Since the seminal work of Daniele Mortari (“Moon-Sun Attitude Sensor,” Journal of Spacecraft and Rockets, Vol. 34, No. 3, 1997, pp. 360–364), the concept of an attitude sensor using images of illuminated celestial bodies has been pushed forward through the years. The basic idea consists of extracting two independent directions from the image of a celestial body, namely, the camera-to-planet and the planet-to-sun directions. The former is estimated from the center of an ellipse fitted to the imaged limb points and the latter from the symmetry axis of the illuminated region. These assumptions, however, only hold for far-distant spherical targets. In this work, the problem is reformulated in the framework of projective camera transformations of quadrics and conics, and an algorithm estimating the line of sight to the planet and the illumination direction from the limb and terminator ellipses, respectively, is presented. The method is applicable to any ellipsoidlike celestial body having known orientation. The algorithm is first validated on synthetically generated images and then tested using real pictures of Dione and Enceladus satellites gathered from Cassini spacecraft. Results show that the sensor concept returns rms errors in the order of the angular width of a pixel in computing the nadir direction, and subdegree accuracy in computing the sun direction.

自Daniele Mortari（“月日太阳姿态传感器”，《航天器和火箭杂志》，卷 34（No. 3，1997，pp。360–364），使用照明的天体图像的姿态传感器的概念已经被推动了很多年。基本思想包括从天体图像中提取两个独立的方向，即相机到行星的方向和行星到太阳的方向。前者是从拟合到成像肢体点的椭圆的中心估计的，而后者是从被照明区域的对称轴估计的。但是，这些假设仅适用于远距离的球形目标。在这项工作中，该问题在二次曲面和圆锥投影的投影相机变换的框架中重新提出，并提出了一种算法，该算法分别估计到行星的视线以及从肢体和终结者椭圆产生的照明方向。该方法适用于具有已知取向的任何椭球状天体。该算法首先在合成生成的图像上进行验证，然后使用从卡西尼号飞船收集的狄奥尼和土卫二卫星的真实图片进行测试。结果表明，传感器概念在计算天底方向时返回的均方根误差为像素的角宽度，而在计算太阳方向时则返回亚度精度。