We describe the development of a lightweight, high-resolution surveillance camera for deployment on high altitude platform systems. The instrument is designed to operate at an altitude of ∼20 km and has an expected ground resolution of better than 120 mm with an appropriate sensor. While designed specifically for imaging at visible wavelengths, it is shown that the design is capable of diffraction-limited imaging at NIR and SWIR wavelengths up to 2.5 μm. We have combined a range of materials from aluminum and titanium alloys through to carbon fiber-reinforced plastic to produce an instrument with structural components that match the thermal expansion of the optical glasses used. The use of these materials has resulted in an instrument that weighs <2 kg, including a sensor package, and is designed to weigh <3 kg once integrated with an enclosure and actuated gimbal. The successful testing of two prototype systems is described, including several design outcomes from the program intended for implementation in advance of flight trials.
KEYWORDS: Actuators, Mirrors, Microsoft Foundation Class Library, Aberration correction, Composites, Carbon, Active optics, Surface finishing, Atmospheric corrections, Space mirrors
Large precision composite mirrors for space missions and telescopes can be heavy, massive and expensive to fabricate. In this work, the mass of the mirrors is reduced by using space approved carbon fiber reinforced polymer (CFRP) material and employing micro-fiber composite (MFC) actuators for aberration correction and phase manipulation in an active/adaptive optical mirror system. The carbon fiber mirror is fabricated with 16 layers of prepreg composite MTM44- 1/IMS65 carbon fiber and one layer of polishable resin. The layers are cured under pressure in an autoclave machine in a pressure and temperature-controlled environment. 2 different piezoelectric actuators, Push actuators and MFC actuators, are tested and the phase shift, form factor and surface deformation due to the active actuators are compared. Push actuators are the most common means of active optics. CFRP structure and surface deformation after actuator’s effect are investigated theoretically using finite element analysis with the aid of COMSOL software and by optical experiments.
KEYWORDS: Mirrors, Actuators, Composites, Carbon, Surface finishing, Optics manufacturing, Microsoft Foundation Class Library, Polishing, Prototyping, Active optics
In this work, we are aiming to reduce the mass of large precision mirrors for space missions by using space approved composite materials. We report the development of an active/adaptive optics prototype of carbon fiber reinforced polymer mirrors using a pre-impregnated (pre-preg) composite MTM44-1/IMS65. The carbon fiber mirror has 16 layers of carbon fiber and one layer of polishable resin which compensate the well-known problem of ‘’fiber print through’’. The development of a fabrication method, suited for creating a CFRP mirror is outlined. As all materials will change properties to some degree, during cool down to cryogenic temperatures, FEA model is employed to investigate the change on overall form and figure of the mirror. Characterizing this dimensional change is critical in insuring that any mirror material can be used in this environment and, if required, corrected either by utilizing a deformable mirror control systems or by correction in the optical system. Two different piezoelectric actuators are modelled and used to create an active composite reflector. Push actuators and micro fiber composite (MFC) actuators are simulated and the performance of them are compared by surface deformation and dynamic response.
Over half of the light incident on the Earth from the Universe falls within the Far-Infrared (FIR) region of the spectrum. Due to the deleterious effects of the Earth's atmosphere and instrument self-emission, astronomical measurements in the FIR require space-borne instrumentation operating at cryogenic temperatures. These instruments place stringent constraints on the mechanical and thermal properties of the support structures at low temperatures. With high stiffness, tensile strength, strength-to-mass ratio, and extremely low thermal conductivity, carbon fibre reinforced polymers (CFRPs) are an important material for aerospace and FIR astronomical applications, however, little is known about their properties at cryogenic temperatures. We have developed a test facility for exploring CFRP properties down to 4 K. We present results from our ongoing study in which we compare and contrast the performance of CFRP samples using different materials, and multiple layup configurations. Current results include an evaluation of a cryostat dedicated for materials testing and a custom cryogenic metrology system, and preliminary cryogenic thermal expansion measurements. The goal of this research is to explore the feasibility of making CFRP-based, lightweight, cryogenic astronomical instruments.
The next generation of space-borne instruments for far infrared astronomical spectroscopy will utilize large diameter,
cryogenically cooled telescopes in order to achieve unprecedented sensitivities. Low background, ground-based cryogenic
facilities are required for the cryogenic testing of materials, components and subsystems. The University of Lethbridge
Test Facility Cryostat (TFC) is a large volume, closed cycle, 4 K cryogenic facility, developed for this purpose. This paper
discusses the design and performance of the facility and associated metrology instrumentation, both internal and external
to the TFC. Additionally, an apparatus for measuring the thermal and mechanical properties of carbon-fiber-reinforced
polymers is presented.
KEYWORDS: Composites, Space telescopes, Mirrors, Finite element methods, Telescopes, Space telescopes, Mirrors, Telescopes, Cryogenics, Finite element methods, Space mirrors, Polymers, Interferometers, Data modeling
The FP7 project, FISICA (Far Infrared Space Interferometer Critical Assessment), called for the
investigation into the suitability of Carbon fiber Reinforced Plastic (CFRP) for a 2m primary mirror. In this paper,
we focus on the major challenge for application, the development of a mirror design that would maintain its form at
cryogenic temperatures. In order to limit self-emission the primary is to be cooled to 4K whilst not exceeding a form
error of 275nm PV. We then describe the development of an FEA model that utilizes test data obtained from a
cryogenic test undertaken at the University of Lethbridge on CFRP samples. To conclude, suggestions are made in
order to advance this technology to be suitable for such an application in order to exploit the low density and
superior specific properties of polymeric composites.
Many important astrophysical processes occur at wavelengths that fall within the far-infrared band of the EM spectrum, and over distance scales that require sub-arc second spatial resolution. It is clear that in order to achieve sub-arc second resolution at these relatively long wavelengths (compared to optical/near-IR), which are strongly absorbed by the atmosphere, a space-based far-IR interferometer will be required. We present analysis of the optical system for a proposed spatial-spectral interferometer, discussing the challenges that arise when designing such a system and the simulation techniques employed that aim to resolve these issues. Many of these specific challenges relate to combining the beams from multiple telescopes where the wavelengths involved are relatively short (compared to radio interferometry), meaning that care must be taken with mirror surface quality, where surface form errors not only present potential degradation of the single system beams, but also serve to reduce fringe visibility when multiple telescope beams are combined. Also, the long baselines required for sub-arc second resolution present challenges when considering propagation of the relatively long wavelengths of the signal beam, where beam divergence becomes significant if the beam demagnification of the telescopes is not carefully considered. Furthermore, detection of the extremely weak far-IR signals demands ultra-sensitive detectors and instruments capable of operating at maximum efficiency. Thus, as will be shown, care must be taken when designing each component of such a complex quasioptical system.
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