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NASA NTRS2004

Integrated Modeling Activities for the James Webb Space Telescope: Optical Jitter Analysis

This is a continuation of a series of papers on the integrated modeling activities for the James Webb Space Telescope(JWST). Starting with the linear optical model discussed in part one, and using the optical sensitivities developed in part two, we now assess the optical image motion and wavefront errors from the structural dynamics. This is often referred to as "jitter: analysis. The optical model is combined with the structural model and the control models to create a linear structural/optical/control model. The largest jitter is due to spacecraft reaction wheel assembly disturbances which are harmonic in nature and will excite spacecraft and telescope structural. The structural/optic response causes image quality degradation due to image motion (centroid error) as well as dynamic wavefront error. Jitter analysis results are used to predict imaging performance, improve the structural design, and evaluate the operational impact of the disturbance sources.

Hyde, T. Tupper↗
NASA NTRS2004

Integrated Modeling Activities for the James Webb Space Telescope: Structural-Thermal-Optical Analysis

The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2011. This is a continuation of a series of papers on modeling activities for JWST. The structural-thermal-optical, often referred to as STOP, analysis process is used to predict the effect of thermal distortion on optical performance. The benchmark STOP analysis for JWST assesses the effect of an observatory slew on wavefront error. Temperatures predicted using geometric and thermal math models are mapped to a structural finite element model in order to predict thermally induced deformations. Motions and deformations at optical surfaces are then input to optical models, and optical performance is predicted using either an optical ray trace or a linear optical analysis tool. In addition to baseline performance predictions, a process for performing sensitivity studies to assess modeling uncertainties is described.

Johnston, John D.↗
NASA NTRS2004

Microshutter Arrays for James Webb Space Telescope

Two-dimensional MEMS microshutter arrays are being developed at NASA Goddard Space Flight Center for use in the near-infrared region on the James Webb Space Telescope (JWST). The microshutter arrays are designed for the selective transmission of light with high efficiency and high contrast. The JWST environment requires cryogenic operation at 35K. Microshutter arrays are fabricated out of silicon-oxide-insulated (SOI) silicon wafers. Arrays are close-packed silicon nitride membranes with a pixel size of 100x200 p. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with a minimized mechanical stress concentration. The mechanical shutter arrays are fabricated using MEMS technologies. The processing includes a multi- layer metal deposition and patterning of shutter electrodes and magnetic pads, reactive ion etching (NE) of the front side to form shutters out of the nitride membrane, an anisotropic back-etch for wafer thinning, followed by a deep RIE (DRIE) back-etch down to the nitride shutter membrane to form W e s and relieve shutters from the silicon substrate. An additional metal deposition and patterning is used to form back electrodes. Shutters are actuated using a magnetic force and latched using an electrostatic force. . . . KEYWORDS: microshutter, MEMS, RIE, DRIE, micro-optics, near inbred, space telescope

Li, Mary J.↗
NASA NTRS2004

Green Bank Telescope Observations of Interstellar Glycolaldehyde: Low Temperature Sugar

Interstellar glycolaldehyde (CH20HCHO) has been detected with the 100-m Green Bank Telescope (GBT) toward the star-forming region Sagittarius B2(N) by means of the 1(sub 10)-1(sub 01),2(sub 11)-2(sub 02),3(sub 12)-3(sub 0), and 4(sub 13)-4(sub 04) rotational transitions at 13.48, 15.18, 17.98, and 22.14 GHz, respectively. An analysis of these four high signal- to-noise rotational transitions yields a glycolaldehyde state temperature of ~8 K. Previously reported emission line detections of glycolaldehyde with the NRAO 12-m telescope at mm-wavelengths (71 GHz to 103 GHz) are characterized by a state temperature of -50 K. By comparison the GBT detections are surprisingly strong and seen in emission at 13.48 GHz, emission and absorption at 15.18 GHz, and absorption at 17.98 GHz and 22.14 GHz. We attribute the strong absorption observed by the GBT at the higher frequencies to the correspondingly smaller GBT beams coupling better to the continuum source(s) in Sagittarius B2(N). A possible model for the two-temperature regions of glycolaldehyde is discussed.

