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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Optically controlled phased-array antenna technology for space communication systems

Using MMICs in phased-array applications above 20 GHz requires complex RF and control signal distribution systems. Conventional waveguide, coaxial cable, and microstrip methods are undesirable due to their high weight, high loss, limited mechanical flexibility and large volume. An attractive alternative to these transmission media, for RF and control signal distribution in MMIC phased-array antennas, is optical fiber. Presented are potential system architectures and their associated characteristics. The status of high frequency opto-electronic components needed to realize the potential system architectures is also discussed. It is concluded that an optical fiber network will reduce weight and complexity, and increase reliability and performance, but may require higher power.

Kunath, Richard R.↗
NASA NTRS1992

Slot antenna SIS mixers for submillimeter wavelengths

We are developing improved versions of a slot antenna SIS mixer which we have previously described. The initial work demonstrated a double sideband noise temperature of 420 K for a 500 GHz quasi-optical SIS mixer employing a twin-slot antenna on a quartz dielectric substrate. A quartz hyperhemispherical lens is used to focus the incoming radiation onto the twin-slot antenna. The advantages of a twin-slot antenna include a low impedance (35 omega) and a clean, symmetric beam pattern into the dielectric with a 70 percent efficiency. In our original mixer, the radiation was coupled from the two slot antennas onto superconducting microstrip lines which fed the SIS junction. By performing an impedance transformation using tapered lines and by feeding the radiation from the two slots to the junction in parallel, the effective (real) impedance seen by the junction was reduced to just 4 omega. This very low impedance allowed a junction area of 2.3 sq micron to be used at 500 GHz, which was manufactured using optical lithography. However, no attempt was made to tune out the junction capacitance. We estimate that this capacitance reduces the impedance coupling efficiency to eta(sub Z) approx. equals 0.23, for our junction with omega R(sub N) C = 5.3 at 500 GHz. The recent development of techniques using electron-beam lithography to manufacture junctions with very small areas (approx. equals 0.1 sq microns) now allows considerably more flexibility in the design of SIS mixer circuits. We have redesigned the slot-antenna mixer to take advantage of this possibility. In particular, we have included a novel circuit which allows the junction capacitance to be tune out over a broad bandwidth. For instance, mixers designed for 800 GHz using NbN/MgO/NbN junctions with realistic parameters achieve a 3 dB impedance bandwidth of nearly 400 GHz. Furthermore, our circuit uses only short lengths of microstrip and should be less sensitive to RF losses than other designs. The improved impedance match should give a large reduction in noise temperature as compared to our previous mixer. The new devices are currently under fabrication. Further details of the design and any available experimental results are discussed.

Zmuidzinas, Jonas↗
NASA NTRS1985

Vibration/Libration Interaction Dynamics During the Orbiter Based Deployment of Flexible Members

Essential features of a general formulation for studying librational dynamics of a large class of spacecraft during deployment of flexible members are reviewed. The formulation is applicable to a variety of missions ranging from deployment of antennas, booms and solar panels to manufacturing of trusses for space platforms using the space shuttle. The governing nonlinear, non-autonomous and coupled equations of motion are extremely difficult to solve even with the help of a computer, not to mention the cost involved. To get some appreciation as to the complex interactions between flexibility, deployment and attitude dynamics as well as to help pursue stability and control analysis, the equations are linearized about their nominal deflected equilibrium configuration. The procedure is applied to the Space Shuttle based deployment of boom and plate-like members. Results suggest substantial influence of the inertia parameter, flexural rigidity of the appendages, orbit eccentricity, deployment velocity, initial conditions, etc. on the system response. The results should prove useful in planning of the Orbiter based experiments aimed at assessing effectiveness of procedures for studying dynamics and control of flexible orbiting members.

Modi, V. J.↗
NASA NTRS1985

Proceedings of the Workshop on Identification and Control of Flexible Space Structures, volume 1

Identification and control of flexible space structures were studied. Exploration of the most advanced modeling estimation, identification and control methodologies to flexible space structures was discussed. The following general areas were discussed: space platforms, antennas, and flight experiments; control/structure interactions - modeling, integrated design and optimization, control and stabilization, and shape control; control technology; control of space stations; large antenna control, dynamics and control experiments, and control/structure interaction experiments.

