静电悬浮式三轴加速度传感器设计及其空间应用前景论述外文翻译@中英文翻译@外文文献翻译

1 静电悬浮式三轴加速度传感器设计及其空间 应用前景论述 摘要 静电悬浮几三轴加速度计的针对太空的微重力水平设计的，理论分析表明加速度计最大的量程为 35 g0,分辨率为 1ng0,她可以满足多方面的太空应用。同时分析了可能存在的误差源。研究了一些相关技术和加工工艺。基于设计一种高精度的加速度计，本文提出了一种用于低轨道卫星的测量重力加速度的加速度计的理论设计方案。 一般来讲，获得来自人造卫星的地球重力的方法如下所示：使用 GPS 数据获得作用于卫星的合力，非重力性质的力使用卫星上的微型加速度计检测，二者之差就是我们 要求的重力，它与地球重力场有直接的联系。最后我们得出如下结论：用于重力加速度检测的最适频宽为 0.0008 Hz to 0.15 Hz。理论结果将对将来卫星上重力场的检测具有一定的价值。 关键词 ：静电悬浮 加速度计 重力场检测 分辨率 GPS 频带 引言 微重力是太空环境的主要特性，为了精确的监控空间的微重力场，必须设计一种低偏差，高分辨率的特殊加速度传感器，静电悬浮加速度计在低于 1HZ 的低频带具有很高的分辨率和精度。因此，它在地球场检测和微重力科学中具有得天独厚的优势。已经有好多种静电悬浮加 速度计面世。 CHAMP 公司的 STAR 加速度计，由法国的 ONERA 发展而来，用于检测卫星上的非重力加速度计其频带从足够的频带的交流电到 0.05HZ。这些力包括空气阻力，太阳射线压力。地面返照率以及姿态调整力。 STAR 生产了一批量程为 10 g0 ，在 10-4 Hz 到 10-1 HZ 内 Z轴和 Y 轴分辨率小于 0.3ng 的加速度计。 ASTRE 加速度计，和 ESA 合作。在 STS-78 任务期间，检测了剩余的微重力干扰其频带从交流电到不到 1 Hz。 ASTRE 加速度计量程精确到 1 mg 。 精度小于 1ng 是一种高性 能的加速度计。用于精确检测空间站或太空实验室的环境因素。 MACEK 的加速度计，得到 GRANT 的大力支持，被用于 STS-79 的仪表盘上用于检测微重力作用。项目团的数据显示： MACEK 的量程为 40 g0 ， 精度达到了 150 ng0.静电悬浮微型加速度计 (MESA)的研发目的。是为了在微观水平提供精确稳定的加速度， MESA 计划被用于空间的微重力检测诸如微重力科学支持的空间2 屏蔽和国际空间站。 静电悬浮加速度计设计的理论分析 如图所示静电悬浮加速度传感器 主要由一个中心检测质量和六个电容极板组成 ,外加固定极板 用的外壳 (图中未示出 ) 。检测质量采用立方体结构设计 ,由金属材料制成 ；电容极板由绝缘材料并在其内表面溅射金属薄膜加工而成 1. 2 静电悬浮原理 静电悬浮式三轴测量加速度传感器在进行地面检测时 ,由于在垂直于地面方向 (设为 x 方向 ) 中心质量块受到地球吸引力的作用 , 因此必须给质量块施加一反方向的静电力 ,以使其达到力平衡 ,并通过反馈电压的施力作用使中心质量块在 x 、y 、 z 三方向均处于零位 (平衡位置 ) 附近 , 实现悬浮。而当传感器工作于空间飞行器上时 , 惯 性力平衡了地球引力 ,因此仅需施力反馈回路的作用便可实现中心质量块的悬浮。 1. 3 电容位移检测原理 不失一般性 ,此处仅讨论一个方向 ( x 轴 ) 位移的电容检测原理 ,其它两轴的检测原理相同。当无加速度输入时 ,控制回路使检测质量处于初始平衡位置 (零位 ) ,检测质量表面距相对两极板的距离相等 ,如图 2 所示。此时电容 C1 与 C2 相等。当存在加速度输入时 ,检测质量沿与加速度相反的方向发生微小位移 , C1 和 C2 分别改变 ,两者电容之差 C 可化简 ddSCCC 212 2 （ 1） 式中 为真空介电常数 ； S 为电容极板面积 ； d 为电容极板与检测质量之间的距离 ； d 为检测质量微小位移。 1. 4 加速度测量原理 当检测质量因加速度的输入而发生位移时 , 引起电容变化 , 进而由控制电路3 产生反馈施力电压 Uf ,两电极板电压由原来的定值偏置电压 Us 分别变为 Us + Uf 和 Us - Uf ,从而对检测质量产生静电力为： 2221ddUUddUUSF fsfse （ 2） 式中 Us 为偏置电压 ； Uf = A C 为 反馈施力电压 ； A 为检测电路增益。由力平衡条件 ma = F( m 为检测质量块的质量 ； a 为外界输入的加速度 ) , 可得到加速度与检测到的反馈电压的关系 当检测质量 (立方体 ) 体积为 l3 , 材料密度为 时 ,则上式变为 fsfs UdlSUUmdSUa23222 （ 3） 通过测量反馈电压便可以知道外界输入的加速度值。 重力场检测在太空中的应用 由德国航天局组建的 CHAMP 项目组，致力于地球监测的多方位研究。它的目的之一就是精确重现地球的重力场。高灵敏度加速度计 STAR 被用来检测非重力性质的作用力。 GPS 接受器被用来精确确定卫星的轨道。 GPS 的数据显示，作用于 CHAMP 的合力是可测的。两者的差值便是地球重力，这种力与地球重力常有直接的联系。地球重力加速度，非重力加速度 和合力的加速度存在以下关系： grav inontotal aag （ 4） g 是地球引力的加速度； totala 是合力的总体加速度由 GPS 数据得 到； gravinona 是非重力加速度由仪表上的加速度计得到；从上面的公式可以看出，如果测得合力的总体加速度和非重力加速度，则可以确定地球引力加速度。但是，这里必须声明，在矢量标定之前，必须让时间匹配同时完成坐标转换 .大气层阻力和太阳射线压力是加速度计在 200-500 km 高空可检测的主要的非重力性质力。它们可以由以下两个公式大致得到： 2VMAF airair （ 5） sunsunradi MAF （ 6） 如果卫星的结构是专门为检测地球引力场定做的，非重力加速度 4 应该小于 10 g0.MA航天飞行器的正交化比， 是空气的密度， V 是飞行器相对于空气的速率， sun 是太阳射线能量的密度，air 和sun 分别是大气层阻力和太阳射线压力的系数。 vfh （ 7） 为了满足地球重力场的的检测，合理的检测频带是非常重要的。飞行器在300-500 km的低轨道运行时速率大约为 8 km/s. 设在地球重力场中太空分辨力为 km，更高的检测频率可以定义为： vfh （ 8） 从上面的公式可以得到频率为 0.146 Hz。在二级模型中， 大约是 10,000 km,，因此频率应该减少到 0.0008 Hz. 地球重力场的空间检测目的是为了把中等模型定义到更低的级别，因此加速度计的频带范围应该是 0.0008 Hz (or lower) to 0.15Hz. 5 ELECTROSTATICALLY SUSPENDED TRIAXIAL ACCELEROMETER AND ITS FUTURE SPACE APPLICATION ABSTRACT An electrostatically suspended triaxial accelerometer is tentatively designed for space applications. Theoretical analysis shows that the maximum measurable acceleration of the accelerometer is expected to be 35 g0, and that the resolution is ，expected to be 1ng0, which would meet many space applications. Some error sources of the accelerometer are analyzed. The related techniques and machining processes is being studied.Based on the high performance of the accelerometer, a theoretical method for the Earth gravitational acceleration measurement from low-orbit small satellite is described. Basically, the method to obtain the Earth gravitational field fro m satellite is the following: the total forces acting on the satellite are obtained by the precise orbit determination using GPS data, the non-gravitational forces are measured using a precise micro-accelerometer on the satellite, and the