Hollis, J. M.↗
NASA NTRS2003

Space Telescope Imaging Spectrograph Co-Investigator Support

The purpose of this contract has been to support investigation of astronomical problems primarily using data from the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST). As a Co-investigator on STIS, I participated in several projects, which will be described below. The research resulted in 19 papers in refereed journals, 8 papers published in conference proceedings, and 27 papers presented at meetings. There are still at least four papers submitted or in press, as well as some additional research yet to be written up for publication. The research has also produced one master's thesis and two PhD dissertations currently underway, with one to be completed Spring 2003. Undergraduates have participated in the analysis of supporting observations. One student has published some of his results in a web- based refereed publication for undergraduate research (www.jyi.org). I have given several talks to the general public describing results from the HST as well as the results of my research. I have been named the UNLV Regents' Outstanding Faculty Member for 1995 and received the 2002 College of Science Distinguished Researcher's Award as a result of these activities.

Weistrop, Donna↗
NASA NTRS2003

XML: James Webb Space Telescope Database Issues, Lessons, and Status

This paper will present the current concept using extensible Markup Language (XML) as the underlying structure for the James Webb Space Telescope (JWST) database. The purpose of using XML is to provide a JWST database, independent of any portion of the ground system, yet still compatible with the various systems using a variety of different structures. The testing of the JWST Flight Software (FSW) started in 2002, yet the launch is scheduled for 2011 with a planned 5-year mission and a 5-year follow on option. The initial database and ground system elements, including the commands, telemetry, and ground system tools will be used for 19 years, plus post mission activities. During the Integration and Test (I&T) phases of the JWST development, 24 distinct laboratories, each geographically dispersed, will have local database tools with an XML database. Each of these laboratories database tools will be used for the exporting and importing of data both locally and to a central database system, inputting data to the database certification process, and providing various reports. A centralized certified database repository will be maintained by the Space Telescope Science Institute (STScI), in Baltimore, Maryland, USA. One of the challenges for the database is to be flexible enough to allow for the upgrade, addition or changing of individual items without effecting the entire ground system. Also, using XML should allow for the altering of the import and export formats needed by the various elements, tracking the verification/validation of each database item, allow many organizations to provide database inputs, and the merging of the many existing database processes into one central database structure throughout the JWST program. Many National Aeronautics and Space Administration (NASA) projects have attempted to take advantage of open source and commercial technology. Often this causes a greater reliance on the use of Commercial-Off-The-Shelf (COTS), which is often limiting. In our review of the database requirements and the COTS software available, only very expensive COTS software will meet 90% of requirements. Even with the high projected initial cost of COTS, the development and support for custom code over the 19-year mission period was forecasted to be higher than the total licensing costs. A group did look at reusing existing database tools and formats. If the JWST database was already in a mature state, the reuse made sense, but with the database still needing to handing the addition of different types of command and telemetry structures, defining new spacecraft systems, accept input and export to systems which has not been defined yet, XML provided the flexibility desired. It remains to be determined whether the XML database will reduce the over all cost for the JWST mission.

Detter, Ryan↗
NASA NTRS2004

The Role of Integrated Modeling in the Design and Verification of the James Webb Space Telescope

The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2011. System-level verification of critical optical performance requirements will rely on integrated modeling to a considerable degree. In turn, requirements for accuracy of the models are significant. The size of the lightweight observatory structure, coupled with the need to test at cryogenic temperatures, effectively precludes validation of the models and verification of optical performance with a single test in 1-g. Rather, a complex series of steps are planned by which the components of the end-to-end models are validated at various levels of subassembly, and the ultimate verification of optical performance is by analysis using the assembled models. This paper describes the critical optical performance requirements driving the integrated modeling activity, shows how the error budget is used to allocate and track contributions to total performance, and presents examples of integrated modeling methods and results that support the preliminary observatory design. Finally, the concepts for model validation and the role of integrated modeling in the ultimate verification of observatory are described.

Mosier, Gary E.↗
NASA NTRS2004

Spitzer Space Telescope Spectroscopy of the Kepler Supernova Remnant

The Infrared Spectrograph on the Spitzer Space Telescope was used for observations of the Kepler supernova remnant, with all four instrument modules targeted on the bright infrared knot located at 17h30m35.80s,-21d28m54.0s (J2000). The low spectral resolution modules data show a dust continuum spectrum consistent with dust grains heated by high-energy electrons, while the high resolution modules data show atomic emission line ratios consistent with excitation by a high velocity shock of greater than 100 kilometers per second and electron densities of approximately 1,000 per centimeter. The abundance ratios for the six detected elements show signs of heavy-element enhancement. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology. Support for this work was provided by NASA's Office of Space Science.

