Flight Mechanics/Estimation Theory Symposium 1988

This conference publication includes 28 papers and abstracts presented at the Flight Mechanics/Estimation Theory Symposium on May 10 to 11, 1988. Sponsored by the Flight Dynamics Division of Goddard Space Flight Center, this symposium features technical papers on a wide range of issue related to orbit-attitude prediction, determination and control; attitude sensor calibration; attitude determination error analysis; attitude dynamics; and orbit decay and maneuver strategy. Government, industry, and the academic community participated in the preparation and presentation of these papers

Flight Mechanics/Estimation Theory Symposium, 1991

Twenty-six papers and abstracts are presented. A wide range of issues related to orbit attitude prediction, orbit determination, and orbit control are examined including attitude sensor calibration, attitude dynamics, and orbit decay and maneuver strategy. Government, industry, and the academic community participated in the preparation and presentation of these papers

Flight Mechanics/Estimation Theory Symposium, 1989

Numerous topics in flight mechanics and estimation were discussed. Satellite attitude control, quaternion estimation, orbit and attitude determination, spacecraft maneuvers, spacecraft navigation, gyroscope calibration, spacecraft rendevous, and atmospheric drag model calculations for spacecraft lifetime prediction are among the topics covered

Flight Mechanics/Estimation Theory Symposium, 1990

This conference publication includes 32 papers and abstracts presented at the Flight Mechanics/Estimation Theory Symposium on May 22-25, 1990. Sponsored by the Flight Dynamics Division of Goddard Space Flight Center, this symposium features technical papers on a wide range of issues related to orbit-attitude prediction, determination and control; attitude sensor calibration; attitude determination error analysis; attitude dynamics; and orbit decay and maneuver strategy. Government, industry, and the academic community participated in the preparation and presentation of these papers

Flight Mechanics/Estimation Theory Symposium, 1992

This conference publication includes 40 papers and abstracts presented at the Flight Mechanics/Estimation Theory Symposium on May 5-7, 1992. Sponsored by the Flight Dynamics Division of Goddard Space Flight Center, this symposium featured technical papers on a wide range of issues related to orbit-attitude prediction, determination, and control; attitude sensor calibration; attitude determination error analysis; attitude dynamics; and orbit decay and maneuver strategy. Government, industry, and the academic community participated in the preparation and presentation of these papers

Evolution and Reengineering of NASA's Flight Dynamics Facility (FDF)

The NASA Goddard Space Flight Center's Flight Dynamics Facility (FDF) is a multimission support facility that performs ground navigation and spacecraft trajectory design services for a wide range of scientific satellites. The FDF also supports the NASA Space Network by providing orbit determination and tracking data evaluation services for the Tracking Data Relay Satellite System (TDRSS). The FDF traces its history to early NASA missions in the 1960's, including navigation support to the Apollo lunar missions. Over its 40 year history, the FDF has undergone many changes in its architecture, services offered, missions supported, management approach, and business operation. As a fully reimbursable facility (users now pay 100% of all costs for FDF operations and sustaining engineering activities), the FDF has faced significant challenges in recent years in providing mission critical products and services at minimal cost while defining and implementing upgrades necessary to meet future mission demands. This paper traces the history of the FDF and discusses significant events in the past that impacted the FDF infrastructure and/or business model, and the events today that are shaping the plans for the FDF in the next decade. Today's drivers for change include new mission requirements, the availability of new technology for spacecraft navigation, and continued pressures for cost reduction from FDF users. Recently, the FDF completed an architecture study based on these drivers that defines significant changes planned for the facility. This paper discusses the results of this study and a proposed implementation plan. As a case study in how flight dynamics operations have evolved and will continue to evolve, this paper focuses on two periods of time (1992 and the present) in order to contrast the dramatic changes that have taken place in the FDF. This paper offers observations and plans for the evolution of the FDF over the next ten years. Finally, this paper defines the mission model of the future for the FDF based on NASA's current mission list and planning for the Constellation Program. As part of this discussion the following are addressed: the relevance and benefits of a multi-mission facility for NASA's navigation operations in the future; anticipated technologies affecting ground orbit determination; continued incorporation of Commercial Off-the-shelf (COTS) software into the FDF; challenges of a business model that relies entirely on user fees to fund facility upgrades; anticipated changes in flight dynamics services required; and considerations for defining architecture upgrades given a set of cost drivers

