Deployable optics comprised of an electroformed, replicated nickel optical surface supported by a reinforced shape memory resin composite substrate have the potential to meet the requirements for rapid fabrication of lightweight, monolithic, deployable, large optics. Evaluation has been completed for various composite constructions including shape memory resin, carbon fiber reinforcement and syntactic fillers bonded to the electroformed nickel surface. Results from optical and structural performance tests on the 0.5 meter aperture deployable test items are also applicable to non-deployable replicated composite optics.
Shape memory composite materials (SMC materials) are being developed by our program to make deployable space optics. The basic procedure involves electroforming an approximately 20 micron thin Ni surface onto a convex master and then casting the shape memory composite material onto the plated master. When good adhesion between the Ni and the SMC material is obtained, the Ni and SMC material come off the master in one piece. The result is a shiny mirror whose metallic surface remains intact after stowing and deploying of the mirror. Achieving the requisite adhesion requires treating the Ni prior to the application of the SMC material. The techniques we use to treat the Ni and the results of making mirrors are described.
Advances in earth and space instrumentation will come from future optical systems that provide large, deployable collecting areas of low areal mass density (< 10 kg/sq meter), affordable costs of fabrication ($10k/sq meter), and production times of a few years or less. Laminated optics comprised of an electroformed, replicated nickel optical surface supported by a reinforced shape memory resin composite substrate have the potential to meet the requirements for rapid fabrication of lightweight, monolithic, stowable, large optics, where large is defined to be 8 meters in diameter or larger. The high stiffness of a deployable composite substrate and a high quality, thin, electroformed metal optical surface combine the best properties of these disparate materials to provide a robust yet lightweight mirror system to meet the needs of future missions. The unique properties of shape memory resins in the composite provide a larger range of design parameters for production of usable optics. Results are presented from optical and structural tests of various surface and substrate constructions that may be solutions to the key issues, which are primarily material interface stress control, stability, and deployment repeatability. Initial requirements analysis and material properties measurements that determine both system and individual material target performance are presented.
The next generation of X-ray observatories requires large area optics, with optimal angular resolution, minimal mass, and affordable fabrication techniques. Furthermore, for survey applications, a Ritchey-Chretien or polynomial design is called for, which precludes the use of foil or glass segment cone approximations. In order to meet these requirements, we have been exploring the use of plasma spraying as a replication technology to improve shape control and stiffness with a minimal mass penalty. Our main improvements to the basic concept is the lamination of the sprayed material with electroformed Ni on the outer surface along with the electroformed Ni inner surface of the mirror. We have also used metal-coated ceramic micro-spheres for the sprayed material and controlled the substrate temperature during spraying. These enhancements show the promise of making the technology viable. An up-to-date characterization of the properties of test pieces are presented.
Dark Energy dominates the mass-energy content of the universe (about 73%) but we do not understand it. Most of the remainder of the Universe consists of Dark Matter (23%), made of an unknown particle. The problem of the origin of Dark Energy has become the biggest problem in astrophysics and one of the biggest problems in all of science. The major extant X-ray observatories, the Chandra X-ray Observatory and XMM-Newton, do not have the ability to perform large-area surveys of the sky. But Dark Energy is smoothly distributed throughout the universe and the whole universe is needed to study it. There are two basic methods to explore the properties of Dark Energy, viz. geometrical tests (supernovae) and studies of the way in which Dark Energy has influenced the large scale structure of the universe and its evolution. DUO will use the latter method, employing the copious X-ray emission from clusters of galaxies. Clusters of galaxies offer an ideal probe of cosmology because they are the best tracers of Dark Matter and their distribution on very large scales is dominated by the Dark Energy. In order to take the next step in understanding Dark Energy, viz. the measurement of the 'equation of state' parameter 'w', an X-ray telescope following the design of ABRIXAS will be accommodated into a Small Explorer mission in lowearth orbit. The telescope will perform a scan of 6,000 sq. degs. in the area of sky covered by the Sloan Digital Sky Survey (North), together with a deeper, smaller survey in the Southern hemisphere. DUO will detect 10.000 clusters of galaxies, measure the number density of clusters as a function of cosmic time, and the power spectrum of density fluctuations out to a redshift exceeding one. When combined with the spectrum of density fluctuations in the Cosmic Microwave Background from a redshift of 1100, this will provide a powerful lever arm for the crucial measurement of cosmological parameters.
