We report on the optical performance of carbon fiber reinforced polymer composite (CFRP) mirrors after 1.49 years exposure onboard the Materials International Space Station Experiment (MISSE 7). Mirror samples were placed on the MISSE 7A tray, outside the ISS from October 2009 and retrieved September 2011. The environment was an extreme environment exposure test, which is considered “worst case” for survivability of composite mirrors for imaging applications in low-earth orbit (LEO) The results from testing the returned flight samples show degradation in two of the mirror’s aluminum coatings. However, the surface figure of one of the coated mirrors remained largely unchanged after the long-duration experiment. Test results will be compared against the original, pre-flight mirror performance for each of the 3 samples.
An active reflective component can change its focal length by physically deforming its reflecting surface. Such elements exist at small apertures, but have yet to be fully realized at larger apertures. This paper presents the design and initial results of a large-aperture active mirror constructed of a composite material called carbon fiber reinforced polymer (CFRP). The active CFRP mirror uses a novel actuation method to change radius of curvature, where actuators press against two annular rings placed on the mirror’s back. This method enables the radius of curvature to increase from 2000mm to 2010mm. Closed-loop control maintains good optical performance of 1.05 waves peak-to-valley (with respect to a HeNe laser) when the active CFRP mirror is used in conjunction with a commercial deformable mirror.
The Naval Research Laboratory and Sandia National Laboratories have been actively researching
the use of carbon fiber reinforced polymer material as optical elements in many optical systems.
Active optical elements can be used to build an optical system capable of changing is optical
zoom. We have developed a two-element optical system that uses a large diameter, thin-shelled
carbon fiber reinforced polymer mirror, actuated with micro-positioning motors, and a high
actuator density micro-electro-mechanical deformable mirror. Combined with a Shack-Hartmann
wavefront sensor, we have optimized this actuated carbon fiber reinforced polymer deformable
mirror's surface for use with a forthcoming reflective adaptive optical zoom system. In this paper,
we present the preliminary results of the carbon fiber reinforced polymer deformable mirror's
surface quality and the development of the actuation of it.
Thin-shelled composite mirrors have been recently proposed as both deformable mirrors
for aberration correction and as variable radius of curvature mirrors for phase diversity,
auto focus, and adaptive optical zoom. The requirements of actuation of a composite
mirror far surpass those for MEMS deformable mirrors. This paper will discuss the
development of a finite element model for a 0.2 meter carbon fiber reinforced polymer
mirror for use as a variable radius of curvature mirror in conjunction with a MEMS
deformable mirror for aberration correction.
Carbon-fiber reinforced polymer (CFRP) composite is an attractive material for fabrication of optics due to its high
stiffness-to-weight ratio, robustness, zero coefficient of thermal expansion (CTE), and the ability to replicate multiple
optics from the same mandrel. We use 8 and 17 cm prototype CFRP thin-shell deformable mirrors to show that residual
CTE variation may be addressed with mounted actuators for a variety of mirror sizes. We present measurements of
surface quality at a range of temperatures characteristic of mountaintop observatories. For the 8 cm piece, the figure
error of the Al-coated reflective surface under best actuator correction is ~43 nm RMS. The 8 cm mirror has a low
surface error internal to the outer ring of actuators (17 nm RMS at 20°C and 33 nm RMS at -5°C). Surface roughness is
low (< 3 nm P-V) at a variety of temperatures. We present new figure quality measurements of the larger 17 cm mirror,
showing that the intra-actuator figure error internal to the outer ring of actuators (38 nm RMS surface with one-third the
actuator density of the 8 cm mirror) does not scale sharply with mirror diameter.
Thin-shelled composite mirrors have been recently proposed as both deformable
mirrors for aberration correction and as variable radius-of-curvature mirrors for
adaptive optical zoom. The requirements on actuation far surpass those for other
MEMS or micro-machined deformable mirrors. We will discuss recent progress
on developing the actuation for these mirrors, as well as potential applications.
