The dynamics and control of large space structures with distributed actuation

Future large space structures are likely to be constructed at much greater length-scales, and lower areal mass densities than has been achieved to-date. This could be enabled by ongoing developments in on-orbit manufacturing, whereby large structures are 3D-printed in space from raw feedstock materials. This thesis proposes and analyses a number of attitude control strategies which could be adopted for this next generation of ultra-lightweight, large space structures. Each of the strategies proposed makes use of distributed actuation, which is demonstrated early in the thesis to reduce structural deformations during attitude manoeuvres. All of the proposed strategies are considered to be particularly suitable for structures which are 3d-printed on-orbit, due to the relative simplicity of the actuators and ease with which the actuator placement or construction could be integrated with the on-orbit fabrication of the structure itself. The first strategy proposed is the use of distributed arrays of magnetorquer rods. First, distributed torques are shown to effectively rotate highly flexible structures. This is compared with torques applied to the centre-of-mass of the structure, which cause large surface deformations and can fail to enact a rotation. This is demonstrated using a spring-mass model of a planar structure with embedded actuators. A torque distribution algorithm is then developed to control an individually addressable array of actuators. Attitude control simulations are performed, using the array to control a large space structure, again modelled as a spring-mass system. The attitude control system is demonstrated to effectively detumble a representative 75×75m flexible structure, and perform slew manoeuvres, in the presence of both gravity-gradient torques and a realistic magnetic field model. The development of a Distributed Magnetorquer Demonstration Platform is then presented, a laboratory-scale implementation of the distributed magnetorquer array concept. The platform consists of 48 addressable magnetorquers, arranged with two perpendicular torquers at the nodes of a 5×5 grid. The control algorithms proposed previously in the thesis are implemented and tested on this hardware, demonstrating the practical feasibility of the concept. Results of experiments using a spherical air bearing and Helmholtz cage are presented, demonstrating rest-to-rest slew manoeuvres and detumbling around a single axis using the developed algorithms. The next attitude control strategy presented is the use of embedded current loops, conductive pathways which can be integrated with a spacecraft support structure and used to generate control torques through interaction with the Earth’s magnetic field. Length-scaling laws are derived by determining what fraction of a planar spacecraft’s mass would need to be allocated to the conductive current loops in order to produce a torque at least as large as the gravity gradient torque. Simulations are then performed of a flexible truss structure, modelled as a spring-mass system, for a range of structural flexibilities and a variety of current loop geometries. Simulations demonstrate rotation of the structure via the electromagnetic force on the current carrying elements, and are also used to characterise the structural deformations caused by the various current loop geometries. An attitude control simulation is then performed, demonstrating a 90◦ slew manoeuvre of a 250×250 m flexible structure through the use of three orthogonal sets of current loops embedded within the spacecraft. The final concept investigated in this thesis is a self-reconfiguring OrigamiSat, where reconfiguration of the proposed OrigamiSat is triggered by changes in the local surface optical properties of an origami structure to harness the solar radiation pressure induced acceleration. OrigamiSats are origami spacecraft with reflective panels which, when flat, operate as a conventional solar sail. Shape reconfiguration, i.e. “folding” of the origami design, allows the OrigamiSat to change operational modes, performing different functions as per mission requirements. For example, a flat OrigamiSat could be reconfigured into the shape of a parabolic reflector, before returning to the flat configuration when required to again operate as a solar sail, providing propellant-free propulsion. Shape reconfiguration or folding of OrigamiSats through the use of surface reflectivity modulation is investigated in this thesis. First, a simplified, folding facet model is used to perform a length-scaling analysis, and then a 2d multibody dynamics simulation is used to demonstrate the principle of solar radiation presure induced folding. A 3d multibody dynamics simulation is then developed and used to demonstrate shape reconfiguration for different origami folding patterns. Here, the attitude dynamics and shape reconfiguration of OrigamiSats are found to be highly coupled, and thus present a challenge from a control perspective. The problem of integrating attitude and shape control of a Miura-fold pattern OrigamiSat through the use of variable reflectivity is then investigated, and a control algorithm developed which uses surface reflectivity modulation of the OrigamiSat facets to enact shape reconfiguration and attitude manoeuvres simultaneously

