Tethers

A tether of sufficient strength, capable of being lengthened or shortened and having appropriate apparatuses for capturing and releasing bodies at its ends, may be useful in propulsion applications. For example, a tether could allow rendezvous between spacecraft in substantially different orbits without using propellant. A tether could also allow co-orbiting spacecraft to exchange momentum and separate. Thus, a reentering spacecraft (such as the Shuttle) could give its momentum to one remaining on orbit (such as the space station). Similarly, a tether facility could gain momentum from a high I(sub sp)/low thrust mechanism (which could be an electrodynamics tether) and transfer than momentum by means of a tether to payloads headed for many different orbits. Such a facility would, in effect, combine high I(sub sp) with high thrust, although only briefly. An electrodynamic tether could propel a satellite from its launch inclination to a higher or lower inclination. Tethers could also allow samples to be taken from bodies such as the Moon. Three types of tether operations are illustrated. The following topics are discussed: (1) tether characteristics; (2) tether propulsion methods--basics, via momentum transfer, and electrodynamic tether propulsion; and (3) their use in planetary exploration

Labor Unions Seen as Good for Workers, Not U.S. Competitiveness

Analyzes survey findings on views of private and public sector unions; their effects on salary and benefits, working conditions, productivity, availability of good jobs, and U.S. companies' global competitiveness; and which side to take in disputes

The Nature of Precautionary Wealth

This paper uses the Panel Study of Income Dynamics to provide some of the first direct evidence that wealth is systematically higher for consumers with greater income uncertainty. However, the apparent pattern of precautionary saving is not consistent with a standard parameterization of the life cycle model in which consumers are patient enough to begin saving for retirement early in life: wealth is estimated to be less sensitive to uncertainty in permanent income than implied by that model. Instead, our results suggest that over most of their working lifetime, consumers behave in accordance with the 'buffer-stock' models of saving described in Carroll (1992) or Deaton (1991), in which consumers hold wealth principally to insulate consumption against near term fluctuations in income.

How Important is Precautionary Saving?

We estimate the fraction of the wealth of a sample of PSID respondents that is held because some households face greater income uncertainty than others. We first derive an equation characterizing the theoretical relationship between wealth and uncertainty in a buffer-stock model of saving. Next, we estimate that equation using PSID data; we find strong evidence that households engage in precautionary saving. Finally, we simulate the wealth distribution that would prevail if all households had the same uncertainty as the lowest-uncertainty group. We find that between 39 and 46 percent of wealth in our sample is attributable to uncertainty differentials across groups.