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Results for “space-based interferometry”

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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NASA NTRS1992

Prospect of space-based interferometry at EUV and soft X-ray wavelengths

We review the current capabilities of high-resolution, spectroscopic, space-borne instrumentation available for both solar and stellar observations in the EUV and soft X-ray wavelength regimes, and describe the basic design of a compact, all-reflection interferometer based on the spatial heterodyne technique; this is capable of producing a resolving power (lambda/Delta-lambda) of about 20,000 in the 100-200 A region using presently available multilayer optical components. Such an instrument can be readily constructed with existing technology. Due to its small size and lack of moving parts, it is ideally suited to spaceborne applications. Based on best estimates of the efficiency of this instrument at soft X-ray wavelengths, we review the possible use of this high-resolution interferometer in obtaining high-resolution full-disk spectroscopy of the sun. We also discuss its possible use for observations of diffuse sources such as the EUV interstellar background radiation.

Welsh, Barry Y.↗
NASA NTRS1992

Science objectives for ground- and space-based optical/IR interferometry

Ground-based interferometry will make spectacular strides in the next decade. However, it will always be limited by the turbulence of the terrestrial atmosphere. Some of the most exciting and subtle problems may only be addressed from a stable platform above the atmosphere. The lunar surface offers such a platform, nearly ideal in many respects. Once built, such a telescope array will not only resolve key fundamental problems, but will revolutionize virtually every topic in observational astronomy. Estimates of the possible performance of lunar and ground-based interferometers of the 21st century shows that the lunar interferometer reaches the faintest sources of all wavelengths, but has the most significant advantage in the infrared.

Ridgway, Stephen T.↗
NASA NTRS1992

Space-based astrometric optical interferometry with POINTS

POINTS, a dual space-based astrometric optical interferometer with nominal baseline length of 2 meters and measurement accuracy of 5 microarcseconds, which could be a powerful new multidisciplinary research tool is introduced. The instrument, including the laser gauges which are a central aspect of the instrument, are described. The design of the spacecraft, and the mission operations, including the bias determination and correction, are discussed. As a candidate for the Astrometric Interferometry Mission (AIM) mission, POINTS could open new areas of astrophysical research and change the nature of the questions being asked in some old areas. As a candidate for the TOPS-1 (Towards Other Planetary Systems) mission, it could be used to perform a definitive search for extra solar planetary systems, either finding and characterizing a large number of them or showing that they are far less numerous than now believed. POINTS, which is small, agile, and mechanically simple, would be the first of a new class of powerful instruments in space and would prove the technology for the larger members of that class to follow.

Reasenberg, R. D.↗
NASA NTRS1992

Multilayer and grazing incidence X-ray/EUV optics; Proceedings of the Meeting, San Diego, CA, July 22-24, 1991

The present conference discusses the Advanced X-ray Astrophysics Facility (AXAF) calibration by means of synchrotron radiation and its X-ray reflectivity, X-ray scattering measurements from thin-foil X-ray mirrors, lobster-eye X-ray optics using microchannel plates, space-based interferometry at EUV and soft X-ray wavelengths, a water-window imaging X-ray telescope, a graded d-spacing multilayer telescope for high energy X-ray astronomy, photographic films for the multispectral solar telescope array, a soft X-ray ion chamber, and the development of hard X-ray optics. Also discussed are X-ray spectroscopy with multilayered optics, a slit aperture for monitoring X-ray experiments, an objective double-crystal spectrometer, a Ly-alpha coronagraph/polarimeter, tungsten/boron nitride multilayers for XUV optical applications, the evaluation of reflectors for soft X-ray optics, the manufacture of elastically bent crystals and multilayer mirrors, and selective photodevices for the VUV.

Hoover, Richard B.↗
NASA NTRS1985

Planetary searches using optical astrometric interferometers

The detectability of planets is discussed, and observations made with an astrometric interferometer (AI) at Mount Wilson are presented. Planets are detectable as a result of their periodic perturbation of the position of a central observable star. This detection requires relative astrometric accuracies of about 3 x 10 to the -4th for Jovian planets and about 3 x 10 to the -7th arcsec for terrestrial planets. The principles governing astrometric interferometry are explained, and it is conjectured that a two-color optical AI on earth should be capable of about 0.0001 arcsec rms accuracy for stars brighter than magnitude 7-10; small one-color space systems should achieve at least 0.00001 arcsec. Owing to atmospheric turbulence, two-color systems permit correction every few milliseconds for the random wavefront tilt. A 3.4-meter baseline interferometer on Mount Wilson has demonstrated arcsec rms fluctuations of about 0.02 for 1-sec samples. Space-based optical astrometric interferometry is also discussed.

