Structural assessment of a space station solar dynamic heat receiver thermal energy storage canister

The structural performance of a space station thermal energy storage (TES) canister subject to orbital solar flux variation and engine cold start up operating conditions was assessed. The impact of working fluid temperature and salt-void distribution on the canister structure are assessed. Both analytical and experimental studies were conducted to determine the temperature distribution of the canister. Subsequent finite element structural analyses of the canister were performed using both analytically and experimentally obtained temperatures. The Arrhenius creep law was incorporated into the procedure, using secondary creep data for the canister material, Haynes 188 alloy. The predicted cyclic creep strain accumulations at the hot spot were used to assess the structural performance of the canister. In addition, the structural performance of the canister based on the analytically determined temperature was compared with that based on the experimentally measured temperature data

Ground test program for a full-size solar dynamic heat receiver

Test hardware, facilities, and procedures were developed to conduct ground testing of a full size, solar dynamic heat receiver in a partially simulated, low Earth orbit environment. The heat receiver was designed to supply 102 kW of thermal energy to a helium and xenon gas mixture continuously over a 94 minute orbit, including up to 36 minutes of eclipse. The purpose of the test program was to quantify the receiver thermodynamic performance, its operating temperatures, and thermal response to changes in environmental and power module interface boundary conditions. The heat receiver was tested in a vacuum chamber using liquid nitrogen cold shrouds and an aperture cold plate. Special test equipment were designed to provide the required ranges in interface boundary conditions that typify those expected or required for operation as part of the solar dynamic power module on the Space Station Freedom. The support hardware includes an infrared quartz lamp heater with 30 independently controllable zones and a closed Brayton cycle engine simulator to circulate and condition the helium xenon gas mixture. The test article, test support hardware, facilities, and instrumentation developed to conduct the ground test program are all described

Two-dimensional magnetism in the pnictide superconductor parent material SrFeAsF probed by muon-spin relaxation

We report muon-spin relaxation measurements on SrFeAsF, which is the parent compound of a newly discovered iron-arsenic-fluoride based series of superconducting materials. We find that this material has very similar magnetic properties to LaFeAsO, such as separated magnetic and structural transitions (TN = 120 K, Ts = 175 K), contrasting with SrFe2As2 where they are coincident. The muon oscillation frequencies fall away very sharply at TN, which suggests that the magnetic exchange between the layers is weaker than in comparable oxypnictide compounds. This is consistent with our specific heat measurements, which find that the entropy change S = 0.05 J/mol/K largely occurs at the structural transition and there is no anomaly at TN.Comment: 4 pages, 3 figure

Integration Assessment of Visiting Vehicle Induced Electrical Charging of the International Space Station Structure

The International Space Station (ISS) undergoes electrical charging in low Earth orbit (LEO) due to positively biased, exposed conductors on solar arrays that collect electrical charges from the space plasma. Exposed solar array conductors predominately collect negatively charged electrons and thus drive the metal ISS structure electrical ground to a negative floating potential (FP) relative to plasma. This FP is variable in location and time as a result of local ionospheric conditions. ISS motion through Earth s magnetic field creates an addition inductive voltage up to 20 positive and negative volts across ISS structure depending on its attitude and location in orbit. ISS Visiting Vehicles (VVs), such as the planned Orion crew exploration vehicle, contribute to the ISS plasma charging processes. Upon physical contact with ISS, the current collection properties of VVs combine with ISS. This is an ISS integration concern as FP must be controlled to minimize arcing of ISS surfaces and ensure proper management of extra vehicular activity crewman shock hazards. This report is an assessment of ISS induced charging from docked Orion vehicles employing negatively grounded, 130 volt class, UltraFlex (ATK Space Systems) solar arrays. To assess plasma electron current collection characteristics, Orion solar cell test coupons were constructed and subjected to plasma chamber current collection measurements. During these tests, coupon solar cells were biased between 0 and 120 V while immersed in a simulated LEO plasma. Tests were performed using several different simulated LEO plasma densities and temperatures. These data and associated theoretical scaling of plasma properties, were combined in a numerical model which was integrated into the Boeing Plasma Interaction Model. It was found that the solar array design for Orion will not affect the ISS FP by more than about 2 V during worst case charging conditions. This assessment also motivated a trade study to determine acceptable plasma electron current levels that can be collected by a single or combined fleet of ISS-docked VVs