Sampling of Glacial Snow for Pesticide Analysis on the High Plateau Glacier of Mount Logan

Recently there have been a number of attempts to determine the presence of pollutants in remote areas of the world. The snow of glaciers is a particularly interesting subject for such work, since it contains a record of past years as well as the present. ... Such pollutants are transported by the atmosphere, and it is especially interesting to know if they are present in precipitation that forms at high altitude. As part of the Ice Field Ranges Research Project (IRRP) of 1970, we undertook the study of another common pollutant, the pesticide DDT. Here we report on our attempt to develop techniques for taking snow samples at high altitude in locations where work had to be done under adverse conditions, and with simple equipment. Samples were taken at an elevation of 5,364 metres on Mount Logan, Yukon Territory, Canada. ... The work was performed at temperatures below -20°C, and often in high winds. At this elevation the effects of hypoxia are quite marked .... when unpacked in the field, quantities of an oily material were found on the [new SIPRE snow] auger. It was not practical to achieve a thorough cleaning under field conditions, but as much of the material as possible was removed by using Coleman Fuel - a highly refined non-leaded gasoline designed for camp stoves. Provision of suitable sample containers was an important aspect of the preparations. Two-gallon wide-mouth Nalgene jugs were used on the glacier. The mouth was large enough so that the snow core could slide into the jug directly from the auger without intermediate handling. As long as the samples remained frozen, they could be stored in plastic. However, since liquid water slowly leaches material from the jugs, the samples were transferred to glass jars as soon as they melted. ... A special effort was made in the precleaning of both jars and jugs because of the low levels of pesticide expected. ... Precautions were taken to avoid contamination during sample collection. The first few samples were discarded in the hope of removing any residual contamination from the auger. During the sampling process the auger was never touched by bare hands or gloves. The only surface which came into contact with the samples before their arrival at the laboratory were the auger and the precleaned jugs and jars. At the end of the work, one sample was deliberately mishandled as a control. It subsequently showed no contamination from either polychlorinated biphenyls (PCBs) or DDT. Nineteen samples were taken at depths of from 1 to 15 metres. The DDT analysis was carried out ... using a gas chromatographic technique .... DDT was not detected in any of the samples. In seven of the samples the lower limit of detectibility for DDT was 5 nanograms per liter. Due to interference, apparently from PCBs, 10 to 50 ng/l of DDT could have been present in the remaining samples and not have been detected by this method. It is suggestive that the samples showing no PCB contamination were the last ones taken. It is likely that the PCB contamination came from the oily material originally on the auger, and that the remnant of this was removed during the early part of the drilling. On the basis of these results it seems that sampling of glacial snow for trace organic pollutants is feasible, even when samples must be taken under unfavourable conditions with primitive techniques. It is of paramount importance to preclean every surface that will come into contact with the sample, both sampling tools, and sample containers. ..

Why Are Unemployment Insurance Claims So Low?

In this paper, we examine the reasons why unemployment insurance (UI) claims have declined so dramatically over the past three decades. The fall in the UI claims rate is concerning because it suggests a reduced countercyclical effectiveness of the UI program. Additionally, weekly initial UI claims are regarded as an important leading indicator of aggregate economic activity, so their meaning has changed. We use a Oaxaca (1973) decomposition approach to identify the main factors for the decline in claims. The procedure suggests what the level of claims would have been later in the period, had values of variables or parameters of the system been at levels observed earlier in the period. Our analysis of state-year data over the past three decades suggests that the decline in UI claims stems from changes in the industrial and occupational mix of employment interacting with changes in UI program features set by individual states. Employment declines in manufacturing and increases in the health-care and education workforce, along with lower potential UI duration and lower wage replacement rates, contribute to the decline in claims. This decline could be offset by federal rules for states to improve benefit access, replacement rates, and durations. Such changes could improve the relevance of UI to the labor market and help restore UI as meaningful social insurance against job loss and as an automatic stabilizer of the macroeconomy