Staelin, D. H.↗
NASA NTRS1993

Radioastron flight operations

Radioastron is a space-based very-long-baseline interferometry (VLBI) mission to be operational in the mid-90's. The spacecraft and space radio telescope (SRT) will be designed, manufactured, and launched by the Russians. The United States is constructing a DSN subnet to be used in conjunction with a Russian subnet for Radioastron SRT science data acquisition, phase link, and spacecraft and science payload health monitoring. Command and control will be performed from a Russian tracking facility. In addition to the flight element, the network of ground radio telescopes which will be performing co-observations with the space telescope are essential to the mission. Observatories in 39 locations around the world are expected to participate in the mission. Some aspects of the mission that have helped shaped the flight operations concept are: separate radio channels will be provided for spacecraft operations and for phase link and science data acquisition; 80-90 percent of the spacecraft operational time will be spent in an autonomous mode; and, mission scheduling must take into account not only spacecraft and science payload constraints, but tracking station and ground observatory availability as well. This paper will describe the flight operations system design for translating the Radioastron science program into spacecraft executed events. Planning for in-orbit checkout and contingency response will also be discussed.

Altunin, V. I.↗
NASA NTRS1991

A moderate space mission for optical interferometry

The Orbiting Stellar Interferometer (OSI) is a proposed space-based observatory which will open exciting new vistas in astronomy and address fundamental scientific questions by making extremely accurate (3 - 30 microarcsecond) astrometric measurements of the positions of stars, quasars, and other astronomical objects as faint as magnitude 20. In addition, it will be able to image objects with a resolution of 5 milliarcseconds. As the first optical interferometer in space, OSI will provide major advances in astrophysics while demonstrating a powerful concept applicable to major space-based observations of the future. The Jet Propulsion Laboratory has developed a preliminary design of OSI to establish its feasibility and to estimate performance that can be achieved in a mission of moderate scale. In this first publication of the results of the first year of study, the science objectives are presented, and the design of the mission, instrument, and spacecraft are discussed.

Gershman, R.↗
NASA NTRS1992

A Lunar Optical-Ultraviolet-Infrared Synthesis Array (LOUISA)

This document contains papers presented at a workshop held to consider 'optical ultraviolet infrared' interferometric observations from the moon. Part 1 is an introduction. Part 2 is a description of current and planned ground-based interferometers. Part 3 is a description of potential space-based interferometers. Part 4 addresses the potential for interferometry on the moon. Part 5 is the report of the workshop's working groups. Concluding remarks, summary, and conclusions are presented in Part 6.

Burns, Jack O.↗
NASA NTRS1986

Optical astronomical interferometry - Requirements on stellar Michelson interferometry and heterodyne interferometry for high-resolution imaging

The requirements for optical path compensation on space-based (no atmospheric-induced disturbance) heterodyne interferometers and generalized Michelson stellar interferometers are developed. It is demonstrated that heterodyne interferometers require optical path compensation to well within the coherence length dictated by its bandwidth, while Michelson stellar interferometers require compensation to a fraction of their utilized wavelength.

Silverglate, P. R.↗
NASA NTRS1989

Optical interferometers for tests of relativistic gravity in space

A space-based astrometric interferometer with a large optical bandwidth is considered. POINTS (Precision Optical INTerferometry in Space) would measure the angular separation of two stars separated by about 90 deg on the sky with a nominal measurement error of 5 microarcseconds (mas). For a pair of mag 10 stars, the observation would require about 10 minutes. It is estimated that the instrument would measure daily the separation of two stars for each of about 60 pairs of stars; a random sequence of such measurements, if suitably redundant, contains the closure information necessary to detect and correct time dependent measurement biases to well below the nominal measurement accuracy. The 90 deg target separation permits absolute parallax measurements in all directions. A redundant observing schedule for 300 stars and 5 quasars would provide extra redundancy to compensate for the quasars' higher magnitude. If a nominal 30-day observation sequence were repeated 4 times per year for 10 years, stellar parameter uncertainties would be obtained of: 0.6 mas, position; 0.4 mas/y, proper motion; and 0.4 mas, parallax. This set of well-observed stars and quasars would form a rigid frame and the stars would serve as reference objects for measurements of all additional targets, as well as being targets of direct scientific interest. The instrument global data analysis since objectives are considered including a relativity test and technology.

Reasenberg, R. D.↗
NASA NTRS1993

Controlled structures technology and the design of an optical interferometer spacecraft

The impact of extremely stringent structural control requirements and controlled structures techniques on the overall design of a spacecraft system is examined. A space-based optical interferometer presents a design case that necessitates the application of controlled structures technology. In order for interferometry to succeed, differential pathlengths between the optical components need to be identical within a fraction of a wavelength of the light (about 25 nm for visible light). This high level of precision must be maintained on a large, flexible structure in the face of common spacecraft vibrational disturbances. Aspects of spacecraft design are examined to determine the impact of structural control on the 'normal' design process. Structural control objectives can drive several choices in subsystem component selection and sizing that minimize the vibrational environment.

Nisbet, Andrew M.↗
NASA NTRS1991

Infrared imaging of extrasolar planets

An optical system for direct detection, in the infrared, of planets orbiting other stars is described. The proposed system consists of a large aperture (about 16 m) space-based telescope to which is attached a specialized imaging instrument containing a set of optical signal processing elements to suppress diffracted light from the central star. Starlight suppression is accomplished using coronagraphic apodization combined with rotational shearing interferometry. The possibility of designing the large telescope aperture to be of a deployable, multiarm configuration is examined, and it is shown that there is some sacrifice in performance relative to a filled, circular aperture.