Structural Design Considerations for a 50 kW-Class Solar Array for NASA's Asteroid Redirect Mission

NASA is planning an Asteroid Redirect Mission (ARM) to take place in the 2020s. To enable this multi-year mission, a 40 kW class solar electric propulsion (SEP) system powered by an advanced 50 kW class solar array will be required. Powered by the SEP module (SEPM), the ARM vehicle will travel to a large near-Earth asteroid, descend to its surface, capture a multi-metric ton (t) asteroid boulder, ascend from the surface and return to the Earth-moon system to ultimately place the ARM vehicle and its captured asteroid boulder into a stable distant orbit. During the years that follow, astronauts flying in the Orion multipurpose crew vehicle (MPCV) will dock with the ARM vehicle and conduct extra-vehicular activity (EVA) operations to explore and sample the asteroid boulder. This paper will review the top structural design considerations to successfully implement this 50 kW class solar array that must meet unprecedented performance levels. These considerations include beyond state-of-the-art metrics for specific mass, specific volume, deployed area, deployed solar array wing (SAW) keep in zone (KIZ), deployed strength and deployed frequency. Analytical and design results are presented that support definition of stowed KIZ and launch restraint interface definition. An offset boom is defined to meet the deployed SAW KIZ. The resulting parametric impact of the offset boom length on spacecraft moment of inertias and deployed SAW quasistatic and dynamic load cases are also presented. Load cases include ARM spacecraft thruster plume impingement, asteroid surface operations and Orion docking operations which drive the required SAW deployed strength and damping. The authors conclude that to support NASA's ARM power needs, an advanced SAW is required with mass performance better than 125 W/kg, stowed volume better than 40 kW/cu m, a deployed area of 200 sq m (100 sq m for each of two SAWs), a deployed SAW offset distance of nominally 3-4 m, a deployed SAW quasistatic strength of nominally 0.1 g in any direction, a deployed loading displacement under 2 m, a deployed fundamental frequency above 0.1 Hz and deployed damping of at least 1%. These parameters must be met on top of challenging mission environments and ground testing requirements unique to the ARM project

Incidence and risk factors for poor ankle functional recovery, and the development and progression of posttraumatic ankle osteoarthritis after significant ankle ligament injury (SALI) : the SALI cohort study protocol

Background: Ankle sprains are one of the most common musculoskeletal injuries, accounting for up to 5% of all Emergency Department visits in the United Kingdom. Ankle injury may be associated with future ankle osteoarthritis. Up to 70% of ankle osteoarthritis cases may be associated with previous ankle injury. There is limited research regarding the association between ankle sprain and ankle osteoarthritis development. The current study aims to phenotype those who suffer significant ankle ligament injuries, identify potential risk factors for ankle injuries and subsequent poor recovery, examine why individuals may develop osteoarthritis, and what factors influence this chance. Methods: In this multicentre cohort study participants were recruited from nine Emergency Departments and two Urgent Care Centres in the United Kingdom. Participants (aged 18–70 years old) were defined as those who had suffered an isolated acute ankle sprain, which was Ottawa Ankle Rules positive, but negative for a significant ankle fracture on x-ray. Age and sex matched controls were also recruited. The controls were individuals who had not suffered a significant ankle injury, including ankle pain, function affected for more than 7 days, or the ankle caused them to report to an Emergency Department. Data is collected through a series of seven questionnaires (at baseline, 3 months, 1 year, 3 years, 5 years, 10 years, and 15 years later). The questionnaires include four sections (demographic questions; index injury, and injury history questions; functional assessment questions; and quality of life questions) and are designed to collect detailed information about the individual, their injury, potential risk factors for ankle sprains and ankle osteoarthritis, plus their medical history and any medication consumed. Discussion: The Significant Ankle Ligament Injury (SALI) study aims to add to the limited knowledge regarding which factors can predict ankle sprains, complaints, and osteoarthritis. This is important because despite ankle sprains being regarded as a benign injury that resolves quickly, residual symptoms are not uncommon months and years after the injury

