211 research outputs found
Development and evaluation of the elastic recovery concept for expandable space structures
Elastic recovery of expandable space structure
Marshall Space Flight Center Research and Technology Report 2019
Today, our calling to explore is greater than ever before, and here at Marshall Space Flight Centerwe make human deep space exploration possible. A key goal for Artemis is demonstrating and perfecting capabilities on the Moon for technologies needed for humans to get to Mars. This years report features 10 of the Agencys 16 Technology Areas, and I am proud of Marshalls role in creating solutions for so many of these daunting technical challenges. Many of these projects will lead to sustainable in-space architecture for human space exploration that will allow us to travel to the Moon, on to Mars, and beyond. Others are developing new scientific instruments capable of providing an unprecedented glimpse into our universe. NASA has led the charge in space exploration for more than six decades, and through the Artemis program we will help build on our work in low Earth orbit and pave the way to the Moon and Mars. At Marshall, we leverage the skills and interest of the international community to conduct scientific research, develop and demonstrate technology, and train international crews to operate further from Earth for longer periods of time than ever before first at the lunar surface, then on to our next giant leap, human exploration of Mars. While each project in this report seeks to advance new technology and challenge conventions, it is important to recognize the diversity of activities and people supporting our mission. This report not only showcases the Centers capabilities and our partnerships, it also highlights the progress our people have achieved in the past year. These scientists, researchers and innovators are why Marshall and NASA will continue to be a leader in innovation, exploration, and discovery for years to come
3-D frequency selective structures
The purpose of this thesis is to investigate novel designs of 3-D FSSs extending the potential functionality of the structure beyond that of its 2D analogue. First, a novel 3-D FSS architecture based on a circular ring unit element is presented. The length of the cylinder is shown to have a significant effect on the frequency characteristics of the FSS, providing tuning and reconfiguration from a band-stop to a band-pass filter response. Dielectric materials can also be introduced in the center of the cylindrical unit cell elements to simultaneously obtain a stop and pass band with a sharp transition. A similar close band response can be obtained using dual cylinder 3-D FSS. Alteration to this length adjusts the frequency characteristics of the FSS, enabling a close band response to be achieved. 3-D FSSs have displayed the ability to set resonant frequency and shift operational filter states with a change in the length of a cylindrical resonator. A new tuning technique using spring resonator element is also proposed in this thesis. The FSS frequency response can be adjusted by changing the spring height, h, with applied pressure. The functional characteristic of the FSS can also be altered between a band-stop and band-pass filter response It is often required that an FSS provides stable performance for various incidence angles. Hence, 3-D FSS with a response that is essentially independent of incident angle is presented. The FSS is a periodic array of 3-D hollow tapered resonators. The TE and TM angular stable is obtained by tapering the width of a cylinder with a square cross-section from upper opening to the lower opening. Impressive frequency stability and transmission characteristics have been achieved up to 80 degrees for both TE and TM incidence angles. A novel 3-D Frequency Selective Surface (FSS) with horn shaped resonators is also proposed which exhibits a very wide stop band. Simulation results prove that the FSS can realize selectivity of waves with a bandwidth more than 57%, and is very stable under oblique TM incidence angles from 0 to 80 degrees. FSSs with high selectivity and compact size are of increasing demand in wireless and mobile communication systems. The FSS with miniaturized resonator elements structure is shown to have a unit cell dimension that is miniaturized to 0.067 λ0, achieved by coupling two meandered wire resonators separated by single thin substrate layer. The FSS produces a stable angular response up to 80 degrees for TE and TM incident angles. The meandered wire resonator structure is also utilized to enable transmission through a subwavelength aperture. The structure exhibits effectively 100% transmission at approximately 1.94 GHz through a square aperture of only 0.035 λ0 0.035 λ0 in size. A complementary subwavelength resonator is also proposed which exhibits a narrow band filter response operating at 1.92 GHz with a fractional bandwidth of 0.04%. The subwavelength structures are sensitive to fabrication tolerances, but are realizable with modern printed circuit fabrication techniques
1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface
A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
Electromagnetic Absorbers Based on Frequency Selective Surfaces
Frequency Selective Surfaces (FSSs) are bidimensional
arrays of particles arranged in a periodic manner.
These surfaces can be lossless or lossy, depending on the
manufacturing process. They can be fabricated by using metallic or
controlled-resistance surface deposition. Lossy surfaces can be also
obtained through the integration of lumped components on a
metallic surface. The use of FSSs has fostered new research lines in
the design of electromagnetic absorbing surfaces, bringing
improvements both in terms of bandwidth/thickness ratio
maximization and in terms of customizability of the absorbing
bandwidth (narrowband, multi-band, wideband, ultra-wideband) for
specific applications. Artificial impedance surfaces (or HighImpedance
Surfaces, - HIS) are thin resonant cavities synthesized
by printing a periodic frequency selective surface on the top of a
grounded dielectric slab. By proper tailoring of the geometrical and
electrical properties of the FSS as well as the substrate, several
electrically-thin absorbing designs can be obtained. Ultranarrowband
absorbers with extremely stable angular behavior, often
addressed as metamaterial absorbers, can be realized by exploiting
only dielectric losses of commercial substrates. Narrowband,
wideband and ultra-wideband configurations are instead
implemented by also resorting to ohmic losses in a non-conductive
FSS. A thorough review of the available absorbers will be presented
together with multi-band and tunable design techniques.
