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Tethered satellite research at the NDSSL consists of broad-based experimental and analytical work. Two-dimensional ground-based experiments utilizing a hovercraft vehicle have been performed to confirm models of tethered satellite end-body motion with respect to the tether itself. Video of the experiment is analyzed with custom computer codes in order to determine the position, velocity, and acceleration of the hovercraft vehicles in the end-body experiments.
The analytical tethered satellite work has focused on determining the equations of motion for tethered satellite end-bodies, determining the deployment characteristics of tethered satellites, and determining the global solution behavior of simple tethered satellite models. Tethered satellite deployment consists of spooling out the tether from one or more of the satellite end-bodies. Current deployment research focuses on generating the equations of motion for this deployment process and numerically simulating the equations of motion in order to understand the behavior the system as a function of several different physical parameters and initial conditions. The NDSSL is also extending small-tether satellite models to describe the deployment for extremely long tethers such as the space elevator.
Tethered satellite dynamics are interesting both as physical systems and as mathematical systems. Research is being performed into the global mathematical structure of the solutions of the (nonlinear) tethered satellite equations of motion. Work is being done to identify and describe equilibria, nullclines, homoclinic and heteroclinic loops, and other interesting mathematical structures. These structures are related to physical tethered satellite behavior in an attempt to develop a toolbox capable of describing the appropriate physical parameters and initial conditions needed to achieve a certain behavior and to describe the behavior exhibited by tethered satellites with certain physical parameters and initial conditions.
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The Tumbleweed is a Martian rover concept designed to cheaply and efficiently investigate broad swaths of the surface of Mars. The Tumbleweed concept is revolutionary in that it relies on the Martian winds for propulsion rather than heavy, expensive, and relatively short-lived motor-battery combinations. Preliminary data indicates that the Tumbleweed is capable of covering more ground than traditional rovers and, with the use of solar cells, having a much longer life span than traditional rovers.
Because the directional control of the Tumbleweed is limited, it must be able to survive over a wide variety of terrain types. Current NDSSL research focuses on developing a numerical simulation model predicting the motion of a Tumbleweed rover as it encounters real terrain scenarios. The research provides an understanding of the range of Tumbleweed design parameters essential for mobility over varied terrain and introduces a numerical model covering rover rolling, sliding, and bouncing behaviors and the transitions between these modes of movement.
A collision model based on Kane’s method of dynamics is used to study the impact between the rover and flat terrain. The model is extended by considering collisions on hills and the effects of drag and the Magnus force on the rover. A numerical model which tracks the motion of the rover and the transition between different terrain types has also been created. Rolling and slide models for a rover in motion have been developed for flat and sloping terrains. Several design case studies which demonstrate the utility of the NDSSL models have also been developed.
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The spinal column, also called the vertebral column, is a complex system of bones, cartilage, muscles, and nerves that provide support and protection to the human body. The spine runs from the base of the skull to the pelvis and is made up of 33 bones called vertebrae that are separated by flat, circular intervertebral discs. With time and the repetitive loading and bending of the spinal column, intervertebral discs start to degenerate and become stiffer and thinner. This is called degenerative disc disease (DDD) and is the main cause of back pain and spinal disorders. To solve this problem, the first approach is a non-surgical treatment, including rest, heat, pain medication, therapy, and chiropractic manipulation. When the pain persists, surgical methods are used to help the patient. Currently the most widely used and approved method is spinal fusion, which consists of removing the degenerated disc and fusing the two adjacent vertebrae together by implanting bone in between. In recent years, artificial disc replacement (ADR) is emerging as a possible alternative to fusion. The concept of this procedure is to mimic as closely as possible the natural vertebral disc in a mechanical system and replace the damaged disc in the spine with the artificial disc. We are currently performing finite element and lumped parameter analyses of different treatments for degenerative disc disease, looking at single-level and multi-level spinal fusion and artificial disc replacement techniques. One of the issues we are particularly interested in is the interplay between scoliosis and degenerative disc disease and how the degree of curvature impacts the type of treatment available to patients with degenerative disc disease.
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