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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
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NASA NTRS2003

Laboratory performance of the Keck interferometer nulling beam combiner

Now that regular visibility squared measurements are routinely achieved, mid-infrared nulling is the next observing mode to be implemented on the Keck Interferometer. This mode's main objective is the characterization of exo-zodiacal dust disks around nearby main sequence stars in support of the TPF space mission. Keck Nuller also shares numerious characteristics with an interferometric TPF, and will then serve as a technical precursor for this mission. We report here the results obtained in the laboratory with the KI mid-IR nulling beam combiner, which is based on a dual polarization Modified Mach Zender combiner and dispersion and achromatic nulling through zinc-selenide dielectric plates.

mid-infrared↗
NASA NTRS2005

Progress in broadband infrared nulling technology for TPF

TPF-I has set for itself a host of challenging technical milestones along its path to demonstrating the feasibility of infrared nulling for planet detection Progress in each of these areas of technical development will be reviewed as well as progress in meeting the overarching technical milestones.

extra-solar planets↗
NASA NTRS2006

Measuring Extended Structure in Stars Using the Keck Interferometer Nuller

The Keck Interferometer Nuller is designed to detect faint off-axis mid-infrared light a few tens to a few hundreds of milliarcseconds from a bright central star. The starlight is suppressed by destructive combination along the long (85 m) baseline, which produces a fringe spacing of 25 mas at a wavelength of 10 m, with the central null crossing the position of the star. The strong, variable mid-infrared background is subtracted using interferometric phase chopping along the short (5 m) baseline. This paper presents an overview of the observing and data reduction strategies used to produce a calibrated measurement of the off-axis light. During the observations, the instrument cycles rapidly through several calibration and measurement steps, in order to monitor and stabilize the phases of the fringes produced by the various baselines, and to derive the fringe intensity at the constructive peak and destructive null along the long baseline. The data analysis involves removing biases and coherently demodulating the short-baseline fringe with the long-baseline fringe tuned to alternate between constructive and destructive phases, combining the results of many measurements to improve the sensitivity, and estimating the part of the null leakage signal which is associated with the finite angular size of the central star. Comparison of the results of null measurements on science target and calibrator stars permits the instrumental leakage - the "system null leakage" - to be removed and the off-axis light to be measured.

nulling interferometry↗
NASA NTRS2006

A Nulling Coronagraph for TPF-C

The nulling coronagraph is one of 5 instrument concepts selected by NASA for study for potential use in the TPF-C mission. This concept for extreme starlight suppression has two major components, a nulling interferometer to suppress the starlight to ~10(sup -10) per airy spot within 2 (lamda)/D of the star, and a calibration interferometer to measure the residual scattered starlight. The ability to work at 2 (lamda)/D dramatically improves the science throughput of a space based coronagraph like TPF-C. The calibration interferometer is an equally important part of the starlight suppression system. It measures the measures the wavefront of the scattered starlight with very high SNR, to 0.05nm in less than 5 minutes on a 5mag star. In addition, the post coronagraph wavefront sensor will be used to measure the residual scattered light after the coronagraph and subtract it in post processing to 1~2x10(sup -11) to enable detection of an Earthlike planet with a SNR of 5~10.

Terrestrial Planet Finder Coronagraph (TPF-C)↗
NASA NTRS2006

Water Vapor Measurement and Compensation in the Near and Mid-infrared with the Keck Interferometer Nuller

A viewgraph presentation describing the methods, motivation and methods for water vapor measurement with the Keck interferometer near and mid infrared radiation band is shown. The topics include: 1) Motivation: Why measure H2O?; 2) Method: How do we measure H2O?; 3) Data: Phase and Group Delays for the K and N Bands; 4) Predicted and Actual Nband Phase and Dispersion; and 5) Validation of Atmospheric Turbulence Models with KI Data.

exozodiacal dust↗
NASA NTRS2005

Accessing Small Inner Working Angles with a Rotating Sub-Aperture Nuller

A new approach to high contrast observations near bright stars with a single-aperture telescope is discussed, which is based on the idea of a rotating separated-aperture nulling interferometer. The approach can be described as a rotating sub-aperture nuller, because it nulls two or more sub-apertures within a single telescope's pupil, and uses baseline rotation to modulate the signals from off-axis sources in a manner similar to that of potential space-based nulling interferometers. The sub-aperture beams can be combined in a number of ways, including a fiber nuller and a rotational shearing interferometer. Such a rotating nulling coronagraph has two great advantages. First, it can be used on a ground-based telescope to test signal reconstruction approaches pertinent to potential space-based nulling interferometers. Moreover, it also has the potential to enable ground-based coronagraphic observations of faint off-axis companions very close to bright stars.

