An investigation of tape spring fold curvature

Tape springs are being used with increasing frequency in today’s space industry to deploy small satellite aerials and array areas. However, to accurately model the deployment of an appendage mounted with tape spring hinges, it is necessary to accurately model the opening moments produced from the material strains in the tape spring fold. These moments are primarily a function of curvature. This paper uses a photographic method to study the post buckling curvatures at the fold location for both two and three dimensional tape spring folds. The results are finally compared to determine the overall data trends

Experimental investigation of tape springs folded in three dimensions

One of the most significant drivers in satellite design is the minimization of mass to reduce the large costs involved in the launch. With technological advances across many fields, it is now widely known that very low-mass satellites can perform a wide variety of missions. However, there is a need for small, efficient, area deployment devices. One possible structural solution for such devices is tape springs. Previous work on tape spring hinges has focused on two-dimensional folds; however, applications exist that incorporate three-dimensional tape spring folds. The properties of three-dimensional tape spring folds are experimentally investigated using a specially designed test rig. The rig is first used to produce comparative two-dimensional data before being used to analyze more complex three-dimensional folds

Experimental analysis of damping across joints in metal plates

In the current world of engineering, structural vibration problems continue impact the design and construction of a wide range of products. Amid the parameters that determine the dynamic behaviour of a structure the one that takes into account the dissipation of energy resulting in the decay of the vibration is the least understood and the most difficult to quantify. The estimation of damping factors is of interest in most branches of engineering sciences. In the field of aircraft structures the damping directly affects the fatigue life, a parameter which is applied conservatively due to the inherent complexity in modelling the damping of built up structures and the potentially catastrophic consequences of a fatigue failure. One of the most important problems is the limited knowledge of how joints affect the damping of the complete structure. This work therefore addresses this issue and focuses on the damping of joints in metal plates as part of a larger project to investigate the damping of built up structures. Various plate configurations are experimentally investigated using two different approaches. The results from the configurations are compared and discussed along with the advantages and disadvantages of each experimental approach. This enables a link to be identified between the damping magnitudes and the mode shapes and joint stiffnesses

A study of joint damping in metal plates

For satellite applications the determination of the correct dynamic behaviour and in particular the structural damping is important to assess the vibration environment for the spacecraft subsystems and ultimately their capability to withstand the launch vibration environment. Therefore, the object of this investigation is to experimentally analyse a range of aluminium panel configurations to study the effect of joints on the damping of the complete structure. The paper begins with a full description of the experimental method used to accurately determine the modal loss factors for each of the panel configurations analysed. Nine different panels were used in the experimental tests, six of which incorporate lap joints variations. The joint parameters investigated include fastener type, bolt torque, fastener spacing, overlap distance and the effect of stiffeners. The damping results of ten different joint variants are presented for each of the first twelve modes of vibration. This data is directly compared to the damping factors of an equivalent monolithic panel. Various specific conclusions are made with respect to each of the joint parameters investigated. However, the primary conclusion is that the mode shape combined with the joint stiffness and joint location can be suggestive as to the likely magnitude increase of the modal loss factor

Coupled disturbance modelling and validation of a reaction wheel model

Microvibrations of a RWA are usually studied in either hard-mounted or coupled conditions, although coupled wheel-structure disturbances are more representative than the hard-mounted disturbances. The coupled analysis method of the wheel-structure is not as well developed as the hard-mounted one. A coupled disturbance analysis method is proposed in this paper. One of the most important factors in coupled disturbance analysis - the accelerance or dynamic mass of the wheel is measured and results are validated with an equivalent FE model. The wheel hard-mounted disturbances are also measured from a vibration measurement platform particularly designed for this study. Wheel structural modes are solved from its analytical disturbance model and validated with the test results. The wheel-speed dependent accelerance analysis method is proposed

Modelling Micro-Vibrations Transmission in Spacecraft Structure

Micro-vibrations on board spacecraft are an issue of growing importance, as some modern payloads, and in particular the new generations of optical instruments require extreme platform stability. These low level mechanical disturbances are usually created by the functioning of mechanical equipment (sources) such as reaction wheels, antenna pointing mechanisms cryo-coolers etc., and cover a wide frequency range. Because of the low level of the vibrations and their wide frequency range, the modeling and analysis of micro-vibrations poses a challenge as the typical structural modeling techniques used in this sector (Finite Element Method (FEM) and Statistical Energy Analysis (SEA)) are reliable only in some areas of the frequency spectrum. The FEM is well suited for low level frequencies; whereas energy methods (e.g. SEA or Energy Finite Element Method EFEA) are suited for high-frequency problems; in the mid-frequency range, finally, other methods (e.g. Hybrid FEA-SEA) tend to be used, even if they’re still not well-established such as the ones named before. However the issue is that there is no single method that can address micro-vibrations in the whole frequency range. In this paper, the methods cited above will be very briefly reviewed and their use in specific micro-vibration prediction problems will be investigated in detail and compared with experimental results. In practice the work presented here uses the Finite Element Method as base-line method to investigate the whole frequency range (say up to 1000 Hz). The FEM predictions are then compared with the experimental results, showing that at medium and high frequencies the response start to deviate significantly from the FEA predictions. The high frequency behavior of the structure will be analyzed using SEA. The mid-frequency range, finally, will be tackled from both directions: from the high frequency side using the Hybrid FE-SEA, whereas from the low frequency side the capability of the standard FEM will be extended using stochastic FEM. The tests are carried out using the structural qualification model of an SSTL satellite bus that has been used to support a high resolution camera. The computational transfer functions and those from the experimental activity will be finally compared using the Modal Assurance Criteria (MAC)

High altitude electrical power generation

This paper investigates the technical feasibility of a system that could be used to collect the solar irradiation at high altitude, convert it into electricity, and then transmit it to the ground via a cable. As a first step to assess the viability of this device, an estimate of the solar irradiation that can be expected at a defined altitude above the ground is presented, based on real atmospheric data. The study demonstrates that locating PV devices at high altitude with the use of an aerostatic platform, could bring a significant advantage in the production of electrical power, if compared with a typical UK ground based PV system. The fundamental equations for a preliminary design of the system are presented together with a first realistic choice of the most relevant engineering parameters that need to be set. An estimate of the cost of the system is provided and the possible risks involved, applications, advantages and disadvantages of the technology are assessed