Perhaps the most compelling piece of science and exploration now under discussion for future space missions is the
direct study of planets circling other stars. Indirect means have established planets as common in the universe but have
given us a limited view of their actual characteristics. Direct observation holds the potential to map entire planetary
systems, view newly forming planets, find Earth-like planets and perform photometry to search for major surface
features. Direct observations will also enable spectroscopy of exoplanets and the search for evidence of simple life in
the universe. Recent advances in the design of external occulters - starshades that block the light from the star while
passing exoplanet light - have lowered their cost and improved their performance to the point where we can now
envision a New Worlds Observer that is both buildable and affordable with today's technology. In this paper we explore
the comparison of scientific capability of external occulters relative to indirect means and to internal coronagraph
missions. We conclude that external occulters logically provide the architecture for the next space mission for exoplanet
studies.
Optical design concepts for the telescope and instrumentation for NASA's New Worlds Observer program are presented. A four-meter multiple channel telescope is discussed, as well as a suite of science instrument concepts. Wide field instrumentation (imager and spectrograph) would be accommodated by a three-mirror-anastigmat
telescope design. Planet finding and characterization, and a UV instrument would use a separate channel that is picked off after the first two mirrors (primary and secondary). Guiding concepts are also discussed.
A key component of our 2008 NASA Astrophysics Strategic Mission Concept Study entitled "An Advanced
Technology Large-Aperture Space Telescope: A Technology Roadmap for the Next Decade" is the
identification of the astrophysics that can be uniquely accomplished using a filled, large-aperture UV/optical
space telescope with an angular resolution 5 - 10 times better than JWST. We summarize here four research
areas that are amongst the prime drivers for such an advanced astronomical facility: 1) the detection of
habitability and bio-signatures on terrestrial mass exoplanets, 2) the reconstruction of the detailed history of
the assembly of stellar mass in the local universe, 3) establishing the mass function and characterizing the
accretion environments of supermassive black holes out to redshifts of z ~ 7, and 4) the precise determination
of growth of structure in the universe by kinematic mapping of the dark matter halos of galaxies as functions
of time and environment.
Perhaps the most compelling piece of science and exploration now under discussion for future space missions is the direct
study of planets circling other stars. Indirect means have established planets as common in the universe but have given us
a limited view of their actual characteristics. Direct observation holds the potential to map entire planetary systems, view
newly forming planets, find Earth-like planets and perform photometry to search for major surface features. Direct
observations will also enable spectroscopy of exoplanets and the search for evidence of simple life in the universe. Recent
advances in the design of external occulters - starshades that block the light from the star while passing exoplanet light -
have lowered their cost and improved their performance to the point where we can now envision a New Worlds Observer
that is both buildable and affordable with today's technology. We will summarize recent studies of such missions and
show they provide a very attractive alternative near term mission.
We discuss the progress that has been made in the understanding of the use of external occulters to observe exoplanetary systems. We show how a starshade can be designed and built in a practical and affordable manner to fully remove starlight and leave only planet light entering a telescope. When coupled to a powerful observatory like the James Webb Space Telescope, an occulter can extinguish the starlight and reveal basic details of the planetary systems around our closest, neighboring stars.
We view broadly the science and technology drivers for both space and ground optical telescopes, in order to identify the unique capabilities and limitations in each domain. This leads us to consider the potential for effective "divisions of labor" and synergies to enhance scientific value. We project the influence of new enabling technologies, human priorities, international collaboration issues, and funding expectations. Finally, we discuss current NASA and ESA optical astronomy mission goals, and speculate on long-term forecasts.
The Stellar Imager (SI) is a far-horizon or "Vision" mission in the NASA Sun-Earth Connection (SEC) Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar activity and its impact on life in the Universe. The science goals of SI require an ultra-high angular resolution, at ultraviolet wavelengths, on the order of 0.1 milliarcsec and thus baselines on the order of 500 meters. These requirements call for a large, multi-spacecraft (>20) imaging interferometer, utilizing precision formation flying in a stable environment, such as in a Lissajous orbit around the Sun-Earth L2 point. SI's resolution (several 100 times that of HST) will make it an invaluable resource for many other areas of astrophysics, including studies of AGN's, supernovae, cataclysmic variables, young stellar objects, QSO's, and stellar black holes. In this paper, we present an update on the ongoing mission concept and technology development studies for SI. These studies are designed to refine the mission requirements for the science goals, define a Design Reference Mission, perform trade studies of selected major technical and architectural issues, improve the existing technology roadmap, and explore the details of deployment and operations, as well as the possible roles of astronauts and/or robots in construction and servicing of the facility.
