Solar array thermal snap and the characteristics of its effect on UARS

The single solar array on the Upper Atmosphere Research Satellite (UARS) is subjected to a thermal distortion when the spacecraft enters and exits the Earth's shadow. The distortion results in a torque that alters the spacecraft attitude. Due to the sudden nature of the attitude discontinuity, the effect has been termed 'thermal snap'. Thermal snap has also been experienced by Landsats 4 and 5. Analyses by the spacecraft builder addressed the impact of the resultant torque on the onboard control system. This paper discusses the results of comparisons between the predicted effects of thermal snap on UARS and actual attitude solutions from UARS telemetry data. In addition, this paper describes the characteristics of the thermal snap on UARS in terms of maximum displacement, solar beta angle, and solar array drive angle. Comparisons are made between the actual times of thermal snaps and the predicted spacecraft sunrise and sunset times. The effects of the UARS thermal snap are summarized and a general comment is made relating possible effects of thermal snap on other satellites. Also, an analysis of UARS attitude solutions that span periods of thermal snap was performed to determine whether the gyro sampling time of 1/8 second is sufficient to properly model the resulting spacecraft attitude without compromising the accuracy requirements. The results of this analysis are discussed

A different kind of archival security: Three cases

Archival security is not just about guarding against theft and vandalism; it is about accountability and ethics and the potential challenges to archives and archivists. This essay considers three cases -the ownership and control of the records of indigenous peoples, the use of records of the U.S. Supreme Court, and the misadminstration of electronic mail messages to the White House. © Taylor & Francis Group, LLC

Submillimeter Wave Astronomy Satellite (SWAS) Launch and Early Orbit Support Experiences

The Submillimeter Wave Astronomy Satellite (SWAS) was successfully launched on December 6, 1998 at 00:58 UTC. The two year mission is the fourth in the series of Small Explorer (SMEX) missions. SWAS is dedicated to the study of star formation and interstellar chemistry. SWAS was injected into a 635 km by 650 km orbit with an inclination of nearly 70 deg by an Orbital Sciences Corporation Pegasus XL launch vehicle. The Flight Dynamics attitude and navigation teams supported all phases of the early mission. This support included orbit determination, attitude determination, real-time monitoring, and sensor calibration. This paper reports the main results and lessons learned concerning navigation, support software, star tracker performance, magnetometer and gyroscope calibrations, and anomaly resolution. This includes information on spacecraft tip-off rates, first-day navigation problems, target acquisition anomalies, star tracker anomalies, and significant sensor improvements due to calibration efforts

BUMC Annual Report

Annual report of the Boston University Medical Center

BUMC Annual Report

Annual report of the Boston University Medical Center

A probabilistic fatigue analysis of multiple site damage

The variability in initial crack size and fatigue crack growth is incorporated in a probabilistic model that is used to predict the fatigue lives for unstiffened aluminum alloy panels containing multiple site damage (MSD). The uncertainty of the damage in the MSD panel is represented by a distribution of fatigue crack lengths that are analytically derived from equivalent initial flaw sizes. The variability in fatigue crack growth rate is characterized by stochastic descriptions of crack growth parameters for a modified Paris crack growth law. A Monte-Carlo simulation explicitly describes the MSD panel by randomly selecting values from the stochastic variables and then grows the MSD cracks with a deterministic fatigue model until the panel fails. Different simulations investigate the influences of the fatigue variability on the distributions of remaining fatigue lives. Six cases that consider fixed and variable conditions of initial crack size and fatigue crack growth rate are examined. The crack size distribution exhibited a dominant effect on the remaining fatigue life distribution, and the variable crack growth rate exhibited a lesser effect on the distribution. In addition, the probabilistic model predicted that only a small percentage of the life remains after a lead crack develops in the MSD panel

BUMC Annual Report

Annual report of the Boston University Medical Center

BUMC Annual Report

Annual report of the Boston University Medical Center

Benefits of maximum likelihood estimators for fracture attribute analysis: Implications for permeability and up-scaling

The authors thank Andrew Hurst for support during the field work, and also Antonio Grippa, Giuseppe Palladino and Gustavo Zvirtes for help and constructive discussions during the field work. We are particularly grateful to Tom Manzocchi for his important comments that greatly improved the first version of this paper. We acknowledge constructive reviews by Julia Gale and Ken McCaffrey, which have greatly improved our manuscript. This work forms part of a NERC New Investigator award for David Healy (NE/I001743/1), which is gratefully acknowledged. Finally, Roberto Emanuele Rizzo is very appreciative of AFES (Aberdeen Formation Evaluation Society) for funding support during his PhD.Peer reviewedPublisher PD