GPS modeling for designing aerospace vehicle navigation systems

The complexity of the design of a Global Positioning System (GPS) user segment, as well as the performance demanded of the components, depends on user requirements such as total navigation accuracy. Other factors, for instance the expected satellite/vehicle geometry or the accuracy of an accompanying inertial navigation system can also affect the user segment design. Models of GPS measurements are used to predict user segment performance at various levels. Design curves are developed which illustrate the relationship between user requirements, the user segment design, and component performance     

Nickel-Cadmium Batteries as Capacitive Filters for Pulsed Loads

This investigation consisted of several tests of specially fabricated nickel-cadmium batteries having circular disk-type electrodes. These batteries were evaluated as filter elements between a constant current power supply and a 5 Hz pulsed load demanding approximately twice the power supply current during the load on a portion of the cycle. Short tests lasting 104 cycles were conducted at up to a 21 C rate and an equivalent energy density of over 40 J/Ib. In addition, two batteries were subjected to 10h dischar cycles, one at a 6.5 C rate and the other at a 13 C rate. Assuming an electrode-to-battery weight ratio of 0.5, these tests represent an energy density of about 7 and 14 J/Ib, respectively. Energy density, efficiency, capacitance, average voltage, and available capacity were tracked during these tests. After 10y capacity degradation was negligible for one battery and about 20 percent for the other. Cadmium electrode failure may be the factor limiting lifetime at extremely low depth of discharge cycling. The output was examined and a simple equivalent circuit was proposed.     

Extraction of mineral elements from inedible wastes of biological components of a life-support system and their utilization for plant nutrition.

Two methods of extracting mineral elements from otherwise deadlock products of a life-support system are presented. We describe first optimum conditions for recovering elements by water extraction from dry wastes of plants, biomass ash, and solid human wastes after passing them through the catalytic furnace; and, second, we describe acid extracts of biogenous elements by 1N and 2N HNO3 from these products. Ways to use the extracts of elements in plant nutrition are considered in order to increase the extent to which the mineral loop of a life-support system can be closed.     

Approximate qualitative spatial reasoning

Qualitative relations between spatial regions play an importantrole in the representation and manipulation of spatial knowledge.The RCC5 and RCC8 systems of relations,used in the Region-Connection Calculus, are of fundamentalimportance. These two systems deal with ideal regions havingprecisely determined location. However,in many practical examples of spatial reasoning,regions are represented by finite approximations rather than known precisely.Approximations may be given by describing how a regionrelates to cells forming a partition of the space underconsideration. Although the RCC5 and RCC8 systems have beengeneralized to ``egg-yolk' regions, in order to modelcertain types of vagueness, their extension to regionsapproximated in this way has not been discussed before.This paper presents two methods, the syntactic and the semantic, by which the RCC5 and RCC8 systemsmay be defined for approximate regions. The syntactic uses algebraicoperations on approximate regions which generalize operations on preciseregions. The semantic method makes use of the set of preciseregions which could be the intended interpretation of anapproximate region. Relationships between these two methods arediscussed in detail.alternative to navigation training with a map.     

Performance of a centrifugal phytotron.

It is possible to cultivate plants under an artificial gravity field generated by a centrifugal device in space. In order to determine an optimal magnitude of gravity, there is a need to investigate the relationship between plant and growth and gravity, including not only reduced gravity but also gravity greater than 1G. A prototype centrifugal phytotron was designed and fabricated in order to investigate the relationship between plant growth and increased gravity. This device enables us to cultivate plants over the long term by controlling environmental conditions in the phytotron such as temperature, relative humidity, CO2 concentration and light intensity. The results of our experiment indicate that plant seeds can germinate and grow even under an artificial gravity which changes sinusoidally from 2G to 4G.     

A computer network with SCADA and case tools for on-line process control in greenhouses.

Climate control computers in greenhouses are used to control heating and ventilation, supply water and dilute and dispense nutrients. They integrate models into optimally controlled systems. This paper describes how information technology, as in use in other sectors of industry, is applied to greenhouse control. The introduction of modern software and hardware concepts in horticulture adds power and extra oppurtunities to climate contol in greenhouses.     

Landsat-4 orbit determination using TDRSS

This paper presents the results of a study to compare the orbit determination accuracy for a Tracking and Data Relay Satellite (TDRS) System (TDRSS)-user spacecraft, Landsat-4, obtained using a Prototype Filter Smoother (PFS), with the accuracy of an established batch-least-squares system, the Goddard Trajectory Determination System (GTDS). The results of Landsat-4 orbit determination provide useful experience for the Earth Observing System (EOS) series of satellites. The filtered and smoothed PFS orbit solutions were compared with the definitive GTDS orbit solutions for Landsat-4; the root-mean-square (RMS) solution difference was 6.6 meters.     

Application of ISFETs in closed-loop systems for greenhouses.

In horticulture, growing in artificial substrates such as rockwool is more and more considered to be a sound alternative to growing in soil. This development enables the opportunity to create closed-loop systems which lower the waste of raw materials and reduce pollution of the environment. Applying closed-loop systems needs precise knowledge of the composition of the recirculating nutrient solution. This paper presents basic principles of a measuring system, which can monitor continuously the concentration of nutrients in water. The system is based on ion-selective field effect transistors (ISFETs). By appropriate calibration, a high accuracy is achieved for pH and potassium measurements in the nutrient solution. An accuracy of better than 10% (mMol/l) has been achieved.     

Consideration in selecting crops for the human-rated life support system: a Linear Programming model.

A Linear Programming model has been constructed which aids in selecting appropriate crops for CELSS (Controlled Environment Life Support System) food production. A team of Controlled Environment Agriculture (CEA) faculty, staff, graduate students and invited experts representing more than a dozen disciplines, provided a wide range of expertise in developing the model and the crop production program. The model incorporates nutritional content and controlled-environment based production yields of carefully chosen crops into a framework where a crop mix can be constructed to suit the astronauts' needs. The crew's nutritional requirements can be adequately satisfied with only a few crops (assuming vitamin mineral supplements are provided) but this will not be satisfactory from a culinary standpoint. This model is flexible enough that taste and variety driven food choices can be built into the model.