Roellig, T. L.↗
NASA NTRS2005

The Space Infrared Interferometric Telescope (SPIRIT)

We report preliminary results of a study of the Space Infrared Interferometric Telescope (SPIRIT), a candidate Origins Probe mission. SPIRIT is a two-element Michelson interferometer operating over a nominal wavelength range 25 to 400 microns and offering a powerful combination of spectroscopy and sub-arcsecond angular resolution imaging in a single instrument. With angular resolution comparable to that of JWST and far-IR sensitivity nearly two orders of magnitude better than that of the Spitzer Space Telescope, SPIRIT will measure the resonant structures in exozodi debris disks to find and characterize extrasolar planets; characterize the atmospheres of selected extrasolar gas giant planets; elucidate the evolution of young stellar systems and their planet-forming potential; and track the luminosity evolution and chemical and dust enrichment of galaxies on a cosmological timescale. SPIRIT could be ready to launch as early as 2015. The SPIRIT study is sponsored by NASA under the Origins Science Mission Concept study program.

Leisawitz, David↗
NASA NTRS1999

Observation and Simulations of the Backsplash Effects in High-Energy Gamma-Ray Telescopes Containing a Massive Calorimeter

Beam test and simulation results are presented for a study of the backsplash effects produced in a high-energy gamma-ray detector containing a massive calorimeter. An empirical formula is developed to estimate the probability (per unit area) of backsplash for different calorimeter materials and thicknesses, different incident particle energies, and at different distances from the calorimeter. The results obtained are applied to the design of Anti-Coincidence Detector (ACD) for the Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST).

Moiseev, Alexander A.↗
NASA NTRS2004

Lessons Learned from the Hubble Space Telescope (HST) Contamination Control Program

Over the past two decades, the Hubble Space Telescope (HST) Contamination Control Program has evolved from a ground-based integration program to a space-based science-sustaining program. The contamination controls from the new-generation Scientific Instruments and Orbital Replacement Units were incorporated into the HST Contamination Control Program to maintain scientific capability over the life of the telescope. Long-term on-orbit scientific data has shown that these contamination controls implemented for the instruments, Servicing Mission activities (Orbiter, Astronauts, and mission), and on-orbit operations successfully protected the HST &om contamination and the instruments from self-contamination.

Hansen, Patricia A.↗
NASA NTRS2005

Mineralogy of Asteroids from Observations with the Spitzer Space Telescope

Visible and near-infrared (approx.0.3 to 4.0 microns) spectroscopy has been successfully employed since the early 1970 s to infer the surface compositions of asteroids. Spectroscopic observations in the thermal infrared (approx.5 to 40 microns) are similarly promising. Silicate spectra in this range are dominated by Si-O stretch and bend fundamentals, and other minerals have similarly diagnostic bands [e.g., 1,2]. Observations in this spectral range are difficult from the ground due to strong telluric absorptions and background emission. Nevertheless, spectral structure has been detected on a few asteroids in the 8 to 14-m range from the ground [3,4], as well as from orbit with the ISO satellite [e.g., 5]. The Spitzer Space Telescope can observe asteroids with much higher sensitivity over a broader wavelength range than is possible from the ground or was possible with ISO. We present results of measurements of asteroids with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope.

Emery, J. P.↗
NASA NTRS2005

Mineralogy of Asteroids from Observations with the Spitzer Space Telescope

Visible and near-infrared (approximately 0.3 to 4.0 microns) spectroscopy has been successfully employed since the early 1970 s to infer the surface compositions of asteroids. Spectroscopic observations in the thermal infrared (approximately 5 to 40 microns) are similarly promising. Silicate spectra in this range are dominated by Si-O stretch and bend fundamentals, and other minerals have similarly diagnostic bands. Observations in this spectral range are difficult from the ground due to strong telluric absorptions and background emission. Nevertheless, spectral structure has been detected on a few asteroids in the 8 to 14-micron range from the ground, as well as from orbit with the ISO satellite. The Spitzer Space Telescope can observe asteroids with much higher sensitivity over a broader wavelength range than is possible from the ground or was possible with ISO. We present results of measurements of asteroids with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope.

Emery, J. P.↗
NASA NTRS2004

Lessons Learned from the Hubble Space Telescope (HST) Contamination Control Program

Over the past two decades, the Hubble Space Telescope (HST) Contamination Control Program has evolved from a ground-based integration program to a space-based science-sustaining program. The contamination controls from the new-generation Scientific Instruments and Orbital Replacement Units were incorporated into the HST Contamination Control Program to maintain scientific capability over the life of the telescope. Long-term on-orbit scientific data has shown that these contamination controls implemented for the instruments, Servicing Mission activities (Orbiter, Astronauts, and mission), and on-orbit operations successfully protected the HST from contamination and the instruments from self-contamination.

