Observability, Eigenvalues, and Kalman Filtering

In higher order Kalman filtering applications the analyst often has very little insight into the nature of the observability of the system. For example, there are situations where the filter may be estimating certain linear combinations of state variables quite well, but this is not apparent from a glance at the error covariance matrix. It is shown here that the eigenvalues and eigenvectors of the error covariance matrix, when properly normalized, can provide useful information about the observability of the system.     

Porous Tube Plant Nutrient Delivery System development: a device for nutrient delivery in microgravity.

The Porous Tube Plant Nutrient Delivery System or PTPNDS (U.S. Patent #4,926,585) has been under development for the past six years with the goal of providing a means for culturing plants in microgravity, specifically providing water and nutrients to the roots. Direct applications of the PTPNDS include plant space biology investigations on the Space Shuttle and plant research for life support in Space Station Freedom. In the past, we investigated various configurations, the suitability of different porous materials, and the effects of pressure and pore size on plant growth. Current work is focused on characterizing the physical operation of the system, examining the effects of solution aeration, and developing prototype configurations for the Plant Growth Unit (PGU), the flight system for the Shuttle mid-deck. Future developments will involve testing on KC-135 parabolic flights, the design of flight hardware and testing aboard the Space Shuttle.