difference between the two is the Earth gravitational force, which is directly linked to the gravitational field. Finally, the suitable frequency bandwidth for the Earth gravitational acceleration measurement is calculated to be from 0.0008 Hz to 0.15 Hz. The theoretical results may have something useful to the future gravitational field measurement from satellite. KEYWORDS: Electrostatically suspended accelerometer； Earth gravitational field measurement； Resolution； GPS； Frequency bandwidth INTRODUCTION The microgravity is one of the major characteristics of the space environment. To finely monitor the space microgravity level, specific accelerometer must be developed with a much lower bias and a high resolution. The electrostatically suspended accelerometer has high resolution and high sensitivity in the very low frequency range below 1Hz. Thus, it gains an advantage in the fields of the Earths observation and microgravity science. 6 Many electrostatically suspended accelerometers have been developed around the world. On board CHAMP, STAR accelerometer 12, developed under ONERA, France, is used to measure all non-gravitational accelerations of the satellite in a sufficient frequency bandwidth from DC to a few tenth of one Hertz. These forces include air drag, solar radiation pressure, Earth albedo and attitude manoeuvres. STAR presents a measurement range of 10 g0 with a resolution of better than 0.3ng0 for y- and z-axes within the bandwidth of 10-4 Hz to 10-1 Hz. ASTRE accelerometer 3, developed under ESA contract, flew on board the Columbia/Life and Microgravity Spacelab during the STS-78 Mission to monitor the residual microgravity disturbance level in the very low frequency range from DC to 1 Hz bandwidth. ASTRE has a full-scale range of 1 mg0 and a resolution of better than 1 ng0, capable of a fine measurement of actual acceleration environment in order to correlate spurious effects on the experiments on board the Space Station or the Spacelab. MACEK accelerometer 4, supported by the GRANT agency of the Czech Republic, was placed on board of the Space Shuttle mission STS-79 to measure the microgravity effects. The mission data indicates that MACEK has a measurement range of 40 g0 and an accuracy of better than 150 ng0. The purpose of the Miniature ElectroStatic Accelerometer (MESA) 5, developed in Canopus Products Inc., USA, is to provide accurate stable acceleration at the micro- and nano-g level. MESA is planed to use in space microgravity applications such as Microgravity Science support on the Space Shuttle and the International Space Station. THEORETICAL DESIGN OF ELECTROSTATIC ACCELEROMETER As shown in Figure 1, the electrostatically suspended triaxial accelerometer mechanics is mainly constituted by a proofmass, six electrode-plates and a housing (the housing is not shown in Fig 1). The proofmass, coated with gold, can be made of Platinum-Rhodium alloy. The electrode-plates can be made of dielectric materials, like porcelain or quartz, also coated with gold. The same electrodes are used for the capacitive position sensing and for exerting the electrostatic forces.7 The principle of operation 67 of this accelerometer depends on the measurement of force that is necessary to maintain the proofmass at the center of the cage. Figure 2 shows the principle of the capacitive sensor along one axis, for example, x-axis. When no acceleration is applied to the center proofmass, the proofmass remains at the original balance position by a control circuit. The gap between the proofmass and the upper electrode equals the distance between the proofmass and the lower electrode, and the capacitance C1 is equal to C2. If a force (introduced by acceleration) is applied to it, the proofmass moves away from the original position. As a result, C1 and C2 change. C , the difference between the two capacitances is ddSCCC 212 