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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
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Irradiance from stars based on blackbody theory

A computer program which calculates a theoretical backbody curve for a star when given only the star's temperature and visual magnitude is presented. The program was written to produce approximate stellar spectra to be used in the design of the Space Telescope Fine Guidance System (FGS). In addition to the blackbody curve, the program calculates the number of photons tht would be received by the Space Telescope per 25 MSEC interval in wavelength increments of 0.2 microns. The equations used for the computations work best for stars that emit primarily in the range of near infrared to ultraviolet.

Jacobs, W. A.↗
NASA NTRS1984

Study of alternate optical and fine guidance sensor designs for the space infrared telescope facility (SIRTF)

A unique optical design was developed that compensates for the coma degraded images caused by field chopping in SIRTF. The conic constants of a Cassegrain telescope were altered to compensate for the coma induced by the secondary mirror tilt. The modulation transfer function is essentially independent of secondary mirror tilt, and diffraction limited image quality is maintained over a several arcminute field during chopping. With an untilted secondary mirror, the coma compensated (CC) design has a smaller field than the unchopped Ritchey-Chretien design; but use of relay optics, such as the inverted Cassegrain design developed for the fine guidance sensor (FGS), can increase the CC telescope's field size. A reactionless secondary mirror chopper mechanism that uses superconducting magnets was studied. The heart producing elements are confined to a reaction plate that is not directly viewed by the IR focal plane. A design was also developed for a low moment of inertia, reticulated HIP beryllium secondary mirror consistent with blank fabrication technology and optical finishing requirements.

Wissinger, A.↗
NASA NTRS1985

Fine guidance sensor design optimization for Space Infrared Telescope Facility (SIRTF)

The present paper is concerned with the general issues of design optimization of a staring mosaic sensor for guide-star tracking, taking into account the choice of the proper interpolation algorithm. It was found that the final choice of algorithm depends on the severity of the positional accuracy requirement and the expected variation in the blur spot shape. The considered track algorithms estimate the position either of the peak or of the centroid of the image of a point source. Attention is given to aspects of problem definition, the total effect of error sources on algorithm accuracy, a parametric analysis of performance behavior, Monte Carlo results, and the design of the SIRTF Fine Guidance Sensor (FGS). The algorithm error, the signal-to-noise error, and the nonuniformity error are examined.

Grossman, S. B.↗
NASA NTRS1987

Fiducial reference for the HIPPARCOS reference system

The groundwork was prepared for observations by the Hubble Space Telescope (HST) to tie the coordinate system of the European Astrometry Satellite HIPPARCOS to an extragalactic (VLBI) reference frame, and to determine the rotation of the HIPPARCOS frame with respect to the extragalactic frame. A total of 90 Extragalactic Optical Objects (EGOs) were determined in the vicinity (angular separation less than 18 arcminutes) of 160 HIPPARCOS stars (brighter than about 11.0 magnitude, mostly SAO stars brighter than 10.5), evenly distributed over the sky, to be used to tie the HIPPARCOS system to the Extragalactic Reference Frame. The pairs are to be observed with the HST Fine Guidance Sensors (FGS), sometimes in conjunction with the HST Planetary Camera, in order to determine the relative positions and motions of the individual HIPPARCOS stars with respect to the EGOs. The data base which contains the optical information used to generate the HST Guaranteed Observing Time (GTO) proposal is included.

Duncombe, R. L.↗
NASA NTRS1991

Scientific results from the Hubble Space Telescope Fine Guidance Sensors

The Fine Guidance Sensors of the Hubble Space Telescope have two roles to play. They are the ultimate pointing and control instruments onboard the spacecraft and they are the primary astrometric instruments of the observatory. Because they are used for every scientific observation with the Hubble Space Telescope, independently of the ultimate scientific instrument being utilized, there is much more experience with them than with any of the other scientific devices. The Fine Guidance Sensors have already serendipitously discovered their first binary star from the Hubble Space Telescope Guide Star Catalog, have been exercised in most of their observing modes, and are able to fulfill their pointing and control functions up to their original specifications (in the absence of external influences). In addition, the imperfections in the primary mirror have minimally affected the performance of the Fine Guidance Sensors. An up-to-date summary of FGS engineering and science will be presented.