Emerging Space Technologies: Macro-scale On-orbit Manufacturing

Advanced additive manufacturing (AM) technologies have the potential to change the way in which satellites and spacecraft are deployed in orbit by removing traditional launch constraints, whether faring volume or launch loads, and allowing space structures to become larger, lighter and more capable with integrated features. These same approaches may also be exploited for on-orbit servicing, thereby potentially extending the operable lifetime of space infrastructure and increasing cost effectiveness. This paper will provide an overview of the key issues associated with on-orbit manufacturing and discuss the use of AM technologies and investigate the next wave of emerging space technologies enabled by on-orbit manufacturing

Emerging space technologies: macro-scale on-orbit manufacturing

Advanced additive manufacturing (AM) technologies have the potential to change the way in which satellites and spacecraft are deployed in orbit by removing traditional launch constraints, whether faring volume or launch loads, and allowing space structures to become larger, lighter and more capable with integrated features. These same approaches may also be exploited for on-orbit servicing, thereby potentially extending the operable lifetime of space infrastructure and increasing cost effectiveness. This paper will provide an overview of the key issues associated with on-orbit manufacturing and discuss the use of AM technologies and investigate the next wave of emerging space technologies enabled by on-orbit manufacturing

Mechanical Design of Self-Reconfiguring 4D-Printed OrigamiSats: A New Concept for Solar Sailing

In this article, a self-reconfiguring OrigamiSat concept is presented. The reconfiguration of the proposed OrigamiSat is triggered by combining the effect of 4D material (i.e. origami’s edges) and changes in the local surface optical properties (i.e., origami’s facets) to harness the solar radiation pressure acceleration. The proposed OrigamiSat uses the principle of solar sailing to enhance the effect of the Sun radiation to generate momentum on the Aluminised Kapton (Al-Kapton) origami surface by transitioning from mirror-like to diffusely reflecting optical properties of each individual facet. Numerical simulations have demonstrated that local changes in the optical properties can trigger reconfiguration. A minimum of 1-m edge size facet is required for a thick-origami to generate enough forces from the Sun radiation. The thick-origami pattern is 3D-printed directly on a thin Al-Kapton film (the solar sail substrate which is highly reflective). An elastic filament (thermoplastic polyurethane TPU) showed best performance when printing directly on the Al-Kapton and the Acrylonitrile Butadiene Styrene with carbon fiber reinforcement (ABS/cc) is added to augment the origami mechanical properties. The 4D material (shape memory polymer) is integrated only at specific edges to achieve self-deployment by applying heat. Two different folding mechanisms were studied: 1) the cartilage-like, where the hinge is made combining the TPU and the 4D material which make the mounts or valleys fully stretchable, and 2) the mechanical hinge, where simple hinges are made solely of ABS/cc. Numerical simulations have demonstrated that the cartilage-like hinge is the most suitable design for light-weight reconfigurable OrigamiSat when using the solar radiation pressure acceleration. We have used build-in electric board to heat up the 4D material and trigger the folding. We envisage embedding the heat wire within the 4D hinge in the future.</jats:p

Magnetic Attitude Control of Gossamer Spacecraft using a 3D-printed, Electrically Conducting Support Structure

An attitude control strategy for gossamer spacecraft is proposed, where control torques are generated by an electrically conducting support structure interacting with the Earth’s magnetic field. A mathematical model of the structure is developed, where the overall torque is found by summation of the Lorentz forces acting upon each current-carrying structural element. Different geometric configurations are shown to allow effective magnetic dipole moments in three orthogonal directions. With this model, the results of dynamic simulation are presented in order to assess the ability of the conducting structure to detumble itself in-orbit, using the classical Bdot control law. The possibility of using this attitude control system to manoeuvre orbital reflectors is then investigated. The required angular accelerations for a large solar reflector in polar orbit to continuously illuminate a fixed point on the Earth’s surface are derived within a simplified model, and compared with those achievable by the conducting structure. Simulation is then used to assess whether the conducting structure is capable of achieving partial attitude control of an orbital reflector, for example to illuminate terrestrial solar power farms at dawn and dusk when their output is low