Carbon fiber reinforced polymer (CFRP) composites provide several advantages as a substrate for thin-shell adaptive
secondary mirrors, including high stiffness-to-weight ratio and low coefficient of thermal expansion (CTE). We have
addressed some of these concerns using a prototype CFRP mirror under actuation. Using 4D and Newton interferometry,
we present measurements of surface quality at a range of temperatures. Under actuator relaxation at room temperature,
its surface error is low (92 nm RMS) and dominated by edge curvature. This error is reduced further under best actuator
correction to 43 nm RMS, placing it into consideration for use in near-IR astronomy. The low surface error internal to
the outer ring of actuators - 17 nm RMS at 60°F and 33 nm RMS at 20°F - suggests that larger mirrors will have a
similar figure quality under actuator correction on ground-based AO systems. Furthermore, the actuator forces required
to correct the figure are small compared to the dynamic range of voice coil actuators (~0.1 N). In addition, surface
roughness is characterized to address the effects of high spatial frequency errors.
The Naval Research Laboratory (NRL) has been exploring Carbon Fiber Reinforced
Polymer (CFRP) material for telescope construction, including all support structures and
optics, resulting in over an order of magnitude reduction in weight over traditional steel
and glass telescopes. This has allowed the exploration of novel micro-positioning motors
for telescope pointing. A typical inertial drive telescope pointing system relies on the
large mass of the optics and telescope assembly. A prototype 0.4 meter telescope has
been developed with a total mass less than 8 kilograms necessitating the investigation of
non-traditional drive systems. This paper reports on many of the prototype 0.4 meter
telescope specifications, including optics, structure and drive hardware. Initial testing is
of the open-loop drive system is also reported.
The Naval Research Laboratory (NRL) has been exploring the use of meter class telescopes using Carbon Fiber Reinforced Polymer (CFRP) material for support structure and optics, resulting in over an order of magnitude reduction in weight over traditional steel and glass telescopes. In conjunction with Composite Mirror Applications (CMA), for the past three years this program has proceeded from conceptual phase to prototype development. In this paper we will review the various stages of this program. We will also present the status of our 0.4 meter and 1.4 meter telescopes. Experimental results from these developments and testing will be shown.
The solar submillimeter-wave telescope (SST) is the only one of its kind dedicated to solar continuous observations.
Two radiometers at 0.740 mm (405 GHz), and four at 1.415 mm (212 GHz) are placed in the Cassegrain focal plane of
the 1.5-m dish at El Leoncito high altitude site, San Juan, Argentina. The aperture efficiencies are close to design
predictions: 20% and 35% for 2 and 4 arcminutes beam sizes at 405 and 212 GHz, respectively. The positioner absolute
pointing accuracy is 10 arcseconds. Spectral coverage is complemented by ground-based mid-infrared telescopes
developed for high cadence observations in the continuum 10 micron band (30 THz), using small apertures and room-temperature
microbolometer cameras. Using the system, a new solar burst spectral component was discovered,
exhibiting fluxes increasing for smaller wavelengths, separated from the well known microwave component. Rapid sub-second
pulsations are common for all bursts. The pulsations onset times of appear to be connected to the launch times of
CMEs. Active regions are brighter for shorter submillimeter-waves. Mid-IR bright regions are found closely associated
with calcium plages and magnetic structures near the solar photosphere. Intense and rapid 10 micron brightening was
detected on active centers in association with weak flares. These results raise challenging difficulties for interpretation.
Presented are unique concepts for space telescopes and optics, based on carbon fiber reinforced polymer (CFRP) thin-shelled
mirror technology. Thin-shell CFRP mirrors have been proven for IR and longer wavelengths and to a large
extent, visible wavelength optics. The unique structural/mechanical and lightweight characteristics of thin shells open
the design possibilities for advanced space telescopes with active/adaptive mirrors. Low weight and general ease of
manufacturing of CFRP structures can result in reduced part-count and inexpensive lightweight telescopes for space
applications. Three advanced mirror concepts will be presented in this paper, 1) Advanced stowage of thin-shell mirrors
for segmented telescopes, 2) advanced deformable mirror concepts, and 3) simple and inexpensive fabrication concepts
using simplified molding tools for space telescope mirrors. Also presented will be empirical data of CFRP thin-shell
mirrors and composite structures produced supporting their use for space telescope applications.
Robert Martin, Robert Romeo, Geoff Barber, Andre Braem, Nick Brook, Bill Cameron, Carmelo D'Ambrosio, Neville Harnew, Kenneth Lessnoff, Fabio Metlica, Dave Websdale
The design, manufacture and testing of lightweight Carbon Fiber Reinforced Polymer (CFRP) converging spherical
mirrors for the RICH-1 Cherenkov detector of LHCb are described. The mirrors have low areal density to minimize the
amount of material in the path of traversing particles and need to be fluorocarbon compatible to avoid degradation in the
C4F10 radiator gas. The total area is about 2m2 and high reflectivity (typically 90%) over the wavelength range 200-600nm is required.