Taff, L. G.↗
NASA NTRS1992

A dual purpose optical truss laser metrology system for a space-based far-IR segmented telescope: Figure maintenance and pointing control

To obtain imaging performance as for monolithic mirrors, large segmented reflectors used for astronomy must be actively aligned and pointed to extreme levels of precision. A system concept for a dual purpose optical truss laser metrology system is described which is used for both figure and alignment maintenance and telescope pointing. A two-stage figure active control approach was developed for several proposed spaceborne far infrared segmented telescopes, one of which is the 10-20 meters Large Deployable Reflector (LDR). The first active control stage, the figure initialization control system, aligns the optical elements (i.e., the primary segments, secondary and focal plane assembly) based on images obtained. The second stage, the figure maintenance control system, maintains the alignment between re-initializations using measurements provided by laser interferometers arranged in an optical truss configuration. It measures the relative positions and alignments of the telescope segments so that a controller can reposition them appropriately. The application of this optical truss for figure maintenance control is the subject of the first part of this paper. The second portion of this paper discusses the application of the optical truss to telescope pointing. Here, the laser metrology system is used to transfer pointing information from an external fine guidance sensor (FGS) to the telescope optical boresight as defined by the primary mirror, secondary mirror, and focal plane assembly. Thus, any alignment variations between the two boresights can be observed and accounted for.

Lau, Kenneth↗
NASA NTRS1993

Determination and characterization of the Hubble Space Telescope pointing stability

The Hubble Space Telescope (HST) was designed to maintian a pointing stability (jitter) of 0.007 arc seconds rms throughout every observing period, which can last from a few seconds to several orbits. On-orbit measurements indicate that the hardware excitation induced by the reaction wheels. gyros, high gain antennae, science instrument mechanisms and tape recorders are well within specifications. Unexpectedly, the solar arrays because the dominant source of jitter. Every passage through an orbital terminator produces vibrations which emanate from the solar arrays due to thermal effects, which affect the relative positional stability. Broadband frequencies centered about 0.11 and 0.65 Hz were detected in the frequency content of the vehicle jitter. On-board modifications to the control law have attenuated the disturbance torques and reduced the vehicle jitter close to specification. Replacement of the solar arrays in December, 1993, should eliminate the torque distubances. Astrometric science observations are extremely susceptible to corruption from vehicle jitter. The removal of vehicle jitter from astrometric Transfer function scans of binary stars is explained in detail. A binary star separation of 16 milli-seconds of arc has been achieved, a separation resolution of 10 to 12 milli-seconds of arc appears feasible, with a binary star magnitude of 9 m(sub V). The achievement of this resolution is in part due to vehicle jitter removal. Comparison of vehicle jitter measurements from the position path of the vehicle control law, or from the guiding Fine Guidance Sensors (FGS), are shown to be equivalent to approximately 0.001 arc second.

Bradley, A. J.↗
NASA NTRS1997

Hubble Space Telescope Astrometry Science Team

Topics considered include: Calibration and Astrometry Pipeline; Astrometry Anomaly Analysis; The STAT pipeline and software analysis tools; GTO Program; Parallaxes of Astrophysically Interesting Objects; HST- Hipparcos Extragalactic Link; Ground-Based Observations of Radial Velocities; GTO Globular Cluster Internal Motions; and GTO Hyades Cluster Member FGS Parallaxes.

Benedict, George F.↗
NASA NTRS1997

The 1997 HST Calibration Workshop with a New Generation of Instruments

The Second Servicing mission in early 1997 has brought major changes to the Hubble Space Telescope (HST). Two of the original instruments, Faint Object Spectrograph (FOS) and Goddard High Resolution Spectrograph (GHRS), were taken out, and replaced by completely new instruments, the Space Telescope Imaging Spectrograph (STIS) and the Near Infrared Camera Multi-Object Spectrograph (NICMOS). Two new types of detectors were installed, and for the first time, HST gained infrared capabilities. A new Fine Guidance Sensor (FGS) was installed, with an alignment mechanism that could improve substantially both guiding and astrometric capabilities. With all these changes come new challenges. The characterization of the new instruments has required a major effort, both by their respective Investigation Definition Teams and at the Space Telescope Science Institute. All necessary final calibrations for the retired spectrographs needed to be carried out, and their properties definitively characterized. At the same time, work has continued to improve our understanding of the instruments that have remained on board. The results of these activities were discussed in the 1997 HST (Hubble Space Telescope) Calibration Workshop. The main focus of the Workshop was to provide users with the tools and the understanding they need to use HST's instruments and archival data to the best of their possibilities. This book contains the written record of the Workshop. As such, it should provide a valuable tool to all interested in using existing HST data or in proposing for new observations.

