SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
This paper introduces a new class of simple nonlinear PID-type controllers comprised of a sector-bounded nonlinear gain in cascade with a linear fixed-gain P, PD, PI, or PID controller.
Sublimation and gas flux of volatile ices from porous bodies in the Solar System are important, observable phenomena. Surface erosion and dust build-up on a comet nucleus and coma formation are processes attributable to the flux of sublimating gases. Our computer simulations focus on the gas flux from volatile, icy components in the surface layer of a porous, Jupiter-class comet in order to investigate the relationship of the observed relative molecular abundances in the coma with those in then nucleus. We compare results from one-dimensional and two-dimensional models.
We report the detection of emission from methanol in a compact source coincident with the position of the L1157 infrared source, which we attribute to molecules in the disk surrounding this young, class 0 protostellar object.
This paper uses the parallel calculation of the radiation integral for examination of performance and compiler issues on a Beowulf-class computer. This type of computer, built from mass-market, commodity, off-the-shelf components, has limited communications performance and therefore also has a limited regime of codes for which it is suitable.
A model is presented in which both Fanaroff and Riley class I and II extragalactic jets are produced by magnetized accretion disk coronae in the ergospheres of rotating black holes.
Light-toned, subsurface soil deposits have been excavated by the Mars Exploration Rover (MER) Spirit in six distinct locations along its traverse across the Columbia Hills of Gusev Crater. Samples at two of these sites have been analyzed in detail by the M ssbauer (MB) and Alpha Particle X-ray Spectrometers (APXS), providing information on iron mineralogy and elemental chemistry, respectively. These soils are referred to as "Paso Robles" class deposits.
Exploration Class missions to Mars will require precautions against potential contamination by any native microorganisms that may be incidentally pathogenic to humans. While the results of NASA's Viking biology experiments of 1976 have been generally interpreted as inconclusive for surface organisms, the possibility of native surface life has never been ruled out and more recent studies suggest that the case for biological interpretation of the Viking Labeled Release data may now be stronger than it was when the experiments were originally conducted. It is possible that, prior to the first human landing on Mars, robotic craft and sample return missions will provide enough data to know with certainty whether or not future human landing sites harbor extant life forms. However, if native life is confirmed, it will be problematic to determine whether any of its species may present a medical risk to astronauts. Therefore, it will become necessary to assess empirically the risk that the planet contains pathogens based on terrestrial examples of pathogenicity and to take a reasonably cautious approach to bio-hazard protection. A survey of terrestrial pathogens was conducted with special emphasis on those pathogens whose evolution has not depended on the presence of animal hosts. The history of the development and implementation of Apollo anticontamination protocol and recent recommendations of the NRC Space Studies Board regarding Mars were reviewed. Organisms can emerge in nature in the absence of indigenous animal hosts and both infectious and non-infectious human pathogens are theoretically possible on Mars. The prospect of Martian surface life, together with the existence of a diversity of routes by which pathogenicity has emerged on Earth, suggests that the possibility of human pathogens on Mars, while low, is not zero. Since the discovery and study of Martian life can have long-term benefits for humanity, the risk that Martian life might include pathogens should not be an obstacle to human exploration. As a precaution, however, it is recommended that EVA suits be decontaminated when astronauts enter surface habitats when returning from field activity and that biosafety protocol approximating laboratory BSL 2 be developed for astronauts working in laboratories on the Martian surface. Quarantine of astronauts and Martian materials arriving on Earth should also be part of a human Mars mission and this and the surface biosafety program should be integral to human expeditions from the earliest stages of the mission planning.
When planning an experimental investigation, we are frequently faced with factors that are difficult or time consuming to manipulate, thereby making complete randomization impractical. A split-plot structure differentiates between the experimental units associated with these hard-to-change factors and others that are relatively easy-to-change and provides an efficient strategy that integrates the restrictions imposed by the experimental apparatus. Several industrial and scientific examples are presented to illustrate design considerations encountered in the restricted randomization context. In this paper, we propose classes of split-plot response designs that provide an intuitive and natural extension from the completely randomized context. For these designs, the ordinary least squares estimates of the model are equivalent to the generalized least squares estimates. This property provides best linear unbiased estimators and simplifies model estimation. The design conditions that allow for equivalent estimation are presented enabling design construction strategies to transform completely randomized Box-Behnken, equiradial, and small composite designs into a split-plot structure.