Rodriguez, G.↗
NASA NTRS2010

Atmospheric Compensation for Uplink Arrays via Radiometry

Uplink arrays for communications applications are gaining increased visibility within the NASA and military community due to the enhanced flexibility and reliability they provide. When compared with the conventional large, single aperture antennas currently comprising the Deep Space Network (DSN), for example, smaller aperture antenna arrays have the benefits of providing fault tolerance (reduced single-point failure), reduced maintenance cost, and enhanced capabilities such as electronic beam-steering and multi-beam operation. However, signal combining of antenna array elements spaced many wavelengths apart becomes problematic due to the inherent instability of earth's turbulent atmosphere, particularly at the frequencies of interest to the DSN (i.e., Ka-band). Degradation in the power combining of the individual elements comprising the array arises due to uncorrelated phase errors introduced as the signals propagate through the troposphere. It is well known that the fundamental source of this error is due to the inhomogeneous distribution of water vapor in the atmosphere [1]. Several techniques have been proposed to circumvent this issue, including the use of phase calibration towers and a moon bounce to generate a feedback loop which would provide a means of intermittent calibration of the system phase errors (thermal drifts, atmosphere) [2,3]. However, these techniques require repositioning of the antenna elements to perform this operation which ultimately results in reduced system availability. And, though they are sufficient for compensating for slow varying phase drifts, they are insufficient to compensate for faster varying phase errors, such as those introduced by the atmosphere. In this paper, preliminary radiometry and interferometry measurements collected by the NASA Glenn Research Center are analyzed and indicate that the use of optimized water vapor radiometers as a feedback system in a communications platform could provide the necessary atmospheric compensation technique to enhance the beamforming of uplink arrays.

Nessel, James A.↗
NASA NTRS1986

Robust multivariable controller design for flexible spacecraft

Large, flexible spacecraft are typically characterized by a large number of significant elastic modes with very small inherent damping, low, closely spaced natural frequencies, and the lack of accurate knowledge of the structural parameters. Summarized here is some recent research on the design of robust controllers for such spacecraft, which will maintain stability, and possible performance, despite these problems. Two types of controllers are considered, the first being the linear-quadratic-Gaussian-(LQG)-type. The second type utilizes output feedback using collocated sensors and actuators. The problem of designing robust LQG-type controllers using the frequency domain loop transfer recovery (LTR) method is considered, and the method is applied to a large antenna model. Analytical results regarding the regions of stability for LQG-type controllers in the presence of actuator nonlinearities are also presented. The results obtained for the large antenna indicate that the LQG/LTR method is a promising approach for control system design for flexible spacecraft. For the second type of controllers (collocated controllers), it is proved that the stability is maintained in the presence of certain commonly encountered nonlinearities and first-order actuator dynamics. These results indicate that collocated controllers are good candidates for robust control in situations where model errors are large.

Joshi, Suresh M.↗
NASA NTRS2024

RF Characterization of a Photocurable PEDOT:PSS:PEGDA Conductive Biomaterial for 3D-Printing Implantable Antennas

In this work, we demonstrate photocurable PEDOT:PSS:PEGDA biomaterial as a promising candidate for intracorporeal 3D printing. Intracorporeal 3D printing offers a less invasive method which offer flexibility to tailor the form factor of printed structures. Previous work has demonstrated the feasibility of a robotic probe to 3D-print biological tissues intracorporeally via a minor incision. This same probe could also 3D-print implantable antennas as long as a suitable conductive material is identified in terms of conductivity, biocompatibility, and ability to cure at room/body temperature for safety purposes. We assess the frequency-dependent conductivity of this biomaterial and explore the Radio-Frequency (RF) performance of resulting antennas operating in free-space and inside tissue-emulating phantoms. Results show that PEDOT:PSS biomaterial with 21% and 30% PEGDA content exhibit a conductivity of ~10 4 S/m up to 5 GHz, suitable for wireless implants. Comparing the two, 21% PEGDA content exhibits poorer curing abilities, while 30% PEGDA exhibits slightly lower conductivity. Measurements for 2.4 GHz free-space dipoles conducted in an anechoic chamber reveal only ~0.8 dB and ~1 dB lower gain for PEDOT:PSS:21%PEGDA and PEDOT:PSS:30%PEGDA biomaterial, respectively, as compared to their copper counterpart. For a 5 mm-deep implanted patch antenna, these two biomaterials exhibit 3.05 dB and 3.84 dB higher transmission loss than copper, respectively. If deemed necessary, this performance degradation can be overcome by increasing the overall antenna size since the printing process is now minimally invasive and miniaturization requirements can be relaxed.

3D-printing↗
NASA NTRS2023

Flex-Capsules for the Roman Space Telescope High Gain Antenna Gimbal

The Cable Wrap mechanism has been traditionally used for feeding power and telemetry through each gimbal actuator exiting at the gimbal output flange. Such a mechanism had often utilized round wire bundles or a multitude of single insulated conductors woven together flatwise to handle the angular rotation. Though flexible printed circuit board (PCB) is not a new technology, it was decided to implement it for the Roman Space Telescope (RST) High Gain Antenna Gimbal in an effort to improve reliability with consistency of manufacture and to save mass and minimize required volume. This paper provides a description of what we term Flex-Capsule (a similar vendor flight development is termed Twist Capsule), discusses the reasoning behind choosing a new engineering development over maintaining heritage, and includes commentary pertaining to life cycle analysis, electrical performance, and flexible PCB lubrication. Lessons learned from the design, analysis, and test campaign are also included. The conclusion is that benefits of pursuing the Flex-Capsule over heritage Cable Wrap have been realized.