The next generation of optical/IR telescopes will require large numbers of co-phased mirror segments. Therefore, some form of replication technology is desirable to reduce costs. Electroforming has the advantage that it is a commercially developed technology for replication, and the technology has been widely used for making X-ray mirrors (e.g. XMM-Newton). Composite materials are appealing, since a great deal of development work has been done with composites as well. There are 3 areas that need to be addressed: replication with minimal stress so as to produce a high quality figure; attachment of support of the mirror segment so as to maintain the figure quality; thermal control requirements. Here we present a discussion of the requirements that lead us to select replication as the fabrication technology and the advantages of replication. We report on our first results of making a concave and flat mirrors.
A novel shape memory composite material for the fabrication of thin, lightweight deployable mirrors is presented. The material has been evaluated for shape memory performance and dimensional stability. In addition, preliminary efforts have been directed toward the fabrication of lab-scale, replica mirrors. The concept combines a shape memory composite substrate with an electroplated metal reflective surface to provide a thin mirror with the ability to be deformed for packaging with good shape-recovery on deployment and reasonable post-deployed compliance that facilitates active shape control. The shape memory composite substrates are composed of Elastic Memory Composite (EMC) materials with appropriate reinforcements (i.e. fibers, particulates, or nanoreinforcements). The reflective surfaces are composed primarily of electroplated nickel with a variety of surface preparations to promote good adhesion to the composite substrate and provide optical-quality reflectance. Thin (i.e. less than 508 μm or 20 mils), EMC-composite mirrors have been prepared with adhered, electroplated nickel metal surfaces, which are less than 25.4 μm (i.e. 1 mil) thick. A single method of fabrication has been examined; electroplated thin metal deposition on a mandrel followed by subsequent adhesion to an EMC laminate. Investigative results of material fabrication, packaging and deployment testing, and preliminary optical-performance testing are presented.
<i>APEX</i> is a proposed mission for a Small Explorer (SMEX) satellite. <i>APEX</i> will investigate the density, temperature, composition, magnetic field, structure, and dynamics of hot astrophysical plasmas (log T = ~5-7), which emit the bulk of their radiation at EUV wavelengths and produce critical spectral diagnostics not found at other wavelengths. <i>APEX</i> addresses basic questions of stellar evolution and galactic structure through high-resolution spectroscopy of white dwarf stars, cataclysmic variables, the local interstellar medium, and stellar coronae. Thus <i>APEX</i> complements the <i>Chandra</i>, <i>Newton-XMM</i>, <i>FUSE</i>, and <i>CHIPS</i> missions. The instrument is a suite of 8 near-normal incidence spectrometers (~90-275 Angstroms, resolving power ~10,000, effective area 30-50 cm<sup>2</sup>) each of which employs a multilayer-coated ion-etched blazed diffraction grating and a microchannel plate detector of high quantum efficiency and high spatial resolution. The instrument is mounted on a 3-axis stabilized commercial spacecraft bus with a precision pointing system. The spacecraft is launched by a Taurus vehicle, and payload size and weight fit comfortably within limits for the 2210 fairing. Of order 100 targets will be observed over the baseline mission of 2 years. These are selected carefully to maximize scientific return, and all were detected in the <i>EUVE</i> and the <i>ROSAT</i> WFC surveys.
The next generation of optical/IR telescopes will require large numbers of co-phased segmented mirrors. Therefore, some form of replication technology is desirable to reduce costs. Electroforming has the advantage that it is a commercially developed technology for replication, and the technology has been widely used for making X-ray mirrors (e.g. XMM-Newton). Composite materials are appealing, since a great deal of development work as been done with composites as well. There are 3 areas that need to be addressed: replication with minimal stress so as to produce a high quality figure; attachment of support of the mirror segment so as to maintain the figure quality; and, thermal control requirements. Here we present a discussion of the requirements that lead us to select replication as the fabrication technology and the advantages of replication. We report on our first results of making a concave mirror and testing support methods of flats.