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The limits to accuracy and long term stability in present atomic clocks are examined. Recent proposals for new frequency standards are discussed along with the advantages and disadvantages of frequency standards based on such ideas as laser transitions, single atoms, and atom cooling. The applicability of some of these new techniques to existing standards is examined.
Results of tests of the long term performance of SiGe radioisotope thermoelectric generators (RTG) are presented. Three modules were monitored for 17,000-32,300 hr at hot junction temperatures of 1,085, 1,055, and 1,000 C; coating the unicouples with a 12,000 A thick layer of Si3N4 protected the modules from Si sublimation. Output degraded less than 0.3-0.4%/1,000 hr over the testing period. Life tests on a multihundredwatt (MHW) SiGe generator with 312 couples at a hot shoe temperature of 1,040 C dealt with power of 150 W at 30 V, with 0.5%/1,000 hr performance degradation. Si deposition on the insulation was found to enhance electrical conductance until a saturation point was reached. Disassembly of a test module after 16,750 hr revealed a Mo build-up, SiN4 coating deterioration, and Ti diffustion from the hot shoe to cooler regions of the junction. The presence of an Al2O3 insulator was recognized as preventing coating loss. Performance records from the Voyager and Les-8 satellites' RTG's are compared and show similar, 0.25%/1,000 hr degradation rates; RTG storage is judged to be feasible and the tests lead to projections of a 600,000 hr lifetime for a SiGe RTG.
Long-term intensity data for five pulsars are used to obtain the probability density distribution of intensities for each pulsar, and it is found that they are described satisfactorily by chi-squared distributions. Based on these distributions, the number of new pulsars expected to be found on repeatedly searching the same region of the sky with the same sensitivity is given. Nearly 25 percent more new pulsars are expected to be found on the first repeat search. It is also shown that the luminosity function deduced from either a single survey or surveys with very different sensitivities is not affected by the omission of flux density variations in the calculation of selection effects. Finally, a method is proposed for deriving the luminosity function by combining the different searches of a given area on the basis of a probabilistic approach to the evaluation of selection effects.
A brief overview of long-term cavitation and liquid impingement erosion and modeling methods proposed by different investigators, including the curve-fit approach is presented. A table was prepared to highlight the number of variables necessary for each model in order to compute the erosion-versus-time curves. A power law relation based on the average erosion rate is suggested which may solve several modeling problems. Previously announced in STAR as N83-22386
The long-term clock capabilities of the Johns Hopkins-built hydrogen maser are evaluated by comparing the measured results with international atomic references. The performance of the NR-6 hydrogen maser from April 29, 1984 to April 29, 1986 is examined. It is noted that the timekeeping in a hydrogen maser (NR-6) is comparable to the best standards of Germany and Canada.
This review of the long-term dynamical behavior of Mars covers secular variations of the orbit, oscillations of the obliquity, and polar wandering. Calculations of the large-scale obliquity oscillations of Mars are updated using the most recent orbit theory and contrasted with the earth. The motion for Mars is characterized by about 100,000-yr oscillations driven by differential spin axis and orbit plane precession rates during which the obliquity may change by as much as about 20 deg. The possible role of spin-orbit secular resonances to the spin axis histories of the earth and Mars is also considered. Numerical integrations of the equations of motion indicate that Mars may have passed through resonance as little as 5 Myr ago and that obliquities approaching about 45 deg could have been achieved during such an event.
This is the final report for our Long-Term Space Astrophysics Program (NRA 94-OSS-12) grant NAG 5-3225. The proposal is entitled 'Spectral and Temporal Properties of Black Hole Candidates', and began funding in May 1995, and ran through 31 Aug 2000. The project summary from the original proposal was as follows: 'We will study the spectral and temporal properties of black hole candidates (BHC) by using data from archival sources (e.g., EXOSAT, Ginga, ROSAT) and proposed follow-up observations with modern instruments (e.g., ASCA, XTE). Our spectral studies will focus on identifying the basic characteristics and luminosities of the emission components in the various 'states' of BHC. We hope to understand and quantify the global energetics of these states. Our temporal studies will focus on expanding and classifying our knowledge of BHC variability properties in each state. We will explore the nature of quasi-periodic oscillations in BHC. We will combine our spectral and temporal studies by analyzing time lags and variability coherence between energy channels. In addition, we will investigate ways of correlating observed variability behavior with specific emission components.' We have accomplished many of these goals laid out within the original proposal. As originally proposed, we have utilized both archival and proprietary satellite data. In terms of archival data, we have utilized data from the Advanced Satellite for Cosmology and Astrophysics (ASCA), ROSAT, and the Rossi X-ray Timing Explorer (RXTE). We also obtained proprietary data from ASCA, RXTE, and the Extreme Ultraviolet Explorer (EUVE). In terms of sources, we have examined a wide variety of both galactic black hole candidates and extra-galactic black holes. For the galactic black holes we have observed and analyzed both the low/hard state and the high/soft state. We have performed both spectral and timing analyses on all of these objects. In addition, we have also examined a number of neutron stars or potential neutron stars. All of our research on the above mentioned objects has resulted in one or more publications in peer-reviewed journals. Attached is a list of refereed publications of research results which have been funded by this grant over approximately the past five and a half years. In addition, we have included a list of conference proceedings and other similar reports that have been associated with this grant.
