Interplanetary navigation using pulsating radio sources

Radio beacons with distinguishing signatures exist in nature as pulsating radio sources (pulsars). These objects radiate well determined pulse trains over hundreds of megahertz of bandwidth at radio frequencies. Since they are at known positions, they can also be used as navigation beacons in interplanetary space. Pulsar signals are weak and dispersive when viewed from earth. If an omnidirectional antenna is connected to a wideband receiver (200 MHz bandwidth centered at 200 MHz) in which dispersion effects are removed, nominal spacecraft position errors of 1500 km can be obtained after 24 h of signal integration. An antenna gain of 10 db would produce errors as low as 150 km. Since the spacecraft position is determined from the measurement of the phase of a periodic signal, ambiguities occur in the position measurement. Simultaneous use of current spacecraft navigation schemes eliminates these ambiguities

Conducting a Self-Assessment of a Long-Term Archive for Interdisciplinary Scientific Data as a Trustworthy Digital Repository

4th International Conference on Open RepositoriesThis presentation was part of the session : Conference PresentationsDate: 2009-05-19 03:00 PM – 04:30 PMLong-term preservation and stewardship of scientific data and research-related information is paramount to the future of science and scholarship. Disciplinary and interdisciplinary scientific data archives can offer capabilities for managing and preserving data for research, education, and decision-making activities of future communities representing various scientific and scholarly disciplines. However, meeting the requirements for a trusted digital repository presents challenges to ensure that archived collections will be discoverable, accessible, and usable in the future. Assessing whether scientific data archives meet the requirements for trustworthy repositories will help to ensure that todayâ s collections of scientific data will be available in the future. A continuing self-assessment of a long-term archive for interdisciplinary scientific data is being conducted to identify improvements needed to become a trustworthy repository for managing and providing access to interdisciplinary scientific data by future communities of users. Recommendations are offered for archives of scientific data to meet the requirements of a trustworthy repository.NAS

Techniques for measuring arrival times of pulsar signals 1: DSN observations from 1968 to 1980

Techniques used in the ground based observations of pulsars are described, many of them applicable in a navigation scheme. The arrival times of the pulses intercepting Earth are measured at time intervals from a few days to a few months. Low noise, wide band receivers, amplify signals intercepted by 26 m, 34, and 64 m antennas. Digital recordings of total received signal power versus time are cross correlated with the appropriate pulse template

Planetary radar

The radar astronomy activities supported by the Deep Space Network are reported. The high power S- and X-band radar transmitters at the Goldstone 64 meter station were used for a radar probe of Mars during January, February, and March 1980, which was designed to provide range and Doppler data derived from signals reflected from the Martian surface, taking advantage of the planet's nearness during opposition

Detection of plant stress through multispectral photography

There are no author-identified significant results in this report

Mars: Seasonally variable radar reflectivity

The 1971/1973 Mars data set acquired by the Goldstone Solar System Radar was analyzed. It was established that the seasonal variations in radar reflectivity thought to occur in only one locality on the planet (the Solis Lacus radar anomaly) occur, in fact, over the entire subequatorial belt observed by the Goldstone radar. Since liquid water appears to be the most likely cause of the reflectivity excursions, a permanent, year-round presence of subsurface water (frozen or thawed) in the Martian tropics can be inferred

Development of a State-Space Aeroelastic Model of a Flexible T-Tail Aircraft for Flutter Analysis

Flutter prediction is an important part of the preliminary design process of any new aircraft. Current analysis methods include coupled fluid structure interaction codes and doublet lattice panel codes. The computation resources and time required for CFD solutions makes them unattractive for preliminary design and doublet lattice models require considerable pre and post processing to provide satisfactory results. Thus, a process for developing an analytical model to facilitate rapid design changes and the implementation of active control systems is the main motivation of this thesis. An analytical model is developed by first deriving the equations of motion of the structure for unforced vibration. Then the generalized aerodynamic forcing functions for incompressible, compressible subsonic, and supersonic flow are derived. Next, Roger’s Approximation is used to form a state-space model that describes the forced vibration of the system. The results of the normal mode calculations show that the process used to model the T-tail can accurately predict the unforced vibrational characteristics of the system. The flutter results show that the process developed in this thesis yields a conservative estimation of the flutter dynamic pressure while still capturing the behavior of the transonic dip

Analysis of data systems requirements for global crop production forecasting in the 1985 time frame

Data systems concepts that would be needed to implement the objective of the global crop production forecasting in an orderly transition from experimental to operational status in the 1985 time frame were examined. Information needs of users were converted into data system requirements, and the influence of these requirements on the formulation of a conceptual data system was analyzed. Any potential problem areas in meeting these data system requirements were identified in an iterative process

A procedure used for a ground truth study of a land use map of North Alabama generated from LANDSAT data

A land use map of a five county area in North Alabama was generated from LANDSAT data using a supervised classification algorithm. There was good overall agreement between the land use designated and known conditions, but there were also obvious discrepancies. In ground checking the map, two types of errors were encountered - shift and misclassification - and a method was developed to eliminate or greatly reduce the errors. Randomly selected study areas containing 2,525 pixels were analyzed. Overall, 76.3 percent of the pixels were correctly classified. A contingency coefficient of correlation was calculated to be 0.7 which is significant at the alpha = 0.01 level. The land use maps generated by computers from LANDSAT data are useful for overall land use by regional agencies. However, care must be used when making detailed analysis of small areas. The procedure used for conducting the ground truth study together with data from representative study areas is presented