Near Space Applications Research Articles

Electro-optical characterization of a novel surface DBD plasma actuator operating in typical gas rarefaction conditions of near-space applications

The present work provides an experimental investigation of a novel surface dielectric barrier discharge plasma actuator consisting of a 0.3 mm-thick alkali-free quartz substrate as dielectric barrier material and titanium-tungsten electrodes. The device is manufactured using ultraviolet lithography and CMOS processes, and experiments are conducted under sinusoidal plasma actuation in a vacuum chamber with pressure ranging from 20 kPa to 0.01 Pa. Intensified high-speed visualizations of the plasma discharge and electrical signals (current/voltage/power) define the diagnostic toolbox. Results highlight that at 20 kPa the plasma discharge is driven by the formation of micro sparks on the inner edge of the exposed electrode, propagating downstream in larger current structures. At 1 kPa, the plasma discharge becomes more glow-type with negative current regimes longer than the positive ones, while the voltage signals preserve their sinusoidal shape. In such a plasma regime, the discharge extends over the entire region covered by the electrodes, suggesting the use of larger grounded electrodes to further enlarge the actuation region. Furthermore, the momentum action of the plasma discharge is not anymore unidirectional as it acts on the whole device plane. At pressure between 50 Pa and 2.5 Pa, the plasma discharge is unstable exhibiting a fast modification of the plasma discharge. Below 2.5 Pa, it becomes a volumetric full glow-type, extending its action mainly upstream with a higher plasma density on the exposed electrode. The establishment of the new plasma regime at a pressure below 2.5 Pa affects the electrical dissipated power and asymmetry of voltage and current signals.

Experimental and numerical analyses of electrohydrodynamic force according to air pressure

Electrohydrodynamic (EHD) force produced by corona discharge is considered as a new thrust for solar-powered aircraft and stratosphere balloons in near space. However, its performance at low air pressures remains to be clarified. An experiment of measuring the EHD force at 0.02 atm–1.0 atm (1 atm = 1.01325×105 Pa) is carried out with the wire-to-cylinder geometric structure. The ion distribution is analyzed by using the drift-diffusion model with two-dimensional numerical simulation. The experimental result shows that the EHD force is not linearly related to the corona discharge current at low air pressures. Numerical simulation finds that the proportion of ions in the counter-direction electric field increases from approximately 0.36% to 30% when the pressure drops from 1.0 atm to 0.2 atm. As a result, the EHD force with a constant power supply drops faster than the previous theoretical prediction in the ground experiment, suggesting that the consideration of counter-direction EHD force is necessary to improve the ionic wind propulsion efficiency in near-space applications.

Electrohydrodynamic thruster for near-space applications

Studies of the lifting force of an electrohydrodynamic thruster based on a corona discharge in wire-to-cylinder geometry in a rarefied atmosphere have been carried out. Electrohydrodynamic cell parameters at three interelectrode gaps of 50, 100, and 150 mm and at pressures from 1 to 0.05 atm with positive corona discharge were investigated. The experimental system included a vacuum chamber, an EHD thruster, a high voltage power source (HVDC), and a thrust, voltage, and current acquisition system was created. The effectiveness of the thruster reached 26 mN/W at atmospheric pressure at a 150 mm gap. At a pressure of 0.05 atm (corresponds to an altitude of 20 km) the maximum thrust per unit length was 1.8 mN/m and the thrust-to-power ratio was 0.5 mN/W. Theoretical and experimental data on the normalized effectiveness on the altitude of the thruster were obtained.