Exercise countermeasures are the most commonly utilized approach for maintaining the health and performance of astronauts during spaceflight missions. However, International Space Station (ISS) exercise countermeasure hardware reliability and prescriptions are not at a point of departure to support exploration-class missions. The JSC Exercise Countermeasures Project (ECP) plans to use ISS as a research and hardware evaluation platform to define and validate improved exercise hardware, prescriptions, and monitoring strategies to support crewmember operations on the Moon and Mars. The ECP will partner with JSC's Space Medicine Division to standardize elements of ISS exercise prescriptions to better understand their efficacy and to propose modified prescriptions for implementation that may be used in the crew exploration vehicle and/or lunar habitat. In addition, evaluations of the ISS treadmill harness will be conducted to define and improve fit and function, and assess the next generation medical monitoring devices such as the portable unit for metabolic analysis and the muscle atrophy research and exercise system for completion of periodic fitness evaluations during lunar and Mars travel. Finally, biomechanical data from ISS crew exercise sessions will be obtained to better understand loading and restraint systems, and identify the physiologic requirements during ISS extravehicular activities that may be analogous to extended excursions from the lunar habitat. It is essential to optimize exercise prescriptions, hardware, and monitoring strategies for exploration initiatives using ISS as a platform before the planned retirement of the Shuttle in 2010 and the declining NASA emphasis on ISS to maximize knowledge before embarking on travel to the Moon and Mars.
To test the idea that ultraluminous X-ray sources (ULXs) in external galaxies represent a class of accreting Intermediate-Mass Black Holes (IMBHs), we have undertaken a program to identify ULXs and a lower luminosity X-ray comparison sample with the highest quality data in the Chandra archive. We establish a general property of ULXs that the most X-ray luminous objects possess the fattest X-ray spectra (in the Chandra band pass). No prior sample studies have established the general hardening of ULX spectra with luminosity. This hardening occurs at the highest luminosities (absorbed luminosity > or equals 5x10(exp 39) ergs/s) and is in line with recent models arguing that ULXs are actually stellar-mass black holes. From spectral modeling, we show that the evidence originally taken to mean that ULXs are IMBHs - i.e., the "simple IMBH model" - is nowhere near as compelling when a large sample of ULXs is looked at properly. During the last couple of years, XMM-Newton spectroscopy of ULXs has to some large extent begun to negate the simple IMBH model based on fewer objects. We confirm and expand these results, which validates the XMM-Newton work in a broader sense with independent X-ray data. We find (1) that cool disk components are present with roughly equal probability and total flux fraction for any given ULX, regardless of luminosity, and (2) that cool disk components extend below the standard ULX luminosity cutoff of 10(exp 39) ergs/s, down to our sample limit of 10(exp 38:3) ergs/s. The fact that cool disk components are not correlated with luminosity damages the argument that cool disks indicate IMBHs in ULXs, for which a strong statistical support was never made.
This report discusses the performance of silicon germanium, wideband gain amplifiers under extreme temperatures. The investigated devices include Texas Instruments THS4304-SP and THS4302 amplifiers. Both chips are manufactured using the BiCom3 process based on silicon germanium technology along with silicon-on-insulator (SOI) buried oxide layers. The THS4304-SP device was chosen because it is a Class V radiation-tolerant (150 kRad, TID silicon), voltage-feedback operational amplifier designed for use in high-speed analog signal applications and is very desirable for NASA missions. It operates with a single 5 V power supply [1]. It comes in a 10-pin ceramic flatpack package, and it provides balanced inputs, low offset voltage and offset current, and high common mode rejection ratio. The fixed-gain THS4302 chip, which comes in a 16-pin leadless package, offers high bandwidth, high slew rate, low noise, and low distortion [2]. Such features have made the amplifier useful in a number of applications such as wideband signal processing, wireless transceivers, intermediate frequency (IF) amplifier, analog-to-digital converter (ADC) preamplifier, digital-to-analog converter (DAC) output buffer, measurement instrumentation, and medical and industrial imaging.
Mud volcanoes provide a unique low-temperature window into the Earth s subsurface - including the deep biosphere - and may prove to be significant sources of atmospheric methane. The identification of analogous features on Mars would provide an important new class of sites for geological and astrobiological exploration. We report new work suggesting that features in Acidalia Planitia are most consistent with their being mud volcanoes.
The parameters and restrictions for a horizontal flow ISO Class 6 Clean room to support the assembly of the new LRO (Lunar Reconnaissance Orbiter) were unusual. The project time line was critical. A novel Clean room design was developed and built within the time restraints. This paper describes the design criteria, timing, successful performance, and future benefits of this unique Clean room project.
