Andrew Viquerat

Review of Inflatable Booms for Deployable Space Structures: Packing and Rigidization

Inflatable structures offer the potential of compactly stowing lightweight structures, which assume a fully deployed state in space. An important category of space inflatables are cylindrical booms, which may form the structural members of trusses or the support structure for solar sails. Two critical and interdependent aspects of designing inflatable cylindrical booms for space applications are i) packaging methods that enable compact stowage and ensure reliable deployment, and ii) rigidization techniques that provide long-term structural ridigity after deployment. The vast literature in these two fields is summarized to establish the state of the art.

Reactive Collision Avoidance for Unmanned Aerial Vehicles Using Doppler Radar

Research into reactive collision avoidance for unmanned aerial vehicles has been conducted on unmanned terrestrial and mini aerial vehicles utilising active Doppler radar obstacle detection sensors. Flight tests conducted by flying a mini UAV at an obstacle have confirmed that a simple reactive collision avoidance algorithm enables aerial vehicles to autonomously avoid obstacles. This builds upon simulation work and results obtained using a terrestrial vehicle that had already confirmed that active sensors and a reactive collision avoidance algorithm are able to successfully find a collision free path through an obstacle field.

Bistable Over the Whole Length (BOWL) CFRP Booms for Solar Sails

This paper presents novel ultra-light booms for solar sails and other large deployable space structures. These CFRP booms have a unique property: bistability over the whole length (BOWL), which enables simple and compact deployment mechanism designs that can reduce overall system mass. They were produced to solve some of the previously encountered problems with bistable composite tubular booms that reduced their optimal length and scalability due to local buckling phenomena when the diameter of the coil increased. A new low-cost manufacturing technique, which consists of using braids with a variable angle change over the boom length, was found to have a positive effect in reducing that tendency. An analytical model is used to explain this behavior and predict the secondary stable state properties and natural diameter of the coiled/packed boom. A 3.6 m tape spring version of these bistable CFRP booms has been designed for a 25 m2 Gossamer Sail Deorbiter of future space assets and is being considered for an upcoming solar sail demonstration mission called CubeSail. Larger booms are being designed for a new scalable roll-up solar array concept.

Functional and Qualification Testing of the InflateSail Technology Demonstrator

Figure 1. InflateSail deploys two structures from a 3U CubeSat: a 1 m long inflatable mast, and a 10 m2 drag augmentation sail supported by four CFRP booms. InflateSail is a technology demonstration mission for a drag deorbiting system. Two gossamer structures are deployed from a 3U CubeSat: a 1 m long inflatable-rigidisable mast, and a 10 m drag sail supported by bistable CFRP deployable booms; see Figure 1. The InflateSail satellite will be launched as part of the European QB50 mission in 2016. The objectives of the InflateSail mission are to verify the functionality of the deployable structures on board, and to illustrate the potential of the sailmast system as an end-of-life deorbiting solution for larger satellites. The deployable sail would increase a host satellite’s aerodynamic drag, thus reducing its orbital decay time. The inflatable mast provides an offset between the centre-of-mass of the host satellite and the centre-of-pressure of the gossamer sail, which facilitates passive attitude stabilisation and thereby maximises the presented drag area. Additionally, InflateSail will demonstrate the use of an aluminium-polymer laminate inflatable cylinder as a lightweight deployable structural member, and use a Cool Gas Generator (CGG) for storage and release of the inflation gas. This paper describes the InflateSail payloads, and focuses on the functional and qualification testing performed to ensure the gossamer payloads will survive launch, and will deploy successfully in space.

Demonstrator Flight Missions at the Surrey Space Centre Involving Gossamer Sails

This paper presents an overview of the different gossamer sail flight projects being undertaken at the Surrey Space Centre. The missions consist of a 25 m2 solar sail to be launched in Q1 2014 (CubeSail), a gossamer deorbiter for future European space assets (DGOSS), a scalable sailcraft that will demonstrate satellite deorbiting in Low Earth Orbit (DeorbitSail), and a drag sail that uses inflatable and rigidizable technology to be flown as part of the QB50 mission (InflateSail). The key technologies currently being developed for each project will be summarized and the most relevant scientific results presented.

An Examination of Crease Removal in Rigidizable Inflatable Metal-Polymer Laminate Cylinders

Inflatable cylinders with metal-polymer laminate skins can be used to construct extremely lightweight deployable structures for space applications. These structures undergo a rigidization process in which slight over-inflation leads to the permanent removal of the storage folds in the skin. While the folds are removed, small residual creases remain in the laminate. The extent to which these creases are removed depends on the skin material used, the inflation pressure, and the orientation of the creases with respect to the cylinder axis. The effective removal of creases is critical to the formation of a robust structure. In this paper the removal of creases in several different metal-polymer laminates is analysed experimentally. The materials chosen for these experiments consist of aluminum metal plies and, PET, biaxially oriented PET or polyimide polymeric plies. The laminates range in thickness from 28 μm to 117.9 μm, and consist of two or three plies.

