A Maintenance-Free Battery Charge Control Approach for Nickel-Hydrogen Batteries

The most common battery charging approaches for nickel-hydrogen batteries suffer from two key limitations. They either consistently under- or overcharge the battery or they require accurate knowledge of the battery capacity. For the ORBCOMM constellation of 36 small communications satellites, regular overcharging is unacceptable because it decreases battery life. Worse, the lost life occurs when the satellite constellation is facing its greatest usage demand. On the other hand, obtaining an accurate knowledge of the battery capacity requires an upfront effort to develop the necessary engineering tools and characterize battery performance. In addition, the satellite operator must bear the recurring expense of continuously estimating the capacity over the 5-year design life of each spacecraft. To avoid these limitations, the ORBCOMM system employs a patented battery charging approach that estimates the battery charging efficiency by computing the amount of charge received by the battery as a function of the input charge. The full point of the battery is easily determined since the charge efficiency drops as the battery charge approaches its capacity. The battery charge is estimated by computing the moles of H2 gas in the cell; the input charge is simply the integral of the charge current. So, the charge efficiency is proportional to the rate of change of the moles of H2 gas with respect to the input charge, or dM/dC. This maintenance-free approach enables the charging routine to perfectly fill the batteries-without overcharging-independent of the battery capacity. Any algorithm based upon a derivative estimate poses a noise rejection challenge. The dMldC approach is no different. The battery charge control system must be adept enough to respond to decreases in dM/dC yet stable enough to avoid the inherent signal to noise problem at low charge rates. The effectiveness and pitfalls of the dM/dC battery charge algorithm are highlighted using data from the 26 ORBCOMM constellation spacecraft launched between December 1997 and September 1998

Creating Large Space Platforms from Small Satellites

With the advent of micro-satellites and nano-satellites, many have begun to study the unique attributes of dozens or hundreds of such satellites operating in constellations. But, do these small satellites necessarily need to function separately on orbit? Orbital\u27s unique MicroStar platform offers the possibility of creating a large, rigid space structure with impressive capabilities from a Pegasus-class mission. In its single-ring configuration, up to eight MicroStar spacecraft can be launched on a single Pegasus® rocket. Rather than separating each of the eight spacecraft, the stack of eight (or two stacks of four) could be unfurled to create a single space structure more than 8 meters in length. Since each individual component is itself a spacecraft, the net capability is impressive. The total spacecraft--called a supersat-is capable of generating up to 2.5kW of power, more than half of which may be devoted to the payload. The supers at also boasts very high reliability, since the multiple spacecraft offer inherent redundancy. Using this technique, large apertures could be constructed for certain missions offering advantages that in the past have only been obtainable in much larger systems. Based upon the geometry used, multi-aperture systems might also be possible. This paper provides several examples of how this spacecraft concept may be applied to missions previously reserved for much larger-and more expensive-systems

Environment Agency review of methods for determining organic waste biodegradability and municipal waste diversion.

The Environment Agency is required to regulate the landfilling of biodegradable organic wastes and their diversion from landfilling. Simple, cost effective, reliable and widely applicable methods for the measurement of organic waste and its biodegradability are needed for this activity. A review of such methods was carried out in order to select promising methods for an experimental screening exercise. The review considered both biological and non-biological methods including simple methods that may provide a surrogate measurement of waste biodegradability instead of the time-consuming biological methods. The biological methods selected for further evaluation were the aerobic specific oxygen uptake rate (SOUR) and dynamic respiration index (DRI) tests, and the anaerobic biochemical methane potential (BMP) test. The non-biological methods selected for further evaluation were dry matter (DM), loss on ignition (LOI), total organic carbon (TOC), total nitrogen (TN), water extractable dissolved organic carbon (DOC), BOD and COD, the lignin and cellulose content and the cellulase hydrolysis method. These tests are being evaluated on a wide variety of typical organic materials that might be found in municipal solid waste (MSW) such as newspaper corrugated paper, compost, kitchen waste (vegetable and animal), garden wastes (grass and twigs), nappies, cotton and wool textiles

Characterisation of untreated and treated biodegradable wastes

As part of a Defra sponsored project (WRT220), approximately 40 biodegradable wastes were characterised according to biodegradability (DR4 and BM100), total PTE content, C:N ratio and biochemical composition. Two leaching tests were employed; upflow percolation test and a one step LS10 test; eluates were analysed for TOC, pH, electrical conductivity, PTEs and a range of cations and anions. This paper contains a limited set of data for a selection of untreated and treated waste types representing four waste treatment processes (composting, MBT, MHT, anaerobic digestion). The DR4 and BM100 tests were found to be appropriate for a wide range of waste types but where possible they should be used in conjunction with other related tests. Longer-term MBT composting processes appeared to produce compost material with reduced ammonium concentrations and extractability of some PTEs. Carbon content (carbon analyzer - LECO) could be estimated as C = LOI/1.9 which is a routine operation. N LECO values were approximately 12% greater than the equivalent N Kjeldahl values

Application of DR4 and BM100 Biodegradability tests to treated and untreated organic wastes

