The space debris population has greatly increased over the last few decades. Active debris removal (ADR) methods may become necessary to remove those objects in orbit that pose the biggest collision risk. Those ADR methods that require contact with the target, show complications if the target is rotating at high speeds. Observed rotations can be higher than 60 deg/s combined with precession and nutation motions. "Natural" rotational damping in upper stages has been observed for some space debris objects. This phenomenon occurs due to the eddy currents induced by the Earth's magnetic field in the predominantly conductive materials of these man made rotating objects. Existing solutions for the analysis of eddy currents require time-consuming finite element models to solve a Poisson equation throughout the volume. The first part of this paper presents a new method to compute the eddy current torque based on the computation of a new tensor called the 'Magnetic Tensor'. The general theory to compute this tensor by Finite Element Method is given as well as a particular Frame Model. This last model enables an explicit formula to be determined to evaluate the magnetic tensor. Analytical solutions for the spherical shell, the open cylinder and flat plates are given for the magnetic tensor and the eddy current torque model is validated with existing published work. The second part of the paper presents an active de-tumbling method for space debris objects based on eddy currents. The braking method that is proposed has the advantage of avoiding any kind of mechanical contact with the target. The space debris object is subjected to an enhanced magnetic field created from a chaser spacecraft which has one or more deployable structures with an electromagnetic coil at its end. The braking time and the possible induced precession is analysed for a metallic spherical shell considering different ratios of conductive vs. non-conductive material. The paper finalises with a case study based on the de-tumbling of an Ariane-4 Upper Stage H10 under the effect of the gravity gradient and a preliminary analysis of the non-uniformity of the magnetic field is presented.
Tape springs, defined as thin metallic strips with an initially curved cross-section, are an attractive structural solution and hinge mechanism for small satellite deployable structures because of their low mass, low cost, and general simplicity. They have previously been used to deploy booms and array panels in various configurations that incorporate a two-dimensional deployment of the tape. However, applications currently exist that incorporate three-dimensional tape springs folds. 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 publication uses a photographic method to analyse the curvature assumptions of twodimensional tape spring folds and to define the curvature trends for three-dimensional tape spring folds as a basis for calculating the opening moment. It is found that although a variation in the curvature can be seen for three-dimensional tape spring folds, its effect is secondary to the tape thickness tolerance. Therefore, constant curvature models are concluded to be accurate enough for general tape fold applications.
The cyclic nature of the stick-slip phenomenon may cause catastrophic failures in drillstrings or at the very least could lead to the wear of expensive equipment. Therefore, it is important to study the drilling parameters which can lead to stickslip, in order to develop appropriate control methods for suppression. This paper studies the stick-slip oscillations encountered in drill-strings from both numerical and experimental points of view. The numerical part is carried out based on path-following methods for nonsmooth dynamical systems, with a special focus on the multistability in drill-strings. Our analysis shows that, under a certain parameter window, the multistability can be used to steer the response of the drill-strings from a sticking equilibrium or stick-slip oscillation to an equilibrium with constant drill-bit rotation. In addition, a small-scale downhole drilling rig was implemented to conduct a parametric study of the stick-slip phenomenon. The parametric study involves the use of two flexible shafts with varying mechanical properties to observe the effects that would have on stick-slip during operation. Our experimental results demonstrate that varying some of the mechanical properties of the drill-string could in fact control the nature of stick-slip oscillations.
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. = opposite sense peak moment bend angle in the skewed system max 0− = equal sense peak moment bend angle in the skewed system µ = skew angle of tape spring σ yield = material yield stress Nomenclature
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