How many Earth-approaching asteroids are there?

The discovery process of Earth-approaching asteroids is formulated as a periodic sampling problem from an urn with replacement. It presumes as unchanging number of such objects over recent historical times, a fixed limiting magnitude/angular speed combination for detection probability, and allows for the possibility of the lack of detection or the lack of sufficient observations to refine an orbit at the first noticed apparition. While simple, the model is sufficiently powerful to show that an estimate of the number of Earth-approaching minor planets is impossible. This conclusion is insensitive to uncertainties in perturbing influences, celestial mechanics, or a model for the distribution of the orbital element sets of these minor planets

An analysis of the Hubble Space Telescope fine guidance sensor fine lock mode

There are two guiding modes of the Hubble Space Telescope (HST) used for the acquisition of astronomical data by one of its six scientific instruments. The more precise one is called Fine Lock. Command and control problems in the onboard electronics has limited Fine Lock to brighter stars, V less than 13.0 mag, instead of fulfilling its goal of V = 14.5 mag. Consequently, the less precise guiding mode of Coarse Track (approximately 40 milli-arc seconds) has to be used fairly frequently. Indeed, almost half of the scientific observations to have been made with the HST will be compromised. The only realistic or extensive simulations of the Fine Lock guidance mode are reported. The theoretical analysis underlying the Monte Carlo experiments and the numerical computations clearly show both that the control electronics are severely under-engineered and how to adjust the various control parameters to successfully extend Fine Lock guiding performance back to V = 14.0 mag and sometimes beyond

Optimal searches for asteroids

Optimal searches for a fixed object are discussed, and the rigorous analytical results of discrete search theory are presented. The totally optimal, the uniformly optimal, the locally optimal, and the fastest searches are shown to be identical under not too restrictive assumptions. The mathematical formalism is illustrated by an Earth-approaching asteroid search and optimal searches for such objects are explicitly constructed. The approximation that Earth-approaching asteroids are fixed is equivalent to having a very high ( equiv 100 sq degs/hour) search rate. Generalizations to other types of astronomical search are briefly mentioned

The discovery circumstances of Earth-approaching asteroids

The discovery circumstances are analyzed for all Earth-approaching asteroids detected in the last twenty-four years. In particular, topocentric angular velocities, opposition distance, geocentric and heliocentric distances, phase angle, and lunar phase at discover were calculated in an effort to separate any selection effects between chance and purposeful (i.e., as the result of a systematic search) discoveries. Another motivation was the possibility of discerning useful clues how to search more efficiently for such objects. There are 60 minor planets in the sample. The principal result is that the discovery of Earth-approaching asteroids is dominated by serendipity. Therefore, searching for them at the current relatively bright limits at less than a very high rate seems pointless

A search for Earth-crossing asteroids

Improvements made in both resolution element size and sensitivity in EBSICON cameras are discussed. An up-to-date illustration of what an asteroid detection now looks like is provided. Shown are four phases during the realignment of the live (white) and reference (black) frames. As one passes through the sequence the stars' images overlap and become grey, while the displaced images of the asteroid do not cancel

Gamma ray burst astrometry 2: Numerical tests

Since the announcement of the discovery of sources of gamma ray radiation in 1973, many more reports of such bursts have been published. Numerous artificial satellites have been equipped with gamma ray detectors including GRO. Unfortunately, almost no progress has been made in identifying the sources of this high energy radiation. Only one visible counterpart is known. It is suspected that this is a consequence of the methods currently used to define gamma ray burst source 'error boxes'. An alternative procedure was proposed in 1988 by Taff. Herein, Monte Carlo simulations are reported of the efficacy of this technique using realistic burst timing uncertainties and satellite location errors as well as a variety of satellite constellations. Since these are controlled numerical experiments, the dependence is examined of the statistics of the errors in the deduced burst wavefront normal as a function of the timing inconsistencies, detector location standard deviations, and especially the number and distribution of the detectors. The results clearly show that an arc minute prediction of a unique burst location is routinely obtainable once there are at least two interplanetary detectors

Analyzing Space-Based Interferometric Measurements of Stars and Network Measurements of Gamma-Ray Bursts

