Concept for advanced satellite communications and required technologies

The advanced communications technology satellite (ACTS) program of NASA is aimed at the development of high risk technologies that will enable exploiting higher frequency bands and techniques for improving frequency reuse. The technologies under development include multiple beam spacecraft antennas, on-board switching and processing, RF devices and components and advanced Earth stations. The program focus is on the Ka-band (30/20 GHz) as the implementing frequency since it has five times the bandwidth of either the C- or Ku-bands. However, the technology being developed is applicable to other frequency bands as well and will support a wide range of future communications systems required by NASA, other Government agencies and the commercial sector. An overview is presented of an operational 30/20 GHz satellite system that may evolve. How the system addresses service requirements is discussed, and the technology required and being developed is considered

Exploring Code Clones in Programmable Logic Controller Software

The reuse of code fragments by copying and pasting is widely practiced in software development and results in code clones. Cloning is considered an anti-pattern as it negatively affects program correctness and increases maintenance efforts. Programmable Logic Controller (PLC) software is no exception in the code clone discussion as reuse in development and maintenance is frequently achieved through copy, paste, and modification. Even though the presence of code clones may not necessary be a problem per se, it is important to detect, track and manage clones as the software system evolves. Unfortunately, tool support for clone detection and management is not commonly available for PLC software systems or limited to generic tools with a reduced set of features. In this paper, we investigate code clones in a real-world PLC software system based on IEC 61131-3 Structured Text and C/C++. We extended a widely used tool for clone detection with normalization support. Furthermore, we evaluated the different types and natures of code clones in the studied system and their relevance for refactoring. Results shed light on the applicability and usefulness of clone detection in the context of industrial automation systems and it demonstrates the benefit of adapting detection and management tools for IEC 611313-3 languages.Comment: 8 pages, 2 figures, 2 tables, COMET Center SCCH (FFG #844597), etfa201

Low-thrust orbit raising in continuous sunlight while thrusting in a plane perpendicular to the earth-sun line

Low-thrust orbit raising in continuous sunlight during satellite thrusting in plane perpendicular to earth-sun lin

Study of extraterrestrial disposal of radioactive wastes. Part 1: Space transportation and destination considerations for extraterrestrial disposal of radioactive wastes

A feasibility study of extraterrestrial disposal of radioactive waste is reported. This report covers the initial work done on only one part of the NASA study, that evaluates and compares possible space destinations and space transportation systems. The currently planned space shuttle was found to be more cost effective than current expendable launch vehicles by about a factor of 2. The space shuttle requires a third stage to perform the waste disposal missions. Depending on the particular mission, this third stage could be either a reusable space tug or an expendable stage such as a Centaur

Telecommunications forecast for ITU Region 2 to the year 1995

Telecommunications activity was studied. The primary objective was to forecast the need for fixed service satellites (FSS) by countries within ITU Region 2 excluding the United States and Greenland. Forecasts of telecommunications equipment needs were developed as a yardstick of the relative level of telecommunications activity among developing countries within the region. A likely scenario for the implementation of domestic and regional communications satellites is forecasted to provide services to and among countries in ITU Region 2. By 1995, it is forecast that 15 fixed service satellites will be implemented. A forecast of the countries requirements indicates that, with the possible exception of Canada, this constellation of satellites will meet these countries' needs to beyond the year 2000

Wide area coverage radar imaging satellite for earth applications

A preliminary study was made of a radar imaging satellite for earth applications. A side-looking synthetic-aperture radar was considered and the feasibility of obtaining a wide area coverage to reduce the time required to image a given area was investigated. Two basic approaches were examined; low altitude sun-synchronous orbits using a multibeam/multifrequency radar system and equatorial orbits up to near-synchronous altitude using a single beam system. Surveillance and mapping of ice on the Great Lakes was used as a typical application to focus the study effort

Analytical sun synchronous low-thrust manoeuvres

Article describes analytical sun synchronous low-thrust manoeuvres

The Economic Impacts of Wolves on Calf Production on Western Montana Cattle Ranches Beyond Direct Depredation

A novel sample of 18 western Montana cow-calf ranching operations were analyzed over a 16 year time period (1995-2010) using an ordinary least squares linear regression estimation model with robust standard errors focused on the potential effects wolves may have on average calf weight gain. Incorporating calf sex, calf breed, ranch, and year fixed effects into the estimation model, a vector of variables that changed both across ranches and over time were used to significantly explain (F = 59.32; p \u3c 0.001) the variation in yearly average calf weaning weights on sample ranches with fairly good accuracy (R2 = 0.846). The use of hormone implanting (â=24.5), calf age (â=.34), annual aggregate precipitation (â=2.16), annual aggregate snowfall (â=-0.24), annual average temperature (â=4.27), and the standard deviation of NDVI (â=1.67) were found to be significant at least at the .1 level. One measure used to account for wolf presence on sample ranches based on yearly estimated wolf home range data from Montana Fish, Wildlife & Parks was found to have an insignificant effect on average calf weight (p = .569). The other measure used to account for wolf presence on sample ranches was found to be a significant factor on calf weight gain. On average, sample ranches that experienced at least one Wildlife Service (WS) confirmed wolf depredation on the ranch, weaned calves that were approximately 20 pounds lighter than ranches that did not have a WS confirmed wolf depredation in the same year, holding all else constant. The results suggest that calves on western Montana ranches that experience at least one WS wolf depredation in a year gain 20 pounds less weight than if there hadn’t been a WS confirmed wolf kill which directly correlates to decreased economic revenue received by affected ranchers