coronagraphy↗
NASA NTRS2005

Study on the Station Keeping Maintenance for the TPF Mission

The main goal of this paper is to extend the results of Gomez et al, 2001, related to the execution of the formation manoeuvres of the TPF constellation, including the controls for the station keeping and allowing a greater flexibility in the basic manoeuvres to be done by the formation.

terrestrial planet finder (TPF)↗
NASA NTRS2003

Adaptive Nulling: A New Enabling Technology for Interferometric Exoplanet

Deep, stable nulling of starlight requires careful control of the amplitudes and phases of the beams that are being combined. The detection of earth-like planets using the interferometer architectures currently being considered for the Terrestrial Planet Finder mission require that the E-field amplitudes are balanced at the level of approx. 0.1%, and the phases are controlled at the level of 1 mrad (corresponding to approx.1.5 nm for a wavelength of 10 microns). These conditions must be met simultaneously at all wavelengths across the science band, and for both polarization states, imposing unrealistic tolerances on the symmetry between the optical beamtrains. We introduce the concept of a compensator that is inserted into the beamtrain, which can adaptively correct for the mismatches across the spectrum, enabling deep nulls with realistic, imperfect optics. The design presented uses a deformable mirror to adjust the amplitude and phase of each beam as an arbitrary function of wavelength and polarization. A proof-of-concept experiment will be conducted at visible/near-IR wavelengths, followed by a system operating in the Mid-IR band.

planet detection↗
NASA NTRS2006

Adaptive Nulling for the Terrestrial Planet Finder Interferometer

Deep, stable starlight nulls are needed for the direct detection of Earth-like planets and require careful control of the intensity and phases of the beams that are being combined. We are testing a novel compensator based on a deformable mirror to correct the intensity and phase at each wavelength and polarization across the nulling bandwidth. We have successfully demonstrated intensity and phase control using a deformable mirror across a 100nm wide band in the near-IR, and are in the process of conducting experiments in the mid-IR wavelengths. This paper covers the current results and in the mid-IR.

amplitude and phase correction↗
NASA NTRS2006

A Laboratory Experiment for Demonstrating Post-Coronagraph Wave Front Sensing and Control for Extreme Adaptive Optics

Direct detection of exo-planets from the ground will become a reality with the advent of a new class of extreme-adaptive optics instruments that will come on-line within the next few years. In particular, the Gemini Observatory will be developing the Gemini Planet Imager (GPI) that will be used to make direct observations of young exo-planets. One major technical challenge in reaching the requisite high contrast at small angles is the sensing and control of residual wave front errors after the starlight suppression system. This paper will discuss the nature of this problem, and our approach to the sensing and control task. We will describe a laboratory experiment whose purpose is to provide a means of validating our sensing techniques and control algorithms. The experimental demonstration of sensing and control will be described. Finally, we will comment on the applicability of this technique to other similar high-contrast instruments.

coronography↗
NASA NTRS2004

Terrestrial Planet Finder Interferometer: Architecture, Mission Design, and Technology Development

This slide presentation represents an overview progress report about the system design and technology development of two interferometer concepts studied for the Terrestrial Planet Finder (TPF) project. The two concepts are a structurally-connected interferometer (SCI) intended to fulfill minimum TPF science goals and a formation-flying interferometer (FFI) intended to fulfill full science goals. Described are major trades, analyses, and technology experiments completed. Near term plans are also described. This paper covers progress since August 2003

nulling↗
NASA NTRS2005

Terrestrial Planet Finder Interferometer 2005

Activities Affected by Budget Adjustment: Formation Acquisition Sensor, Cryo Structures, Cryo Delay Line, Cryocooler, Design Team, System Modeling. Other Activities include: Formation Flying, Cryogenic Operations, Starlight suppression, and System Design and Modeling.

interferometry↗
NASA NTRS2017

Segmented Aperture Interferometric Nulling Testbed (SAINT) II: Component Systems Update

"This work presents updates to the coronagraph and telescope components of the Segmented Aperture Interfer-ometric Nulling Testbed (SAINT). The project pairs an actively-controlled macro-scale segmented mirror withthe Visible Nulling Coronagraph (VNC) towards demonstrating capabilities for the future space observatoriesneeded to directly detect and characterize a significant sample of Earth-sized worlds around nearby stars inthe quest for identifying those which may be habitable and possibly harbor life. Efforts to improve the VNCwavefront control optics and mechanisms towards repeating narrowband results are described. A narrative isprovided for the design of new optical components aimed at enabling broadband performance. Initial work withthe hardware and software interface for controlling the segmented telescope mirror is also presented."

high-contrast imaging↗