Long-term climate data records about aerosols are needed in order to improve understanding of air quality, radiative forcing, and for many other applications. The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) provides a global well-calibrated 13- year (1997-2010) record of top-of-atmosphere radiance, suitable for use in retrieval of atmospheric aerosol optical depth (AOD). Recently, global aerosol products derived from SeaWiFS with Deep Blue algorithm (SWDB) have become available for the entire mission, as part of the NASA Making Earth Science data records for Use in Research for Earth Science (MEaSUREs) program. The latest Deep Blue algorithm retrieves aerosol properties not only over bright desert surfaces, but also vegetated surfaces, oceans, and inland water bodies. Comparisons with AERONET observations have shown that the data are suitable for quantitative scientific use [1],[2]. The resolution of Level 2 pixels is 13.5x13.5 km2 at the center of the swath. Level 3 daily and monthly data are composed by using best quality level 2 pixels at resolution of both 0.5ox0.5o and 1.0ox1.0o. Focusing on the southwest Asia region, this presentation shows seasonal variations of AOD, and the result of comparisons of 5-years (2003- 2007) of AOD from SWDB (Version 3) and MODIS Aqua (Version 5.1) for Dark Target (MYD-DT) and Deep Blue (MYD-DB) algorithms.
To find means of alleviating muscle atrophy induced by long-term microgravity, the effects of a 19-week-long heavy-resistance training regime (using either concentric muscle actions only or concentric and eccentric muscle actions) on the strengths of the exercised knee extensor muscle group were investigated in two groups of male human subjects performing two types of training exercises: supine leg press or/and seated knee extension. Results show that a training program in which both the concentric and the eccentric muscle action was performed led to substantially greater increases in maximal muscle strength than when only concentric exercises were performed.
Candidate atomic oxygen protective coatings for long-term low Earth orbit (LEO) spacecraft were evaluated using the Los Alamos National Laboratory O-atom exposure facility. The coatings studied include Teflon, Al2O3, SiO2, and SWS-V-10, a silicon material. Preliminary results indicate that sputtered PTFE Teflon (0.1 micrometers) has a fluence lifetime of 10 to the 19th power O-atoms/cm (2), and sputtered silicon dioxide (0.1 micrometers), aluminum oxide (0.1 micrometers), and SWS-V-10, a silicone, (4 micrometers) have fluence lifetimes of 10 to the 20th power to 10 to the 21st power O-atoms/cm (2). There are large variations in fluence lifetime data for these coatings.
The international community has long recognized the need to coordinate observations of Earth from space. In 1984, this situation provided the impetus for creating the Committee on Earth Observation Satellites (CEOS), an international coordinating mechanism charged with coordinating international civil spaceborne missions designed to observe and study planet Earth. Within CEOS, its Working Group on Calibration and Validation (WGCV) is tasked with coordinating satellite-based global observations of vegetation. Currently, several international organizations are focusing on the requirements for Earth observation from space to address key science questions and societal benefits related to our terrestrial environment. The Global Vegetation Workshop, sponsored by the WGCV and held in Missoula, Montana, 7-10 August, 2006, was organized to establish a framework to understand the inter-relationships among multiple, global vegetation products and identify opportunities for: 1) Increasing knowledge through combined products, 2) Realizing efficiency by avoiding redundancy, and 3) Developing near- and long-term plans to avoid gaps in our understanding of critical global vegetation information. The Global Vegetation Workshop brought together 135 researchers from 25 states and 14 countries to advance these themes and formulate recommendations for CEOS members and the Global Earth Observation System of Systems (GEOSS). The eighteen oral presentations and most of the 74 posters presented at the meeting can be downloaded from the meeting website (www.ntsg.umt.edu/VEGMTG/). Meeting attendees were given a copy of the July 2006 IEEE Transactions on Geoscience and Remote Sensing Special Issue on Global Land Product Validation, coordinated by the CEOS Working Group on Calibration and Validation (WGCV). This issue contains 29 articles focusing on validation products from several of the sensors discussed during the workshop.