The Wasp-Waist Nebula was discovered in the IRAC c2d survey of the Ophiuchus starforming clouds. It is powered by a well-isolated, low-luminosity, low-mass Class 0 object. Its weak outflow has been mapped in the CO (3-2) transition with the JCMT, in 2.12 micron H2 emission with WIRC (the Wide-Field Infrared Camera) on the Hale 5-meter, and, most recently, in six H2 mid-infrared lines with the IRS (InfraRed Spectrograph) on-board the Spitzer Space Telescope; possible jet twisting structure may be evidence of unique core dynamics. Here, we report results of recent VLA ammonia mapping observations of the dense gas envelope feeding the central core protostellar system. We describe the morphology, kinematics, and angular momentum characteristics of this unique system. The results are compared with the envelope structure deduced from IRAC 8-micron absorption of the PAH (polycyclic aromatic hydrocarbon) background emission from the cloud.
MCAT (Meter-Class Autonomous Telescope) is a 1.3m f/4 Ritchey-Chr tien on a double horseshoe equatorial mount that will be deployed in early 2011 to the western pacific island of Legan in the Kwajalein Atoll to perform orbital debris observations. MCAT will be capable of tracking earth orbital objects at all inclinations and at altitudes from 200 km to geosynchronous. MCAT s primary objective is the detection of new orbital debris in both low-inclination low-earth orbits (LEO) and at geosynchronous earth orbit (GEO). MCAT was thus designed with a fast focal ratio and a large unvignetted image circle able to accommodate a detector sized to yield a large field of view. The selected primary detector is a close-cycle cooled 4Kx4K 15um pixel CCD camera that yields a 0.9 degree diagonal field. For orbital debris detection in widely spaced angular rate regimes, the camera must offer low read-noise performance over a wide range of framing rates. MCAT s 4-port camera operates from 100 kHz to 1.5 MHz per port at 2 e- and 10 e- read noise respectively. This enables low-noise multi-second exposures for GEO observations as well as rapid (several frames per second) exposures for LEO. GEO observations will be performed using a counter-sidereal time delay integration (TDI) technique which NASA has used successfully in the past. For MCAT the GEO survey, detection, and follow-up prediction algorithms will be automated. These algorithms will be detailed herein. For LEO observations two methods will be employed. The first, Orbit Survey Mode (OSM), will scan specific orbital inclination and altitude regimes, detect new orbital debris objects against trailed background stars, and adjust the telescope track to follow the detected object. The second, Stare and Chase Mode (SCM), will perform a stare, then detect and track objects that enter the field of view which satisfy specific rate and brightness criteria. As with GEO, the LEO operational modes will be fully automated and will be described herein. The automation of photometric and astrometric processing (thus streamlining data collection for environmental modeling) will also be discussed.
The LCROSS (Lunar Crater Observation and Sensing Satellite) project presented a number of challenges to the preparation for mission operations. A class D mission under NASA s risk tolerance scale, LCROSS was governed by a $79 million cost cap and a 29 month schedule from "authority to proceed" to flight readiness. LCROSS was NASA Ames Research Center s flagship mission in its return to spacecraft flight operations after many years of pursuing other strategic goals. As such, ARC needed to restore and update its mission support infrastructure, and in parallel, the LCROSS project had to newly define operational practices and to select and train a flight team combining experienced operators and staff from other arenas of ARC research. This paper describes the LCROSS flight team development process, which deeply involved team members in spacecraft and ground system design, implementation and test; leveraged collaborations with strategic partners; and conducted extensive testing and rehearsals that scaled in realism and complexity in coordination with ground system and spacecraft development. As a testament to the approach, LCROSS successfully met its full mission objectives, despite many in-flight challenges, with its impact on the lunar south pole on October 9, 2009.
An oral/visual presentation sharing aspects of open class performance limits.
The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) is leading the design and build of the new world-class vibroacoustic test capabilities at the NASA GRC s Plum Brook Station in Sandusky, Ohio, U.S.A. Benham Companies, LLC is currently constructing modal, base-shake sine and reverberant acoustic test facilities to support the future testing needs of NASA s space exploration program. The large Reverberant Acoustic Test Facility (RATF) will be approximately 101,000 ft3 in volume and capable of achieving an empty chamber acoustic overall sound pressure level (OASPL) of 163 dB. This combination of size and acoustic power is unprecedented amongst the world s known active reverberant acoustic test facilities. The key to achieving the expected acoustic test spectra for a range of many NASA space flight environments in the RATF is the knowledge gained from a series of ground acoustic tests. Data was obtained from several NASA-sponsored test programs, including testing performed at the National Research Council of Canada s acoustic test facility in Ottawa, Ontario, Canada, and at the Redstone Technical Test Center acoustic test facility in Huntsville, Alabama, U.S.A. The majority of these tests were performed to characterize the acoustic performance of the modulators (noise generators) and representative horns that would be required to meet the desired spectra, as well as to evaluate possible supplemental gas jet noise sources. The knowledge obtained in each of these test programs enabled the design of the RATF sound generation system to confidently advance to its final acoustic design and subsequent ongoing construction.