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根据上述星敏感器支架的指向性标定及校正理论,对某相机的星敏感器支架装调进行了试验研究。根据卫星总体技术要求,星敏感器支架的指向轴q要求与相机的坐标轴xyz的夹角分别为37.2491°、76.8521°、55.8810°,指向精度要求优于30”。星敏感器支架与相机坐标的位姿关系如图6所示。对相机和星敏感器支架对接面的平面度进行修研保证平面度优于0.005 mm后,将星敏感器支架安装在相机本体上,将相机x、z轴通过经纬仪监测调至与大地水平面平行,用平晶贴靠星敏感器支架与星敏感器的连接面,通过两台经纬仪交互测量获得星敏感器支架实际坐标与相机坐标关系,为保证测量数据的精确,对qx和qz重复测量三次取平均值,然后利用该结果进行其余坐标轴夹角关系求解,qx和qz的三次测量结果如表1所示。再根据总体对星敏感器支架的指向性技术要求,求解星敏感器支架理论坐标与相机坐标的关系,理论和实际数据对比如表2所示。
First Second/(°) Third/(°) Average/(°) qx 37.4154 37.4162 37.4161 37.4159 qz 55.665 55.6650 55.6646 55.6649 Table 1. Measurement results of qx and qz
根据星敏感器支架坐标与相机坐标实际和理论关系的对比可知:星敏感器支架安装后其指向轴的指向误差分别为:∆qx=0.1668°, ∆qy=0.0909°, ∆qz=−0.2126°。根据星敏感器支架实际姿态坐标系与相机坐标系的坐标轴夹角关系求解实际姿态的RPY角,得
${\theta _x}$ =−13.0570°,${\theta _y}$ =54.6196°,${\theta _z}$ =0。再根据星敏感器支架理论姿态坐标系与相机坐标系的坐标轴夹角关系求解理论姿态的RPY角,得${\theta _x}'$ =−13.1479,${\theta _y}'$ =54.8294,${\theta _z}'$ =0。根据上述角度可求星敏感器支架实际坐标系到理论坐标系的姿态变换矩阵为:Camera coordinate system x/(°) z/(°) y/(°) Coordinate system of
bracket for star sensorTheory q 37.2491 55.8810 76.8521 m 54.8294 144.8294 90 n 100.7159 97.5287 13.1479 Reality q 37.4159 55.6649 76.9430 m 54.6196 144.6169 90 n 100.6145 97.5163 13.057 Table 2. Relationship comparison between actual coordinate, theoretical coordinate of bracket for star sensor and camera coordinate
根据该矩阵可求星敏感器支架实际坐标系到理论坐标系的RPY角。得Rx=−0.0917°, Ry=0.2063°, Rz= 0.0458°。由于Rz不影响星敏感器支架指向轴与相机坐标系的姿态关系,因此不对该偏差量进行修调。对星敏感器支架与星敏感器对接面修研前,需先确定4个检测位置点,然后计算4个检测点的修研量。为了方便计算,测点按坐标方向取规则矩形的4个角点,同时将星敏感器支架实际坐标系的原点设置在其中一个测点上。对接面的结构尺寸如图7所示,其中lA0A1=173 mm,lA0A3=188 mm。实际测点位置如图8所示,4个测点全部设置在星敏感器的连接螺纹孔附近。
根据测量点的位置关系及姿态变换角度,求得各测量点修调量,然后将修调量最大负值点归零。可得各点的修调量可表示为:
按上述求解量进行去量修研,同时需保证修调后平面度优于0.005 mm。修调完对星敏感器支架重新安装后进行姿态复测,测量步骤同第一次测量,对qx、qz测量三次取平均值求解,测量结果如表3所示,最终坐标关系计算结果如表4所示。
First/(°) Second/(°) Third/(°) Average/(°) qx 37.2403 37.2405 37.2416 37.2408 qz 55.8860 55.8850 55.8855 55.8855 Table 3. Measurement results of qx and qz after the first grinding and calibration
Camera coordinate system x/(°) z/(°) y/(°) Coordinate system of
bracket for star sensorq 37.2408 55.8855 76.8606 m 54.8355 144.8355 90 n 100.7098 97.5228 13.1394 Table 4. Retest result after the first grinding and calibration
根据测量结果,可求星敏感器支架在第一次修研后指向轴的指向误差分别为:∆qx=−0.0082°,∆qy=0.0085°,∆qz=0.0045°。相比于修调前其指向精度明显提高。然后按照第一次计算步骤进行第二次修调量的计算,并进行第二次修研。第二次修调去量的结果为:δA0=0.019 mm,δA1=0,δA2=0.019 mm,δA3=0.038 mm。修研结束后,进行星敏感器支架指向轴精度复测,结果如表5所示。
Camera coordinate system x/(°) z/(°) y/(°) Coordinate system of
bracket for star sensorq First 37.2489 55.8806 - Second 37.2482 55.8804 - Third 37.2481 55.8804 - Average 37.2484 55.8805 76.8545 Table 5. Retest result after the second grinding and calibration
从结果可计算,第二次修调后星敏感器支架指向轴精度∆qx=−2.52″,∆qy=8.64″,∆qz=−1.8″。该精度满足指标要求,因此完成对星敏感器支架的精密装调。在星感器支架的指向性标定及校正过程中,经纬仪的测试误差为2″,平晶的平行度误差约为2″,研磨修正的误差可控制在1″以内,因此受上述因素限制最终星敏感器支架的指向性精度最高可达到5″量级。对于上述修正结果,基本已接近极限精度。将修正前和两次修正后的星敏感器支架指向精度列于表6中,将偏差量取绝对值后用柱形图表示,如图9所示。
Situation Included angle relationship ∆qx/(″) ∆qy/(″) ∆qz/(″) Before correction 600.48 327.24 −765.36 After first correction −29.52 30.6 16.2 After second correction −2.52 8.64 −1.8 Table 6. Comparison of deviation before and after calibration of star senstor support
Directivity calibration and correction of bracket for star sensor
doi: 10.3788/IRLA20210875
- Received Date: 2022-02-10
- Rev Recd Date: 2022-03-25
- Publish Date: 2022-09-28
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Key words:
- star sensor bracket /
- pointing accuracy /
- interactive measurement /
- posture transformation
Abstract: In order to ensure the high-precision pointing of bracket for star sensor after installation, a technical method for quantitative grind of bracket for star sensor was proposed. Firstly, we established the star sensor bracket’s coordinate system by constructing the virtual horizontal axis, then obtained the angle relationship between any two coordinate axes by the theodolite interactive measurement and sequential solving strategy. According to the results, we got the posture transformation matrix between star sensor bracket’s actual coordinate system and the space camera’s coordinate system. By the technical requirements of the star sensor bracket’s installing, we acquired the posture transformation matrix between the ideal star sensor bracket’s coordinate system and the space camera’s coordinate system. Then, we obtained the posture transformation matrix from the actual coordinate system to the ideal coordinate system by bridge of the camera coordinate system. According to this result, the corrective value of bracket for star sensor was accurately solved. The experimental research shows that this method can improve the star sensor bracket’s pointing accuracy from the initial 760″ to less than 10″ after two rounds of iteration, which proves effectiveness of the method. At the same time, directivity calibration and correction of bracket for star sensor can also guide the precise assembly and adjustment of other two components with spatial free angle relationship.