Thermal Cycle Testing of the Powersphere Engineering Development Unit

During the past three years the team of The Aerospace Corporation, Lockheed Martin Space Systems, NASA Glenn Research Center, and ILC Dover LP have been developing a multifunctional inflatable structure for the PowerSphere concept under contract with NASA (NAS3-01115). The PowerSphere attitude insensitive solar power-generating microsatellite, which could be used for many different space and Earth science purposes, is ready for further refinement and flight demonstration. The development of micro- and nanosatellites requires the energy collection system, namely the solar array, to be of lightweight and small size. The limited surface area of these satellites precludes the possibility of body mounting the solar array system for required power generation. The use of large traditional solar arrays requires the support of large satellite volumes and weight and also requires a pointing apparatus. The current PowerSphere concept (geodetic sphere), which was envisioned in the late 1990 s by Mr. Simburger of The Aerospace Corporation, has been systematically developed in the past several years.1-7 The PowerSphere system is a low mass and low volume system suited for micro and nanosatellites. It is a lightweight solar array that is spherical in shape and does not require a pointing apparatus. The recently completed project culminated during the third year with the manufacturing of the PowerSphere Engineering Development Unit (EDU). One hemisphere of the EDU system was tested for packing and deployment and was subsequently rigidized. The other hemisphere was packed and stored for future testing in an uncured state. Both cured and uncured hemisphere components were delivered to NASA Glenn Research Center for thermal cycle testing and long-term storage respectively. This paper will discuss the design, thermal cycle testing of the PowerSphere EDU

An HDG Method for Dirichlet Boundary Control of Convection Dominated Diffusion PDE

We first propose a hybridizable discontinuous Galerkin (HDG) method to approximate the solution of a \emph{convection dominated} Dirichlet boundary control problem. Dirichlet boundary control problems and convection dominated problems are each very challenging numerically due to solutions with low regularity and sharp layers, respectively. Although there are some numerical analysis works in the literature on \emph{diffusion dominated} convection diffusion Dirichlet boundary control problems, we are not aware of any existing numerical analysis works for convection dominated boundary control problems. Moreover, the existing numerical analysis techniques for convection dominated PDEs are not directly applicable for the Dirichlet boundary control problem because of the low regularity solutions. In this work, we obtain an optimal a priori error estimate for the control under some conditions on the domain and the desired state. We also present some numerical experiments to illustrate the performance of the HDG method for convection dominated Dirichlet boundary control problems

Libraries and open society; Popper, Soros and digital information

This paper examines the role of libraries and information services, in promoting the ‘open society’ espoused by Karl Popper and George Soros. After a brief discussion of the nature of an ‘open society’, the paper covers the role played by provision of knowledge and information, of new technology, particularly the Internet, and of critical thinking and digital literacy in the development of this form of society. Conclusions are drawn for the role of libraries and librarians, with seven general principles suggested: • provision of access to a wide variety of sources without ‘negative’ restriction or censorship • provision of ‘positive’ guidance on sources, based on open and objective criteria • a recognition that a ‘free flow of information’ though essential, is not sufficient • a recognition that provision of factual information, while valuable, is not enough • a need for a specific concern for the effect of new ICTs, and the Internet in particular • promotion of critical thinking and digital literacy • a need for explicit consideration of the ethical values of librarie

The possibilities and limits of political contestation in times of ‘urban austerity’

This paper seeks to provide a conceptual framework in which to examine the social practices of contemporary austerity programmes in urban areas, including how these relate to different conceptions of crisis. Of current theoretical interest is the apparent ease with which these austerity measures have been accepted by urban governing agents. In order to advance these understandings we follow the recent post-structuralist discourse theory ‘logics’ approach of Glynos and Howarth (2007), focusing on the relationship between hegemony, political and social logics, and the subject whose identificatory practices are key to understanding the form, nature and stability of discursive settlements. In such thinking it is not only the formation of discourses and the mobilisation of rhetoric that are of interest, but also the manner in which the subjects of austerity identify with these. Through such an approach we examine the case of the regeneration/economic development and planning policy area in the city government of Birmingham (UK). In conclusion, we argue that the logics approach is a useful framework through which to examine how austerity has been uncontested in a city government, and the dynamics of acquiescence in relation to broader hegemonic discursive formations