ST5-224 Fluxgate Magnetometer

Each ST5 spacecraft includes a low power science-grade fluxgate magnetometer. The magnetometer design is based on heritage from earlier missions such as Polar, FAST, and the Australian mission, FedSat. The magnetometers were developed at the University of California, Los Angelese (UCLA).

UCLA's ST5 fluxgate magnetometer is the product of a long series of successful spaceflight magnetometers. The sensors are boom mounted and have no active components. Drive, sense and feedback signals travel along the boom cable between the sensors and the electronics board on the spacecraft. The electronics generates the fluxgate drive signal, detects the second harmonic of this signal, nulls the field surrounding the sensor, and provides a digital reading of the current needed to null each of the sensors. This signal is then sent to the telemetry system. There is no microprocessor in this simple design. The magnetometer has two commandable ranges, 64,000 and 1000 nT.

The fluxgate sensors in the UCLA magnetometer are manufactured using the latest low-noise ring-core technology. UCLA purchased the last of the ring-core material in 1998 and had it fabricated into small (3/8" and 5/8") cores in anticipation of future missions such as ST5. The sensors are similar to the standard UCLA design flown on many previous missions. The feedback windings enclose the cores so that in operation the cores themselves are never exposed to strong fields orthogonal to the sense axis that can cause distortions at the level of about 1 part in 104. Thus the sensors are ultralinear and no harmonics of the spin tone is produced in high fields as have been reported for other missions. The lack of active components on the sensors means that they are very tolerant of temperature extremes. They were qualified at over 100C on Galileo and have operated after being immersed in liquid nitrogen (-196C).

The ST5 magnetometer uses the classic fluxgate circuit. Sensor mass and power are kept low with a dual core series drive circuit. The dynamic range is changed from 64,000 nT to 1000 nT by altering the closed loop response from 64,000 nT range to 5000 nT, and then amplifying the signal to get to a 1000 nT range. This method keeps the noise low in both ranges. One gain change command line switches both elements.

ST5 Magnetometer Design Specifications:

Total Mass: 361g + 250g (chassis)
Electronics Board Mass: 220g
Chassis: 250g
Sensor Mass: 75g
Interface Cable: < 66g
Electronic Unit Volume: 10x20x5 cm
Sensor Volume: 4x4x6 cm
Interface Cable: < 100 cm
Power Consumption, Electronics: 500 mW
Power Consumption, Sensor: 50 mW
Range Selection: 1000, 64,000 nT
Data Rate 16 vectors/s
Data Resolution: 18 bits (1:range, 1:sign, 16:value)

ST5航天器配备了一台低功耗、科学级磁通门磁力仪。该磁力仪的设计源自于早期任务，如极地、快速星（FAST）以及澳大利亚的FedSat任务。磁力仪由加州洛杉矶大学（UCLA）开发。

UCLA的ST5磁通门磁力仪是长期成功航天器磁力仪的产物。传感器安装在支架上，且无任何活动部件。驱动、传感和反馈信号沿着支架电缆在传感器与航天器上的电子板之间传输。电子板生成磁通门驱动信号，检测该信号的二次谐波，抵消围绕传感器的磁场，并提供每个传感器抵消所需的电流的数字读数。该信号随后被发送至遥测系统。该简单设计中不含微处理器。磁力仪具有两个可编程量程，分别为64,000和1,000 nT。

UCLA磁力仪中的磁通门传感器采用最新的低噪声环形磁芯技术制造。UCLA于1998年购买了最后一批环形磁芯材料，并将其加工成小型（3/8英寸和5/8英寸）磁芯，以备ST5等未来任务之需。传感器与之前许多任务中使用的标准UCLA设计相似。反馈线圈包围磁芯，确保在操作过程中磁芯本身不会暴露于与传感轴正交的强磁场中，从而避免在约1/104的水平上产生扭曲。因此，传感器具有超线性特性，在高磁场中不会产生如其他任务所报告的旋转声调谐波。传感器上无活动部件意味着其对温度极端变化具有极高的容忍度。它们在伽利略任务中经受了超过100摄氏度的考验，并且在液氮浸泡（-196摄氏度）后仍能正常工作。

ST5磁力仪采用经典的磁通门电路。通过双核心串联驱动电路，传感器质量和功耗保持较低。动态范围可通过改变从64,000 nT量程到5,000 nT的闭环响应，然后放大信号以达到1,000 nT量程。此方法在两个量程中均能保持低噪声。一个增益变化命令即可切换两个元件。

ST5磁力仪设计规格如下：

总质量：361g + 250g（底座）
电子板质量：220g
底座：250g
传感器质量：75g
接口电缆：< 66g
电子单元体积：10x20x5 cm
传感器体积：4x4x6 cm
接口电缆：< 100 cm
功耗（电子）：500 mW
功耗（传感器）：50 mW
量程选择：1,000, 64,000 nT
数据速率：16矢量/s
数据分辨率：18位（1:范围，1:符号，16:值）