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At least 883 records · Page 49
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NASA NTRS1995

An atlas of monthly mean distributions of SSMI surface wind speed, AVHRR/2 sea surface temperature, AMI surface wind velocity, TOPEX/POSEIDON sea surface height, and ECMWF surface wind velocity during 1993

The following monthly mean global distributions for 1993 are presented with a common color scale and geographical map: 10-m height wind speed estimated from the Special Sensor Microwave Imager (SSMI) on a United States (U.S.) Air Force Defense Meteorological Satellite Program (DMSP) spacecraft; sea surface temperature estimated from the Advanced Very High Resolution Radiometer (AVHRR/2) on a U.S. National Oceanic and Atmospheric Administration (NOAA) satellite; 10-m height wind speed and direction estimated from the Active Microwave Instrument (AMI) on the European Space Agency (ESA) European Remote Sensing (ERS-1) satellite; sea surface height estimated from the joint U.S.-France Topography Experiment (TOPEX)/POSEIDON spacecraft; and 10-m height wind speed and direction produced by the European Center for Medium-Range Weather Forecasting (ECMWF). Charts of annual mean, monthly mean, and sampling distributions are displayed.

Halpern, D.↗
NASA NTRS1995

Anticipated uncertainty budgets of PRARETIME and T2L2 techniques as applied to ExTRAS

The Experiment on Timing Ranging and Atmospheric Soundings, ExTRAS, was conceived jointly by the European Space Agency, ESA, and the Russian Space Agency, RSA. It is also designated the 'Hydrogen-maser in Space/Meteor-3M project'. The launch of the satellite is scheduled for early 1997. The package, to be flown on board a Russian meteorological satellite includes ultra-stable frequency and time sources, namely two active and auto-tuned hydrogen masers. Communication between the on-board hydrogen masers and the ground station clocks is effected by means of a microwave link using the modified version for time transfer of the Precise Range And Range-rate Equipment, PRARETIME, technique, and an optical link which uses the Time Transfer by Laser Link, T2L2, method. Both the PRARETIME and T2L2 techniques operate in a two-directional mode, which makes it possible to carry out accurate transmissions without precise knowledge of the satellite and station positions. Due to the exceptional quality of the on-board clocks and to the high performance of the communication techniques with the satellite, satellite clock monitoring and ground clocks synchronization are anticipated to be performed with uncertainties below 0.5 ns (1 sigma). Uncertainty budgets and related comments are presented.

Thomas, Claudine↗
NASA NTRS1994

Cosmic heavy ion tracks in mesoscopic biological test objects

Since more than 20 years ago, when the National Academy of Sciences and the National Research Council of the U.S.A. released their report on 'HZE particle effects in manned spaced flight', it has been emphasized how difficult - if not even impossible - it is to assess their radiobiological impact on man from conventional studies where biological test organisms are stochastically exposed to 'large' fluences of heavy ions. An alternative, competing approach had been realized in the BIOSTACK experiments, where the effects of single cosmic as well as accelerator - heavy ions on individual biological test organisms could be investigated. Although presented from the beginning as the preferable approach for terrestrial investigations with accelerator heavy ions too ('The BIOSTACK as an approach to high LET radiation research'), only recently this insight is gaining more widespread recognition. In space flight experiments, additional constraints imposed by the infrastructure of the vehicle or satellite further impede such investigations. Restrictions concern the physical detector systems needed for the registration of the cosmic heavy ions' trajectories as well as the biological systems eligible as test organisms. Such optimized procedures and techniques were developed for the investigations on chromosome aberrations induced by cosmic heavy ions in cells of the stem meristem of lettuce seeds (Lactuca sativa) and for the investigation of the radiobiological response of Wolffia arriza, which is the smallest flowering (water) plant. The biological effects were studied by the coworkers of the Russian Institute of Biomedical Problems (IBMP) which in cooperation with the European Space Agency ESA organized the exposure in the Biosatellites of the Cosmos series. Since biological investigations and physical measurements of particle tracks had to be performed in laboratories widely separated, the preferred fixed contact between biological test objects and the particle detectors until the geometrical correlation between tracks and organisms has been established could not be maintained. This gave rise to half a dozen of coordinate systems for different measurements which finally had to be related to a single stack reference system.

