Artificial gravity

The use of artificial gravity in extended space flight is reviewed. Topics examined include synergistic factors, gravity loading, gravity magnitude, uniformity of gravity field, and effects of slow rotation.     

Radiation protection in space

Radiation environment, basic concepts of radiation protection, and specific aspects of the space radiation field are reviewed. The discussion of physico-chemical and subcellular radiation effects includes mechanisms of radiation action and cellular consequences. The discussion of radiobiological effects includes unique aspects of HZE particle effects, space flight findings, terrestrial findings, analysis of somatic radiation effects and effects on critical organs, and early and delayed effects. Other topics include the impact of the space flight environment, measurement of radiation exposure, establishing radiation protection limits, limitations in establishing space-based radiation exposure limits, radiation protection measures, and recommendations.     

An objective determination of +Gz acceleration tolerance

Until recently, human +Gz acceleration tolerance has relied solely on subjective criteria relating to loss of vision. By use of newly developed noninvasive instrumentation using a transcutaneous Doppler flow system, objective end point criteria have been developed based on measured blood flow to the head. The system consists of miniature 8 MHz Doppler sensors (2 x 1 x 0.5 cm) placed on the forehead over both frontal branches of the temporal arteries to detect blood flow velocity from back scattered ultrasound. Its use has allowed for correlation of altered, decreased and actual reversal of eye level blood flow with subsequent central light loss. Over 100 subjects have now been studied during more than 2,000 centrifuge runs. Objective changes in temporal artery flow velocity consistently preceded visual degradation for each subject during all acceleration profiles. No subject has gone unconscious without first exhibiting a minimum 6 sec of total flow cessation. Retrograde flow followed by complete flow cessation always preceded central light loss. Results indicate that this method can be successfully used with a wide variety of tasks during exposure to +Gz acceleration. It is recommended for use during evaluation of protective maneuvers or devices on the centrifuge or during actual flight in high performance aircraft. It may also serve as a potential safety monitor during space Shuttle re-entry if there is doubt about a passenger's cardiovascular status.     

Introduction

The introduction to a special issue on weightlessness countermeasures provides a brief overview of weightlessness countermeasures and examines the physiology of spaceflight, which includes short- and long-term effects of weightlessness and physiological adaptation.     

A Method of Trigonometric Interpolation for Processing Radio Direction-Finding Signals

Radio direction-finding techniques that use amplitude-trigonometric interpolation between signals received at a circular antenna array are reexamined. The accuracy of this class of direction-finding system is limited by interpolation, gain mistracking, and additive-noise errors. The channel gain mistracking error is shown to be significantly lower than previously estimated. Typical calculations show that the trigonometric interpolation technique is an order of magnitude more accurate than previously supposed.