Solar sails with the capability of generating a tangential radiation pressure at the sun-pointing attitude, such as refractive sails can provide more efficient methods for attitude and orbital control of sailcraft. This paper presents the concept of gradient-index sail as an advanced class of refractive sail, which operates by guiding the solar radiation through a structure made of graded refractive index material. The design of the sail refractive index distribution is achieved by transformation optics, which is then realized by the effective refractive index of non-resonant bulk metamaterials made of silica. The methods for fabrication of the proposed three-dimensional gradient-index sail were discussed. The performance of the sail was evaluated by using ray tracing for a broad spectrum of solar radiation under the normal incidence angle, which showed an efficiency of 90.5% for generation of a tangential radiation pressure. The orbital control of the tangential-radiation-pressure-generating (TRPG) sails was studied and it was shown that the full orbital control including the modification of orbital axes, eccentricity, and inclination can be applied by changing the attitude of the sail merely around the sun-sail axis, while the sail keeps the sun-pointing attitude at every point of the orbit.

具有在太阳指向姿态下产生切向辐射压力能力的太阳帆，如折射帆，可以为帆船的姿态和轨道控制提供更有效的方法。本文提出了梯度折射率帆的概念，作为高级折射帆，它通过引导太阳辐射通过由渐变折射率材料制成的结构来工作。帆折射率分布的设计是通过变换光学实现的，然后通过由二氧化硅制成的非共振体超材料的有效折射率来实现。讨论了所提出的三维梯度指数帆的制造方法。通过对法向入射角下的宽光谱太阳辐射使用射线追踪来评估帆的性能，其显示产生切向辐射压力的效率为 90.5%。研究了切向辐射压力产生（TRPG）帆的轨道控制，结果表明，通过改变帆的姿态，可以实现包括轨道轴、偏心率和倾角修正在内的全轨道控制。太阳帆轴，而帆在轨道的每一点保持指向太阳的姿态。