Casertano, S.↗
NASA NTRS1999

STS-103 Flight Day 5 Highlights and Crew Activities Report

Highlights of the fifth day of the STS-103 mission on board the space shuttle Discovery are shown in this videotape. The mission was led by Commander Curtis L. Brown, with Pilot Scott J Kelly, and Mission Specialists Steven L. Smith, Jean-Francois Clervoy, John M. Grunsfeld, Michael Foale, and Claude Nicollier. The main purpose of the mission was to service the Hubble Space Telescope (HST). The primary objective of the mission was to replace all six of the gyroscopes that make up the three Rate Sensor Units. In addition the Astronauts installed a new computer. During the 5th day Michael Foale and Claude Nicollier performed the servicing of the HST in an 8 hour 10 minute Extravehicular Activity (EVA). The servicing included the removal of the old computer and the installation of a new, faster computer with more memory. They also installed a new outer thermal layer to protect the computer. After this was finished the astronauts replaced one of the Fine Guidance Sensors (FGS), an optical sensor which allows NASA to point the telescope in the desired direction. The video includes actual live views of the HST in the shuttle's service bay, and footage of the repair and servicing EVA.

Source record↗
NASA NTRS1999

Hubble Space Telescope Servicing Mission 3A

The Hubble Space Telescope's purpose is to spend 20 years probing the farthest and faintest reaches of the cosmos. Crucial to fulfilling this objective is a series of on-orbit servicing missions. Hubble was placed in orbit on April 25, 1990, by the shuttle Discovery and subsequent servicing followed in December 1993 and February 1997. The third in the series of planned servicing missions for the Hubble Space Telescope was scheduled for June 2000. This third Servicing Mission has been separated into two flights. The first of these flights, Servicing Mission 3A, is scheduled for December 1999, and the second, Servicing Mission 3B, is scheduled for 2001. The fourth Servicing Mission is scheduled for 2003 with a "close-out" Mission in 2010. Three instruments are currently in active scientific use on Hubble - the Wide Field and Planetary Camera 2, the Space Telescope Imaging Spectrograph, and Fine Guidance Sensor I R, which has been designated as the prime FGS for astrometric science. Other instrument bays are occupied by the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), which is now dormant due to the depletion of its solid nitrogen cryogen, the Faint Object Camera, which has been decommissioned, and the corrective optical device called COSTAR, which is no longer needed.

Source record↗
NASA NTRS2003

The James Webb Telescope Instrument Suite Layout: Optical System Engineering Considerations for a Large, Deployable Space Telescope

The James Webb Space Telescope (JWST) is a space-based, infrared observatory designed to study the early stages of galaxy formation in the Universe. The telescope will be launched into an elliptical orbit about the second Lagrange point and passively cooled to 30-50 K to enable astronomical observations from 0.6 to 28 microns. A group from the NASA Goddard Space Flight Center and the Northrop Grumman Space Technology prime contractor team has developed an optical and mechanical layout for the science instruments within the JWST field of view that satisfies the telescope s high-level performance requirements. Four instruments required accommodation within the telescope's field of view: a Near-Infrared Camera (NIRCam) provided by the University of Arizona; a Near-Mared Spectrometer (NIRSpec) provided by the European Space Agency; a Mid-Infrared Instrument (MIRI) provided by the Jet Propulsion Laboratory and a European consortium; and a Fine Guidance Sensor (FGS) with a tunable filter module provided by the Canadian Space Agency. The size and position of each instrument's field of view allocation were developed through an iterative, concurrent engineering process involving the key observatory stakeholders. While some of the system design considerations were those typically encountered during the development of an infrared observatory, others were unique to the deployable and controllable nature of JWST. This paper describes the optical and mechanical issues considered during the field of view layout development, as well as the supporting modeling and analysis activities.