Diner, David J.↗
NASA NTRS1987

Aperture-synthesis interferometry at optical wavelengths

The prospects for applying aperture-synthesis interferometry to the optical domain are reviewed. The radio examples such as the VLA provide a model, since the concepts are equally valid for radio and optical wavelengths. If scientific problems at the milliarc-second resolution level (or better) are to be addressed, a space-based optical array seems to be the only practical alternative, for the same reasons that dictated array development at radio wavelengths. One concept is examined, and speculations are offered concerning the prospects for developing real systems. Phase-coherence is strongly desired for a practical array, although self-calibration and phase-closure techniques allow one to relax the restriction on absolute phase stability. The design of an array must be guided by the scientific problems to be addressed.

Burke, Bernard F.↗
NASA NTRS1989

Frequency stable high power lasers in space

The concept of a laser heterodyne gravity wave antenna that would operate in solar orbit with a one million kilometer path length is discussed. Laser technology that would be appropriate for operation of this space-based gravity wave detector is also discussed. The rapid progress in diode laser coupled with the energy storage and potentially sub-Hertz linewidths of solid state lasers, and the possibility of efficient frequency conversion by nonlinear optical techniques defines a technology that is appropriate for laser interferometry in space. The present status of diode-laser-pumped, solid state lasers is summarized and future progress is projected in areas of linewidth control, high average power, operating efficiency, and operational lifetimes that are essential for space-based applications.

Byer, Robert L.↗
NASA NTRS1988

A low frequency radio array for space

This paper considers the need for and the possibility of constructing and operating a low-frequency array in space, the Low Frequency Space Array (LFSA), which is presently in its developmental phase, to form an entirely space-based synthesis interferometer for high-resolution high-sensitivity sky surveying and source imaging over the frequency range from about 1 to about 30 MHz. It is emphasized that there is a wealth of new astronomical information to be found in the as yet unexplored frequency range below 30 MHz, the wavelengths at which only interferometry is practicable. A possible instrumental concept for an LFSA spacecraft is described together with orbits, hardware, and subsystems.

Weiler, K. W.↗
NASA NTRS1991

A fiber-coupled heterodyne interferometric displacement sensor

Space-based interferometers and large segmented reflectors will require precision metrology with nanometer accuracy for active control systems. This paper summarizes an experimental study of an optical heterodyne interferometer with resolution of about 3 nm. Optical signals are carried to and from the interferometer by optical fibers to avoid thermally loading the reflector panels. Heterodyne detection provides far greater precision than does traditional interferometry.

Nerheim, Noble↗
NASA NTRS1986

Viscoelastic deformation near active plate boundaries

Model deformations near the active plate boundaries of Western North America using space-based geodetic measurements as constraints are discussed. The first six months of this project were spent gaining familarity with space-based measurements, accessing the Crustal Dynamics Data Information Computer, and building time independent deformation models. The initial goal was to see how well the simplest elastic models can reproduce very long base interferometry (VLBI) baseline data. From the Crustal Dynamics Data Information Service, a total of 18 VLBI baselines are available which have been surveyed on four or more occasions. These data were fed into weighted and unweighted inversions to obtain baseline closure rates. Four of the better quality lines are illustrated. The deformation model assumes that the observed baseline rates result from a combination of rigid plate tectonic motions plus a component resulting from elastic strain build up due to a failure of the plate boundary to slip at the full plate tectonic rate. The elastic deformation resulting from the locked plate boundary is meant to portray interseismic strain accumulation. During and shortly after a large interplate earthquake, these strains are largely released, and points near the fault which were previously retarded suddenly catch up to the positions predicted by rigid plate models. Researchers judge the quality of fit by the sum squares of weighted residuals, termed total variance. The observed baseline closures have a total variance of 99 (cm/y)squared. When the RM2 velocities are assumed to model the data, the total variance increases to 154 (cm/y)squared.

Ward, S. N.↗
NASA NTRS1992

Mission operations system for Russian space Very-Long-Baseline Interferometry mission

A mission operations system developed to meet the unique requirements of the prospective Russian space VLBI mission Radioastron is described. The challenges associated with the Radioastron operations are mainly due to the interrelationship between the space-based telescope and the ground observatories, and the mission's international character. The Radioastron project includes radio observatories located in 17 different countries, tracking facilities in possibly seven different countries, orbit determination centers in Russia and USA, and widely located data processing facilities. In addition, unique scheduling constraints arise from the competing demands placed on the ground observatory time by earth-based VLBI experiments, and the tracking station time by a Japanese space interferometry mission VSOP, which is expected to be in orbit concurrently with Radioastron. A diagram illustrating the organizational structure of the Radioastron project during operations is presented.

Altunin, V. I.↗