There is ever growing demand for satellite constellations that perform global positioning, remote sensing, earth-imaging and relay communication. In these highly prized orbits, there are many obsolete and abandoned satellites and components strewn posing ever-growing logistical challenges. This increased demand for satellite constellations pose challenges for space traffic management, where there is growing need to identify the risks probabilities and if possible mitigate them. These abandoned satellites and space debris maybe economically valuable orbital real-estate and resources that can be reused, repaired or upgraded for future use. On-orbit capture and servicing of a satellite requires satellite rendezvous, docking and repair, removal and replacement of components. Launching a big spacecraft that perform satellites servicing is one credible approach for servicing and maintaining next-generation constellations. By accessing abandoned satellites and space debris, there is an inherent heightened risk of damage to a servicing spacecraft. Under these scenarios, sending multiple, small-robots with each robot specialized in a specific task is a credible alternative, as the system is simple and cost-effective and where loss of one or more of robot does not end the mission. Inherent to this network of small robots is the need for ground surveillance and observation of the system both to provide real-time information about the space debris, in addition to providing position, navigation and tracking support capabilities. Eliminating the need for a large spacecraft or positioning the large spacecraft at safe distance to provide position, navigation and tracking support simplifies the system and enable the approach to be extensible with the latest ground-based sensing technology. In this work, we analyze the feasibility of sending multiple, decentralized robots that can work cooperatively to perform capture of the target satellite as first steps to on-orbit satellite servicing. We further analyze the extent of how a ground-based civilian surveillance system can be used to provide real-time observation support in place of using a larger, on-orbit servicing mothership. The multi-robot system will be deployed in a formation interlinked with spring-tethers in one of several configurations include an 'x' configuration. These tethered small robots will perform one-time autonomous rendezvous, capture and servicing of satellites in LEO and GEO orbits. Use of spring tether enables dynamic capture of a target object that maybe freely tumbling or travelling at different velocities in the range of 15 m/s or more. The tether enables converting a translational motion into an angular snagging motion much like bola used by prehistoric hunters to snag a prey. Using multiple tethered robots, it may be possible to apply differential control to capture a spacecraft under more desirable angular and linear velocities. However, there also exists challenges of mitigating tangled tethers. The option exists for each robot to disconnect from its tether to avoid complex tangled scenarios. The tethers may be rolled up to shorten or lengthen the cord length between these robots. After docking with the target satellite, each robot secures itself on the satellites surface using spiny gripping actuators. The multi-robot system can crawl on the satellite's surface with each robot moving one by one using rolling and hopping mobility capabilities. If any robot loses grip, the multirobot system with robots anchored to the surface keeps the entire system secure. The system can also be used to carry larger components and place them on a specific location on a target satellite. The rolling up of the tethers enables fine level position control of a larger object. Through this distributed controls approach, the risk is distributed, and a collective of small robots can perform multiple servicing tasks on the satellite simultaneously. A variation of this scenario is to use these small-robots to perform assembly of large passive space structures and warehousing of large space structures.
|Original language||English (US)|
|State||Published - Sep 6 2018|
ASJC Scopus subject areas