ST5-094 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、科学级的霍尔效应磁力仪。该磁力仪的设计源于早期任务，如Polar、FAST以及澳大利亚的FedSat任务。磁力仪由加州洛杉矶大学（UCLA）研发。

UCLA的ST5霍尔效应磁力仪是长期成功航天磁力仪系列产品的结晶。传感器安装在延伸杆上，无任何活动部件。驱动、感应和反馈信号沿着延伸杆电缆在传感器与航天器电子板之间传输。电子板生成霍尔效应驱动信号，检测该信号的二次谐波，消除环绕传感器的磁场，并提供消除每个传感器所需的电流的数字读数。该信号随后被发送至遥测系统。该简单设计中不包含微处理器。磁力仪具有两个可编程量程，分别为64,000和1,000纳特。

UCLA磁力仪中的霍尔效应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，以备未来如ST5等任务之需。传感器与UCLA标准设计相似，曾在许多先前任务中飞行。反馈线圈包围磁芯，使得在运行过程中，磁芯本身永远不会暴露于与感应轴垂直的强磁场中，这可能导致大约1/104级别的失真。因此，传感器具有超线性特性，在强磁场中不会产生如其他任务所报告的旋音谐波。传感器上无活动部件意味着它们对温度极端变化非常耐受。在伽利略任务中，它们在超过100摄氏度的温度下进行了资格认证，并且在液氮（-196摄氏度）浸泡后仍能正常运行。

ST5磁力仪采用经典的霍尔效应电路。通过双核心串联驱动电路，传感器质量和功耗均保持较低。动态范围通过改变从64,000纳特量程到5,000纳特闭环响应，然后放大信号以获得1,000纳特量程来改变。这种方法在两个量程中均能保持低噪声。一个增益更改命令行即可切换两个元件。

ST5磁力仪设计规格如下：

总质量：361克 + 250克（机架）
电子板质量：220克
机架：250克
传感器质量：75克
接口电缆：< 66克
电子单元体积：10x20x5厘米
传感器体积：4x4x6厘米
接口电缆：< 100厘米
电子功耗：500毫瓦
传感器功耗：50毫瓦
量程选择：1,000、64,000纳特
数据速率：16向量/秒
数据分辨率：18位（1：量程，1：符号，16：值）