Bos, Brent↗
NASA NTRS2004

JWST ISIM Distortion Analysis Challenge

Very tight distortion requirements are imposed on the JWST's ISM structure due to the sensitivity of the telescope's mirror segment and science instrument positioning. The ISIM structure is a three dimensional truss with asymmetric gusseting and metal fittings. One of the primary challenges for ISIM's analysis team is predicting the thermal distortion of the structure both from the bulk cooldown from ambient to cryo, and the smaller temperature changes within the cryogenic operating environment. As a first cut to estimate thermal distortions, a finite element model of bar elements was created. Elements representing joint areas and metal fittings use effective properties that match the behavior of the stack-up of the composite tube, gusset and adhesive under mechanical and thermal loads. These properties were derived by matching tip deflections of a solid model simplified T-joint. Because of the structure s asymmetric gusseting, this effective property model is a first attempt at predicting rotations that cannot be captured with a smeared CTE approach. In addition to the finite element analysis, several first order calculations have been performed to gauge the feasibility of the material design. Because of the stringent thermal distortion requirements at cryogenic temperatures, a composite tube material with near zero or negative CTE is required. A preliminary hand analysis of the contribution of the various components along the distortion path between FGS and the other instruments, neglecting second order effects were examined. A plot of bounding tube longitudinal and transverse CTEs for thermal stability requirements was generated to help determine the feasibility of meeting these requirements. This analysis is a work in progress en route to a large degree of freedom hi-fidelity FEA model for distortion analysis. Methods of model reduction, such as superelements, are currently being investigated.

Cifie, Emmanuel↗
NASA NTRS2004

A Formal Methods Approach to the Analysis of Mode Confusion

The goal of the new NASA Aviation Safety Program (AvSP) is to reduce the civil aviation fatal accident rate by 80% in ten years and 90% in twenty years. This program is being driven by the accident data with a focus on the most recent history. Pilot error is the most commonly cited cause for fatal accidents (up to 70%) and obviously must be given major consideration in this program. While the greatest source of pilot error is the loss of situation awareness , mode confusion is increasingly becoming a major contributor as well. The January 30, 1995 issue of Aviation Week lists 184 incidents and accidents involving mode awareness including the Bangalore A320 crash 2/14/90, the Strasbourg A320 crash 1/20/92, the Mulhouse-Habsheim A320 crash 6/26/88, and the Toulouse A330 crash 6/30/94. These incidents and accidents reveal that pilots sometimes become confused about what the cockpit automation is doing. Consequently, human factors research is an obvious investment area. However, even a cursory look at the accident data reveals that the mode confusion problem is much deeper than just training deficiencies and a lack of human-oriented design. This is readily acknowledged by human factors experts. It seems that further progress in human factors must come through a deeper scrutiny of the internals of the automation. It is in this arena that formal methods can contribute. Formal methods refers to the use of techniques from logic and discrete mathematics in the specification, design, and verification of computer systems, both hardware and software. The fundamental goal of formal methods is to capture requirements, designs and implementations in a mathematically based model that can be analyzed in a rigorous manner. Research in formal methods is aimed at automating this analysis as much as possible. By capturing the internal behavior of a flight deck in a rigorous and detailed formal model, the dark corners of a design can be analyzed. This paper will explore how formal models and analyses can be used to help eliminate mode confusion from flight deck designs and at the same time increase our confidence in the safety of the implementation. The paper is based upon interim results from a new project involving NASA Langley and Rockwell Collins in applying formal methods to a realistic business jet Flight Guidance System (FGS).

Butler, Ricky W.↗
NASA NTRS2006

The 2005 HST Calibration Workshop Hubble After the Transition to Two-Gyro Mode

The 2005 HST Calibration Workshop was held at the Space Telescope Science Institute during October 26, 2005 to bring together members of the observing community, the instrument development teams, and the STScI instrument support teams to share information and techniques. Presentations included the two-gyro performance of HST and FGS, advances in the calibration of a number of instruments, the results of other instruments after their return from space, and the status of still others which are scheduled for installation during the next servicing mission. Cross-calibration between HST and JWST was discussed, as well as the new Guide Star Catalog and advances in data analysis software. This book contains the published record of the workshop, while all the talks and posters are available electronically on the workshop Web site.

