A report describes the personal radiation protection system (PRPS), which has been invented for use on the International Space Station and other spacecraft. The PRPS comprises walls that can be erected inside spacecraft, where and when needed, to reduce the amount of radiation to which personnel are exposed. The basic structural modules of the PRPS are pairs of 1-in. (2.54-cm)-thick plates of high-density polyethylene equipped with fasteners. The plates of each module are assembled with a lap joint. The modules are denoted bricks. A report discusses the attitude-control system of a proposed spacecraft that would derive at least part of its propulsion from a solar sail. The spacecraft would include a bus module containing three or more reaction wheels, a boom attached at one end to the bus module and attached at its other end to a two-degree-of-freedom (DOF) gimbal at the nominal center of mass of a sail module. Each DOF of the gimbal could be independently locked against rotation or allowed to rotate freely. By using the reaction wheels to rotate the bus when at least one gimbal DOF was in the free state, the center of mass (CM) of the spacecraft could be shifted relative to the center of pressure (CP) on the solar sail. The resulting offset between the CM and CP would result in a solar torque, which could be used to change the attitude of the spacecraft. The report discusses numerous aspects of the dynamics and kinematics of the spacecraft, along with the relationships between these aspects and the designs of such attitude-control-system components as sensors, motors, brakes, clutches, and gimbals.
This work was done by Edward Mettler and Scott Ploen 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 Machinery/Automation category. NPO-30522
This Brief includes a Technical Support Package (TSP).
Attitude Control for a Solar-Sail Spacecraft
(reference NPO30522) is currently available for download from the TSP library.
Don't have an account?
Overview
The document titled "Attitude Control for Solar-Sail Spacecraft" from NASA's Jet Propulsion Laboratory outlines the technical aspects and methodologies for controlling the orientation of solar-sail spacecraft. Central to the design is the sailcraft bus module, which is connected to a sail module via a 2-meter boom and a gimbal mechanism that allows for two degrees of freedom (DOF). This configuration enables the adjustment of the center of mass (CM) of the sailcraft system, which is crucial for generating solar torque by creating an offset between the CM and the center of solar pressure (CP).
The document details how the gimbal hinges can be locked or unlocked independently, allowing for precise control during maneuvers. When the hinges are free, the system can utilize reaction wheels to apply torque about the pitch and yaw axes, facilitating attitude adjustments without significant interaction with the flexible sail structure. This "kinematic de-coupling" is essential to minimize structural excitation and maintain stability during operations.
During maneuvers, the boom and bus can be rotated to generate solar torque, which accelerates the sail to a desired slew rate. After the maneuver, the system returns to a torque equilibrium position, aligning the solar pressure force vector with the CM. The bi-state gimbal is then locked until the next maneuver is required. The document also discusses the use of reaction wheels for roll control and the potential for small thrusters to unload stored momentum, although thruster use is expected to be infrequent in deep space missions.
For attitude determination, the spacecraft employs a combination of precision star trackers, gyros, and coarse sun sensors, ensuring accurate orientation and inertial rate measurements. The system is designed to handle small perturbations and maintain trajectory path following accuracy typical of deep space solar sailing missions.
Overall, the document emphasizes the innovative approaches to attitude control in solar-sail spacecraft, highlighting the balance between maneuverability, structural integrity, and the effective use of solar pressure for propulsion. This technology represents a significant advancement in aerospace engineering, with potential applications beyond space exploration.
