A report discusses the ability to control the attitude and translation degrees-of-freedom of a solar sail vehicle by changing its center of gravity. A movement of the spacecraft's center of mass causes solar- pressure force to apply a torque to the vehicle. At the compact core of the solar-sail vehicle lies the spacecraft bus which is a large fraction of the total vehicle mass. In this concept, the bus is attached to the spacecraft by two single degree-of-freedom linear tracks. This allows relative movement of the bus in the sail plane. At the null position, the resulting solar pressure applies no torque to the vehicle. But any deviation of the bus from the null creates an offset between the spacecraft center of mass and center of solar radiation pressure, resulting in a solar-pressure torque on the vehicle which changes the vehicle attitude. Two of the three vehicle degrees of freedom can be actively controlled in this manner. The third, the roll about the sun-line, requires a low-authority vane/propulsive subsystem.
Translation control of the vehicle is achieved by directing the solar-pressure- induced force in the proper inertial direction. This requires attitude control. Attitude and translation degrees-of freedom are therefore coupled. A guidance law is proposed, which allows the vehicle to station-keep at an appropriate point on the inertially-rotating Sun-Earth line. Power requirements for moving the bus are minimal. Extensive software simulations have been performed to demonstrate the feasibility of this concept.
This work was done by Gurkirpal Singh of Caltech for NASA's Jet Propulsion Laboratory.
NPO-44129
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Overview
The document titled "Attitude and Translation Control of a Solar Sail Vehicle" (NPO-44129) from NASA's Jet Propulsion Laboratory discusses the design and control mechanisms of a solar sail spacecraft intended for the Geostorm mission. The primary objective of this mission is to position the spacecraft near the sub-L1 point on the Sun-Earth line to provide early warnings of solar storms that could impact Earth.
The spacecraft is designed for a mission duration of 18 months, which necessitates minimizing the use of expendable resources. To achieve this, the document addresses the challenge of six degrees of freedom (6-DoF) control of the vehicle using primarily non-propulsive means. The proposed solution involves actively controlling the position of the spacecraft's center of mass, which allows the solar pressure force to generate torque on the vehicle, thus facilitating attitude control.
The spacecraft consists of two main components: a large solar sail and a compact core (the bus) that houses the essential hardware. The bus is connected to the sail via a system of two degrees of freedom linear tracks, enabling relative motion within the sail plane. At a null position, solar pressure does not apply torque; however, any deviation from this position shifts the center of mass, creating a torque that alters the vehicle's attitude. This method allows for the active control of two of the three degrees of freedom, while the third degree, roll about the sun-line, requires a low-authority vane or propulsive subsystem.
The document highlights the novelty of this approach, as traditional attitude control methods often rely on expendables or small vanes. The proposed method leverages the solar radiation pressure for both propulsion and attitude control, demonstrating a more sustainable and efficient means of maneuvering the spacecraft.
Extensive software simulations have been conducted to validate the feasibility of this concept, indicating that the power requirements for the relative transitions of the bus are manageable. The document serves as a technical support package under NASA's Commercial Technology Program, aiming to disseminate aerospace-related developments with potential broader applications in technology and science.
Overall, this work represents a significant advancement in solar sail technology and its application in space missions, particularly in monitoring solar activity.
