Satellite communications for disaster relief operations

The use of existing and planned communication satellite systems to provide assistance in the implementation of disaster relief operations on a global basis was discussed along with satellite communications system implications and their potential impact on field operations in disaster situations. Consideration are given to the utilization of both INTELSAT and MARISAT systems operating at frequencies ranging from 1.5 to 4 GHz and to the size and type of ground terminals necessary for satellite access. Estimates of communication requirements for a global system are given. Some discussion of cost estimates for satellite services to support operations are included. Studies of communication satellites for both pre and post disaster applications conducted for NOAA are included as well as recent experiments conducted in conjunction with the Office of Foreign Disaster Assistance of the Agency for International Development

The 30/20 GHz experimental communications satellite system

NASA is continuing to pursue an agressive satellite communications technology development program focused on the 30/20 GHz frequency band. A review of the program progress to date is presented. Included is a discussion of the technology program status as well as a description of the experimental system concept under study. Expected system performance characteristics together with spacecraft and payload configuration details including weight and power budget is presented. Overall program schedules of both the technology development and the flight system development are included

The Influence of Swirl Brakes and a Tip Discharge Orifice on the Rotordynamic Forces Generated by Discharge-to-Suction Leakage Flows in Shrouded Centrifugal Pumps

This paper reports on experiments conducted in the Rotor Force Test Facility at the California Institute of Technology to examine the effects of a tip leakage restriction and swirl brakes on the rotordynamic forces due to leakage flows on an impeller undergoing a prescribed circular whirl. The experiments simulate the leakage flow conditions and geometry of the Alternate Turbopump Design (ATD) of the Space Shuttle High Pressure Oxygen Turbopump and are critical to evaluating the pump's instability problems. Results indicate the detrimental effects of a discharge orifice and the beneficial effects of adding swirl brakes. Plots of the tangential and normal forces versus whirl frequency ratio show a substantial increase in these forces along with destabilizing resonances when a discharge orifice is added. When swirl brakes are added, some of the detrimental effects of the orifice are reduced. For the tangential force, a significant reduction occurs and a destabilizing resonance appears to be eliminated. For the normal force, although the overall force is not reduced, once again a destabilizing resonance appears to be eliminated

Satellites using the 30/20 GHz band

A review of the future options open to satellite system planners focuses attention on the use of the 30/20 GHz band. Very broad bandwidths available, coupled with a primary allocation for fixed satellite service, make the band very attractive. NASA, in concert with the system and service supplier industries, is planning a research and development program aimed at flight demonstration of 30/20 satellite systems which it is hoped will lead to operational system use in the early 1990's. The communication system concepts and the spacecraft systems necessary to support these for operational use in 1990 and beyond are discussed

The Influence of Swirl Brakes on the Rotordynamic Forces Generated by Discharge-to-Suction Leakage Flows in Centrifugal Pumps

Increasing interest has been give to swirl brakes as a means of reducing destabilizing rotordynamic forces due to leakage flows in new high speed rocket turbopumps. Although swirl brakes have been used successfully in practice (such as with the Space Shuttle HPOTP), no experimental test until now have been performed to demonstrate their beneficial effect over a range of leakage flow rates. The present study investigates the effect of swirl brakes on rotordynamic forces generated by discharge-to-suction leakage flows in the annulus of shrouded centrifugal pumps over a range of subsynchronous whirl ratios and various leakage flow rates. In addition, the effectiveness of swirl brakes in the presence of leakage inlet (pump discharge) swirl is also demonstrated. The experimental data demonstrates that with the addition of swirl brakes a significant reduction in the destabilizing tangential force for lower flow rates is achieved. At higher flow rates, the brakes are detrimental. In the presence of leakage inlet swirl, brakes were effective over all leakage flow rates tested in reducing the range of whirl frequency ratio for which the tangential force is destabilizing

Laser Velocimeter Measurements in the Leakage Annulus of a Whirling Shrouded Centrifugal Pump

Previous experiments conducted in the Rotor Force Test Facility at the California Institute of Technology have thoroughly examined the effect of leakage flows on the rotordynamic forces on a centrifugal pump impeller undergoing a prescribed circular whirl. These leakage flows have been shown to contribute substantially to the total fluid induced forces acting on a pump. However, to date nothing is known of the flow field in the leakage annulus of shrouded centrifugal pumps. No attempt has been made to qualitatively or quantitatively examine the velocity field in the leakage annulus. Hence the test objective of this experiment is to acquire fluid velocity data for a geometry representative of the leakage annulus of a shrouded centrifugal pump while the rotor is whirling using laser velocimetry. Tests are performed over a range of whirl ratios and a flowrate typical of Space Shuttle Turbopump designs. In addition to a qualitive study of the flow field, the velocity data can be used to anchor flow models

Comparison of Rocket Performance using Exhaust Diffuser and Conventional Techniques for Altitude Simulation

A rocket engine with an exhaust-nozzle area ratio of 25 was operated at a constant chamber pressure of 600 pounds per square inch absolute over a range of oxidant-fuel ratios at an altitude pressure corresponding to approximately 47,000 feet. At this condition, the nozzle flow is slightly underexpanded as it leaves the nozzle. The altitude simulation was obtained first through the use of an exhaust diffuser coupled with the rocket engine and secondly, in an altitude test chamber where separate exhauster equipment provided the altitude pressure. A comparison of performance data from these two tests has established that a diffuser used with a rocket engine operating at near-design nozzle pressure ratio can be a valid means of obtaining altitude performance data for rocket engines

A population-based study of glutathione-S-transferase M1, T1 and P1 genotypes

A retrospective study on healthy, unrelated subjects was conducted in order to estimate population glutathione-S-transferases (GST) genotype frequencies in Slovak population of men and compare our results with already published data (GSEC project)^1^. A further aim of the study was to evaluate frequencies of the _GST_ polymorphisms also in patients with prostate cancer in order to compare the evaluated proportions with those found in the control subjects. Analysis for the _GST_ gene polymorphisms was performed by PCR and PCR-RFLP. We found that the proportions are not significantly different from those estimated in a European multicentre study or from the results published by another group in Slovakia. We found significantly increased age-standardized prostate cancer prevalence rates in the carriers of _GSTM1_ null genotype (P = 0.037) and trend for such an increase in the carriers of _GSTP1_ polymorphism when compared with the respective groups of non-carriers. Because understanding of the contribution of _GST_ gene polymorphisms and their interactions with other relevant factors may improve screening diagnostic assays for prostate cancer, we discuss issues of study feasibility, study design, and statistical power, which should be taken into account in planning further trials

How Low Should You Go? Low Response Rates and the Validity of Inference in IS Questionnaire Research

We believe IS researchers can and should do a better of job of improving (assuring) the validity of their findings by minimizing nonresponse error. To demonstrate that there is, in fact, a problem, we first present the response rates reported in six well-regarded IS journals and summarize how nonresponse error was estimated and handled in published IS research. To illustrate how nonresponse error may bias findings in IS research, we calculate its impact on confidence intervals. After demonstrating the impact of nonresponse on research findings, we discuss three post hoc remedies and three preventative measures for the IS researcher to consider. The paper concludes with a general discussion about nonresponse and its implications for IS research practice. In our delimitations section, we suggest directions for further exploring external validity