Space Webs based on Rotating Tethered Formations
- Paper number
IAC-06-D1.1.04
- Author
Dr. Giovanni B. Palmerini, University of Rome "La Sapienza", Italy
- Coauthor
Prof. Silvano Sgubini, University of Rome "La Sapienza", Italy
- Coauthor
Mr. Marco Sabatini, University of Rome "La Sapienza", Italy
- Year
2006
- Abstract
Several on-going studies indicate the interest for large, light structures, shaped as fish nets or webs, along which “ropes” small spacecraft (“agents”) could move like spiders to position and re-locate, at will, pieces of hardware devoted to specific missions. The concept could be considered as a material extension of the formations or swarms, where all system members are completely free and should manoeuvre in order to acquire a desired configuration. The advantage of having instead a “hard” link among the different grids lays in the partition of the tasks among system components and in a possible overall reduction of the system parts, complexity and cost. In fact, a small number of agents could be considered as executing, as movers, all tasks concerning the location of the payloads on the web, while the moveable hardware, actually exploiting mission goals, is completely passive and lacks of mobility capabilities (and of all the subsystems related to). Implementation of different kinds of missions at the same time on the same web should be also considered as a remarkable advantage. Multiple platform space interferometers, requiring strict accuracy in the distance and orientation determination between different S/C, are a good example of a mission where this concept could be useful. In fact, their control system could be very complicated and their lifetime could be substantially limited by the high propellant consumption due to almost continuous thrusting required to maintain precise baselines. Adoption of a web could greatly help, and its drawback, i.e. the difficulties in deploying and maintaining the underlying structure, should be compared with control and lifetime advantages for the simpler imaging systems hanged on. Unfortunately, there is no stable configuration for an orbiting, two dimensional web made by light, flexible tethers which could not support compression forces. In fact, one of the sides will always lay out of the stable configuration dictated by gravity gradient effect. A first solution is to locate steerable thrusters in certain grids, but such an answer looks as a "half way back” to the traditional formation concept. A different possible solution is to make use of centrifugal forces to pull the net, with a reduced number of simpler thrusters to initially acquire the required spin. The advantage of this concept is that the formation, which will be as circular shaped as possible, behaves as a single spin-stabilized unit: forces necessary to maintain relative distances between platforms are provided by tethers’ tension and no propulsion system is then required. In this paper a theoretical dynamic analysis of a simplified rotating tethered connected formation is performed, in order to evaluate the spinning velocity able to satisfy the requirement for the stability of the system. The model adopted overlaps simpler elements, each of them given by a tether connecting two extreme bodies accommodating the spinning thrusters. The combination of these “diameter-like” elements provides the circular web. The formation is primarily considered as subjected to Keplerian laws only, but its behaviour under perturbation forces and thermal inputs is also investigated. A sketch of possible applications will be also provided in order to show the interest of the proposed concept.
- Abstract document
- Manuscript document
IAC-06-D1.1.04.pdf (🔒 authorized access only).
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