Manufacturing processes and practical examples will be also
addressed, and the most interesting fields of application of the
presented structures will be described
Enhancing wireless communication system performance through modified indoor environments
This thesis reports the methods, the deployment strategies and the resulting system
performance improvement of in-building environmental modification. With the
increasing use of mobile computing devices such as PDAs, laptops, and the expansion
of wireless local area networks (WLANs), there is growing interest in increasing
productivity and efficiency through enhancing received signal power. This thesis
proposes the deployment of waveguides consisting of frequency selective surfaces
(FSSs) in indoor wireless environments and investigates their effect on radio wave
propagation. The received power of the obstructed (OBS) path is attenuated
significantly as compared with that of the line of sight (LOS) path, thereby requiring
an additional link budget margin as well as increased battery power drain. In this
thesis, the use of an innovative model is also presented to selectively enhance radio
propagation in indoor areas under OBS conditions by reflecting the channel radio
signals into areas of interest in order to avoid significant propagation loss.
An FSS is a surface which exhibits reflection and/or transmission properties as a
function of frequency. An FSS with a pass band frequency response was applied to an
ordinary or modified wall as a wallpaper to transform the wall into a frequency
selective (FS) wall (FS-WALL) or frequency selective modified wall (FS-MWALL).
Measurements have shown that the innovative model prototype can enhance 2.4GHz (IEEE 802.11b/g/n) transmissions in addition to the unmodified wall, whereas
other radio services, such as cellular telephony at 1.8GHz, have other routes to
penetrate or escape.
The FSS performance has been examined intensely by both equivalent circuit
modelling, simulation, and practical measurements. Factors that influence FSS
performance such as the FSS element dimensions, element conductivities, dielectric
substrates adjacent to the FSS, and signal incident angles, were investigated. By
keeping the elements small and densely packed, a largely angle-insensitive FSS was
developed as a promising prototype for FSS wallpaper. Accordingly, the resultant can
be modelled by cascading the effects of the FSS wallpaper and the ordinary wall (FSWALL) or modified wall (FS-MWALL). Good agreement between the modelled,
simulated, and the measured results was observed.
Finally, a small-scale indoor environment has been constructed and measured in a
half-wave chamber and free space measurements in order to practically verify this
approach and through the usage of the deterministic ray tracing technique. An initial
investigation showing that the use of an innovative model can increase capacity in
MIMO systems. This can be explained by the presence of strong multipath
components which give rise to a low correlated Rayleigh Channel. This research work
has linked the fields of antenna design, communication systems, and building
architecture
DESIGN, ANALYSIS AND VALIDATION OF A TWIST REFLECTOR MONOPULSE ANTENNA SYSTEM WITH RADOME
PhDThis thesis presents a new approach to the hardware test environment for a twist reflector
monopulse antenna system with a radome extending current measurement practice. New
research is presented on the optimisation of the design of a twist reflector monopulse
antenna system with a radome, signi cantly improving the design and the design process.
A unique extension to current measurement practice, for single channel antennas, is presented to determine the best practice method on phase stable measurements of a multi-
channel antenna on a moving positioner. A novel axis transform for a 3 axis positioner
system located within an anechoic chamber is derived. It allows for true performance
measurement of a twist reflector antenna with a radome. This progresses the field of antenna measurement as, uniquely, this axis transform allows the aberration caused by the
antenna radome to be measured and included.
Design improvements have been made on polarisation selective grids, the matched thickness of the radome and a new software method that removes the need for a comparator and
increases the robustness of the antenna system. Polarisation selective grids, constructed
from a set of parallel conductors, have a wide range of uses in antenna systems. This thesis
shows that the depth of a copper grid line can be reduced to 15 m and still provide better
than -25 dB cross-polar isolation. This is contrary to current understanding at 30 times
the skin depth. A new combined approach to radome thickness optimisation is presented
that reduces the time taken to calculate the optimal thickness by over 3 orders of magnitude and the computer memory by over 2 orders of magnitude without compromising
accuracy. The use of a digital comparator is described and leads to a novel method to
compensate for a failed feed element, verifi ed in both simulation and anechoic chamber
measurements
System design of the Pioneer Venus spacecraft. Volume 1: Executive summary
The NASA Ames Research Center Pioneer Venus Project objective is to conduct scientific investigations of the planet Venus using spin stabilized spacecraft. The defined approach to accomplish this goal is to implement a multiprobe spacecraft mission and an orbiter spacecraft mission. Candidate launch vehicles for the Pioneer Venus missions were the Thor/Delta and Atlas/Centaur. The multiprobe spacecraft consists of a probe bus, one large probe, and three small probes. The probes are designed to survive to the surface of Venus, and to make in situ measurements of the Venusian atmosphere; the probe bus enters the atmosphere and makes scientific measurements until it burns out. The orbiter mission uses a spacecraft designed to orbit Venus for 225 days with an orbit period of about 24 hours (h). The probe bus and orbiter designs are to use a common spacecraft bus
Radar Technology
In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design
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