3d-printed, electrically conductive structures for magnetic attitude control

The use of embedded current loops for the attitude control of large, flexible spacecraft is investigated. Length-scaling laws are derived by determining what fraction of a planar spacecraft’s mass would need to be allocated to the conductive current loops in order to produce a torque at least as large as the gravity gradient torque. Simulations are then performed of a flexible truss structure, modelled as a spring-mass system, for a range of structural flexibilities and a variety of current loop geometries. Simulations demonstrate rotation of the structure via the electromagnetic force on the current carrying elements, and are also used to characterise the structural deformations caused by the various current loop geometries. An attitude control simulation is performed, demonstrating a 90◦ slew manoeuvre of a 250 × 250 m flexible structure through the use of three orthogonal sets of current loops embedded within the spacecraft

Emerging space technologies: macro-scale on-orbit manufacturing

Advanced additive manufacturing (AM) technologies have the potential to change the way in which satellites and spacecraft are deployed in orbit by removing traditional launch constraints, whether faring volume or launch loads, and allowing space structures to become larger, lighter and more capable with integrated features. These same approaches may also be exploited for on-orbit servicing, thereby potentially extending the operable lifetime of space infrastructure and increasing cost effectiveness. This paper will provide an overview of the key issues associated with on-orbit manufacturing and discuss the use of AM technologies and investigate the next wave of emerging space technologies enabled by on-orbit manufacturing

Emerging Space Technologies: Macro-scale On-orbit Manufacturing

Advanced additive manufacturing (AM) technologies have the potential to change the way in which satellites and spacecraft are deployed in orbit by removing traditional launch constraints, whether faring volume or launch loads, and allowing space structures to become larger, lighter and more capable with integrated features. These same approaches may also be exploited for on-orbit servicing, thereby potentially extending the operable lifetime of space infrastructure and increasing cost effectiveness. This paper will provide an overview of the key issues associated with on-orbit manufacturing and discuss the use of AM technologies and investigate the next wave of emerging space technologies enabled by on-orbit manufacturing

Distributed magnetic attitude control for large space structures

The utility of distributed magnetic torque rods for the attitude control of a large space structure is investigated. Distributed arrays of actuators offer advantages such as distributing structural loads, increasing fault tolerance, allowing structures to be designed modularly, and additionally the actuators may be integrated with on-orbit fabrication strategies. First, distributed torques are shown to effectively rotate highly flexible structures. This is compared with torques applied to the centre-of-mass of the structure, which cause large surface deformations and can fail to enact a rotation. This is demonstrated using a spring–mass model of a planar structure with embedded actuators. A distributed torque algorithm is then developed to control an individually addressable array of actuators. Attitude control simulations are performed, using the array to control a large space structure, again modelled as a spring–mass system. The attitude control system is demonstrated to effectively detumble a representative 75 × 75 m flexible structure, and perform slew manoeuvres, in the presence of both gravity-gradient torques and a realistic magnetic field model

Integrated attitude and shape control for OrigamiSats with variable surface reflectivity

OrigamiSats, a new concept in solar sailing, are origami spacecraft with reflective panels that, when flat, operate as a conventional solar sail. Shape reconfiguration, i.e. “folding” of the origami design, allows the OrigamiSat to change operational modes, performing different functions as per mission requirements. For example, a flat OrigamiSat could be reconfigured into the shape of a parabolic reflector, before returning to the flat configuration when required to operate again as a solar sail, providing propellant-free propulsion. The attitude dynamics and shape reconfiguration of OrigamiSats are known to be highly coupled, thus presenting a challenge from a control perspective. This paper investigates the problem of integrating attitude and shape control of a Miura-fold pattern OrigamiSat through the use of variable reflectivity, allowing differences in solar radiation pressure to be used to enact shape reconfiguration and attitude manoeuvres. A closed-loop feedback controller is presented which combines and balances the attitude and shape control requirements, and gain-scheduling is implemented to address some specific features of the system dynamics. Numerical simulations of the multibody dynamics of the system are used to test the proposed controller and simulations of some example manoeuvres are performed which demonstrate the system’s performance