CFRP (carbon fiber reinforced plastic) is an attractive material for fabrication of optical systems. The stiffness-to-weight
ratio of CFRP is high, the coefficient of thermal expansion is low, the structure thermalizes rapidly, and many of
the structural properties can be tailored to the application. We have used CFRP and CFRP-aluminum sandwich panels
extensively in the structures of astronomical, optical telescopes up to 1.5m diameter aperture. In designing the optical
structures, we have chosen some key fabrication techniques with CFRP that take advantage of the mechanical properties.
This paper discusses the design and fabrication of 2 major telescope projects. The 1m ULTRA telescope has both the
optics and the OTA fabricated from CFRP. This telescope has been recently installed at the SDSU Mt. Laguna
Observatory near San Diego. A 1.4m telescope for the Naval Research Lab is being designed and fabricated at CMA.
The optics, OTA, and the mount are all being fabricated using CFRP composites. The result is a lightweight structure
which can be moved or deployed as necessary.
The use of composite materials in the fabrication of optical telescope mirrors offers many advantages over conventional
methods, including lightweight, portability and the potential for lower manufacturing costs. In the construction of the
substrate for these mirrors, sandwich construction offers the advantage of even lower weight and higher stiffness.
Generally, an aluminum or Nomex honeycomb core is used in composite applications requiring sandwich construction.
However, the use of a composite core offers the potential for increased stiffness and strength, low thermal distortion
compatible with that of the facesheets, the absence of galvanic corrosion and the ability to readily modify the core
properties. In order to design, analyze and optimize these mirrors, knowledge of the mechanical properties of the core is
essential. In this paper, the mechanical properties of a composite triangular cell core (often referred to as isogrid) are
determined using finite element analysis of a representative unit cell. The core studied offers many advantages over
conventional cores including increased thermal and dimensional stability, as well as low weight. Results are provided
for the engineering elastic moduli of cores made of high stiffness composite material as a function of the ply layup and
cell size. Finally, in order to illustrate the use of these properties in a typical application, a 1.4-m diameter composite
mirror is analyzed using the finite element method, and the resulting stiffness and natural frequencies are presented.
Presented is a poster presentation relating to the final assembly and testing of the Ultra Lightweight Telescope for
Research in Astronomy, ULTRA [1]. The program is a 3-year Major Research Instrumentation (MRI) program funded
by NSF. Objectives are to demonstrate carbon fiber reinforced plastic (CFRP) composite mirrors for ground-based
optical telescopes. Presented will be final assembly of the telescope including the unique features of the system
including the 27 kg primary mirror, hexapod secondary mirror control, motorized iris for the primary mirror cover. Also
presented are results of the optical testing of the 0.4m mirrors used as developmental optics in the program.
The portability of meter-class telescopes has been limited by the weight of the mirror, tube assembly and the mount required to provide pointing and tracking. The novel lightweight carbon fiber reinforced polymer telescopes being developed for array population at the Naval Prototype Optical Interferometer are orders of magnitude lighter than traditional telescopes. When combined with a lightweight carbon fiber mount, these telescopes will be easily transportable from one telescope station to another to change the interferometer baseline. The mount for a lightweight telescope is currently under development at Composite Mirror Applications, Inc. This paper reports on the design constraints of the mount, the scalability to larger aperture telescopes and the integration of sensors to measure the performance characteristics of this system during operation.
Adaptive optics systems are commonly added onto conventional astronomical telescopes to improve the wavefront quality in the presence of atmospheric turbulence. Recent successes in the development of carbon fiber reinforced polymer telescopes have significantly reduced the weight of meter class telescopes making them portable, however, most adaptive optics systems continue to be constructed on large optical benches. The Navy Prototype Optical Interferometer is developing several 1.4 m portable telescope with internal wavefront correction. As part of this upgrade, a prototype 0.4 m aperture telescope has been constructed and a light weight, compact adaptive optics system is being developed. We present in this paper the design of an adaptive optics system for the lightweight telescope. The key to this system is the incorporation of a compact wavefront correction device and a novel collimation optic within the base of the telescope.