Survey of averaging and multirevolution methods for long-term orbit prediction. A technical approach with the following features is recommended: (1) averaged variation-of-parameter equations, (2) analytical expressions for oblateness and third-body effects, (3) definite integrals for atmospheric drag and lunar effects (for long-period orbits), (4) nonsingular equinoctial element formulation, (5) multistep numerical integration processes, and (6) precise osculating-to-mean element transformation. Several orbital predictions illustrate the contribution of this technical approach to overall accuracy and efficiency. Future development of the analytical averaging method in nonsingular coordinates by automated manipulation of literal series is discussed.
This document has been prepared by Geosyntec Consultants, Inc. (Geosyntec) to present and discuss the findings of the 2014 and 2015 Long-Term Monitoring (LTM) activities that were completed at the Launch Complex 39 (LC39) Observation Gantry Area (OGA) located at the John F. Kennedy Space Center (KSC), Florida (Site). The remainder of this report includes: (i) a description of the Site location; (ii) summary of Site background and previous investigations; (iii) description of field activities completed as part of the annual LTM program at the Site; (iv) groundwater flow evaluation; (v) presentation and discussion of field and analytical results; and (vi) conclusions and recommendations. Applicable KSC Remediation Team (KSCRT) Meeting minutes are included in Attachment A. This Annual LTM Letter Report was prepared by Geosyntec Consultants (Geosyntec) for NASA under contract number NNK12CA13B, Delivery Order NNK13CA39T project number PCN ENV2188.
This report presents a summary of the groundwater monitoring activities that occurred in February 2024 at two sites in the Vehicle Assembly Building (VAB) Area Long-Term Monitoring (LTM) program at the John F. Kennedy Space Center, Florida. The two sites are Fire Station 3 (formerly Fire Station 6) (FS3) – Solid Waste Management Unit (SWMU) 106 and Launch Complex 39 Observation Gantry Area (LC39OGA) – SWMU 107.
This report presents the groundwater sampling results from the National Aeronautics and Space Administration (NASA) Industrial Area (IA) 2021-2022 Long-Term Monitoring (LTM) activities and results of the 2023 DPT activities at three of the sites. The NASA IA LTM Program includes the following 14 sites: - Ransom Road Landfill (RRLF) – Solid Waste Management Unit (SWMU) 003 - Orsino Storage Yard (ORSY) – SWMU 004 - Building M7-0505 Treatment Tank Area (M505) – SWMU 039 - Hypergol Maintenance Facility Hazardous Waste South Staging Area (HMF South) – SWMU 070 - Operations and Checkout Building (O&C) – SWMU 076 - Vertical Processing Facility (VPF) – SWMU 077 - Environmental Health Facility (EHF) – SWMU 079 - Kennedy Athletic, Recreation, and Social Park 1 (KARS Park 1) – SWMU 084 - Engineering Development Laboratory (EDL) – SWMU 085 - Launch Equipment Test Facility (LETF) – SWMU 091 - Mobil Service Station (MOBIL) – SWMU 093 - General Services Administration Seized Property (GSSP) – SWMU 095 - Space Station Processing Facility (SSPF) – SWMU 098 - Fuel Storage Area #1 Underground Storage Tank (UST) [Building 1044] (FSA1) – Potential Release Location (PRL) 157 Groundwater levels were gauged at each site during the 2021 and 2022 LTM field activities. Sampling events for the IA LTM Program are conducted seasonally during the dry and wet seasons, which occur in May and November, respectively. The sites in the NASA IA LTM Program are sampled on annual, biennial, or 5-year sampling frequencies based on historical trends. Due to contract transitions and monitoring well installations, 2021 dry season activities were conducted during September 2021, while dry season activities for 2022 resumed in May 2022.
Fidelity and sequencing requirements of simulation stimuli for lunar landing and long term space missions
Electric drive system provides low speed, long term tracking of targets that move at a sidereal rate. It utilizes eddy-current energized actuators that are free from radio frequency interference generation and a solid state feedback amplifier with provisions for antibacklash biasing.
Experimental design of high voltage low current power source for unmanned, long term space mission