Analysis of random signal combinations for spacecraft pointing stability

Methods for obtaining the probability density function of random signal combustions are discussed. These methods provide a realistic criteria for the design of control systems subjected to external noise with several important applications for aerospace problems

Image dissector camera system study

Various aspects of a rendezvous and docking system using an image dissector detector as compared to a GaAs detector were discussed. Investigation into a gimbled scanning system is also covered and the measured video response curves from the image dissector camera are presented. Rendezvous will occur at ranges greater than 100 meters. The maximum range considered was 1000 meters. During docking, the range, range-rate, angle, and angle-rate to each reflector on the satellite must be measured. Docking range will be from 3 to 100 meters. The system consists of a CW laser diode transmitter and an image dissector receiver. The transmitter beam is amplitude modulated with three sine wave tones for ranging. The beam is coaxially combined with the receiver beam. Mechanical deflection of the transmitter beam, + or - 10 degrees in both X and Y, can be accomplished before or after it is combined with the receiver beam. The receiver will have a field-of-view (FOV) of 20 degrees and an instantaneous field-of-view (IFOV) of two milliradians (mrad) and will be electronically scanned in the image dissector. The increase in performance obtained from the GaAs photocathode is not needed to meet the present performance requirements

Health behavior during periods of stressful uncertainty: associations with emotions, cognitions, and expectation management.

Objective: The present study examined how cognitions and emotions characteristic of awaiting uncertain news influenced healthy (diet/exercise) and unhealthy (alcohol use) behaviors in three samples of people awaiting important news.Design: Study 1 examined voting-eligible citizens during the month prior to learning the results of the 2016 U.S. presidential election. Study 2 examined the experience of law graduates across four months while they awaited the results of their bar exam (i.e., the licensing exam they need to pass to practice law). Study 3 examined current or recent PhD students searching for a job on the academic job market.Results: Though the findings were somewhat mixed across studies, they generally suggest a relationship between positive emotions and health-promoting behaviors and between worry and alcohol use, with less consistent relationships between outcome expectations and health behaviors.Conclusion: Taken together, these results offer a promising set of initial findings to understand health behavior in the context of awaiting uncertain news and provide a foundation for future investigations on the topic

Bracing Later and Coping Better: Benefits of Mindfulness During a Stressful Waiting Period.

People frequently await uncertain news, yet research reveals that the strategies people naturally use to cope with uncertainty are largely ineffective. We tested the role of mindfulness for improving the experience of a stressful waiting period. Law graduates awaiting their bar exam results either reported their trait mindfulness (Study 1; N = 150) or were instructed to practice mindfulness meditation (Study 2; N = 90). As hypothesized, participants who were naturally more mindful or who practiced mindfulness managed their expectations more effectively by bracing for the worst later in the waiting period and perceived themselves as coping better. Additionally, participants who were low in dispositional optimism and high in intolerance of uncertainty benefited most from mindfulness (relative to control) meditation. These findings point to a simple and effective way to wait better, particularly for those most vulnerable to distress

On the evolution of non-axisymmetric viscous fibres with surface tension, inertia and gravity

We consider the free boundary problem for the evolution of a nearly straight slender fibre of viscous fluid. The motion is driven by prescribing the velocity of the ends of the fibre, and the free surface evolves under the action of surface tension, inertia and gravity. The three-dimensional Navier-Stokes equations and free-surface boundary conditions are analysed asymptotically, using the fact that the inverse aspect ratio, defined to be the ratio between a typical fibre radius and the initial fibre length, is small. This first part of the paper follows earlier work on the stretching of a slender viscous fibre with negligible surface tension effects. The inclusion of surface tension seriously complicates the problem for the evolution of the shape of the cross-section. We adapt ideas applied previously to two-dimensional Stokes flow to show that the shape of the cross-section can be described by means of a conformal map which depends on time and distance along the fibre axis. We give some examples of suitable relevant maps and present numerical solutions of the resulting equations. We also use analytic methods to examine the coupling between stretching and the evolution of the cross-section shape

ST/STIS Spectroscopy of the White Dwarfs in the Short-Period Dwarf Novae LL And and EF Peg

We present new HST/STIS observations of the short-period dwarf novae LL And and EF Peg during deep quiescence. We fit stellar models to the UV spectra and use optical and IR observations to determine the physical parameters of the whitedwarfs in the systems, the distances to the binaries, and the properties of thesecondary stars. Both white dwarfs are relatively cool, having T_{eff} near 15000K, and consistent with a mass of 0.6 M-sun. The white dwarf in LL And appears to be of solar abundance or slightly lower while that in EF Peg is near 0.1-0.3 solar. LL And is found to be 760 pc away while EF Peg is closer at 380 pc. EF Peg appears to have an ~M5V secondary star, consistent with that expected for its orbital period, while the secondary object in LL And remains a mystery.Comment: Accepted in Ap

Graphical techniques to assist in pointing and control studies of orbiting spacecraft

Computer generated graphics are developed to assist in the modeling and assessment of pointing and control systems of orbiting spacecraft. Three-dimensional diagrams are constructed of the Earth and of geometrical models which resemble the spacecraft of interest. Orbital positioning of the spacecraft model relative to the Earth and the orbital ground track are then displayed. A star data base is also available which may be used for telescope pointing and star tracker field-of-views to visually assist in spacecraft pointing and control studies. A geometrical model of the Hubble Space Telescope (HST) is constructed and placed in Earth orbit to demonstrate the use of these programs. Simulated star patterns are then displayed corresponding to the primary mirror's FOV and the telescope's star trackers for various telescope orientations with respect to the celestial sphere

Generation of pseudo-random numbers

Practical methods for generating acceptable random numbers from a variety of probability distributions which are frequently encountered in engineering applications are described. The speed, accuracy, and guarantee of statistical randomness of the various methods are discussed

A stochastic model for photon noise induced by charged particles in multiplier phototubes of the space telescope fine guidance sensors

The Space Telescope (ST) is subjected to charged particle strikes in its space environment. ST's onboard fine guidance sensors utilize multiplier phototubes (PMT) for attitude determination. These tubes, when subjected to charged particle strikes, generate spurious photons in the form of Cerenkov radiation and fluorescence which give rise to unwanted disturbances in the pointing of the telescope. A stochastic model for the number of these spurious photons which strike the photocathode of the multiplier phototube which in turn produce the unwanted photon noise are presented. The model is applicable to both galactic cosmic rays and charged particles trapped in the Earth's radiation belts. The model which was programmed allows for easy adaption to a wide range of particles and different parameters for the phototube of the multiplier. The probability density functions for photons noise caused by protons, alpha particles, and carbon nuclei were using thousands of simulated strikes. These distributions are used as part of an overall ST dynamics simulation. The sensitivity of the density function to changes in the window parameters was also investigated