twist capsule↗
NASA NTRS2023

Flex-Capsule for the Roman Space Telescope High Gain Antenna Gimbal

The Cable Wrap mechanism has been traditionally used for feeding power and telemetry through each gimbal actuator exiting at the Gimbal output flange. Such a mechanism had often utilized round wire bundles, or a multitude of single insulated conductors woven together flatwise to handle the angular rotation. Though flexible printed circuit board (PCB) is not a new technology, it was decided to implement it for the Roman Space Telescope (RST) High Gain Antenna Gimbal in an effort to improve reliability with consistency of manufacture and to save mass and minimize required volume. This paper provides a description of what we term Flex-Capsule (a similar vendor flight development is termed Twist Capsule), discusses the reasoning behind choosing a new engineering development over maintaining heritage, and includes commentary pertaining to life cycle analysis, electrical performance, and flexible PCB lubrication. Lessons learned from the design, analysis, and test campaign are also included. The conclusion is that benefits of pursuing the Flex-Capsule over heritage Cable Wrap have been realized.

twist capsule↗
NASA NTRS2007

Using EIGER for Antenna Design and Analysis

EIGER (Electromagnetic Interactions GenERalized) is a frequency-domain electromagnetics software package that is built upon a flexible framework, designed using object-oriented techniques. The analysis methods used include moment method solutions of integral equations, finite element solutions of partial differential equations, and combinations thereof. The framework design permits new analysis techniques (boundary conditions, Green#s functions, etc.) to be added to the software suite with a sensible effort. The code has been designed to execute (in serial or parallel) on a wide variety of platforms from Intel-based PCs and Unix-based workstations. Recently, new potential integration scheme s that avoid singularity extraction techniques have been added for integral equation analysis. These new integration schemes are required for facilitating the use of higher-order elements and basis functions. Higher-order elements are better able to model geometrical curvature using fewer elements than when using linear elements. Higher-order basis functions are beneficial for simulating structures with rapidly varying fields or currents. Results presented here will demonstrate curren t and future capabilities of EIGER with respect to analysis of installed antenna system performance in support of NASA#s mission of exploration. Examples include antenna coupling within an enclosed environment and antenna analysis on electrically large manned space vehicles.

Champagne, Nathan J.↗
NASA NTRS1986

Near millimeter wave imaging/multi-beam integrated antennas

Some preliminary results on a mixer design which is suitable for integration with tapered slot antennas have been obtained and published. This mixer design was tested both in a 4 to 10 GHz model, and (slightly modified) at 94 GHz. The latter utilized the same Hewlett-Packard beam-lead diodes which were used as detector diodes in the linearly tapered slot antennas (LTSA) arrays. These diodes are the most rugged to be found, and generally survive well on the flexible Kapton substrates. The 4 to 10 GHz version of this mixer has less than 6 dB conversion loss over an octave bandwidth. It uses a slot ring in a balanced configuration, and requires the LO to be fed through a separate port. A different design for a mixer which may be integrated with an LTSA antenna element is discussed. This mixer was tested at 38 GHz with the same HP beam-lead diodes, and has less than 10 dB conversion loss. Further work on mixers has emphasized theoretical modeling, using a computer program, which takes into account the effect of excess noise of Schottky-barrier diodes for the first time. Calculated results agree quantitatively with measured results on millimeter wave mixers.

Yngvesson, K. Sigfrid↗
NASA NTRS1995

Low profile antennas for MSAT applications

For MSAT applications, a number of different antennas have been designed and investigated. They include low gain omnidirectional antennas and medium gain to high gain directional antennas. The latter include both portable and vehicular antennas. While portable units are desirable to be low profile and low cost, the vehicular antennas have proved to be the most challenging antenna types for the mobile satellite application. The results of our efforts in design of such antennas are described briefly. Low profile designs are emphasized in most cases, and microstrip type radiators are therefore selected. The single radiator provides low gain omnidirectional patterns and is optimized for low cost applications. It provides low gains around 2-6 dBic and is useful mostly for the data transmission. Medium to high gain antennas are developed as arrays of omnidirectional elements. Again, different designs are optimized to meet the needs of different applications. For portable units, the array configuration can be flexible and is optimized for maximum broadside gains. For vehicular units, however the configurations are desirable to be low profile, or compact, and have means for scanning the antenna beam. For simplicity, fixed beam antennas with mechanical beam scan are selected. For these antennas, as well, different designs, having low profile or compact size, are selected and optimized to meet the MSAT gain and G/T requirements.