Design of interstellar digital communication links: Some insights from communication engineering

The design of an end-to-end digital interstellar communication system at radio frequencies is discussed, drawing on the disciplines of digital communication engineering and computer network engineering in terrestrial and near-space applications. One goal is a roadmap to the design of such systems, aimed at future designers of either receivers (SETI) or transmitters (METI). In particular we emphasize the implications arising from the impossibility of coordination between transmitter and receiver prior to a receiver's search for a signal. A system architecture based on layering, as commonly used in network and software design, assists in organizing and categorizing the various design issues and identifying dependencies. Implications of impairments introduced in the interstellar medium, such as dispersion, scattering, Doppler, noise, and signal attenuation are discussed. Less fundamental (but nevertheless influential) design issues are the motivations of the transmitter designers and associated resource requirements at both transmitter and receiver. Unreliability is inevitably imposed by non-idealities in the physical communication channel, and this unreliability will have substantial implications for those seeking to convey interstellar messages.

COLLABORATIVE LEARNING THROUGH VARIABLE LIFT CONTROL FOR NEAR-SPACE APPLICATIONS

This paper describes a collaborative capstone project on variable lift control for near-space applications. The project was intended to enhance collaborative learning of undergraduate students, assisted by several other organizations, including the amateur radio community, high-school students and teachers.

Flexible, Lightweight, Amorphous Silicon Based Solar Cells on Polymer Substrate for Space and Near-Space Applications

ABSTRACTUnited Solar Ovonic has leveraged its history of making amorphous silicon solar cells on stainless steel substrates to develop amorphous silicon alloy (a-Si:H)-based solar cells and modules on ∼25 μm thick polymer substrate using high-throughput roll-to-roll deposition technology for space and near-space applications. The solar cells have a triple-junction a-Si:H/a-SiGe:H/a-SiGe:H structure deposited by conventional plasma enhanced CVD (PECVD) using roll-to-roll processing. The cells have distinct advantages in terms of high specific power (W/kg), high flexibility, ruggedness, rollability for stowage, and irradiation resistance. The large area (23.9 cm x 32.1 cm) individual cells manufactured in large quantity can be readily connected into modules and have achieved initial, 25 °C, AM0 aperture-area efficiency of 9.8% and initial specific power of 1200 W/kg. We have conducted light-soak studies and measured the temperature coefficient of the current-voltage characteristics to determine the stable values at an expected operating temperature of 60 °C. The stable total-area efficiency and specific power at 60 °C are 7.2% and 950 W/kg, respectively. In this paper, we review the challenges and progress made in development of the cells, highlight some applications, and discuss current efforts aimed at improving performance.

Aerodynamic and Mission Performance of a Winged Balloon Guidance System

A winged balloon guidance system exploits the natural wind-field variation with the altitude available in planetary atmospheres to generate passive lateral control forces on a balloon using a tether-deployed aerodynamic surface below the balloon. Several balloon guidance system topics are discussed, including development status, physics and aerodynamics, systems performance, concept of operations, and the near-space applications of this technology for scientific, communications, and defense applications.

Statistical wind analysis for near-space applications

Statistical wind models were developed based on the existing observational wind data for near-space altitudes between 60 000 and 100 000 ft (18–30 km) above ground level (AGL) at two locations, Akon, OH, USA, and White Sands, NM, USA. These two sites are envisioned as playing a crucial role in the first flights of high-altitude airships. The analysis shown in this paper has not been previously applied to this region of the stratosphere for such an application. Standard statistics were compiled for these data such as mean, median, maximum wind speed, and standard deviation, and the data were modeled with Weibull distributions. These statistics indicated, on a yearly average, there is a lull or a “knee” in the wind between 65 000 and 72 000 ft AGL (20–22 km). From the standard statistics, trends at both locations indicated substantial seasonal variation in the mean wind speed at these heights. The yearly and monthly statistical modeling indicated that Weibull distributions were a reasonable model for the data. Forecasts and hindcasts were done by using a Weibull model based on 2004 data and comparing the model with the 2003 and 2005 data. The 2004 distribution was also a reasonable model for these years. Lastly, the Weibull distribution and cumulative function were used to predict the 50%, 95%, and 99% winds, which are directly related to the expected power requirements of a near-space station-keeping airship. These values indicated that using only the standard deviation of the mean may underestimate the operational conditions.