Space Shuttle Body Flap Actuator Bearing Testing for NASA Return to Flight

The Space Shuttle body flap is located beneath the main engine nozzles and is required for proper aerodynamic control during orbital descent. Routine inspection of one of four body flap actuators found one of the actuator bearings had degraded and blackened balls. A test program was initiated to demonstrate that it is acceptable to operate bearings which are degraded from operation over several flights. This test exposed the bearing to predicted flight axial loads, speeds and temperatures. Testing at 140 F has been completed, and results indicate the previously flown bearings are acceptable for up to 12 additional missions. Additional testing is underway to determine the lubricant life at various temperatures and stresses and to further understand the mechanism that caused the blacken balls. Initial results of this testing indicates that bearing life is shorten at room temperature possibly due fact that higher temperature (140 F) accelerates the flow of grease and oil into the wear surfac

Probabilistic Analysis of Space Shuttle Body Flap Actuator Ball Bearings

A probabilistic analysis, using the 2-parameter Weibull-Johnson method, was performed on experimental life test data from space shuttle actuator bearings. Experiments were performed on a test rig under simulated conditions to determine the life and failure mechanism of the grease lubricated bearings that support the input shaft of the space shuttle body flap actuators. The failure mechanism was wear that can cause loss of bearing preload. These tests established life and reliability data for both shuttle flight and ground operation. Test data were used to estimate the failure rate and reliability as a function of the number of shuttle missions flown. The Weibull analysis of the test data for the four actuators on one shuttle, each with a 2-bearing shaft assembly, established a reliability level of 96.9 percent for a life of 12 missions. A probabilistic system analysis for four shuttles, each of which has four actuators, predicts a single bearing failure in one actuator of one shuttle after 22 missions (a total of 88 missions for a 4-shuttle fleet). This prediction is comparable with actual shuttle flight history in which a single actuator bearing was found to have failed by wear at 20 missions

The AzTEC mm-Wavelength Camera

AzTEC is a mm-wavelength bolometric camera utilizing 144 silicon nitride micromesh detectors. Herein we describe the AzTEC instrument architecture and its use as an astronomical instrument. We report on several performance metrics measured during a three month observing campaign at the James Clerk Maxwell Telescope, and conclude with our plans for AzTEC as a facility instrument on the Large Millimeter Telescope.Comment: 13 pages, 15 figures, accepted for publication in Monthly Notice

Critical Review of Norovirus Surrogates in Food Safety Research: Rationale for Considering Volunteer Studies

The inability to propagate human norovirus (NoV) or to clearly differentiate infectious from noninfectious virus particles has led to the use of surrogate viruses, like feline calicivirus (FCV) and murine norovirus-1 (MNV), which are propagatable in cell culture. The use of surrogates is predicated on the assumption that they generally mimic the viruses they represent; however, studies are proving this concept invalid. In direct comparisons between FCV and MNV, their susceptibility to temperatures, environmental and food processing conditions, and disinfectants are dramatically different. Differences have also been noted between the inactivation of NoV and its surrogates, thus questioning the validity of surrogates. Considerable research funding is provided globally each year to conduct surrogate studies on NoVs; however, there is little demonstrated benefit derived from these studies in regard to the development of virus inactivation techniques or food processing strategies. Human challenge studies are needed to determine which processing techniques are effective in reducing NoVs in foods. A major obstacle to clinical trials on NoVs is the perception that such trials are too costly and risky, but in reality, there is far more cost and risk in allowing millions of unsuspecting consumers to contract NoV illness each year, when practical interventions are only a few volunteer studies away. A number of clinical trials have been conducted, providing important insights into NoV inactivation. A shift in research priorities from surrogate research to volunteer studies is essential if we are to identify realistic, practical, and scientifically valid processing approaches to improve food safety

The Visibility of (In)security: The Aesthetics of Planning Urban Defences Against Terrorism

Urban defences against terrorism have traditionally been based on territorial interventions that sought to seal off and surveil certain public and private spaces considered targets. Lately, though, a much wider range of crowded and public spaces have been viewed as potential targets and thus have been identified as requiring additional security. This has immense implications for the experience of the ‘everyday’ urban landscape. Drawing on contemporary notions that incorporate the study of aesthetics and emotions within critical security and terrorism studies, this article discusses the visual impact of counter-terrorism security measures. It analyses the ‘transmission’ of symbolic messages, as well as the variety of ways in which security might be ‘received’ by various stakeholders. The analysis takes place against the backdrop of concern that obtrusive security measures have the capacity to radically alter public experiences of space and in some cases lead to (intended and unintended) exclusionary practices or a range of negative emotional responses. The article concludes by outlining a ‘spectrum of visible security’ ranging between traditional obtrusive fortified approaches and approaches that embed security features seamlessly or even ‘invisibly’ into the urban fabric

Life of Pennzane and 815Z-Lubricated Instrument Bearings Cleaned with Non-CFC Solvents

Life tests were conducted on instrument scanner ball bearings cleaned with 3 types of non-ozone depleting solvents and compared with those cleaned with a conventional CFC-113 (Freon) solvent. The test bearings were lubricated with the standard space oil (Bray 815Z, Fomblin Z25) and a more recent synthetic space oil (Pennzane 2001). Lives with replacement solvents equaled or exceeded those obtained with CFC-113 baseline, indicating that alternate cleaning solvents were acceptable. Pennzane lubricated bearings enjoyed a significant life advantage (>5X) over those lubricated with Bray 815Z oil in these oscillatory gimbal bearing tests. Many of the Pennzane bearings are still exhibiting acceptable torque traces after more than 25,000 hr of test