Shafai, L.↗
NASA NTRS2007

Antenna Technology and other Radio Frequency (RF) Communications Activities at the Glenn Research Center in Support of NASA's Exploration Vision

NASA s Vision for Space Exploration outlines a very ambitious program for the next several decades of the Space Agency endeavors. Ahead is the completion of the International Space Station (ISS); safely flight the shuttle (STS) until 2010; develop and fly the Crew Exploration Vehicle (Orion) by no later than 2014; return to the moon by no later than 2020; extend human presence across the solar system and beyond; implement a sustainable and affordable human and robotic program; develop supporting innovative technologies, knowledge and infrastructure; and promote international and commercial participation in exploration. To achieve these goals, a series of enabling technologies must be developed or matured in a timely manner. Some of these technologies are: spacecraft RF technology (e.g., high power sources and large antennas which using surface receive arrays can get up to 1 Gbps from Mars), uplink arraying (reduce reliance on large ground-based antennas and high operation costs; single point of failure; enable greater data-rates or greater effective distance; scalable, evolvable, flexible scheduling), software define radio (i.e., reconfigurable, flexible interoperability allows for in flight updates open architecture; reduces mass, power, volume), and optical communications (high capacity communications with low mass/power required; significantly increases data rates for deep space). This presentation will discuss some of the work being performed at the NASA Glenn Research Center, Cleveland, Ohio, in antenna technology as well as other on-going RF communications efforts.

Miranda, Felix A.↗
NASA NTRS1978

Galileo dual-spin attitude and articulation control system

Galileo, the first outer planet explorer to be configured as a dual spinner, will conduct intensive investigation of Jupiter's atmosphere, satellites, and magnetosphere. The exacting mission, coupled with the inherently complex spin and flexible body dynamics of the vehicle, demands careful design of the Galileo Attitude and Articulation Control System (AACS). A brief overview of the Galileo mission and spacecraft is presented, followed by a detailed discussion on the mechanization of the AACS and the many factors that influence its design. Included are discussions on attitude determination and control, high-gain antenna pointing, science scan platform pointing, nutation damping, wobble compensation, spin and despin control, and propellant migration and boom flexibility effects.

Ward, R. S.↗
NASA NTRS1988

Flexible spacecraft maneuver - Inverse attitude control and modal stabilization

A control law is presented for three-axis rotational maneuvers of a spacecraft (orbiter)-beam-tip body (antenna or a reflector) configuration based on nonlinear inversion and modal velocity feedback. Using invertibility and functional reproducibility results, a decoupling attitude control law is presented such that, in the closed-loop system, the attitude angles of the spacecraft are independently controlled using the control moments acting on the space vehicle. This controller asymptotically decouples the flexible dynamics from the rigid one and also allows the decomposition of the elastic dynamics into two subsystems representing the transverse deflections of the beam in two orthogonal planes. These low-order subsystems are used for derivation of a modal velocity feedback stabilizer using the force and moment actuators at the end body. Simulation results are presented to show that, in the closed-loop system, attitude control and elastic mode stabilization are accomplished in spite of the parameter uncertainty and disturbance torque input in the system.

Singh, Sahjendra N.↗
NASA NTRS2007

Characteristics of a Linearly Tapered Slot Antenna (LTSA) Conformed Longitudinally Around a Cylinder

The family of tapered slot antennas (TSA s) is suitable for numerous applications. Their ease of fabrication, wide bandwidth, and high gain make them desirable for military and commercial systems. Fabrication on thin, flexible substrates allows the TSA to be conformed over a given body, such as an aircraft wing or a piece of clothing for wearable networks. Previously, a Double Exponentially Tapered Slot Antenna (DETSA) was conformed around an exponential curvature, which showed that the main beam skewed towards the direction of curvature. This paper presents a Linearly Tapered Slot Antenna (LTSA) conformed longitudinally around a cylinder. Measured and simulated radiation patterns and the direction of maximum H co-polarization (Hco) as a function of the cylinder radius are presented.

Jordan, Jennifer L.↗
NASA NTRS1986

Nonlinear attitude control of flexible spacecraft under disturbance torque

A control law for large-angle single-axis rotational maneuvers of a spacecraft-beam-tip body (an antenna or a reflector) configuration is presented. It is assumed that an unknown but bounded disturbance torque is acting on the spacecraft. A model reference adaptive torque control law is derived for the slewing of the space vehicle. This controller includes a dynamic system in the feedback path and requires only attitude angle and rate of the space vehicle for feedback. For damping out the elastic motion excited by the slewing maneuver, a stabilizer is designed assuming that a torquer and a force actuator are available at the tip body. The stabilizer uses only the flexible modes for the synthesis of the control law. Simulation results are presented to show that fast, large-angle rotational maneuvers can be performed using the adaptive controller and the stabilizer in spite of the presence of continuously acting unknown torque on the spacecraft.

Singh, Sahjendra N.↗