A paper discusses the effect of the dynamic interaction taking place within a formation composed of a rigid and a deformable vehicle, and presents the concept of two or more tethered spacecraft flying in formation with one or more separated freeflying spacecraft.
Although progress toward formation flight of nontethered spacecraft has already been achieved, the document cites potential advantages of tethering, including less consumption of fuel to maintain formation, very high dynamic stability of a rotating tethered formation, and intrinsically passive gravity-gradient stabilization. The document presents a theoretical analysis of the dynamics of a system comprising one free-flying spacecraft and two tethered spacecraft in orbit, as a prototype of more complex systems. The spacecraft are modeled as rigid bodies and the tether as a mass-less spring with structural viscous damping. Included in the analysis is a study of the feasibility of a centralized control system for maintaining a required formation in low Earth orbit. A numerical simulation of a retargeting maneuver is reported to show that even if the additional internal dynamics of the system caused by flexibility is considered, high pointing precision can be achieved if a fictitious rigid frame is used to track the tethered system, and it should be possible to position the spacecraft with centimeter accuracy and to orient the formation within arc seconds of the desired direction also in the presence of low Earth orbit environmental perturbations. The results of the study demonstrate that the concept is feasible in Earth orbit and point the way to further study of these hybrid tethered and free-flying systems for related applications in orbit around other Solar System bodies.
This work was done by Marco B. Quadrelli 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-30730
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Formation Flying of Tethered and Nontethered Spacecraft
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Overview
The document titled "Formation Flying of Tethered and Nontethered Spacecraft" from NASA's Jet Propulsion Laboratory discusses the advantages and applications of utilizing satellite formation flight, particularly in imaging and sensing missions. One of the primary benefits highlighted is the ability to synthesize large sensor apertures without the need for large physical structures, which can significantly reduce costs and complexity.
The document emphasizes the unique synergy between tethered spacecraft technology and formation flying. Tethered spacecraft can maintain their orbits at varying lengths without consuming fuel, which alleviates the fuel budget for missions involving multiple cooperative vehicles. This capability allows for the maintenance of large apertures at a fraction of the cost compared to traditional formation flying with separated units. Tethered vehicles are also naturally gravity-gradient stabilized, making them ideal for planetary sensing applications.
The text outlines various configurations for formation flying, including scenarios for planetary surface and subsurface imaging, where a long tether connects multiple spacecraft to provide stereoscopic images of ground objects. By reconfiguring the formation, different spatial topologies can be achieved, allowing for simultaneous coverage of various ground locations.
Additionally, the document discusses the application of formation flying in space interferometry, particularly for extra-solar planet detection and imaging. In this setup, tethered light collectors can spin around a central point, creating a stable arrangement that enhances sky coverage. The free-flying spacecraft in the formation can act as a sensing array, while the tethered spacecraft serves as an information processing unit due to its quasi-stationary role.
The overarching theme of the document is the potential for high-precision formation flying of both tethered and non-tethered spacecraft, facilitated by advanced control technologies. The proposed concepts aim to enhance autonomy, reconfiguration capabilities, and scientific returns from space missions.
In summary, the document presents a comprehensive overview of the innovative approaches to satellite formation flight, highlighting the benefits of tethered technology and its applications in various scientific and commercial contexts, ultimately aiming to improve the efficiency and effectiveness of space missions.
