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Interferometer systems are described in the form of publications and reports. 'Distance Meter Helps Track the Stars', 'Berkeley Heterodyne Interferometer', 'Infrared Heterodyne Spectroscopy of CO2 on Mars', and 'A 10 micron Heterodyne Stellar Interferometer' are papers reported.
The NASA Space Telescope (ST) is a 2.4-m aperture, f/24 Ritchey-Chretien telescope coupled to five on-board astronomical scientific packages. The very accurate line-of-sight stability required by ST during operating periods of up to 24 hours is maintained by the Pointing Control System whose optical system, the Fine Guidance Subsystem (FGS), is described. The Pointing Control System includes three identical FGSs, any two of which provide line-of-sight stabilization by tracking guide stars while the third performs astrometry. The optical system for the ST FGS performs the field aberration correction within the FGS near a pupil plane measuring only 52.7 mm. The design is simple and easily corrected, and offers substantial advantages over the traditional approach in terms of manufacturability.
Hybrid superconductor magnet bearings (HSMB's) utilize high temperature superconductors (HTS's) together with permanent magnets to form a frictionless interface between relatively rotating parts. They are low mass, stable, and do not incur expenditure of energy during normal operation. There is no direct physical contact between rotor and stator, and hence there is no wear and tear. However, just as any other applications of HTS's, it requires a very cold temperature to function. Whereas this might be perceived as a disadvantage on earth, it is of no great concern in space or on the moon. To astronomers, the moon is an excellent site for an observatory, but the cold and dusty vacuum environment on the moon precludes the use of mechanical bearings on the telescope mounts. Furthermore, drive mechanisms with very fine steps, and hence bearings with extremely low friction are needed to track a star from the moon, because the moon rotates very slowly. All aspects considered, the HSMB is about the only candidate that fits in naturally. Here, we present a design for one such bearing, capable of supporting a telescope that weighs about 3 lbs on Earth.
This paper contains a critical comparison of estimators minimizing Wahba's loss function. Some new results are presented for the QUaternion ESTimator (QUEST) and EStimators of the Optimal Quaternion (ESOQ and ESOQ2) to avoid the computational burden of sequential rotations in these algorithms. None of these methods is as robust in principle as Davenport's q method or the Singular Value Decomposition (SVD) method, which are significantly slower. Robustness is only an issue for measurements with widely differing accuracies, so the fastest estimators, the modified ESOQ and ESOQ2, are well suited to sensors that track multiple stars with comparable accuracies. More robust forms of ESOQ and ESOQ2 are developed that are intermediate in speed.
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The James Webb Space Telescope (JWST) will provide breakthrough capabilities for the study of Solar System objects. JWST is a large aperture, cryogenic, infrared-optimized, general purpose space observatory under construction by NASA, ESA, and CSA for launch in 2018. The JWST instrumentation will provide imaging. coronagraphy, and spectroscopy between 6000A to 29 microns. This spectral region contains many atomic, molecular, and particulate diagnostics that are especially relevant for the study of gaseous, rocky and icy bodies in the Solar System. This talk describes the concept for observations of moving targets, including the system design for acquiring and tracking guide stars to hold the science target fIxed in the instrument field of view.
NASA's Small Business Innovation Research (SBIR) program focuses on technological innovation by investing in development of innovative concepts and technologies to help NASA mission directorates address critical research needs for Agency programs. This report highlights eight of the innovative SBIR 2014 Phase I and Phase II projects that emphasize one of NASA Glenn Research Center's six core competencies-Communication Technology and Development. The technologies cover a wide spectrum of applications such as X-ray navigation, microsensor instrument for unmanned aerial vehicle airborne atmospheric measurements, 16-element graphene-based phased array antenna system, interferometric star tracker, ultralow power fast-response sensor, and integrated spacecraft navigation and communication. Each featured technology describes an innovation, technical objective, and highlights NASA commercial and industrial applications. This report provides an opportunity for NASA engineers, researchers, and program managers to learn how NASA SBIR technologies could help their programs and projects, and lead to collaborations and partnerships between the small SBIR companies and NASA that would benefit both.
The paper presents a comprehensive star observation and tracking strategy, which uses a computer simulation of the Space Station orbital mechanics, system constraints, and Astrometric Telescope Facility (ATF) tracking maneuvers over a long observational period. This approach may be used to obtain data which may assist in the preliminary systems definition of the ATF. Results are given for an analysis which uses a restricted target set in order to demonstrate the disproportionate effect of the galactic-photon-rate index on the observation times for each star.
We compute starburst models for M82, making use of recent theoretical tracks of stellar evolution. Detailed comparisons of our models and those of others demonstrate this technique to be quite reliable, with relatively little change in output parameters as a function of the selection of theoretical tracks or of estimates of the observational characteristics of the stars along these tracks. The models are matched to the observational constraints for M82 summarized by McLeod et al. (1993). The rate of star formation and time of observation were thoroughly optimized to produce the most favorable fit to the observations, but we still found that the recently proposed forms for the solar-neighborhood IMF cannot produce starbursts adequate to fit the observations of this galaxy. We then explored adjustments to the shape of the IMF to improve the fit to M82. We find (1) the shape of the IMF for high-mass stars need not be different from that observed locally; and (2) the most likely modification to the IMF in M82 is that stars with masses below a few solar masses form much less commonly than in the solar neighborhood.