The aerobic DR4 and anaerobic BM100 biodegradability tests are currently applied in England and Wales for monitoring the reduction in biological municipal waste (BMW) achieved by mechanical biological treatment (MBT) plants (Environment Agency 2005). The protocol is applied only when outputs are landfilled and is based on estimating the reduction in potential biogas production between the MBT input, municipal solid waste (MSW), and all of the landfilled outputs, using the BM100 test. As this is a long term 100 day test the more rapid 4 day DR4 test may also be applied as this has been shown to correlate with the BM100 test. We have now applied the DR4 and BM100 tests to 132 organic waste samples including untreated and treated BMW and specific organic wastes. The results indicate that the correlation between the DR4 and BM100 tests has proved valid for mixed MSW derived BMW wastes. However when both tests are applied to specific organic wastes such as turkey feathers, cardboard packaging waste and pizza food wastes the correlation between the tests is less strong. It is concluded that the use of the DR4 and BM100 test correlation is valid for its designed application (monitoring MBT processes treating MSW derived mixed BMW), but that caution should be exercised when applying both tests to specific single component organic wastes

Latitudinal Shear Instabilities during Type I X-ray Bursts

Coherent oscillations have been observed during Type I X-ray bursts from 14 accreting neutron stars in low mass X-ray binaries, providing important information about their spin frequencies. However, the origin of the brightness asymmetry on the neutron star surface producing these oscillations is still not understood. We study the stability of a zonal shearing flow on the neutron star surface using a shallow water model. We show that differential rotation of >2% between pole and equator, with the equator spinning faster than the poles, is unstable to hydrodynamic shear instabilities. The unstable eigenmodes have properties well-matched to burst oscillations: low azimuthal wavenumber m, wave speeds 1 or 2% below the equatorial spin rate, and e-folding times close to a second. Instability is related to low frequency buoyantly driven r-modes that have a mode frequency within the range of rotation frequencies in the differentially rotating shell. We discuss the implications for burst oscillations. Growth of shear instabilities may explain the brightness asymmetry in the tail of X-ray bursts, although some fine tuning of the level of differential rotation and a spin frequency near 300 Hz are required in order for the fastest growing mode to have m=1. If shear instabilities are to operate during a burst, temperature contrasts of 30% across the star must be created during ignition and spreading of the flash.Comment: To appear in ApJ (12 pages, 11 figures

Use of qualitative methods alongside randomised controlled trials of complex healthcare interventions: methodological study

Objective To examine the use of qualitative approaches alongside randomised trials of complex healthcare interventions

An automated tool for formulating linear covariance analysis problems

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992.Includes bibliographical references (p. 99).by Andrew W. Lewin.M.S

Translating research into policy and practice in developing countries: a case study of magnesium sulphate for pre-eclampsia.

BACKGROUND: The evidence base for improving reproductive health continues to grow. However, concerns remain that the translation of this evidence into appropriate policies is partial and slow. Little is known about the factors affecting the use of evidence by policy makers and clinicians, particularly in developing countries. The objective of this study was to examine the factors that might affect the translation of randomised controlled trial (RCT) findings into policies and practice in developing countries. METHODS: The recent publication of an important RCT on the use of magnesium sulphate to treat pre-eclampsia provided an opportunity to explore how research findings might be translated into policy. A range of research methods, including a survey, group interview and observations with RCT collaborators and a survey of WHO drug information officers, regulatory officials and obstetricians in 12 countries, were undertaken to identify barriers and facilitators to knowledge translation. RESULTS: It proved difficult to obtain reliable data regarding the availability and use of commonly used drugs in many countries. The perceived barriers to implementing RCT findings regarding the use of magnesium sulphate for pre-eclampsia include drug licensing and availability; inadequate and poorly implemented clinical guidelines; and lack of political support for policy change. However, there were significant regional and national differences in the importance of specific barriers. CONCLUSION: The policy changes needed to ensure widespread availability and use of magnesium sulphate are variable and complex. Difficulties in obtaining information on availability and use are combined with the wide range of barriers across settings, including a lack of support from policy makers. This makes it difficult to envisage any single intervention strategy that might be used to promote the uptake of research findings on magnesium sulphate into policy across the study settings. The publication of important trials may therefore not have the impacts on health care that researchers hope for

The Living With a Star Geospace Missions

The Geospace Missions are the second major mission element in NASA’s Living With a Star program. The missions are designed to help scientists understand, and eventually predict, the response of the geo-space system to solar activity. The investigations will be carried out by two pairs of spacecraft and a high-altitude far ultraviolet (FUV) imager. This observatory network provides the first opportunity to make multi-point in situ measurements of the ionosphere-thermosphere (I-T) system and the radiation belts (RB) with coordinated measurements between the two regions. The first two spacecraft are the I-T Storm Probes (I-TSP), which will study mid-latitude ionospheric vari-ability. They will be launched on a Taurus-class launch vehicle into a 450km circular orbit at 60° inclina-tion. The second pair of spacecraft is the RB Storm Probes (RBSP) that will study the dynamics of radiation belt ions and electrons. These spacecraft will be launched on a Delta II-class launch vehicle into a low inclination, near-GTO orbit. The launch timelines are phased to enable all four spacecraft to make observations at or near solar maximum when solar and geospace activity are the most frequent and severe. The FUV imager will fly on a mission of opportunity in conjunction with I-TSP and RBSP as a payload on a high-altitude spacecraft. One of the greatest challenges of the Geospace Missions is performing groundbreaking science on four dedicated platforms and an imaging instrument within a $400 million total budget. Advancements in small satellite technology and capabilities have enabled the missions; future developments could greatly improve the quality and quantity of science that can be performed with the limited funding resources. This paper provides a brief overview of the I-TSP and RBSP mission requirements, discusses some of the key system-level design challenges, and presents candidate spacecraft concepts