Stability of Relative Equilibria in the Full Two-Body Problem

The stability of relative equilibrium solutions for the interaction of two massive bodies is explored. We restrict ourselves to the interaction between an ellipsoid and a sphere, both with finite mass. The study of this problem has application to modeling the relative dynamics of binary asteroids, the motion of spacecraft about small bodies, and the dynamics of gravity gradient satellites. The relative equilibrium can be parameterized by a few constants, including the mass ratio of the two bodies, the shape of the ellipsoid, and the normalized distance between the two bodies. Planar stability is characterized over this range of parameter values. When restricted to motion in the symmetry plane, the dynamical problem can be reduced to a two-degrees of freedom Hamiltonian system, which allows for an efficient computation of stability characteristics of the relative equilibria. Future work will look at full stability of these relative equilibria.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73952/1/annals.1311.006.pd

Effect of Density Inhomogeneity on YORP: The case of Itokawa

The effect of density inhomogeneity on the YORP effect for a given shape model is investigated. A density inhomogeneity will cause an offset between the center of figure and the center of mass and a re-orientation of the principal axes away from those associated with the shape alone. Both of these effects can alter the predicted YORP rate of change in angular velocity and obliquity. We apply these corrections to the Itokawa shape model and find that its YORP angular velocity rate is sensitive to offsets between its center of mass and center of figure, with a shift on the order of 10 meters being able to change the sign of the YORP effect for that asteroid. Given the non-detection of YORP for Itokawa as of 2008, this can shed light on the density distribution within that body. The theory supports a shift of the asteroid center of mass towards Itokawa's neck region, where there is an accumulation of finer gravels. Detection of the YORP effect for Itokawa should provide some strong constraints on its density distribution. This theory could also be applied to asteroids visited by future spacecraft to constrain density inhomogeneities.Comment: 23 pages, 3 figure

Stability of Sun-Synchronous Orbits in the Vicinity of a Comet

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77384/1/AIAA-41655-200.pd

Talk and Texts at Work: Beyond language and literacy skills

In this paper I discuss changing work practices in post-bureaucratic organisations (Heckscher and Donellon 1994, Iedema 2003) as a move from a focus on how those in control formulate what is to happen at the level of work, towards requiring workers to verbalise how they see themselves as being able to contribute to the organisation. Workers are increasingly asked to talk about their work, and to negotiate their understandings of their work with others in the workplace – they are becoming discourse workers. This discourse work is integral to the increasing textualisation of work. These work practices are imbued with tensions as workers try to make sense of, and learn, new ways of ‘being’ a worker, and an important site of this struggle and learning is working in teams.