Larry A. Harrah

Light Curing Rigidizable Inflatable Wing

The objective of this study was to prove the feasibility of using light-curing resins to rigidize an inflatable wing for terrestrial and space applications. Current inflatable wings rely on the continuous presence of an inflation gas to maintain their shape. Rigidization of inflatable wings provides several potential advantages, including reducing the vulnerability to punctures, increasing stiffness and load-carrying capability, allowing a higher aspect ratio for high altitude efficiency and longer missions, and reducing weight by eliminating the make up pressurization supply. This study was a multifaceted approach that included defining operating environments for Mars survey craft and military UAVs; analyzing wing loads during deployment and rigidization as a function of internal pressure and leak rate to determine needed rigidization times; developing rapid cure resin formulations with long shelf lives; fabricating, deploying, and rigidizing a wing half-span; and testing and characterizing the rigidized wing. Results show that the wings must deploy and cure rapidly at low temperatures for some missions. The maximum time allowed for the resin to rigidize is the range in time that the inflated and unrigidized wing maintains structural integrity to fly and provide lift for the vehicle while the wing is undergoing rigidization. A series of epoxy acrylate-based resin formulations were developed that cure in 10 seconds or less at 0qC. These resins also exhibited greater than 10 year storage lifetimes in accelerated aging studies and showed mechanical properties close to thermally cured aerospace epoxies. A half-span demonstration Eppler 398 airfoil was fabricated from E-glass fabric/ATI-ROCTME37X1 resin and a polyurethane bladder. After fabrication, the wing was packed and deployed two times. The unrigidized prepreg material was very compliant and was able to be packed tightly. After the packing and deployment trials were completed, the wing was inflated to 7 psig and given a 30-minute solar cure. The rigidized wing exhibited the desired high stiffness without inflation pressure.

Resin and Manufacturing Development for Light Curing Inflatable Composite Booms

†† ‡‡ Inflatable structures that become rigid after reaching the required shape are a promising approach for fabricating large space structures. A need exists for a controlled, clean rigidization technology to harden inflatable spacecraft after they have achieved the required shape. This program is addressing that need through the development of a family of radiation (ultraviolet [UV] and visible light) curable resins for structural composite matrices termed Ridigization on Commandi (ROC). These resins are being formulated to cure in low-temperature conditions with varying kinetics at low power inputs and at various wavelengths. This program is investigating cure using internal light sources under a blanket of multi-layer insulation (MLI). A study of using visible light emitting diodes (LEDs) for the internal light sources is presented in this paper. Topics covered include selection of LEDs and resin sensitizers that are active at those wavelengths, modeling of resin cure kinetics, measurement of resin mechanical properties after curing with LEDs, modeling of LED placement in isogrid booms, and manufacturing of isogrid booms using internal LEDs. Results show that the use of internal cure with LEDs is a viable approach for rigidizing inflatable space structures with low power in cold conditions. When optimized, the ROC technology will provide a versatile rigidization technology for the inflatables community.

Light Rigidizable Inflatable Wings for UAVs

The objective of this ongoing study is to prove the feasibility of using light-curing resins to rigidize an inflatable wing for terrestrial and space applications. Current inflatable wings rely on the continuous presence of an inflation gas to maintain their shape. Rigidization of inflatable wings provides several potential advantages, including reducing the vulnerability to punctures, increasing stiffness and load-carrying capability, allowing a higher aspect ratio for high altitude efficiency and longer missions, and reducing weight by eliminating the make up pressurization supply. A previous multifaceted study included defining operating environments for Mars survey craft and military UAVs; analyzing wing loads during deployment and rigidization as a function of internal pressure and leak rate to determine needed rigidization times; developing rapid cure resin formulations with long shelf lives; fabricating, deploying, and rigidizing a wing half-span; and testing and characterizing the rigidized wing. Results show that the wings must deploy and cure rapidly at low temperatures for some missions. The maximum time allowed for the resin to rigidize is the range in time that the inflated and unrigidized wing maintains structural integrity to fly and provide lift for the vehicle while the wing is undergoing rigidization. The current work includes internal light selection for wing rigidization, evaluation of urethane acrylate resin systems, and wing design and analysis.

Thermal Reversibility and Morphing of Light Curing Inflatable Composite Booms

Adherent Technologies, Inc. has been developing a light-curing resin technology (Rigidization on CommandTM) to allow the fabrication of inflatable structures that can be easily packed and deployed with hardening to a stable structure taking place on-orbit. One of the more significant criticisms of ROC technology has been the perceived idea that the systems are not reversible. While not reversible in the true chemical sense (i.e., the systems cannot be “uncured”), thermal reversibility is possible. All indicators are that these systems can, in fact, be fabricated on Earth, then packed and deployed in space, eliminating existing concerns regarding the quality of the on-orbit structures created using ROC technology. If the systems are rigidized on-orbit, a means exists for correcting defects if necessary.

Potential use of photovolatile polymers in solar sails

Extremely thin films are required for solar sails: possibly too fragile for handling, storage, and deployment. This work explores the use of photovolatile polymer coatings for the reinforcement of solar sails. The concept is that thick polymer films may be used to support and deploy thin films, but then decompose in sunlight (photo-degrade) and evaporate into space leaving the fully deployed sail at a very low mass. Additionally, these remarkable polymers degrade in the presence of (solar) ultraviolet light to result in gaseous products. As the volatile gas departs from the substrate, a high percentage of mass is lost until an ultra-thin solar sail remains. In addition to mass loss, the photovolatile coating produces a thrust that augments the photon momentum propulsion and results in a “propellantless” system with enhanced specific impulse. The coating also provides the strength and durability to protect the fragile sail film during the packing, launching and deployment phases of the mission. This approa...

Polysilylene copolymers for ultrafast scintillator applications. 2. Thin film formulations

Abstract Ultrafast scintillator fluors based on poly(silylene) copolymers have been developed in our laboratory for use in fast counting applications. The absorption and fluorescence spectra of this copolymer are quite sharp compared with most aromatic fluors and result in severe reabsorption problems. This reabsorption limits the usefulness of these materials in typical host solvents for liquid or plastic scintillator formulations. However, this reabsorption does not inhibit their use as thin films and we have demonstrated thin film scintillators with neat fluor polymer that gave superior light output relative to more conventional polymeric scintillator formulations.