-20 pT rms). It has an extremely high stability < 0.05 nT/year. VFM consists of a CSC (Compact Spherical Coil) sensor, non redundant, mounted on the deployable boom, an internally redundant data processing unit (DPU) and the connecting harness. The spherical coils that create a homogeneous vector field inside the sphere are mounted on an isotropic and extremely stable mechanical support. In feedback conditions the sensor is used as a nulling device and the coils define uniquely the magnetic axes of the sensor. The VFM exhibits high linearity (< 1ppm), a component accuracy of 0.5 nT and precision of 50 pT rms. The operation of the fluxgate sensor is based on the extreme symmetry of the positive and negative magnetic saturation levels of the ferromagnetic sensor core material. Continuous probing of the core saturation levels by a high frequency excitation magnetization current enables the sensor to detect deviations from the zero field with only tens of pT noise and sub-nT long term stability. The mounting of the VFM sensor is using a sliced adaptor ring. The optical bench ensures mechanical stability of the system. Three star trackers provide full accuracy attitude. Instrument mass, power consumption 1 kg, 1 W Dimension of sensor head (CSC) Mass, power 82 mm Ø 280 g, ~ 250 mW Dimension of DPU Mass of DPU, power 100 x 100 x 60 mm 750 g, ~1 W Data rate Dynamic range ±65536.0 nT to 0.0625nT (21 bit) Omnidirectional linearity ±0.0001% of full scale (±0.1nT in ±65536nT) Intrinsic sensor noise 15 pTRMS in the band 0.01-10 Hz (6.6 pTRMS Hz-1/2 at 1 Hz) Intrinsic electronics noise 50 pTRMS in the band 0.01-10 Hz (15 pTRMS Hz-1/2 at 1 Hz) Sampling rate 50 Hz, linear phase filter, -3dB frequency 13.1 Hz Temperature range -20ºC to +40ºC (Operating performance) -40ºC to +50ºC (Survival performance) Thermal behavior - Offset - Scale factors - Non-orthogonality angles ~0 nT/ºC (CSC), ~0.1 nT/ºC (electronics) ~10 ppm/ºC (CSC), ~2 ppm/ºC (electronics) ~0 arcsec/ºC (0.06, 0.07, 0.04) Zero stability (thermal & long term) < ± 0.5 nT Absolute accuracy of Ørsted magnetometer parameters (relative to ASM & STR): - Offset < 0.2 nT (~120 dB) - Scale factors < 0.0005% - Axes orthogonality < 0.0006º (~2 arcsec) - Axis alignment < 0.0002º (~7 arcsec) Ørsted magnetometer with 3 offsets, 3 scale factors & 3 angles for 6.5year: Accuracy < 0.5 nT (en)
Broader concept
- MAGNETOMETERS (en)
Change note
- 2018-07-11 11:07:24.0 [mmorahan] Insert Concept add broader relation (VFM [03d748ff-7398-4ea8-87e7-38d0ef3e6167,367835] - MAGNETOMETERS [deac2632-5c17-4d15-ae92-c61ebc5a405a,348905]);
- 2018-07-11 11:10:31.0 [mmorahan] insert AltLabel (id: null category: primary text: Vector Field Magnetometer language code: en); insert Definition (id: null text: VFM is the prime instrument of the Swarm mission developed at DTU Space. The objective is to measure the magnetic field vector, on the boom, together with the star tracker for precise attitude measurement. The boom mounted Swarm vector magnetometer instrument consist of a triple star sensor block and a CSC (Compact Spherical Coil) vector magnetometer sensor, mounted on a stable optical bench (Figure 8). Each satellite contains the optical bench with one CSC and three CHU (Camera Head Unit). The three star sensor units are arranged with the boresights 90º from each other so as to ensure that only one CHU may be affected by Sun or Moon intrusion at any given time. Hereby an attitude solution accurate in all three degrees of freedom can be delivered to the CSC throughout the entire mission. The CSC sensor and the triple star sensor block are mounted on either end of a highly stable mechanical structure. The CSC vector sensor is supported by a zero CTE (Coefficient of Thermal Expansion) CFRP (Carbon Fiber Reinforced Polymer) adapter that on the one end matches the zero CTE CFRP tube, used to displace the CSC sensor from the star sensor heads (CHU), and on the other end matches the 32 ppm CTE CSC sensor, by means of a finger section. The rotational symmetry of this design ensures an excellent angular stability. The other end of the CFRP tube is attached to a CSiC