NASA's Terrestrial Planet Finder mission
Explore the source record for details and available documents.
TPF Terrestrial Planet Finder↗
Engineering topics
Coulter, D. R.
Publications and source records attributed to Coulter, D. R..
NASA's Terrestrial Planet Finder mission: the search for habitable planets
This paper describes the current status of TPF as well as outlines the plans for near term science investigations, mission studies and technology development leading to a mission architecture selection in the 2006 time frame in support of a launch by the middle of the next decade.
TPF Terrestrial Planet Finder↗
NASA advanced cryocooler technology development program
This paper presents an overview of the ACTDP program including programmatic objectives and timelines, and conceptual details of the cooler concepts under development.
cryocooler↗
ITTT: a state-of-the-art ultra-lightweight all-Be telescope
The Infrared Technology Testbed Telescope (ITTT) is a demonstration telescope meeting the needs of the SIRTF mission. It is a Ritchey-Cretien form designed for diffraction limited performance at 6.5 um, at 5.5 K with an 85 cm. clear aperture.
infrared telescope cryogenic stability beryllium S↗
The SIRTF Telescope Test Facility: The First Year
The SIRTF Telescope Test Facility (STTF) consists of an optical dewar for testing mirrors of up to 1m diameter and f less than 6 at temperatures from 300K to 5K and a phase shift interferometer for optical characterization. The STTF was brought on line in early 1995.
Cryogenic↗
Recent Advances in Cryogenic Optics Technology for Space Infrared Telescope and Interferometer Systems
In this paper we will describe recent advances in the development of optical systems for future space infrared telescope and interferometer applications which will operate at very low or cryogenic temperatures (T less then or equal to 77K) with emphasis on beryllium and silicon carbide optics.
optical↗
Direct measurements of nonlinear absorption and refraction in solutions of phthalocyanines
Direct measurements are reported of the excited singlet-state absorption cross section and the associated nonlinear refractive cross section using picosecond pulses at 532 nm in solutions of phthalocyanine and naphthalocyanine dyes. By monitoring the transmittance and far-field spatial beam distortion for different pulsewidths in the picosecond regime, it is shown that both the nonlinear absorption and refraction are fluence (energy-per-unit-area) rather than irradiance dependent. Thus, excited-state absorption is the dominant nonlinear absorption process, and the observed nonlinear refraction is also due to real population excitation.
Wei, T. H.↗
Amorphous silicon deposition diagnostics using coherent anti-Stokes Raman spectroscopy
This paper reports on an in situ silicon deposition process diagnostics, using CARS performed at state-of-the-art a-Si:H film deposition conditions in a reactor designed for a-Si:H solar cell fabrication. The diagnostics procedure measures the silane depletion in an RF plasma as a function of the silane flow rate (where the relationship is linear between 50-percent depletion, at a flow rate of 5.6 sccm, and about 8-percent depletion, at 80 sccm) and the RF power (where the silane depletion is linearly dependent on the RF power in the region of 4 to 12 W). The linear RF power dependence of the silane depletion is considered to be consistent with the mechanism of silane decomposition primarily by electron impact dissociations, while the flow rate dependence is interpreted in terms of the residence time of the SiH4 molecules in the glow discharge region, where an increase of the residence time at a low flow rate results in a high depletion ratio.
Shing, Y. H.↗
The effects of energetic proton bombardment on polymeric materials: Experimental studies and degradation models
This report describes 3 MeV proton bombardment experiments on several polymeric materials of interest to NASA carried out on the Tandem Van De Graff Accelerator at the California Institute of Technology's Kellogg Radiation Laboratory. Model aromatic and aliphatic polymers such as poly(1-vinyl naphthalene) and poly(methyl methacrylate), as well as polymers for near term space applications such as Kapton, Epoxy and Polysulfone, have been included in this study. Chemical and physical characterization of the damage products have been carried out in order to develop a model of the interaction of these polymers with the incident proton beam. The proton bombardment methodology developed at the Jet Propulsion Laboratory and reported here is part of an ongoing study on the effects of space radiation on polymeric materials. The report is intended to provide an overview of the mechanistic, as well as the technical and experimental, issues involved in such work rather than to serve as an exhaustive description of all the results.
Coulter, D. R.↗
Electronic energy transfer and quenching in copolymers of styrene and 2-(2-prime-hydroxy -5-prime-vinylphenyl)-2H-benzotriazole Photochemical processes in polymeric systems. X
Intensity and lifetime quenching of the polystyrene monomer and excimer fluorescence emission by a pendant quencher have been studied in the solid state and in solution for a series of copolymers of styrene and 2-(2-prime-hydroxy-5-prime-vinylphenyl)-2H-benzotriazole. Two mechanisms of quenching have been identified. One involves interception of the migrating monomer excitation by the quencher, and the other involves a single-step Foerster energy-transfer process from the excimer traps to a quencher. The relative efficiencies of these two quenching mechanisms in the solid state and in solution have been compared and related to the efficiency of electronic energy migration. An estimate of the excimer trap concentration in solid polystyrene is also reported.
