Next generation curved deployable flexible booms for high precision applications

Deployable flexible strips resembling carpenters' tape measures have been used to deploy and support devices such as antennas and solar panels for some time. These curved strips are often referred to as "booms", especially when they also act as structural members. Perhaps the most famous example was the Viking Lander soil collection arm, which could be reeled up or extended as required. These booms are usually constructed from thin curved sheets of metal, or laminates of fibre reinforced polymer. Some of these booms possess the property of "bistability", which means they do not need to be constrained once they have been coiled up.

Flexible deployable booms have found other uses in deploying antennas and imaging systems on the battlefield, inserting monitoring equipment into nuclear power plants, deploying a flexible solar array from the International Space Station (ROSA experiment), and very recently in forming the masts of the InflateSail drag deorbiting sail: the first European sail to be deployed in space, and one of the first successful demonstrations of orbital debris removal technology.

These booms have several advantages over deployable systems consisting of rigid links joined by hinges or sliders, including simplicity, a very small number of moving parts, and they often can be made to be very lightweight. However, two main limitations of these flexible booms are that the vast majority to those developed to date only deploy in a straight line, and that the exact geometry and deployed length of boom cannot be very accurately controlled.

Recently, versions of these deployable booms that are not only curved in one direction (like a tape measure), but have "double curvature" have started to be studied in earnest. These booms can be deployed into a whole array of new shapes such as parabolas, a torus, and even helices. This opens up a number of new possible applications, such as lightweight deployable parabolic dishes, large tent supports, and as active elements in directional antennas.

In our project, we will accelerate the technology readiness level (TRL) of this technology by developing the design and modelling tools required to work with doubly-curved deployable flexible booms (focussing mainly on fibre reinforced laminate materials), and improving the manufacturing methods and deployment mechanisms in an effort to make booms with the necessary geometric precision and dimensional stability to be used in RF and optical systems. To design these highly constrained flexible structures we will be adapting a very powerful equation solving technique called polynomial continuation to seek out the perfect laminate fibre angles and thicknesses to get the mechanical behaviour required. To model the behaviour of the booms we will be generating novel energy methods to predict coiled and deployed shapes, building on methods we have already developed in this field.

To motivate the development of these technologies, the University of Surrey is partnering with Surrey Satellite Technology (SSTL) and RolaTube Technology Ltd. (RTL) to build two new devices making use of curved flexible deployable booms. With RTL we are constructing a directional helical antenna that unwinds from a small motorised hub, deploying its own ground plane at the same time. With SSTL we are developing a novel Earth imaging telescope barrel consisting of multiple curved strips which deploy simultaneously to form the outer barrel. The telescope strip is an especially interesting device because it requires a single curvature in the deployed state where it forms part of the barrel of the telescope, but quite a complicated double curvature when coiled into a ring around the base of the telescope.

The current generation of flexible deployable booms are used in both terrestrial and space applications where they form structural elements within deployable solar and antenna arrays, are used as masts for solar and drag sails, and act as support arms for scientific equipment in hazardous environments. The deployable flexible booms used in these applications tend to have quite simple geometries, in that they roll up into a cylindrical coil, and deploy out in a straight line like a tape measure. The precise deployed shape often cannot be controlled well.

This project is taking the inherent advantages of simplicity, reliability and robustness that have made these booms popular, and is opening up a new range of possibilities for the technology by introducing more complicated geometries, while also enforcing tighter tolerances on the precise shape the booms have when deployed, and the extent to which they shrink and expand as the temperature changes. In doing so a range of new applications in which a precisely controlled but curved shape is required can be considered. Such applications include the use of the boom itself as an antenna element, as a support for deployable curved reflecting dishes, or even as a support for optical devices which require a high degree of precision in placement and subsequent stability.

The way we will achieve this is by improving the mathematical models to predict the behaviour of these curved "banana" and helix shaped deployable flexible booms. In doing so we will be exploiting the results of three EPSRC Industrial CASE studentships, all focussed on bistable composite booms, as well as the results of an existing University of Surrey and Surrey Satellite Technology collaboration in developing rigid linked telescopic deployable optics for small satellites. The mathematical models we develop will be tested as we manufacture two motivating technologies as part of the project: a deployable helical antenna and ground plane device for terrestrial and space applications, and a deployable flexible telescope barrel for Earth observation from small satellites.

Academic beneficiaries include groups and departments currently researching deployable structures, bistable and multistable structures, and compliant structures. There are currently researchers in these fields at Cambridge, Imperial College, Bath, and Caltech in the USA, but there are many others. We will achieve this by sharing the results of our work at academic conferences and in journals. In addition, documentation and metadata, including experimental data and numerical data sets generated by the polynomial continuation design process, will be made available through the "Surrey Research Insight" portal at http://epubs.surrey.ac.uk (made accessible for at least 10 years beyond the most recent request for access). This metadata will be linked with publications stemming from this research, and the Grant number and details listed.

Industrial beneficiaries include companies making regular use of deployable structures in their products (such as RolaTube Technology, Oxford Space Systems, and Surrey Satellite Technology). The results of this project will be shared with such companies by working directly with them, co-supervising students, or through means of dissemination such as conferences and workshops.

Further downstream, beneficiaries of the products enabled by this technology will include those making use of the improved Earth observation capabilities in continuous or rapid return coverage of disasters, and lower cost coverage in less time critical applications like vegetation and pollution monitoring. The improved capabilities of lightweight deployable flexible structures will also benefit both the UK and US militaries (to date, some of the biggest customers for these technologies), who are making more frequent use of equipment based on these technologies in the field.