Shape correction of thin mirrors in a reconfigurable modular space telescope

In order to facilitate the construction of future large space telescopes, the development of low cost, low mass mirrors is necessary. However, such mirrors suffer from a lack of structural stability, stiffness, and shape accuracy. Active materials and actuators can be used to alleviate this deficiency. For observations in the visible wavelengths, the mirror surface must be controlled to an accuracy on the order of tens of nanometers. This paper presents an exploration of several mirror design concepts and compares their effectiveness at providing accurate shape control. The comparison test is the adjustment of a generic mirror from its manufactured spherical shape to the shape required by various off-axis mirrors in a segmented primary mirror array. A study of thermal effects is also presented and, from these results, a recommended design is chosen

Fourier Transforms By White-Light Interferometry: Michelson Stellar Interferometer Fringes

The white-light compensated rotational shear interferometer (coherence interferometer) was developed in an effort to study the spatial frequency content of passively illuminated white-light scenes in real-time and to image sources of astronomical interest at high spatial frequencies through atmospheric turbulence. This work was inspired by Professor Goodman's studies of the image formation properties of coherent (laser) illuminated transparencies. We discovered that real-time image processing is possible using white-light interferometry. The concept of a quasimonoplanatic approximation is introduced as a parallel to the quasimonochromatic approximation needed to describe the theory of Fourier transform spectrometers. This paper describes the coherence interferometer and reviews its image formation properties under the conditions of quasimonoplanacity and describes its development and its applications to physical optics, optical processing and astrophysics including the search for exoplanets

Astronomical search for origins: Are we alone?

Recent advances in astronomical research have led to a much-improved understanding of the evolution of the physical Universe. Recent advances in biology and genetics have led to a much-improved understanding of our biological Universe. Scientists now believe that we have the research tools to begin to answer one of man’s two most compelling research questions: Are we alone? and How did we get here? This paper reviews the requirements and challenges we face to engineer and build the large space-based systems of interferometers and innovative single-aperture telescopes to detect and characterize in detail earth type planets around stars other than our sun

Basic Optics for the Astronomical Sciences

This text was written to provide engineers and students of astronomy an understanding of optical science—the study of the generation, propagation, control, and measurement of optical radiation—as it applies to telescopes and instruments for astronomical research in the areas of astrophysics, astrometry, exoplanet characterization, and planetary science. The book provides an overview of the elements of optical design and physical optics within the framework of the needs of the astronomical community

Evolution of imaging spectrometry: past, present, and future

An overview of the physical principals of imaging spectrometry for detailed characterization of remote objects and of gas vapors is given. The terms multi-spectral, hyperspectral, and ultra-spectral are defined within the framework of applications and instrument system design approaches. History of the development of imaging spectrometers is reviewed. We are at the threshold of major commercial efforts for these instrument systems

Telescope revolution

The scientific and technical challenges facing the astronomical community during the next decade are discussed within the framework of new technology and technical management issues. The astronomical telescope and instrument communities of industry, academia and government need to be prepared to meet the challenges of 21st century Astronomy. Emphasis is given to ground-based optical and infrared astronomy

Challenges to optimizing a telescope system to detect and characterize exo-solar planetary systems

Novel optical design and engineering ideas are needed to build the large space telescopes for the direct detection and characterization of exo-solar system planets. For example, the Terrestrial Planet Finder Coronagraph requires a primary mirror 4 x 8 meters in size that is >10 x smoother than the 2.8 meter HST mirror and have a uniform reflectivity across the mirror to within 0.1%. The telescope system will need to control scattered light to within a part in 10 billion. The Terrestrial Planet Finder Interferometer will be a white-light, broadband infrared interferometer with a baseline in excess of 50 meters. In addition to direct imaging, planets masses and orbits can be derived from very precise measurements of the position of a star as it moves across the background. Interferometers provide the highest accuracy measurements of relative positions We will show that the optical design and the mechanical layout & configuration for these new telescopes need to be optimized for polarization as well as scattered light. Material science and coating technology plays an important role in the optimization of these systems. Stress across the surface of a mirror and stress within the optical thin film introduces polarization dependent scattered light. A new method to measure the anisotropy of the polarization-reflectivity of thin metal films on large astronomical mirrors is described

Self-induced polarization anisoplanatism

This paper suggests that the astronomical science data recorded with low F# telescopes for applications requiring a known point spread function shape and those applications requiring instrument polarization calibration may be compromised unless the effects of vector wave propagation are properly modeled and compensated. Exoplanet coronagraphy requires “matched filter” masks and explicit designs for the real and imaginary parts for the mask transmittance. Three aberration sources dominate image quality in astronomical optical systems: amplitude, phase and polarization. Classical ray-trace aberration analysis used today by optical engineers is inadequate to model image formation in modern low F# high-performance astronomical telescopes. We show here that a complex (real and imaginary) vector wave model is required for high performance, large aperture, very wide-field, low F# systems. Self-induced polarization anisoplanatism (SIPA) reduces system image quality, decreases contrast and limits the ability of image processing techniques to restore images. This paper provides a unique analysis of the image formation process to identify measurements sensitive to SIPA. Both the real part and the imaginary part of the vector complex wave needs to be traced through the entire optical system, including each mirror surface, optical filter, and all masks. Only at the focal plane is the modulus squared taken to obtain an estimate of the measured intensity. This paper also discusses the concept of the polarization conjugate filter, suggested by the author to correct telescope/instrument corrupted phase and amplitude and thus mitigate6, in part the effects of phase and amplitude errors introduced by reflections of incoherent white-light from metal coatings

Space optics contributions by the College of Optical Sciences over the past 50 years

We present a review of the contributions by students, staff, faculty and alumni to the Nation’s space program over the past 50 years. The balloon polariscope led the way to future space optics missions. The missions Pioneer Venus (large probe solar flux radiometer), Pioneer 10/11 (imaging photopolarimeter) to Jupiter and Saturn, Hubble Space Telescope (HST), and next generation large aperture space telescopes are discussed

Innovative pupil topographies for sparse aperture telescopes and SNR

Since the first application of the telescope to astronomy in 1610, most new astronomical discoveries require larger and larger radiation collecting areas. Today, the twin 10-meter Keck telescopes are operational and several 30-meter-aperture class telescopes are being planned. Optical interferometers and sparse aperture ground telescopes for astronomy have been proposed and built. Fienup showed the dependence between exposure time and the dilution factor of the aperture needed to maintain image quality.1 Carpenter suggests a sparse aperture telescope system for the purpose of imaging across the surfaces of stars.2 This paper demonstrates that the ability to reconstruct images from white-light extended sources with different contrast levels also depends on the specific pupil topography that is applied to the telescope system. Signal-to-noise ratios for recorded images are calculated for scene contrast, pupil shape, detector full-well, detected photons, and exposure times