Coulter, D. R.↗
Laser Photoacoustic Technique Detects Photo-Oxidation
Laser photoacoustic instrument detects small amounts of oxidation in polymers. Instrument used to evaluate resistance to oxidation in Sunlight of polymer encapsulants for solar-cell arrays. With instrument, researchers monitor samples for early stages of photooxidation and study primary mechanisms of oxidation and degradation. Effects of these mechanisms masked during later stages.
Liange, R. H.↗
Direct observation of the excited-state proton transfer and decay kinetics of internally hydrogen-bonded photostabilizers in copolymer films
The excited-state dynamics of a 2-hydroxyphenylbenzotriazole (HPB) photostabilizer copolymerized with polystyrene are reported. HPB fluorescence from these copolymer films is observed at approximately 630 nm, characteristic of the proton-transferred excited state of HPB, and it has a risetime of less than 10 ps and a decay time of 28 + or - 4 ps at room temperature. Measurement of the relative fluorescence quantum yield as a function of temperature gives the activation energy for nonradiative decay of this state to be E/hc = 259 + or 25/cm.
Oconnor, D. B.↗
Bonding Solar-Cell Modules
Status of research program on chemical bonding for solar-cell arrays subject of 57-page report. Program aimed at identifying, developing, and validating weather-stable chemical bonding promoters. Materials key to ensuring long life in encapsulated photovoltaic modules for electric-power generation. To be cost-effective, modules must hold together for at least 20 years, reliably resisting delamination and separation of component materials
Coulter, D. R.↗
Chemical bonding technology for terrestrial photovoltaic modules
Encapsulated photovoltaic modules must hold together for 20 years, reliably resisting delamination and separation of any of the component materials. Delamination of encapsulation materials from each other, or from solar cells and interconnects, can create voids for accumulation of water, promoting corrosive failure. Delamination of silicone elastomers from unprimed surfaces was a common occurrence with early modules, but the incidences of silicone delamination with later modules decreased when adhesion promoters recommended by silicone manufacturers were used. An investigation of silicone delamination from unprimed surfaces successfully identified the mechanism, which was related to atmospheric oxygen and moisture. This early finding indicated that reliance on physical bonding of encapsulation interfaces for long life in an outdoor environment would be risky. For long outdoor life, the material components of a module must therefore be held together by weather-stable adhesion promoters that desirably form strong, interfacial chemical bonds.
Coulter, D. R.↗
Pulse radiolysis of epoxy-based matrix materials
Electron beam pulse radiolysis (600 KeV, 3 nsec) experiments have been carried out on epoxy-based matrix materials. Time and wavelength resolved emission and transient absorption techniques as well as ESR studies have been utilized to identify and monitor short lived reactive intermediates resulting from energetic electron impact. An energy deactivation model based on the results of this work has been developed. Recombination of primary charged species is found to be fast, resulting in the formation of longer lived excited electronic states and radicals which control the subsequent energy deactivation.
Coulter, D. R.↗
Polymers in solar energy utilization
A laser photoacoustic technique (LPAT) has been verified for performing accelerated life testing of outdoor photooxidation of polymeric materials used in solar energy applications. Samples of the material under test are placed in a chamber with a sensitive microphone, then exposed to chopped laser radiation. The sample absorbs the light and converts it to heat by a nonradiative deexcitation process, thereby reducing pressure fluctuations within the cell. The acoustic signal detected by the microphone is directly proportional to the amount of light absorbed by the specimen. Tests were performed with samples of ethylene/methylacrylate copolymer (EMA) reprecipitated from hot cyclohexane, compressed, and molded into thin (25-50 microns) films. The films were exposed outdoors and sampled by LPAT weekly. The linearity of the light absorbed with respect to the acoustic signal was verified.Correlations were established between the photoacoustic behavior of the materials aged outdoors and the same kinds of samples cooled and heated in a controlled environment reactor. The reactor tests were validated for predicting outdoor exosures up to 55 days.
Liang, R. H.↗
Mechanisms of Interactions of Energetic Electrons with Epoxy Resins
The mechanism of deactivation of energy of excitation in a resin system was investigated on optical excitation as well as excitation by high energy electrons. This mechanism involves formation of excited state complexes, known as exciplexes which have a considerable charge transfer character. This mechanism will be used to develop a degradation model for epoxy matrix materials deployed in a space environment.
Gupta, A.↗