Koekemoer, Anton M.↗
NASA NTRS2010

Flagging and Correction of Pattern Noise in the Kepler Focal Plane Array

In order for Kepler to achieve its required less than 20 PPM photometric precision for magnitude 12 and brighter stars, instrument-induced variations in the CCD readout bias pattern (our "2D black image"), which are either fixed or slowly varying in time, must be identified and the corresponding pixels either corrected or removed from further data processing. The two principle sources of these readout bias variations are crosstalk between the 84 science CCDs and the 4 fine guidance sensor (FGS) CCDs and a high frequency amplifier oscillation on less than 40% of the CCD readout channels. The crosstalk produces a synchronous pattern in the 2D black image with time-variation observed in less than 10% of individual pixel bias histories. We will describe a method of removing the crosstalk signal using continuously-collected data from masked and over-clocked image regions (our "collateral data"), and occasionally-collected full-frame images and reverse-clocked readout signals. We use this same set to detect regions affected by the oscillating amplifiers. The oscillations manifest as time-varying moir pattern and rolling bands in the affected channels. Because this effect reduces the performance in only a small fraction of the array at any given time, we have developed an approach for flagging suspect data. The flags will provide the necessary means to resolve any potential ambiguity between instrument-induced variations and real photometric variations in a target time series. We will also evaluate the effectiveness of these techniques using flight data from background and selected target pixels.

Kolodziejczak, Jeffery J.↗
NASA NTRS1999

Hubble Space Telescope: Servicing Mission 3A. Media Reference Guide

Since its launch in April 1990, the Hubble Space Telescope (HST) has provided scientific data and images of unprecedented resolution from which many new and exciting discoveries have been made. The Telescope's purpose is to spend 20 years probing the farthest and faintest reaches of the cosmos. Crucial to fulfilling this objective is a series of on-orbit manned servicing missions. The First Servicing Mission (SM1) took place in December 1993 and the Second Servicing Mission (SM2) was flown in February 1997. During these missions, astronauts perform planned repairs and maintenance activities to restore and upgrade the observatory s capabilities. To facilitate this process, the Telescope s designers configured science instruments and several vital engineering subsystems as Orbital Replacement Units (ORU) -- modular packages with standardized fittings accessible to astronauts in pressurized suits. Hubble's Third Servicing Mission has been separated into two parts: Servicing Mission 3A (SM3A) will fly in Fall of 1999 and Servicing Mission 3B (SM3B) is planned for 2001. The principal objective of SM3A is to replace all six gyroscopes that compose the three Rate Sensor Units (RSU). In addition, space-walking astronauts will install a new Advanced Computer that will dramatically increase the computing power, speed, and storage capability of HST. They will change out one of the Fine Guidance Sensors (FGS) and replace a tape recorder with a new Solid State Recorder (SSR). The Extravehicular Activity (EVA) crew also will install a new S-band Single-Access Transmitter (SSAT), and Voltage/Temperature Improvement Kits (VIK) for the Telescope s nickel-hydrogen batteries. Finally, they will begin repair of the multilayer insulation on Hubble s outer surface. During SM3B astronauts will install a new science instrument, the Advanced Camera for Surveys (ACS), and an Aft Shroud Cooling System (ASCS) for the other axial science instruments. They will attach a new cryogenic cooler to the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). They also will replace the HST flexible Solar Arrays with new high-performance rigid arrays.

FROM↗
NASA NTRS2011

An Overview of Thermal Distortion Modeling, Analysis, and Model Validation for the JWST ISIM Structure

The James Webb Space Telescope (JWST) is a large, infrared-optimized space telescope consisting of the following elements: (1) Optical telescope element (OTE) (2) Integrated science instrument module (ISIM) (3) Spacecraft (4) Sunshield The Integrated Science Instrument Module (ISIM) consists of the JWST science instruments (NIRCam, MIRI, NIRSpec), a fine guidance sensor (FGS), the ISIM Structure, and thermal and electrical subsystems. JWST's instruments are designed to work primarily in the infrared range of the electromagnetic spectrum, and the instruments and telescope operate at cryogenic temperatures (approximately 35 K for the instruments). The development and validation of a thermal distortion modeling and analysis capability for the JWST ISIM Structure was successfully completed. The modeling and analysis approach was grounded in initial constituent materials testing and benchmarked to test results at the composite bonded joint, subassembly, and fullscale flight hardware levels. Comparison of analysis predictions and test results from this series of incremental cryogenic thermal distortion tests demonstrates that the model validation goals are achieved.

Johnston, John↗