Solar energy is the ideal power choice for high-altitude long-endurance airships. Photovoltaic array and its operation is one of the most critical aspects to the stratospheric airship's design and capabilities, but the research on thermal characteristics of photovoltaic array for the airship's design is rare. This paper develops the thermodynamic models of photovoltaic array and airship, based on which the three-dimensional temperature profile and output power of photovoltaic array are presented, the effects of the latitude, time of the year, wind speed, and insulation on the power output of the photovoltaic array are investigated, and the effects of photovoltaic array on thermal characteristics of the airship are explored. The results indicate that the latitude, time of the year, wind speed, and insulation affect the quantity and distribution of output power of photovoltaic array, and that the photovoltaic array can aggravate the superheat or supercool of the airship, so that the airship's hull requires higher intensity, expandability, and ductibility.

Research on Thermal Characteristics of Photovoltaic Array of Stratospheric Airship

The term “biological complexes” broadly encompasses particles as diverse as multisubunit enzymes, viral capsids, transport cages, molecular nets, ribosomes, nucleosomes, biological membrane components and amyloids. The complexes represent a broad range of stability and composition. Atomic force microscopy offers a wealth of structural and functional data about such assemblies. For this review, we choose to comment on the significance of AFM to study various aspects of biology of selected non-membrane protein assemblies. Such particles are large enough to reveal many structural details under the AFM probe. Importantly, the specific advantages of the method allow for gathering dynamic information about their formation, stability or allosteric structural changes critical for their function. Some of them have already found their way to nanomedical or nanotechnological applications. Here we present examples of studies where the AFM provided pioneering information about the biology of complexes, and examples of studies where the simplicity of the method is used toward the development of potential diagnostic applications.

AFM of biological complexes: what can we learn?

On the basis of some assumptions and simplifications, a thermal model is developed to describe the heat transfer behavior of stratospheric airships. The Runge-Kutta method is adopted to solve the governing equations. Considering the airship flight state, control style, and working environment, some of its basic characteristics and thermal performances are investigated. The variations in the temperatures of the film, internal helium, and internal air of the airship with altitude during its ascent and descent are obtained. The results reveal that among the influencing factors, the airship velocity, air filling, and air venting seriously affect its thermal performance. When the airship ascends in the adiabatic situation or the venting velocity reaches a specific value above 11 km, the temperature of the film could drop to its damage point, which would seriously influence the airship operation.

Thermal Performance of Stratospheric Airships During Ascent and Descent

Thermal modeling of stratospheric airships

Effects of solar array on the thermal performance of stratospheric airship

The High Altitude Airship (HAA) has various potential applications and mission scenarios that require onboard energy harvesting and power distribution systems. The energy source considered for HAAs is solar photon energy that allows the use of either photovoltaic (PV) cells or advanced thermoelectric (ATE) converters. Both PV cells and an ATE system were briefly compared to identify the advantages of ATE for HAA applications in this study. Utilizing the estimated high efficiency of a three-staged ATE in a tandem mode, the ATE generates a higher quantity of harvested energy than PV cells for mission scenarios. When the ATE performance figure of merit of 5 is considered, the cascaded efficiency of a three-staged ATE system approaches an overall efficiency greater than 60%. Based on this estimated efficiency, the configuration of a HAA and the power utility modules are defined.

Power Technology for Application-Specific Scenarios of High Altitude Airships

Currently available power storage systems, such as those used to supply power to microelectronic devices, typically consist of a single centralized canister and a series of wires to supply electrical power to where it is needed in a circuit. As the size of electrical circuits and components become smaller, there exists a need for a distributed power system to reduce Joule heating, wiring, and to allow autonomous operation of the various functions performed by the circuit. Our research is being conducted to develop a bio-nanobattery using ferritins reconstituted with both an iron core (Fe-ferritin) and a cobalt core (Co-ferritin). Both Co-ferritin and Fe-ferritin were synthesized and characterized as candidates for the bio-nanobattery. The reducing capability was determined as well as the half-cell electrical potentials, indicating an electrical output of nearly 0.5 V for the battery cell. Ferritins having other metallic cores are also being investigated, in order to increase the overall electrical output. Two dimensional ferritin arrays were also produced on various substrates, demonstrating the necessary building blocks for the bio-nanobattery. The bio-nanobattery will play a key role in moving to a distributed power storage system for electronic applications.

