Houfei Fang

Concept Study of a 35-m Spherical Reflector System for NEXRAD in Space Application

NASA, under the Earth Science Technology Program, is currently developing a novel instrument concept with associated antenna technologies for a space-based 35-meter diameter, Ka-band (35-GHz) Doppler, radar for monitoring hurricanes, cyclones and severe storms from a geostationary orbit. The objectives of the system under study are measuring hurricane precipitation intensity (quantitative rainfall rate), dynamics, and life cycle, thus providing temporal information critical for creating advanced warning systems and improving numerical model prediction of track, intensity, rain rate, and hurricane-induced floods. The practical benefits derived from this kind of space system such as enhanced public safety, better emergency response and mitigation of property loss and economic impacts are evidently clear. However, space-based antenna system of this size and of this bandwidth capability is not attainable as a single-launch system with todays deployable structural technology. The concept study work presented here includes concept trades and analysis, and discussions on the challenges associated with designing, analyzing, fabricating, and testing of this large antenna system, potential issues and problems, and recommendations for potential solutions.

Prospects of Large Deployable Reflector Antennas for a New Generation of Geostationary Doppler Weather Radar Satellites

A novel mission concept, namely NEXRAD in Space, has been developed for detailed monitoring of hurricanes, cyclones, and severe storms from a geostationary orbit. This mission concept requires a space deployable 35-m diameter reflector that operates at 35GHz with a surface figure accuracy requirement of 0.21 mm RMS. This reflector is well beyond the current state-of-the-art. To implement this mission concept, several potential technologies associated with large, lightweight, spaceborne reflectors have been investigated by this study. These spaceborne reflector technologies include mesh reflector technology, inflatable membrane reflector technology and Shape Memory Polymer reflector technology.

Optimized Gore/Seam Cable Actuated Shape Control of Gossamer Membrane Reflectors

This investigation explores the feasibility of using an active gore/seam cable-based control system to reduce global root mean square figure errors due to thermal loading and inflation effects (W error) in large, gossamer, inflatable membrane reflectors. Analysis is performed on an inflated spherical membrane with polyvinylidene-fluorideactuated radial cables, for which the cable lengths and attachment points are designed via genetic algorithm optimization. It is found that throughproper tailoring of the cable lengths, significant global rootmean squarefigureerror reduction is achieved. Specifically, root mean square errors due to on-orbit thermal loading were reduced by approximately 75%with a 104-cable active gore/seam cable-control system that has amass equal to 15% the original reflector. Similarly,W errorswere reduced by approximately 95%with a 104-gore/seam cable-control systemwith a mass ratio of 12%. Finally, to deal with simultaneous W error and thermal loading with uncertain relative magnitudes, a hybrid gore/seam cable-control configuration based on a combination of independently optimized thermal andW-error cable patterns is considered. By adjusting the weights of a hybrid objective function, the gore/ seam cable-control system demonstrated robust shape-control performance for combined loading conditions. Because of the relatively lightweight designs and shape-control effectiveness, the gore/seam cable-shape-control concept seems promising for future gossamer reflector applications.

Optimal Design of Initial Surface Profile of Deployable Mesh Reflectors Via Static Modeling and Quadratic Programming

Large deployable high-frequency RF mesh reflectors are being envisioned for future space missions. This paper presents an initial study on surface shaping of such a mesh reflector. The deployable mesh reflector in consideration is modeled as a three-dimensional truss and a mathematical model considering static equilibrium of member tensions and external mounting forces is derived. Two optimization methods then are proposed to systematically determine an initial profile of the reflector. The initial profile so determined warrants that the deformed reflector surface matches the one by design and that the member tension forces fall in a specified range. The proposed mounting strategy is demonstrated on an 835-node mesh reflector.

Design and Technologies Development for an Eight-Meter Inflatable Reflectarray Antenna

This paper presents the mechanical and RF architectures of an 8-meter diameter multiple-band reflectarray antenna. Development of major components and aspects of the reflectarray antenna is also discussed. The most fundamental structural component of this reflectarray antenna is the Spring Tape Reinforced Aluminum Laminate Inflatable/Self- Rigidizable boom. The development of inflatable/self-rigidizable boom is an integrated part of our effort for developing the 8-meter multiple-band reflectarray antenna. Besides the inflatable/self-rigidizable boom technology, this paper also discusses other major technical challenges encountered in developing this reflectarray antenna, as well as technologies developed associated with these challenges. These technologies include double catenary for membrane tensioning, membrane flatness testing, spacing system for precisely separating membrane layers, multi-layer membrane fabrication process, and off-gravity system for studying the deployment process. In order to develop aforementioned technologies, several sub-scale engineering models have been assembled and the deployment of the antenna has been successfully demonstrated by this study.

Development of a 7-meter inflatable reflectarray antenna

This paper presents the structural and mechanical development of a 7-meter inflatable/self-rigidizable reflectarray antenna that is intended for space communication applications.

Shape Control of Large Membrane Reflector with PVDF Actuation

A high precision membrane reflector shape control system is presented by this paper. In this system, PVDF polymer actuators are attached to the back of the reflector to produce contraction/expansion forces to adjust the shape of the membrane reflector. An analytical model of the system which includes the membrane reflector, actuator and controller was developed to investigate the functionality of this control system on a 35-m diameter membrane reflector. The performance of this system under external disturbances such as in space thermal loads and W-error due to inflation has been investigated by this study. The feasibility of this control system has been demonstrated by numerical cases.

Large and High Precision Inflatable Membrane Reflector

Several planned Earth Science and Space Science observing missions require apertures that are larger than can currently be launched due to payload mass or payload volume constraints. Additionally, if the volume of the stowed antenna could be greatly reduced, there are proposed missions that could accommodate additional observing sensors to maximize mission benefits. There are other missions that require operations in higher frequencies than are currently compatible with the shape accuracy limitations of the current generation of deployable antenna. Inflatable antenna concepts have been proposed in the past as a method for deploying larger apertures from smaller packaged volumes. However, the shape accuracy achievable with these concepts generally prevents consideration of these concepts for higher frequency applications.

Experimental Study of a Membrane Antenna Surface Adaptive Control System

Due to their ultra lightweight and high packaging efficiency, membrane reflectors are getting more and more attention for mission architectures that need extremely large in-space deployable antennas. However, maintaining the surface shape of a membrane reflector to the instrument precision requirements is a very challenging problem. This experimental study investigated using PVDF membrane piezoelectric material as actuators to control the surface figures of membrane reflectors. The feasibility of this approach is demonstrated by several sets of test results.

THERMAL DISTORTION ANALYSES OF A THREE-METER INFLATABLE REFLECTARRAY ANTENNA

Gossamer space structures are relatively large, flimsy, and lightweight. As a result, they are more easily affected or degraded by space thermal environments compared to other space structures. This study examines the structural integrity of a Three-Meter Ka-Band Inflatable/Self-Rigidizable Reflectarray Antenna under space thermal environments. Space thermal environments discussed by this paper include Earth, Mars, and Jupiter orbits. The most critical structural components of this antenna are the two Spring Tape Reinforced Aluminum Laminate Inflatable/Self-Rigidizable Booms. The effects of the thermal distortion of the booms to surface deviation of the Radio Frequency membrane are also investigated.