Ronald E. Allred

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.

UV RIGIDIZABLE CARBON-REINFORCED ISOGRID INFLATABLE BOOMS

The objective of this study was to demonstrate sunlight cure (UV) of a carbon fiber-reinforced open isogrid tube for Gossamer-type spacecraft. An epoxybased resin was developed and characterized that cures in sunlight at low temperatures (10°C) on carbon and carbon/glass hybrid tows. 1.5-m-long open isogrid tubes were fabricated using wet filament winding techniques. The tubes were sunlight cured and tested for degree of cure and mechanical properties. The demonstration hardware had a 99 percent cure and showed peak buckling loads equivalent to thermally cured tubes. This technology will allow fabrication of large, lightweight and low cost inflatable Gossamer structures that have significantly improved compliant packing efficiency without degradation of deployed precision and mechanical performance.

Rigidization-on-Command (ROC) Resin Development for Lightweight Isogrid Booms with MLI

The Rigidization-on-Command uf8ea (ROC uf8ea) resin development has focused on the development of resin systems that use UV light cure for rigidization. Polymeric sensitizers have been incorporated into the resin formulations to promote cure using Pen-Ray lamps and UV light-emitting diodes (LEDs). Formulations containing the polymeric sensitizers were examined by FTIR and DSC. Complete cure was observed after 15 min. exposure with the Pen-Ray lamps. Performance of the Pen-Ray lamps and UV LEDs was thoroughly characterized. Thermal models were developed to optimize the performance of the of the MLI insulation thermal oven used for orbital cure of the boom. Results show that -12 °C is the lowest temperature required for cure of the ROC uf6db resin systems.

UV rigidized carbon-reinforced isogrid boom for Gossamer applications

This work examined the feasibility of curing carbon fiber-reinforced open isogrid structures using sunlight. An orbital thermal analysis was conducted for these Gossamer structures with no insulation to determine the temperature profiles during the cure process. An epoxy-based resin was developed that showed near complete cure on carbon and hybrid carbon/glass tows and also cured at low temperatures. Demonstration hardware cured in sunlight and tested in compression to failure performed as well as similar thermally cured isogrid composites.

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.

Open-Celled Rigid Foams for Self-Deploying Foam Antenna Structures

The overall goal of this program is the development of an open-celled urethane foam system for use in self-deploying antenna structures. Advantages of such a system relative to current inflatable or self-deploying systems include high volumetric efficiency of packing, inherent restoring force, low (or no) outgassing, low thermal conductivity, high dynamic damping, mechanical isotropy, infinite shelf life, and easy fabrication with methods amenable to construction of large structures (i.e., spraying). The performance of our rigid open-cell foam systems, their crush and recovery behavior, potential packing scenarios, RF performance, and modeling are discussed.

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...