2 （ 1） where, is the vacuum dielectric constant； S is the area of the golden electrode； d is the gap between the proofmass and the electrode； d is the small displacement of the proofmass. When the proofmass leaves off the balance position, the feedback circuit brings a feedback voltage to the electrodes, which can apply an electrostatic force on the proofmass to move it back. The electrostatic force eF can be described as 2221ddUUddUUSF fsfse （ 2） where, sU is originally voltage applied on the electrodes； fU is the feedback voltage . According to the force balance condition, Fma (where m is the mass of the 8 proofmass； a is the applied acceleration), we can find the relationship between fUand a: fsfs UdlSUUmdSUa23222 (3) SPACE APPLICATION ON GRAVITATIONAL FIELD MEASUREMENT The German CHAMP mission, funded by the German Space Agency, is dedicated to multi-purpose Earths observation 12. One of its main purposes is the accurate recovery of the Earth gravitational field. A very sensitive accelerometer, STAR, is used to measure the non-gravitational forces. A GPS receiver is used to determine the precise orbit of the satellite. From the GPS data, the total forces acting on the CHAMP are obtained. The difference between the two is the gravitational force, which is directly linked to the Earth gravitational field. The relationship between the Earth gravitational acceleration, the non-gravitational acceleration, and the total acceleration can be denoted as the following formula: grav inontotal aag （ 4） where, g is the Earth gravitational acceleration； totala is the total acceleration obtained from GPS data； gravinona is the non-gravitational acceleration measured by on-board accelerometer. From the above formula (6), we can see that, if the non-gravitational acceleration and the total acceleration are measured, the Earth gravitational acceleration can be confirmed. However, it is necessary to point that, before the above vector operation, time matching and coordinate conversion must be made. The atmospheric drag and the solar radiation pressure are the main sources of the non-gravitational forces that the accelerometer may measure in the 200-500 km space 8. They can be approximately calculated by the following two equations (7) and (8). If the structure of the small satellite is carefully designed for the Earth gravitational field measurement, the non-gravitational acceleration introduced by all non-gravitational forces should be smaller than 10 g0. 9 2VMAF airair （ 5） sunsunradi MAF （ 6） where, MA is the spacecraft cross sectional area (perpendicular to the velocity)； is the density of the air； V is the velocity of the spacecraft relative to the air； sun is the density of the solar radiant energy； air and sun are the coefficients of the atmospheric drag and the solar radiation pressure respectively. To meet the measurement of the Earth gravitational field, suitable measurement frequency bandwidth of accelerometer is very important. The velocity (v) of the spacecraft in low orbit of 300-500 km is about 8 km/s. Given the space resolution of the Earth gravitational field model is km, the higher frequency (hf) of measurement is defined by : vfh （ 7） for degree 360 of the Earth gravitational field model, is about 55 km. From the above equation (9), a frequency of 0.146 Hz is obtained. For degree 2 of the model, is about 10,000 km, so the frequency should be decreased to 0.0008 Hz. The purpose of space measurement of the Earth gravitational field is to define the model of middle to lower degree, so the accelerometer should have a frequency bandwidth of 0.0008 Hz (or lower) to 0.15Hz. EFERENCES 1 Touboul P. Foulon B. and Le Clerc. Star, the accelerometer of geodesic mission CHAMP. Melbourne, Australia: 49th International Astronautical Congress, 1998. IAF-98-B.3.07. 2 Perret A. Star, the accelerometric system to measure