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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 289 records · Page 16
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NASA NTRS2003

Dynamics and Origin of Extra-solar Planetary Systems and Microlensing Detection of Extra-solar Planets

We compare a space-based microlensing search for planets, with a ground based microlensing search originally proposed by D. Tytler (Beichman, et al. 1996). Perturbations of microlensing light curves when the lens star has a planetary companion are sought by one wide angle survey telescope and an array of three or four followup narrow angle telescopes distributed in longitude that follow events with high precision, high time resolution photometry. Alternative ground based programs are considered briefly. With the four 2 meter telescopes distributed in longitude in the southern hemisphere in the Tytler proposal, observational constraints on a ground-based search for planets during microlensing events toward the center of the galaxy are severe. Probably less than 100 events could be monitored per year with high precision, high time resolution photometry with only about 42% coverage on the average regardless of how many events were discovered by the survey telescope. Statistics for the occurrence and properties for Jupiter-mass planets would be meaningful but relatively meager four years after the program was started, and meaningful statistics for Earth-mass planets would be non existent. In contrast, the 14,500 events in a proposed 4 year space based program (GEST = Galactic Exoplanet Survey Telescope) would yield very sound statistics on the occurrence, masses and separations of Jupiter-mass planets, and significant constraints on similar properties for Earth-mass planets. The significance of the Jupiter statistics would be to establish the frequency of planetary systems like our own, where terrestrial planets could exist inside the orbits of the giants.

Peale, S. J.↗
NASA NTRS2003

ST7-DRS: A Step Towards Drag-free and High-precision Formation Control

The Space Technology 7 Disturbance Reduction System (ST7-DRS) is an in-space technology demonstration within NASA's New Millennium Program. ST7-DRS is designed to validate system-level technologies that are required for future gravity missions (including the planned LISA gravitational-wave observatory) and for future formation-flying interferometer missions (including the planned MAXIM black-hole imager). ST7-DRS is based around a freely-floating test mass contained within a spacecraft structure that will shield this test mass from all external forces (aside from gravity). The spacecraft position will be continuously controlled, such that the spacecraft, itself, will remain centered about this test mass, essentially flying in formation with it. Colloidal micro-thrusters will be used to control the spacecraft s position to within a few nanometers, over time scales of tens to thousands of seconds. In order to detect the residual acceleration noise on the main test mass, a second test mass will be flown alongside the first, within the same physical spacecraft structure. This test mass will serve as a cross-reference for the first, and will also be used as a reference for the spacecraft's attitude control. The spacecraft's attitude will be controlled to an accuracy of a few milli-arc-seconds, also utilizing the colloidal micro-thrusters. ST7-DRS will consist of an instrument package (containing the test masses) and a set of micro-thrusters, which will be attached to the European Space Agency s SMART-2 spacecraft, set to launch in November 2007.

Houghton, M.↗
NASA NTRS2002

Methods for semi-automated indexing for high precision information retrieval

OBJECTIVE: To evaluate a new system, ISAID (Internet-based Semi-automated Indexing of Documents), and to generate textbook indexes that are more detailed and more useful to readers. DESIGN: Pilot evaluation: simple, nonrandomized trial comparing ISAID with manual indexing methods. Methods evaluation: randomized, cross-over trial comparing three versions of ISAID and usability survey. PARTICIPANTS: Pilot evaluation: two physicians. Methods evaluation: twelve physicians, each of whom used three different versions of the system for a total of 36 indexing sessions. MEASUREMENTS: Total index term tuples generated per document per minute (TPM), with and without adjustment for concordance with other subjects; inter-indexer consistency; ratings of the usability of the ISAID indexing system. RESULTS: Compared with manual methods, ISAID decreased indexing times greatly. Using three versions of ISAID, inter-indexer consistency ranged from 15% to 65% with a mean of 41%, 31%, and 40% for each of three documents. Subjects using the full version of ISAID were faster (average TPM: 5.6) and had higher rates of concordant index generation. There were substantial learning effects, despite our use of a training/run-in phase. Subjects using the full version of ISAID were much faster by the third indexing session (average TPM: 9.1). There was a statistically significant increase in three-subject concordant indexing rate using the full version of ISAID during the second indexing session (p < 0.05). SUMMARY: Users of the ISAID indexing system create complex, precise, and accurate indexing for full-text documents much faster than users of manual methods. Furthermore, the natural language processing methods that ISAID uses to suggest indexes contributes substantially to increased indexing speed and accuracy.

Evaluation Studies↗
NASA NTRS2004

High Precision Metrology on the Ultra-Lightweight W 50.8 cm f/1.25 Parabolic SHARPI Primary Mirror using a CGH Null Lens

For potential use on the SHARPI mission, Eastman Kodak has delivered a 50.8cm CA f/1.25 ultra-lightweight UV parabolic mirror with a surface figure error requirement of 6nm RMS. We address the challenges involved in verifying and mapping the surface error of this large lightweight mirror to +/-3nm using a diffractive CGH null lens. Of main concern is removal of large systematic errors resulting from surface deflections of the mirror due to gravity as well as smaller contributions from system misalignment and reference optic errors. We present our efforts to characterize these errors and remove their wavefront error contribution in post-processing as well as minimizing the uncertainty these calculations introduce. Data from Kodak and preliminary measurements from NASA Goddard will be included.