We present the technical status of the Ultra Lightweight Telescope for Research in Astronomy (ULTRA) program. The program is a 3-year Major Research Instrumentation (MRI) program funded by NSF. The MRI is a collaborative effort involving Composite Mirror Applications, Inc. (CMA), University of Kansas, San Diego State University and Dartmouth College. Objectives are to demonstrate the feasibility of carbon fiber reinforced plastic (CFRP) composite mirror technology for ground-based optical telescopes. CMA is spearheading the development of surface replication techniques to produce the optics, fabricating the 1m glass mandrel, and constructing the optical tube assembly (OTA). Presented will be an overview and status of the 1-m mandrel fabrication, optics development, telescope design and CFRP telescope fabrication by CMA for the ULTRA Telescope.
The focus of the ULTRA Project is to develop and test Ultra-Lightweight Technology for Research applications in
Astronomy. The ULTRA project is a collaborative effort involving the private firm Composite Mirror Applications, Inc
(CMA) and 3 universities: University of Kansas, San Diego State University, and Dartmouth College. Funding for
ULTRA is predominately from a NSF three year MRI program grant to CMA and KU with additional support from
CMA, KU and SDSU. The goal of the ULTRA program is to demonstrate that a viable alternative exists to traditional
glass mirror and steel telescope technology by designing, fabricating and testing a research telescope constructed from
carbon fiber reinforced plastic (CFRP) materials. In particular, a 1m diameter, Cassegrain telescope optics set and
optical tube assembly (OTA) are being designed and fabricated by CMA. The completed telescope will be deployed at
SDSU's Mt Laguna Observatory in a refurbished structure (new dome and mount provided via KU and SDSU). We
expect that a successful completion and testing of this project will lead to future use of CFRP technology in larger
telescopes and segmented telescopes. This paper describes the OTA (optical tube assembly) that has been developed
for the ULTRA project. The mirror technology is described in another paper in this conference. A poster describes the
ULTRA project overview in more detail.
Under contract from the Cornell-Caltech Atacama Telescope Project (CCAT), Composite Mirror Applications, Inc.
(CMA) has undertaken a feasibility design study for the use of Carbon Fiber Reinforced Plastic (CFRP) panels in
forming the primary mirror surface. We review some of the past projects using CFRP panel technology for
millimeter and submillimeter wavelength radio astronomy telescopes. Pros and cons of the technology are
discussed. A particular panel configuration was proposed and computer modeled with finite element analysis
(FEA). The technology of replicated CFRP panels for short wavelength radio astronomical telescopes is mature and
cost effective. For shorter wavelengths into the IR and visible, it is becoming a very attractive alternative to
traditional, heavy glass or metal technologies.
Presented are results of continuing optical mirror development program for the NSF ULTRA Telescope. Development
of a 16-inch f/4.0 parabolic mirror has been undertaken to adequately define scale-up fabrication procedures for 1m and
1.4m mirrors. 16-inch mirrors have been produced to λ/15 rms ( λ=633nm) in the wavefront. These mirrors have been
used to produce astronomical images in a Newtonian telescope and yielded quality optical images. Presented will be
results of the fabrication of the 1m, f/3 parabolic primary mirror mandrel for the 1m ULTRA Telescope. Also presented
will be lab test data and astronomical mages produced under the 16-inch program as well as test data from the
replications from the f/3 1m parabola.
Presented are results of a fabrication program to produce the Ring Imaging Cherenkov, RICH, mirror for the Alpha Magnetic Spectrometer, AMS-02, which is to be placed on the International Space Station. Composite Mirror Applications, Inc., CMA, in Tucson AZ was contracted by Carlo Gavazzi Space, CGS, to produce a conical mirror 1.3m diameter 0.5m in height, from high modulus carbon fiber, flight qualified composite materials, having an optical surface on the inside of the cone. The flight model mirror was completed to specification, yielding nearly 2m2 of replicated optical surface area and weighs 8 kg. CMA measured the surface roughness and slope errors and the mirror dimensions were measured using a CMM at The University of Arizona's Instrument Shop. The results show the mirror meets conformance to the required specifications. The RICH mirror is currently undergoing flight testing and integration.
In this paper we present some preliminary results of an ultra-light weight telescope manufactured entirely with Carbon Fiber Reinforced Polymer (CFRP), including the optics, coupled with a light weight Adaptive Optics (AO) system. This research has many scopes, ranging from long baseline interferometry to laser communications. In this paper we will examine some of the mechanical properties of the telescope and describe the testing that the system is undergoing.
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