The James Webb Space Telescope (JWST) will have the capability to observe Solar System objects having apparent rates of motion up to 30 milliarcseconds/sec. The key science drivers are the study of Kuiper Belt Objects, asteroids, comets, and the outer planets and their moons at near and mid-infrared wavelengths. This poster presents the results from a recent study that defined the conceptual design for a capability for JWST to track and observe moving targets. We illustrate about how guide star acquisition and tracking wi11 be handled while retaining the efficient and flexible execution characteristics of JWST event-driven operations. We also show how the JWST pointing control system can readily support moving target observations. The characteristics of Solar System objects that can be observed by JWST are summarized along with descriptions of the major aspects of moving target science observation planning and on-board event-driven execution.
In this paper we suggest that subjecting the observationally derived properties of protoplanetary disks to the evolutionary interpretation yields new insights into the working of those disks, and offers valuable constraints on their models. We propose that the global properties of individual disks, such as their accretion rates and disk masses, sorted by the mass of the central star, can be indexed by the age of the star to simulate the evolution of a single disk. Using data from published surveys of T Tauri stars, we show that accretion rate data, and disk mass data for the lowest mass stars, form well-defined evolutionary tracks. The higher mass stars show a definitive negative correlation between accretion rates and star ages. We use the time-dependent alpha-disk model of the viscous protoplanetary disk to link the theory to observations. The data are consistent with the standard theoretical paradigm, but not with the layered accretion model. The best fits to the data are obtained for the standard models that start with disks that are about one-third of the mass of the central star and have their angular momenta, j, and alpha-coefficients linked by the relationship j varies as Solar mass(exp 3/2)alpha(exp 1/3). The proportionality constant in this relationship, when derived from the accretion rate data, differs from the constant derived from the disk mass data. We argue that the accretion rate data are more reliable. Taking into account typical values of the specific angular momentum of disk-forming matter, we obtain alpha is greater than or equal to 10(exp -2). A complete time-dependent standard disk model, built on the parameters determined from the best-fit procedure, is presented. Such a model constitutes a good point of departure for various theoretical studies aimed at the issue of formation of planetary systems and the character of protoplanetary disks.
Accurate measurements of neutron star masses are needed to constrain the equation of state of neutron star matter - of importance to both particle physics and the astrophysics of neutron stars - and to identify the evolutionary track of the progenitor stars that form neutron stars. The best measured values of the mass of 4UO900-40 (= Vela XR-l), 1.86 +/- 0.16 Msun (Barziv et al. 2001) and 1.93 +/- 0.20 Msun (Abubekerov et al. 2004), make it a leading candidate for the most massive neutron star known. The direct relationship between the maximum mass of neutron stars and the equation of state of ultra-dense matter makes 4UO900-40 an important neutron star mass to determine accurately. The confidence interval on previous mass estimates, obtained from observations that include parameters determined by non-dynamical methods, are not small enough to significantly restrict possible equations of state. We describe here a purely dynamical method for determining the mass of 4UO900-40, an X-ray pulsar, using the reprocessed UV pulses emitted by its BO.5Ib companion. One can derive the instantaneous radial velocity of each component by simultaneous X-ray and UV observations at the two quadratures of the system. The Doppler shift caused by the primary's rotational velocity and the illumination pattern of the X-rays on the primary, two of the three principal contributors to the uncertainty on the derived mass of the neutron star, almost exactly cancel by symmetry in this method. A heuristic measurement of the mass of 4UO900-40 using observations obtained previously with the High Speed Photometer on HST is given in Appendix A.
X-y mounted, 85 foot diameter, parabolic antenna system for solar, radio star and satellite tracking
A batch mode process which identifies three reference stars within a rotor-mounted star scanner's field-of-view based on the criteria of intensity and geometry was established. The sequential mode which continuously tracks the reference stars provides star transit times and estimates of rotor's spin rate. A least-square estimator was formulated which sequentially determines the spacecraft attitude from sucessive star crossings by minimizing the error in the star and scanner slit normal orthogonality. This spacecraft attitude also provides intermittent updates for the gyro propagated inertial attitude of the despun science platform. Simulation results are presented, showing successful star identification and attitude convergence in the presence of nutation and star transit time uncertainty.
Radio star signal measurement beneath auroral ionosphere for satellite tracking
The Transient Event Rejection for Acquisition and Tracking (TERAT) algorithm governs operation of image-data-acquisition and -processing system. TERAT processes digitized image data to acquire (that is, identify) candidate steady source of light, validate candidate source, and track validated source, all in presence of real or apparent luminous transients represented in image data. Source of light tracked could be star or distant luminous beacon. Transients caused by impacts of ionizing radiation on imaging array of photodetectors or by unsteady light sources not meant to be tracked. TERAT functions with limited data-processing resources. TERAT algorithm currently operational on NASA's TOPEX mission.
The OAO was successfully operating for approximately 11 months and has made over 2500 stellar observations. The OAO control system was a complex system which takes the 4500-lb vehicle through initial stabilization to star tracker control where a pointing accuracy of less than 1 arc minute was achieved. To obtain this pointing accuracy, the system used six orthogonally mounted gimbaled star trackers. The trackers were two gimbaled devices, having a 1-deg field of view with a + or - 43 deg gimbal excursion. The tracker could recognize and track 2.0 magnitude stars or brighter. The flight results indicated spacecraft pointing accuracies of less than 1 arc minute after tracker calibration with spacecraft jitter less than 3 arc seconds.