KEYWORDS: Telescopes, Space telescopes, Stars, Space operations, Interferometers, Sensors, Control systems, Mirrors, Nulling interferometry, Cryogenics
The Cold Interferometric Nulling Demonstration in Space (CINDIS) is a modest-cost technology demonstration mission, in support of interferometer architectures for Terrestrial Planet Finder (TPF). It is designed to provide as complete as possible a demonstration of the key technologies needed for a TPF interferometer at low risk, for a cost less than $300M. CINDIS foregoes scientific objectives at the outset, enabling significant cost savings that allow us to demonstrate important features of a TPF interferometer, such as high-contrast nulling interferometry at 10 μm wavelength, vibration control strategies, instrument pointing and path control, stray light control, and possibly 4-aperture compound nulling.
This concept was developed in response to the NASA Extra-Solar Planets Advanced Concepts NRA (NRA-01-OSS-04); this paper presents the results of the first phase of the study.
Recent studies of exosolar planet detection methods with a space-based visible light coronagraph have shown the feasibility of this approach. However, the telescope optical precision requirements are extremely demanding - a few Angstroms residual wavefront error - which is beyond current capabilities for large optical surfaces. Secondly, the coronagraph depends upon use of masks located at either the pupil or a focus to reject the starlight and image the exosolar planet. Effects of diffraction and light scatter place precision requirements mask manufacturing. To increase understanding and optimize performance of the coronagraph, laboratory experiments backed by end-to-end integrated models are used to project on-orbit performance. Of particular importance is the wavefront propagation through the optical system - from simple Fraunhaufer propagation to vector propagators taking into account 3D structures of the masks. Accurate models, which match test data are then used to evolve the initial coronagraph concepts for in-flight performance. In part I, we discuss error sources and model development to meet mission goals. In part II, a paper to be published at a future date, we compare lab experiment and expected residual error sources.
A coronagraphic telescope is one of the several approaches proposed for finding and characterizing extrasolar planets for the Terestrial Planet Finder (TPF) mission. The coronagraph approach permits one to directly image planets but puts demanding requirements on the optical system performance. The planet flux, in the visible spectrum, is typically 1e10 times less than the star flux. Imaging the planet requires extremely tight tolerancing of the optical system and rigorous management of the disturbance environment. To investigate many of the complex system issues, the Ball Integrated Telescope Model (ITM) was configured to do performance modeling and system trades. The individual discipline models in structural dynamics, optics, controls, signal processing, detector physics, and disturbance modeling are seamlessly integrated into one cohesive model to support efficient system level trades and analysis. The core of the model is formed by the optical toolbox implemented in MATLAB and realized in object-oriented Simulink environment. This paper describes the ITM architecture and concludes with results obtained for two potential TPF coronagraph designs. Disturbance models input into the coupled structural/optical modeling are used to explore some of the system sensitivities.
During our NASA sponsored study of candidate architectures for the Terrestrial Planet Finder mission we estimated the values of observable properties that would be accessible to an instrument intended to detect starlight reflected by a planet in the habitable zone of the system. These properties include architecture and wavelength independent geometrical properties such as angular separation between the star and planet, and timescales associated with orbital motion. Properties that do depend on the detection technique and wavelength include the brightness of the planet, its contrast relative to the star, and variability associated with diurnal and seasonal phenomena. The search space for a reflected light TPF is the range of these parameters calculated for a sample of 200 main sequence stars whose stellar properties make them potential targets. A scientific investigation such as that described by the TPF Science Working Group then leads to requirements on the sensitivity of the system, angular resolution, suppression of starlight and operational efficiency. We will describe our star sample, the search space of planetary observables and apparent system requirements.
KEYWORDS: Planets, Stars, Signal to noise ratio, Space telescopes, Hubble Space Telescope, Coronagraphy, Wavefronts, Exoplanets, Telescopes, Point spread functions
Recent advances in deformable mirror technology for correcting wavefront errors and in pupil shapes and masks for coronagraphic suppression of diffracted starlight enable a powerful approach to detecting extrasolar planets in reflected (scattered) starlight at visible wavelengths. We discuss the planet-finding performance of Hubble-like telescopes using these technical advances. A telescope of aperture of at least 4 meters could accomplish the goals of the Terrestrial Planet Finder (TPF) mission. The '4mTPF' detects an Earth around a Sun at five parsecs in about one hour of integration time. It finds molecular oxygen, ozone, water vapor, the 'red edge' of chlorophyll-containing land-plant leaves, and the total atmospheric column density -- all in forty hours or less. The 4mTPF has a strong science program of discovery and characterization of extrasolar planets and planetary systems, including other worlds like Earth. With other astronomical instruments sharing the focal plane, the 4mTPF could also continue and expand the general program of astronomical research of the Hubble Space Telescope.
