Mark Schenk

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.

Design of a Statically Balanced Tensegrity Mechanism

The combination of static balancing and tensegrity structures has resulted in a new class of mechanisms: Statically Balanced Tensegrity Mechanisms. These are prestressed structures that are in equilibrium in a wide range of positions, and thus exhibit mechanism-like properties. This paper describes the design of a prototype model of a statically balanced tensegrity mechanism based on a classic tensegrity structure.Copyright

Spring-to-Spring Balancing as Energy-Free Adjustment Method in Gravity Equilibrators

Generally, adjustment of gravity equilibrator to a new payload requires energy, e.g. to increase the pre-load of the balancing spring. A novel way of energy-free adjustment of gravity equilibrators is possible by introducing the concept of a storage spring. The storage spring supplies or stores the energy necessary to adjust the balancer spring of the gravity equilibrator. In essence the storage spring mechanism maintains a constant potential energy within the spring mechanism; energy is exchanged between the storage and balancer spring when needed. Various conceptual designs using both zero-free-length springs and regular extension springs are proposed. Two models were manufactured demonstrating the practical embodiments and functionality.© 2009 ASME

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.

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.

Viscoelastic Effects in Metal-Polymer Laminate Inflatable Structures

A 1 m long inflatable-rigidizable mast was developed as a payload for InflateSail: a 3U CubeSat technology demonstration mission. The thin-walled cylindrical mast consists of an aluminum-polymer laminate, and long-term structural performance is ensured through strain-rigidization: the packaging creases are removed through plastic deformation of the aluminum plies. During ground tests it was observed that after rigidization the internal pressure dropped more rapidly than could be accounted for by leakage of inflation gas alone. It was hypothesized that viscoelastic behaviour of the laminate material causes a further, time-dependent (order of seconds), increase in cylinder diameter, with a corresponding drop in internal pressure. Additional experiments revealed an increase in diameter, including large visco-elastic shear in the adhesive of the lap joint. This was not found to be sufficient to fully account for the observed reduction in pressure. An increase in temperature of the gas during inflation, with subsequent cooling down to ambient is thought to cause the additional pressure drop.