bracket holding the three CHUs. The CSiC exhibit a heat distribution capacity second to none, minimizing thermal biases of this section, from the inevitable thermal gradient induced when the sun happens to illuminate any of the three CHUs. Because the CSiC is weakly magnetic, this material can only be used at distances larger than 20 cm from the CSC sensor. Each CHU is fitted with a straylight suppression system that is thermally decoupled from the optical bench. This separation minimizes thermal excursions from the time varying sun impingement over an orbit to less than a few degrees C. The straylight suppression system is mechanically mounted on an external thermal CFRP shroud, which also provides for thermal control of the entire optical bench. The material selection for all thermal protection has been performed to suppress soft or hard magnetic parts as well as parts that can generate magnetic fields under thermal gradients. VFM instrument: The VFM (fluxgate type) is based on the fluxgate transducer using a ringcore with amorphous magnetic material, which has a very low noise (10-20 pT rms). It has an extremely high stability < 0.05 nT/year. VFM consists of a CSC (Compact Spherical Coil) sensor, non redundant, mounted on the deployable boom, an internally redundant data processing unit (DPU) and the connecting harness. The spherical coils that create a homogeneous vector field inside the sphere are mounted on an isotropic and extremely stable mechanical support. In feedback conditions the sensor is used as a nulling device and the coils define uniquely the magnetic axes of the sensor. The VFM exhibits high linearity (< 1ppm), a component accuracy of 0.5 nT and precision of 50 pT rms. The operation of the fluxgate sensor is based on the extreme symmetry of the positive and negative magnetic saturation levels of the ferromagnetic sensor core material. Continuous probing of the core saturation levels by a high frequency excitation magnetization current enables the sensor to detect deviations from the zero field with only tens of pT noise and sub-nT long term stability. The mounting of the VFM sensor is using a sliced adaptor ring. The optical bench ensures mechanical stability of the system. Three star trackers provide full accuracy attitude. Instrument mass, power consumption 1 kg, 1 W Dimension of sensor head (CSC) Mass, power 82 mm Ø 280 g, ~ 250 mW Dimension of DPU Mass of DPU, power 100 x 100 x 60 mm 750 g, ~1 W Data rate Dynamic range ±65536.0 nT to 0.0625nT (21 bit) Omnidirectional linearity ±0.0001% of full scale (±0.1nT in ±65536nT) Intrinsic sensor noise 15 pTRMS in the band 0.01-10 Hz (6.6 pTRMS Hz-1/2 at 1 Hz) Intrinsic electronics noise 50 pTRMS in the band 0.01-10 Hz (15 pTRMS Hz-1/2 at 1 Hz) Sampling rate 50 Hz, linear phase filter, -3dB frequency 13.1 Hz Temperature range -20ºC to +40ºC (Operating performance) -40ºC to +50ºC (Survival performance) Thermal behavior - Offset - Scale factors - Non-orthogonality angles ~0 nT/ºC (CSC), ~0.1 nT/ºC (electronics) ~10 ppm/ºC (CSC), ~2 ppm/ºC (electronics) ~0 arcsec/ºC (0.06, 0.07, 0.04) Zero stability (thermal & long term) < ± 0.5 nT Absolute accuracy of Ørsted magnetometer parameters (relative to ASM & STR): - Offset < 0.2 nT (~120 dB) - Scale factors < 0.0005% - Axes orthogonality < 0.0006º (~2 arcsec) - Axis alignment < 0.0002º (~7 arcsec) Ørsted magnetometer with 3 offsets, 3 scale factors & 3 angles for 6.5year: Accuracy < 0.5 nT language code: en);
- 2019-02-22 17:27:59.0 [mmorahan] insert WeightedRelation (id: null related concept uuid: 054787a6-0c47-43af-a4ee-05c572dd1705 relationship type: null relationship value: null generated by: null); insert WeightedRelation (id: null related concept uuid: ab7f9a64-ca5d-4795-94ff-fd5367d39f9f relationship type: null relationship value: null generated by: null); insert WeightedRelation (id: null related concept uuid: 769a52d4-7db1-4b8e-8d39-6fee4e74d34f relationship type: null relationship value: null generated by: null);
URI
https://gcmd.earthdata.nasa.gov/kms/concept/03d748ff-7398-4ea8-87e7-38d0ef3e6167
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