Hansen, Patricia A.↗
NASA NTRS2005

Thermal System Verification and Model Validation for NASA's Cryogenic Passively Cooled James Webb Space Telescope (JWST)

A thorough and unique thermal verification and model validation plan has been developed for NASA s James Webb Space Telescope. The JWST observatory consists of a large deployed aperture optical telescope passively cooled to below 50 Kelvin along with a suite of several instruments passively and actively cooled to below 37 Kelvin and 7 Kelvin, respectively. Passive cooling to these extremely low temperatures is made feasible by the use of a large deployed high efficiency sunshield and an orbit location a! !he L2 Lagrange p~in!. Another enabling feature is the scale or size of the observatory that allows for large radiator sizes that are compatible with the expected power dissipation of the instruments and large format Mercury Cadmium Telluride (HgCdTe) detector arrays. This passive cooling concept is simple, reliable, and mission enabling when compared to the alternatives of mechanical coolers and stored cryogens. However, these same large scale observatory features, which make passive cooling viable, also prevent the typical flight configuration fully-deployed thermal balance test that is the keystone to most space missions thermal verification plan. JWST is simply too large in its deployed configuration to be properly thermal balance tested in the facilities that currently exist. This reality, when combined with a mission thermal concept with little to no flight heritage, has necessitated the need for a unique and alternative approach to thermal system verification and model validation. This paper describes the thermal verification and model validation plan that has been developed for JWST.

Parrish, Keith↗
NASA NTRS2005

Thermal System Verification and Model Validation for NASA's Cryogenic Passively Cooled James Webb Space Telescope

A thorough and unique thermal verification and model validation plan has been developed for NASA s James Webb Space Telescope. The JWST observatory consists of a large deployed aperture optical telescope passively cooled to below 50 Kelvin along with a suite of several instruments passively and actively cooled to below 37 Kelvin and 7 Kelvin, respectively. Passive cooling to these extremely low temperatures is made feasible by the use of a large deployed high efficiency sunshield and an orbit location at the L2 Lagrange point. Another enabling feature is the scale or size of the observatory that allows for large radiator sizes that are compatible with the expected power dissipation of the instruments and large format Mercury Cadmium Telluride (HgCdTe) detector arrays. This passive cooling concept is simple, reliable, and mission enabling when compared to the alternatives of mechanical coolers and stored cryogens. However, these same large scale observatory features, which make passive cooling viable, also prevent the typical flight configuration fully-deployed thermal balance test that is the keystone to most space missions thermal verification plan. JWST is simply too large in its deployed configuration to be properly thermal balance tested in the facilities that currently exist. This reality, when combined with a mission thermal concept with little to no flight heritage, has necessitated the need for a unique and alternative approach to thermal system verification and model validation. This paper describes the thermal verification and model validation plan that has been developed for JWST. The plan relies on judicious use of cryogenic and thermal design margin, a completely independent thermal modeling cross check utilizing different analysis teams and software packages, and finally, a comprehensive set of thermal tests that occur at different levels of JWST assembly. After a brief description of the JWST mission and thermal architecture, a detailed description of the three aspects of the thermal verification and model validation plan is presented.

Cleveland, Paul E.↗
NASA NTRS2003

The Swift Mission and the REM Telescope

Following a description of the science drive which originated the Swift Mission, this is US NASA MIDEX Mission with the collaboration of Italy and the UK, we will describe the status of the hardware and the observing strategy. The telemetry is carried out via the TDRSS satellite for those communications that need immediate response. The data transfer and the scheduled uploading of routine commands will be done through the ASI Malindi station in Kenia. Both in the US and in Europe a large effort will be done to follow the bursts with the maximum of efficiency and as soon as possible after the alert. We will describe how the ESO VLT telescopes are able to respond to the alert. To address the problematic of the dark bursts and to immediately follow up all of the bursts also in the Near Infrared we designed and built a 60 cm NIR Robotic telescope, REM, to be located on the ESO ground at Cerro La Silla. The instrumentation includes also a low dispersion spectrograph with the capability of multi wavelength optical photometry.

Gehrels, N.↗
NASA NTRS2005

James Webb Space Telescope - the "First Light Machine"

Scheduled to begin is 10 year mission in 2011, the James Webb Space Telescope (JWST) will search for the first luminous objects of the Universe to help answer fundamental questions about how the Universe came to look like it does today. At 6.5 meters in diameter, JWST will be the world's largest space telescope. This talk will review science objectives for JWST and how they are driving the JWST architecture, e.g. aperture, wavelength range and operating temperature. Additionally, the talk will include an overview of the JWST primary mirror technology development effort.

Stahl, H. Phil↗