A document describes a concept for an inertial sensor for measuring the rotation of an inertially stable spacecraft around its center of gravity to within 100 microarc- seconds or possibly even higher precision. Whereas a current proposal for a spacecraft-rotation sensor of this accuracy requires one spacecraft dimension on the order of ten meters, a sensor according to this proposal could fit within a package smaller than 1 meter and would have less than a tenth of the mass. According to the concept, an inertial mass and an apparatus for monitoring the mass would be placed at some known distance from the center of gravity so that any rotation of the spacecraft would cause relative motion between the mass and the spacecraft. The relative motion would be measured and, once the displacement of the mass exceeded a prescribed range, a precisely monitored restoring force would be applied to return the mass to a predetermined position. Measurements of the relative motion and restoring force would provide information on changes in the attitude of the spacecraft. A history of relative- motion and restoring-force measurements could be kept, enabling determination of the cumulative change in attitude during the observation time.
This work was done by David Rosing, Jeffrey Oseas, and Robert Korechoff 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-41926
This Brief includes a Technical Support Package (TSP).
Compact, Precise Inertial Rotation Sensors for Spacecraft
(reference NPO-41926) is currently available for download from the TSP library.
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Overview
The document presents a technical support package from NASA's Jet Propulsion Laboratory detailing innovations in compact, precise inertial rotation sensors for spacecraft. The primary focus is on a new technique for sensing the rotational motions of spacecraft with unprecedented accuracy, specifically in the range of 10-100 microarcseconds, and potentially extending to 1 microarcsecond with careful design. This represents a significant improvement over existing sensors, such as mechanical and optical gyros and accelerometers, which are 10-100 times less sensitive.
The innovation is particularly relevant for missions like the Space Interferometry Mission (SIM) and future projects such as the Terrestrial Planet Finder, which require precise knowledge of spacecraft attitude changes to perform their scientific objectives. Current methods for achieving the necessary attitude sensing involve large opto-mechanical systems, often requiring extensive mass and volume. The proposed sensor technology aims to reduce this mass penalty by providing similar levels of accuracy in a much smaller package, potentially offering mass savings of over 10 times.
The document outlines the technical challenges and motivations behind the development of this technology. It emphasizes the need for accurate rotational motion sensing to support complex space missions, where traditional methods are often too cumbersome and costly. The proposed solution involves monitoring the relative motion of an inertial mass within the spacecraft, strategically placed away from the center of gravity. This setup allows for the measurement of apparent motion caused by the spacecraft's rotation, providing highly accurate data on attitude changes.
Additionally, the document discusses practical considerations for achieving maximum sensitivity, including the importance of understanding mass distribution around the inertial mass and compensating for any perturbations that may affect measurements. Various displacement sensing techniques are mentioned, highlighting the trade-offs between sensitivity, range, mass, volume, and cost.
In summary, this technical support package outlines a significant advancement in spacecraft rotational motion sensing, promising enhanced accuracy and reduced mass requirements, which could greatly benefit current and future NASA missions. The innovation leverages established principles from gravity probe spacecraft, adapting them for more efficient and effective use in space exploration.