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Development of a bionanobattery for distributed power storage systems

Horse spleen ferritin with iron core (Fe-ferritin) and the ferritin reconstituted with cobalt (Co-ferritin) are considered for the concept of a bio-nanobattery that will be a key element to a distributed energy storage system. The Co-ferritin has a good stability and was successfully synthesized and tested for reducing capability. The redox potential of Fe/Co ferritins obtained as a bio-nanobattery unit was 0.50 V. A two - dimensional ferritin array was also fabricated on Si substrate with a c ationized ferritin, by the spin self- assembly (SSA) deposition.

Development of nanoscale power system using biological self-assembly method

The concept of a bio-nanobattery is based on ferritin, an iron storage protein that naturally exists in most biological systems. Biomineralization allows ferritins to reconstitute iron core with various metallic cores. When the ferritin half cells are integrated into a complete battery system, the fabrication of well-organized ferritin arrays is necessary and very important to enhance the overall battery performance, improving the battery power density, the power discharge rate, the compactness of battery size, etc. In this work, a spin self-assembly (SA) method was used for producing a thin-film array structure of ferritins. The spin SA deposition was repeated until two bilayers of cationized and native ferritins or 4 alternating ferritin layers were achieved. High-resolution field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and variable angle spectroscopic ellipsometry (VASE) were used to characterize the multilayered ferritin arrays. The thickness of ferritin multilayer increased linearly as the spin SA deposition was repeated. The spin SA deposition method produced well-organized, uniform, and flat ferritin layers in a much shorter period of time, compared with Langmuir-Blodgett or dipping deposition methods. Such enhancement can be attributed to a strong electrostatic attraction that holds the ferritin layer on the substrate during the spin-coating process while hydrodynamic drag and centrifugal forces remove loosely-bound ferritins.

Fabrication of cell structures for bionanobattery

A bio-nanobattery is an electrical energy storage device that utilizes organic materials and processes on an atomic, or nanometer-scale. The bio-nanobattery under development at NASA s Langley Research Center provides new capabilities for electrical power generation, storage, and distribution as compared to conventional power storage systems. Most currently available electronic systems and devices rely on a single, centralized power source to supply electrical power to a specified location in the circuit. As electronic devices and associated components continue to shrink in size towards the nanometer-scale, a single centralized power source becomes impractical. Small systems, such as these, will require distributed power elements to reduce Joule heating, to minimize wiring quantities, and to allow autonomous operation of the various functions performed by the circuit. Our research involves the development and characterization of a bio-nanobattery using ferritins reconstituted with both an iron core (Fe-ferritin) and a cobalt core (Co-ferritin). Synthesis and characterization of the Co-ferritin and Fe-ferritin electrodes were performed, including reducing capability and the half-cell electrical potentials. Electrical output of nearly 0.5 V for the battery cell was measured. Ferritin utilizing other metallic cores were also considered to increase the overall electrical output. Two dimensional ferritin arrays were produced on various substrates to demonstrate the feasibility of a thin-film nano-scaled power storage system for distributed power storage applications. The bio-nanobattery will be ideal for nanometerscaled electronic applications, due to the small size, high energy density, and flexible thin-film structure. A five-cell demonstration article was produced for concept verification and bio-nanobattery characterization. Challenges to be addressed include the development of a multi-layered thin-film, increasing the energy density, dry-cell bionanobattery development, and selection of ferritin core materials to allow the broadest range of applications. The potential applications for the distributed power system include autonomously-operating intelligent chips, flexible thin-film electronic circuits, nanoelectromechanical systems (NEMS), ultra-high density data storage devices, nanoelectromagnetics, quantum electronic devices, biochips, nanorobots for medical applications and mechanical nano-fabrication, etc.

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Sang-Hyon Chu

Papers

Power Technology for Application-Specific Scenarios of High Altitude Airships

Development of a bionanobattery for distributed power storage systems

Development of nanoscale power system using biological self-assembly method

Fabrication of cell structures for bionanobattery

Bio-Nanobattery Development and Characterization