DEPLOYTECH : nano-satellite testbeds for gossamer technologies

Large deployable space structures are an integral part of reflectors, earth observation satellite antennas and radars, observation and radar targets, radiators, sun shields, solar sails and solar arrays. Launch vehicle faring sizes have not increased in the last three decades, meaning ever more efficient ways of packaging large space structures must be sought. Deployable structures come with the promise and capability of reducing payload mass substantially and allowing for very compact storage of systems during the launch phase. Gossamer structures hold particular promise for systems involving large apertures, solar panels, thermal shields and solar/deorbiting sails. The Technology Readiness Level (TRL) of a great part of these technologies is still very low (in the order of 2-3). The objective of DEPLOYTECH is to develop three specific, useful, robust, and innovative large deployable space structures to a TRL of 6-8 in the next three years. These include: a 10 m^2 (3.6 m diameter) sail structure that uses inflatable technology for deployment and support; a 5x5 m roll-out flexible solar array that utilizes bistable composite booms; and 14 m solar sail CFRP booms with a novel deployment mechanism for extension control.

Modeling the Bistability of Laminated Composite Toroidal Slit Tubes

The bistability of a toroidal slit tube is modeled using the Rayleigh-Ritz method. Approximate explicit expressions for the original stable deployed geometry, and the deformed stowed geometry are used to derive forms for the bending and stretching strain energy. The surface of a torus has varying Gaussian curvature, requiring a new approach to the modeling and analysis of the stable configurations. A comparative study with established straight-BRC models was conducted from which the doubly curved-BRC model presented here predicts second stable state coil radii with 96.25% agreement.

Polynomial continuation in the design of deployable structures

Polynomial continuation, a branch of numerical continuation, has been applied to several primary problems in kinematic geometry. The objective of the research presented in this document was to explore the possible extensions of the application of polynomial continuation, especially in the field of deployable structure design. The power of polynomial continuation as a design tool lies in its ability to find all solutions of a system of polynomial equations (even positive dimensional solution sets). A linkage design problem posed in polynomial form can be made to yield every possible feasible outcome, many of which may never otherwise have been found. Methods of polynomial continuation based design are illustrated here by way of various examples. In particular, the types of deployable structures which form planar rings, or frames, in their deployed configurations are used as design cases. Polynomial continuation is shown to be a powerful component of an equation-based design process. A polyhedral homotopy method, particularly suited to solving problems in kinematics, was synthesised from several researchers’ published continuation techniques, and augmented with modern, freely available mathematical computing algorithms. Special adaptations were made in the areas of level-k subface identification, lifting value balancing, and path-following. Techniques of forming closure/compatibility equations by direct use of symmetry, or by use of transfer matrices to enforce loop closure, were developed as appropriate for each example. The geometry of a plane symmetric (rectangular) 6R foldable frame was examined and classified in terms of Denavit-Hartenberg Parameters. Its design parameters were then grouped into feasible and non-feasible regions, before continuation was used as a design tool; generating the design parameters required to build a foldable frame which meets certain configurational specifications. iv Two further deployable ring/frame classes were then used as design cases: (a) rings which form (planar) regular polygons when deployed, and (b) rings which are doubly plane symmetric and planar when deployed. The governing equations used in the continuation design process are based on symmetry compatibility and transfer matrices respectively. Finally, the 6, 7 and 8-link versions of N-loops were subjected to a witness set analysis, illustrating the way in which continuation can reveal the nature of the mobility of an unknown linkage. Key features of the results are that polynomial continuation was able to provide complete sets of feasible options to a number of practical design problems, and also to reveal the nature of the mobility of a real overconstrained linkage.

A Model of Packaging Folds in Thin Metal-Polymer Laminates

Thin metal-polymer laminates make excellent materials for use in inflatable space structures. By inflating a stowed envelope using pressurized gas, and by increasing the internal pressure slightly beyond the yield point of the metal films, the shell rigidizes in the deployed shape. Structures constructed with such materials retain the deployed geometry once the inflation gas has either leaked away, or it has been intentionally vented. For flight, these structures must be initially folded and stowed. This paper presents a numerical method for predicting the force required to achieve a given fold radius in a three-ply metal-polymer-metal laminate and to obtain the resultant springback. A coupon of the laminate is modeled as a cantilever subject to an increasing tip force. Fully elastic, elastic-plastic, relaxation and springback stages are included in the model. The results show good agreement when compared with experimental data at large curvatures.