We present several scenarios for the development of potential space astronomy missions and instruments over the next fifty years. It has gradually become necessary to extend our planning horizon well beyond the decade scale because of the lengthy development time for ever larger and more complex space missions, especially to enhance the efficient selection of design options for Terrestrial Planet Finder (TPF) and subsequent systems described in NASA's long-term Origins program, such as Life Finder and Planet Imager. Choices between such options should be driven by science goals and priorities, and also by the benefits of coordinating technologies developed in Origins with those needed for other U.S. and international directed-target and survey missions at all wavelengths. Even though there will be inevitable influences of scientific and technical discoveries along the way, sketching out now a variety of possible integrated technology and (to a degree) science roadmaps helps put the potential paths in context, so our early choices may more rapidly lead toward achieving likely science goals in the future.
Visual-wavelength focal plane mosaics with 10 to 100 gigapixels may become available within the next several decades. Silicon sensor read-outs may also enable the reliable detection of individual visual wavelength photons in the near future. Such solid-state photon-counting mosaics, fed by integral-field spectrographs (IFSs) which simultaneously record the spectrum of every image element, may enable astronomers to chart the 3D structure of the entire visible Universe, and trace its physical and chemical evolution from soon after the birth of the first stars to the present. We explore the requirements of a 'cosmic atlas' sensitive to objects having 0.1 times the luminosity of the Milky Way. The proposed cosmic survey has a spatial resolution of about 0.1", a spectral resolution of R ≈ 102 to 103, and cover the wavelength range from the near-UV to the near-IR.
Many new space observatory projects are now being discussed and planned. With the primary goals of useful astronomical research, including detection and characterization of extrasolar planetary systems, the larger of such prospective observatories include the Next-Generation Space Telescope (NGST), Terrestrial Planet Finder (TPF), Darwin, Life Finder (LF), and Planet Imager (PI). Several of these seem particularly useful for SETI searches at optical wavelengths, as do also some smaller proposed space observatories such as Eclipse, Kepler, and GAIA. The new space observatories offer the following capabilities of particular interest to SETI: (1) single, calibrated instruments providing continuous extended time observing a particular planetary system or a wide-angle region containing many possible systems; (2) sensitivity in wavelength regions difficult to observe through the earth's atmosphere due to absorption or to scattered light; (3) very high photometric accuracy to detect small variations in signal from a planetary system; (4) decreased scattered light from our solar system's zodiacal light, depending on observatory orbit location; and (5) the potential of blocking (nulling) most of a star's light, thereby increasing greatly the signal-to-noise ratio (SNR) for detecting light from objects close to the star. We offer some suggestions as to how these new space observatories might be employed or adapted to offer optical SETI capabilities, and provide estimates of their potential performance for that mission.
The main idea of pan sharpening is to combine registered high spatial resolution panchromatic (pan) and lower spatial resolution multispectral imagery to synthesize higher resolution multispectral imagery. The degree of misregistration between bands and the correlation of intensity values are key factors in generating radiometrically accurate and visually crisp output images. There are two components to the projective pan sharpening algorithm. The first component determines the linear radiometric relationship between the pan and multispectral bands and the second processes pixels to produce the sharpened product. The projective pan sharpening algorithm will be ideally suited for generating multispectral products using Lockheed Martin Commercial Remote Sensing System (CRSS) imagery.
KEYWORDS: Sensors, Satellites, Visualization, Signal to noise ratio, Surveillance, Staring arrays, Space operations, Video surveillance, Signal processing, Associative arrays
The RESERVES program sensor concept, a multiwavelength optical system with two standard focal planes, handles many missions by using commandable readout and processing options. Performance (coverage rate, resolution, spectral data) and rapid operational readiness are achieved with the size, power, and communication link constraints of a 450-kg spacecraft. Missions achievable include weather and oceanographic mapping, earth-disk scanning for strategic warming, focused rapid-repeat theater scanning for intratheater missiles, land and ocean remote sensing, and space-object surveillance.
A standard electro-optical sensor can perform several different surveillance
missions to support tactical military users. The missions include environmental
sensing, land and ocean remote sensing, tactical missile tracking, and space
object surveillance. The key is that while the spacecraft is a standard configuration
for all missions, its design is a compromise between the specific requirements
for each mission; the orbit chosen and operations mode for each mission also
vary. Although sub-optimal for any given mission, standard sensor systems have
the advantage of achieving a higher benefit-to-cost ratio by realizing economies
of scale in production and reduced development. Point designs of three different
multi-mission sensors are presented, supported by design analysis, and encompassing
several approaches to telescope design, focal plane design, scanning system
design, data processing system design, and orbits/coverage and operations. The
resulting sensor system designs are highly capable, compared to existing systems,
meet the performance goals established, and yet fit within the tactical satellite
class.
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