Satellite Formation FlyingI have done work with the AF Research Lab to assesses the frequency and average size of maneuvers necessary to stationkeep various satellite formations. Effects from three sources of error are considered: modeling (guidance algorithms are based on simple dynamics), knowledge (navigation errors in position and velocity) and control (execution errors in the burn). A particular focus of my current research is the effect of the Earth’s oblateness on stationkeeping. Even without knowledge or control errors, this perturbation will cause the formation to drift and, therefore, will require maneuvers to maintain position relative to the reference satellite. The effect of this perturbation can be reduced by redefining the nominal trajectory so the target state will lead to an orbit that does not drift with respect to the reference satellite - the J2-invariant orbit described by Schaub and Alfriend.
Tethered FormationsOne potential means of reducing the stationkeeping fuel for a satellite formation is to tether the platforms together. The tethers keep the objects from drifting apart, but unfortunately do not keep them from colliding. To mitiigate this possibility, the entire system is spun up. To keep the system oriented toward Earth, the Likins-Pringle rigid body equilibria are used as a baseline design. A flexible lumped-mass model is used to assess the stability of the tethered system. Three parameters related to the formation size, masses and spin rate are varied in order to find designs that demonstrate desirable dynamic behavior. While none of the current designs are Lyupanov stable, formations with a spin axis near the local vertical are well-behaved over time spans of several orbits.
BiomechanicsThe overarching goal of my biomechanics research is the analysis and optimization of human motion. By coupling computer models of the musculo-skeletal system (and any relevant equipment such as a prosthetic, bicycle, or golf club) with optimization algorithms, we are developing tools that can assist in improving the performance of athletes, amputees, or some who has had an injury. The research is completed with the intention of using it in a clinical setting. In this context, data is collected on the subject's motion from a video capture system (either conventional or a low-cost system that is currently under development and pictured here). The data is compared to the optimized computer model to suggest modifications to the subject's technique and/or improvements in equipment design/adjustments. Eventually, a user-friendly feedback device would be developed to assist in training or rehabilitation of the subject.
Satellite Maneuvering via Electrodynamic Tethers
Space Transportation with a Tether Sling
Asteroid Deflection Using Tethers