Since the announcement of the discovery of sources of bursts of gamma-ray radiation in 1973, hundreds more reports of such bursts have now been published. Numerous artificial satellites have been equipped with gamma-ray detectors including the very successful Compton Gamma Ray Observatory BATSE instrument. Unfortunately, we have made no progress in identifying the source(s) of this high energy radiation. We suspected that this was a consequence of the method used to define gamma-ray burst source "error boxes." An alternative procedure to compute gamma-ray burst source positions, with a purely physical underpinning, was proposed in 1988 by Taff. Since then we have also made significant progress in understanding the analytical nature of the triangulation problem and in computing actual gamma-ray burst positions and their corresponding error boxes. For the former, we can now mathematically illustrate the crucial role of the area occupied by the detectors, while for the latter, the Atteia et al. (1987) catalog has been completely re-reduced. There are very few discrepancies in locations between our results and those of the customary "time difference of arrival" procedure. Thus, we have numerically demonstrated that the end result, for the positions, of these two very different-looking procedures is the same. Finally, for the first time, we provide a sample of realistic "error boxes" whose non-simple shapes vividly portray the difficulty of burst source localization

A search for Earth-crossing asteroids, supplement

The ground based electro-optical deep space surveillance program involves a network of computer controlled 40 inch 1m telescopes equipped with large format, low light level, television cameras of the intensified silicon diode array type which is to replace the Baker-Nunn photographic camera system for artificial satellite tracking. A prototype observatory was constructed where distant artificial satellites are discriminated from stars in real time on the basis of the satellites' proper motion. Hardware was modified and the technique was used to observe and search for minor planets. Asteroids are now routinely observed and searched. The complete observing cycle, including the 2"-3" measurement of position, requires about four minutes at present. The commonality of asteroids and artificial satellite observing, searching, data reduction, and orbital analysis is stressed. Improvements to the hardware and software as well as operational techniques are considered

Managing Cultural Resources On The Alaska Peninsula

Twentieth-century cultural resources provide physical evidence of human relationships with a landscape that has shaped the wilderness areas we know today. These cultural resources enrich the meaning of an area as wilderness, but also present multiple management challenges surrounding visitor use in designated wilderness areas. The National Geographic Society Katmai Expeditions of the 1910s present a case study of how historic trails and their associated artifacts interact not only with present issues toward the dual-enforcement of the National Historic Preservation Act and Wilderness Act, but also with the management of visitor use along a corridor containing relatively recent traces of historically significant activities and events. This study draws on the findings of a 2 018 expedition identifying convergence of a historically significant trail w ith a popular path for backpackers through the Katmai Wilderness and explores the importance of cultural resources in long-distance trail planning and cultural resource management in designated wilderness

Occupational Therapy Student Characteristics Influencing Level II Fieldwork: An Exploratory Study of Mental Health, Confidence, and Mindful Self-Care

Level II fieldwork serves as a critical component of occupational therapy (OT) student education during which students develop and refine skills to become practicing clinicians; however, research on student characteristics that influence the fieldwork experience is limited. The purpose of this study was to explore student mental health, confidence, and mindful self-care practices throughout Level II fieldwork. Ten OT students completing Level II fieldwork participated in this study by completing surveys during the first week, midpoint, and final two weeks of their second Level II fieldwork experience. Each survey contained Cohen’s Perceived Stress Scale (PSS-10), the Student Confidence Questionnaire, and the Mindful Self-Care Scale (MSCS)-SHORT to investigate student stress, confidence, and self-care respectively. Kruskal-Wallis H tests revealed that stress was highest during the first two weeks of fieldwork, confidence increased significantly from the beginning to the end of fieldwork, and self-care practices remained stable over time. Additionally, correlation analyses revealed a positive relationship between confidence and self-care (rs = 0.78, p \u3c 0.01), a negative relationship between stress and confidence (rs = -0.78, p \u3c 0.01), and a negative relationship between self-care and stress (rs = -0.69, p = 0.03). These results have implications for OT students, educators, and fieldwork supervisors as stress reduction techniques and confidence building may be beneficial for student outcomes before and during Level II fieldwork to maximize success through this transitional period from student to clinician