Antonille, Scott↗
NASA NTRS2005

Kinematics of a New High Precision Three Degree-of-Freedom Parallel Manipulator

Closed-form direct and inverse kinematics of a new three degree-of-freedom (DOF) parallel manipulator with inextensible limbs and base-mounted actuators are presented. The manipulator has higher resolution and precision than the existing three DOF mechanisms with extensible limbs. Since all of the manipulator actuators are base-mounted; higher payload capacity, smaller actuator sizes, and lower power dissipation can be obtained. The manipulator is suitable for alignment applications where only tip, tilt, and piston motions are significant. The direct kinematics of the manipulator is reduced to solving an eighth-degree polynomial in the square of tangent of half-angle between one of the limbs and the base plane. Hence, there are at most sixteen assembly configurations for the manipulator. In addition, it is shown that the sixteen solutions are eight pairs of reflected configurations with respect to the base plane. Numerical examples for the direct and inverse kinematics of the manipulator are also presented.

Tahmasebi, Farhad↗
NASA NTRS2005

Cryogenic System for Interferometry of High-precision Optics at 20 K: Design and Performance

This report describes the facility and experimental methods at the Goddard Space Flight Center Optics Branch for the measurement of the surface figure of cryogenically-cooled spherical mirrors using standard phase-shifting interferometry, with a standard uncertainty below 2nm rms. Two developmental silicon carbide mirrors were tested: both were spheres with radius of curvature of 600 mm, and clear apertures of 150 mm. The mirrors were cooled within a cryostat, and the surface figure error measured through a fused-silica window. The GSFC team developed methods to measure the in-situ SFE at 20 K with a combined standard uncertainty below 2 nm rms and the change in SFE with temperature (the cryochange) with a combined standard uncertainty of 0.25 -- 0.75 nm rms. This paper will present the measurement facility, methods, and uncertainty analysis.

Blake,Peter↗
NASA NTRS1995

High Precision Piezoelectric Linear Motors for Operations at Cryogenic Temperatures and Vacuum

The use of an electromechanical device for optically positioning a mirror system during the pre-project phase of the Pluto Fast Flyby mission was evaluated at JPL. The device under consideration was a piezoelectric driven linear motor functionally dependent upon a time varying electric field which induces displacements ranging from submicrons to millimeters with positioning accuracy within nanometers.

piezoelectric linear motor electromechanical optic↗
NASA NTRS1995

High Precision Piezoelectric Linear Motors for Operations at Cryogenic Temperatures and Vacuum

The Jet Propulsion Laboratory evaluated the use of an electromechanical device for optically positioning a mirror system during the pre-project phase of the Pluto-Fast-Flyby (PFF) mission. The device under consideration was a piezoelectric driven linear motor functionally dependent upon a time varying electric field which induces displacements ranging from submicrons to millimeters with positioning accuracy within nanometers. Using a control package, the mirror system provides image motion compensation and mosaicking capabilities. While this device offers unique advantages, there were concerns pertaining to its operational capabilities for the PFF mission. The issues include irradiation effects and thermal concerns. A literature study indicated that irradiation effects will not significantly impact the linear motor's operational characteristics. On the other hand, thermal concerns necessitated an in depth study.

piezoelectric motors↗
NASA NTRS1995

High Precision and Real Time Tracking of Low Earth Orbiters With GPS: Case Studies With TOPEX/POSEIDON and EUVE

TOPEX/POSEIDON carries a dual-frequency 6 channel GPS receiver while EUVE has a 12 channel single frequency receiver. Flying at an altitude of 1334 km, TOPEX/POSEIDON performs precise ocean altimetry, which demands the highest possible accuracy in determining the radial orbit component in post-processing. Radial RMS accuracies of about 2 cm were realized using reduced dynamic tracking techniques. In this approach, orbit errors due to force are substantially reduced by exploiting the geometric strength of GPS to solve for a set of stochastic forces. On EUVE, the emphasis was on evaluating real time positioning techniques with a single frequency receiver. The capability for real time 3D accuracies of 15 m in the presence of Selective Availability was shown. This was validated by comparing to a post-processed differential GPS truth orbit believed accurate to about 1 m.!.

Tracking low-Earth orbiters↗
NASA NTRS2002

High-precision early mission narrow angle sciene with the Space Interferometry Mission

We have developed a technique that allows SIM to measure relative stellar positions with an accuracy of 1 micro-arcsecond at any time during its 5-yr mission. Unlike SIM's standard narrow-angle approach, Gridless Narrow Angle Astrometry (GNAA) does not rely on the global reference frame of grid stars that reaches full accuracy after 5 years. GNAA is simply the application of traditional single-telescope narrow angle techniques to SIM's narrow angle optical path delay measurements. In GNAA, a set of reference stars and a target star are observed at several baseline orientations. A linearized model uses delay measurements to solve for star positions and baseline orientations. A conformal transformation maps observations at different epochs to a common reference frame. The technique works on short period signals (P=days to months), allowing it to be applied to many of the known extra-solar planets, intriguing radio/X- ray binaries, and other periodic sources. The technique's accuracy is limited in the long-term by false acceleration due to a combination of reference star and target star proper motion. The science capability 1 micro-arcsecond astrometric precision - is unique to SIM.

Space Interferometry Mission↗