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Reconfigurable space structures

A proof of concept demonstration for a voxel-based reconfigurable space structure based on electromagnetically actuated picosatellites. Individual modules are embedded with a collection of electromagnets used to reconfigure each with respect to the other via pivoting.

Published onOct 07, 2020
Reconfigurable space structures

Contents

  1. Project Overview

  2. Background

  3. Schedule

  4. Mechanical Design

Project Overview

The aim of this project is to investigate a novel design and control mechanism by which reconfigurable space structures can be constructed—that is, space structures that are able to adapt their form or properties to different environments and load cases in situ. Looking to recent trends in swarm robotics and the miniaturization of spacecraft technologies such as PocketQubes, structural self-reconfiguration is envisioned as a collective of autonomous robotic modules capable of pivoting relative to each other. In particular, electromagnetic actuators are chosen to this end by pivoting cube-shaped spacecraft relative to each other via repulsion (pivot actuation) and attraction(hinge formation), thereby allowing propellant-free, non-contact actuators that require no moving parts. This concept requires development on three fronts: first, modelling the forces of the electromagnetic actuators between neighbouring spacecraft; second, deriving a dynamic model of the spacecraft collective and a control strategy to drive the actuators; and third, electronic and mechanical design and fabrication of several modules to be tested on the zero G flight.

Background

Space structures traditionally aim at carrying out a single task, such as trusses, booms or scaffolds used for the one-time deployment of solar panel arrays. While these structures can be modular to permit assembly into larger structures, the final assemblies are permanent and cannot be reconfigured for other purposes. In order to perform many different tasks, missions today require the integration of many expensive dedicated structures and devices. Future low-cost missions will require spacecraft to adapt to different tasks and respond to unforeseen events, such as the unsuccessful deployment of a solar array. In addition, the realization of future large space telescopes will require either precise formation flying or in-orbit assembly.

Structures capable of morphological adaptation would address many challenges associated with today’s limitations on launch mass and volume, as well as facilitating stowage during launch. Reconfigurable structures could realize new functionality such as the formation of temporary structures to aid in spacecraft inspection and astronaut assistance, actively changing their inertia properties, and enabling replacement or augmentation of the structure with additional modules over multiple launches.

To date, techniques that have been considered as means of achieving reconfigurability include folding, such as self-deploying sun shields; assembly, such as formation flying and docking of individual spacecraft or assembly via robotic manipulation, and even 3D printing. However, self-reconfiguration of large 3D structures using these techniques remains a challenge.

An alternative strategy can be drawn from the field of modular robotics, where structures are formed from individually actuated building blocks connected by temporary joints. In contrast to formation flying, reconfiguration without detachment precludes complex dynamics via a reduction of the degrees of freedom by imposing kinematic constraints similar to those leveraged by traditional deployable structures. Recently, robot collectives have demonstrated acquisition of target configurations via self-folding, and cubic robots have achieved self-reconfigurability in two dimensions via sliding and disassembly, and in three dimensions via pivoting. Moreover, a concept for self-assembly of modular spacecraft using flux-pinning magnet-superconductor pairs to form contact-less hinges has been successfully demonstrated in 2D experiments on air tables. While opposing moments due to gravity remain a challenge to the success and scalability of terrestrial reconfigurable robots, space offers an environment where even small forces can generate significant accelerations when integrated over sufficient timescales.

In this project, we identify a novel concept for forming reconfigurable structures in space by using electromagnetically-actuated spacecraft, using a design based loosely on the PocketQube (PQ) in order to highlight the economic and technical challenges facing the construction of large reconfigurable structures today. We propose a design and deployment mechanism for a set of autonomous cubic spacecraft that acts a fully self-reconfigurable space structure and enumerate the milestones as follows. We begin by showing how air-core electromagnetic coils can be used as actuators between N neighbouring spacecraft, and simulate the forces generated for the chosen coil and spacecraft geometries. Next, we must derive the equations of motion for a multibody spacecraft system and synthesize a controller that drives the collective to pivot between different configurations. Using this, we simulate the full multibody dynamics and demonstrate reconfiguration of the assembly. Finally, we design and fabricate a number of modules for testing on the Zero G flight in order to validate the reconfiguration model.

Schedule of Predicted Tasks by Oct 14

Sep 23 - Sep 30 Implement a naive model of an electromagnetic actuator mechanism. Appraise the sizes and values required of the physical system in order to achieve a working reconfiguration mechanism.

Sep 30 - Oct 7 Mechanical and Electronic design of the module to satisfy the criteria assessed during the previous week.

Oct 7 - Oct 14 Implement a simple mockup of the electrical and mechanical designs in order to showcase a conceptual prototype

Mechanical Design

Individual modules will take the shape of cubic frames, with coils embedded in each edge. Pulsing current through these coils to create electromagnets allow creating repulsive and attractive forces between neighboring modules.

Below is an inspiration board made to inform design choices for the mechanical design of the prototype, including material to help plan the photographic documentation of the project both before and during flight.

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