A report proposes a method of utilizing solar-radiation pressure to keep the axis of rotation of a small spin-stabilized spacecraft pointed approximately (typically, within an angle of 10° to 20°) toward the Sun. Axisymmetry is not required. Simple tilted planar vanes would be attached to the outer surface of the body, so that the resulting spacecraft would vaguely resemble a rotary fan, windmill, or propeller. The vanes would be painted black for absorption of Solar radiation. A theoretical analysis based on principles of geometric optics and mechanics has shown that torques produced by Solar-radiation pressure would cause the axis of rotation to precess toward Sun-pointing. The required vane size would be a function of the angular momentum of the spacecraft and the maximum acceptable angular deviation from Sun-pointing. The analysis also shows that the torques produced by the vanes would slowly despin the spacecraft — an effect that could be counteracted by adding specularly reflecting "spin-up" vanes.
This work was done by Thomas Spilker of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Mechanics category. NPO-40047.
This Brief includes a Technical Support Package (TSP).
Quasi-Sun-Pointing of Spacecraft Using Radiation Pressure
(reference NPO-40047) is currently available for download from the TSP library.
Don't have an account?
Overview
The document is a technical report from NASA's Jet Propulsion Laboratory (JPL) detailing a novel approach to passive attitude control for spin-stabilized spacecraft using solar radiation pressure on canted vanes. Authored by Dr. Thomas R. Spilker, the report outlines the feasibility of an attitude control system that operates without consumable resources, thereby offering potentially unlimited mission lifetimes.
The primary objective of the research is to address the challenges faced by low-cost spacecraft fleets, particularly those designed to monitor solar activity or solar wind characteristics. Traditional active attitude control systems often incur high costs and have limited lifetimes due to their reliance on expendables and power generation. The proposed method leverages the torques generated by solar radiation pressure on fixed, canted vanes to precess the spacecraft's spin axis toward the Sun, effectively maintaining sun-pointing orientation.
The report explains that the torques produced by the vanes are a function of the solar off-pointing angle, with the restoring torque increasing as the angle increases. This passive system eliminates the need for active attitude sensing or computation, making it a simpler and more reliable solution. The vanes are designed as simple planar surfaces, ideally optically black, and are mounted at a fixed distance from the spacecraft's spin axis. The geometry of the vanes is crucial, as it determines the effectiveness of the torque generated.
The document also includes a technical disclosure section that describes the problem motivating the research, the proposed solution, and a detailed explanation of the system's mechanics. The report emphasizes that the design allows for a radially symmetric arrangement of vanes, which can resemble a propeller, enhancing the spacecraft's stability.
In summary, this report presents a significant advancement in spacecraft attitude control technology, highlighting a method that is cost-effective, resource-efficient, and capable of sustaining long-term missions. The findings have implications for future spacecraft designs, particularly in the context of missions that require continuous sun-pointing without the drawbacks of traditional active systems.
