Structural health management technologies for inflatable/deployable structures: Integrating sensing and self-healing

Inflatable/deployable structures are under consideration as habitats for future Lunar surface science operations. The use of non-traditional structural materials combined with the need to maintain a safe working environment for extended periods in a harsh environment has led to the consideration of an integrated structural health management system for future habitats, to ensure their integrity. This article describes recent efforts to develop prototype sensing technologies and new self-healing materials that address the unique requirements of habitats comprised mainly of soft goods. A new approach to detecting impact damage is discussed, using addressable flexible capacitive sensing elements and thin film electronics in a matrixed array. Also, the use of passive wireless sensor tags for distributed sensing is discussed, wherein the need for on-board power through batteries or hardwired interconnects is eliminated. Finally, the development of a novel, microencapuslated self-healing elastomer with applications for inflatable/deployable habitats is reviewed.     

Recent experimental measurements of space platform charging at LEO altitudes

The estimation of the extent of electrical charging of space platforms at low earth orbit (LEO) altitudes has been a subject of interest for a number of years. Early estimates based on theoretical current-voltage relationships of Langmuir and Blodgett and Parker and Murphy predicted a wide range of possible electrical potentials for a platform being actively charged at LEO altitudes. The experimental success of early electron beam experiments suggested that the early theories were incomplete. This has led to the development of space experiments specifically designed to study the degree of electrical charging resulting from electron beam emission, and also supplementary experiments to determine the current voltage relationship of large structures biassed to high voltages in the LEO environment. The paper will discuss some of the results of vehicle electrical potential from recent sounding rocket experiments involving charging of a space platform by both electron beam emission, and by the application of differential bias between elements of the platform.     

A far ultraviolet imager for the International Solar-Terrestrial Physics Mission

The aurorae are the result of collisions with the atmosphere of energetic particles that have their origin in the solar wind, and reach the atmosphere after having undergone varying degrees of acceleration and redistribution within the Earth's magnetosphere. The global scale phenomenon represented by the aurorae therefore contains considerable information concerning the solar-terrestrial connection. For example, by correctly measuring specific auroral emissions, and with the aid of comprehensive models of the region, we can infer the total energy flux entering the atmosphere and the average energy of the particles causing these emissions. Furthermore, from these auroral emissions we can determine the ionospheric conductances that are part of the closing of the magnetospheric currents through the ionosphere, and from these we can in turn obtain the electric potentials and convective patterns that are an essential element to our understanding of the global magnetosphere-ionosphere-thermosphere-mesosphere. Simultaneously acquired images of the auroral oval and polar cap not only yield the temporal and spatial morphology from which we can infer activity indices, but in conjunction with simultaneous measurements made on spacecraft at other locations within the magnetosphere, allow us to map the various parts of the oval back to their source regions in the magnetosphere. This paper describes the Ultraviolet Imager for the Global Geospace Sciences portion of the International Solar-Terrestrial Physics program. The instrument operates in the far ultraviolet (FUV) and is capable of imaging the auroral oval regardless of whether it is sunlit or in darkness. The instrument has an 8° circular field of view and is located on a despun platform which permits simultaneous imaging of the entire oval for at least 9 hours of every 18 hour orbit. The three mirror, unobscured aperture, optical system (f/2.9) provides excellent imaging over this full field of view, yielding a per pixel angular resolution of 0.6 milliradians. Its FUV filters have been designed to allow accurate spectral separation of the features of interest, thus allowing quantitative interpretation of the images to provide the parameters mentioned above. The system has been designed to provide ten orders of magnitude blocking against longer wavelength (primarily visible) scattered sunlight, thus allowing the first imaging of key, spectrally resolved, FUV diagnostic features in the fully sunlit midday aurorae. The intensified-CCD detector has a nominal frame rate of 37 s, and the fast optical system has a noise equivalent signal within one frame of 10R. The instantaneous dynamic range is >1000 and can be positioned within an overall gain range of 10⁴, allowing measurement of both the very weak polar cap emissions and the very bright aurora. The optical surfaces have been designed to be sufficiently smooth to permit this dynamic range to be utilized without the scattering of light from bright features into the weaker features. Finally, the data product can only be as good as the degree to which the instrument performance is characterized and calibrated. In the VUV, calibration of an an imager intended for quantitative studies is a task requiring some pioneering methods, but it is now possible to calibrate such an instrument over its focal plane to an accuracy of ±10%. In summary, very recent advances in optical, filter and detector technology have been exploited to produce an auroral imager to meet the ISTP objectives.     

How Engineers Can Conduct Cost-Benefit Analysis for PHM Systems

Individuals who work in the field of Prognostic and Health Management (PHM) technology have come to understand that PHM can provide the ability to effectively manage the operation, maintenance, and logistic support of individual assets or groups of assets through the availability of regularly updated and detailed health information. Naturally, prospective customers of PHM technology ask: "How will the implementation of PHM benefit my organization?" Typically, the response by individuals in the field is: "Anecdotal evidence indicates that PHM decreases maintenance costs, increases operational availability, and improves safety." This information helps the prospective customer understand the practical benefits of the technology, but that customer stills needs more information to justify their investment in the technology. The customer needs a calculated return on investment (ROI) figure for their particular asset that provides financial assessment of the benefit of the investment. The data, time, and expertise required to conduct a rigorous cost benefit analysis makes the effort seem daunting to the average engineer with little to no fimancial analysis training. The reality is that with a cursory understanding of the asset operation, maintenance, and logistic issues, a useful cost-benefit analysis can be conducted by engineers without business school training. Our purpose herein is to provide a general methodology for conducting a preliminary cost-benefit analysis that calculates an ROI for PHM implementation. We discuss the general types of information needed for the analysis, the quantifying of expected benefits, and the types of supporting data required to validate the benefit assumptions as well as an outline for the costing of PHM technology.