Facius, R.↗
NASA NTRS1994

Wave-current interaction study in the Gulf of Alaska for detection of eddies by synthetic aperture radar

High resolution Esa Remote Sensing Satellite-1 (ERS-1) Synthetic Aperture Radar (SAR) images are used to detect a mesoscale eddy. Such features limit dispersal of pollock larvae and therefore likely influence recruitment of fish in the Gulf of Alaska. During high sea states and high winds, the direct surface signature of the eddy was not clearly visible, but the wave refraction in the eddy area was observed. The rays of the wave field are traced out directly from the SAR image. The ray pattern gives information on the refraction pattern and on the relative variation of the wave energy along a ray through wave current interaction. These observations are simulated by a ray-tracing model which incorporates a surface current field associated with the eddy. The numerical results of the model show that the waves are refracted and diverge in the eddy field with energy density decreasing. The model-data comparison for each ray shows the model predictions are in good agreement with the SAR data.

Liu, Antony K.↗
NASA NTRS1995

United Nations/European Space Agency Workshops on Basic Space Science

In 1958, the United Nations (UN) formally recognized a new potential for international cooperation by establishing an ad hoc Committee on the Peaceful Uses of Outer Space (COPUOS). A year later the Committee became a permanent body, and by 1983 membership had expanded to 53 states, with more than half of the members coming from the developing world. In 1970, COPUOS established the UN Program on Space Applications in order to strengthen cooperation in space science and technology between non-industrialized and industrialized countries. In the last few years, the UN and its COPUOS have paid increasing attention to education and research in space science and technology, including basic space science. In 1991 the UN, in cooperation with ESA, initiated the organization of annual Workshops in Basic Space Science for developing countries. These Workshops are designed to be held in one of the following major regions: Asia and the Pacific, Latin America and the Caribbean, Africa, Western Asia, and Europe. Accordingly, Basic Space Science Workshops have already been held in India (1991), Costa Rica andColombia (1992), and Nigeria (1993). The fourth Workshop was held from 27 June to 1 July 1994 at the Cairo University, in Egypt, for Western Asia.

Haubold, H. J.↗
NASA NTRS1995

Ice flow dynamics of the Greenland ice sheet from SAR interferometry

Synthetic-aperture radar (SAR) interferograms produced from ESA's ERS-1 satellite, provide the first synoptic view of ice flow dynamics of the western sector of the Greenland Ice Sheet. Glacial motion is detected in the radar ranging direction at millimetric scales, across a complete sequence of snow accumulation and melting regimes, despite significant varations in their radar scattering properties. Ice flow evolves from a slow, regular motion at the higher elevations. At lower elevations, motion is strongly convoluted by meter-scale undulations in surface topography, which have a unique interferometric signature that enables a novel approach for retrieving flow direction. Inferred flow directions, combined with surface displacements in the radar ranging direction, yield ice velocity estimates that are within 6% of in-situ measurements gathered along a 40 km survey line. Application of repeat-pass SAR interferometry to the entire Greenland Ice Sheet should enable precise mapping of its ice flow dynamics at an unprecedented level of spatial detail.

Rignot, E.↗
NASA NTRS1995

High-voltage space-plasma interactions measured on the PASP Plus test arrays

The Photovoltaic Array Space Power Plus Diagnostics (PASP Plus) experiment was developed by the Air Force's Phillips Laboratory with support from NASA's Lewis Research Center. It was launched on the Advanced Photovoltaic and Electronics EXperiments (APEX) satellite on August 3, 1994 into a 70 degree inclination, 363 km by 2550 km elliptical orbit. This orbit allows the investigation of space plasma effects on high-voltage operation (leakage current at positive voltages and arcing at negative voltages) in the perigee region. PASP Plus is testing twelve solar arrays. There are four planar Si arrays: an old standard type (used as a reference), the large-cell Space Station Freedom (SSF) array, a thin 'APSA' array, and an amorphous Si array. Next are three GaAs on Ge planar arrays and three new material planar arrays, including InP and two multijunction types. Finally, there are two concentrator arrays: a reflective-focusing Mini-Cassegrainian and a Fresnel-lens focusing Mini-Dome. PASP Plus's diagnostic sensors include: Langmuir probe to measure plasma density, an electrostatic analyzer (ESA) to measure the 30 eV to 30 KeV electron/ion spectra and determine vehicle negative potential during positive biasing, and a transient pulse monitor (TPM) to characterize the arcs that occur during the negative biasing. Through positive biasing of its test arrays, PASP Plus investigated the snapover phenomenon, which took place over the range of +100 to +300 V. It was found that array configurations where the interconnects are shielded from the space plasma (i.e., the concentrators or arrays with 'wrap-through' connectors) have lower leakage current. The concentrators exhibited negligible leakage current over the whole range up to +500 V. In the case of two similar GaAs on Ge arrays, the one with 'wrap-through' connectors had lower leakage current than the one with conventional interconnects. Through negative biasing, PASP Plus investigated the arcing rates of its test arrays. The standard Si array, with its old construction (exposed rough-surface interconnects), arced significantly over a wide voltage and plasma-density range. The other arrays arced at very low rates, mostly at voltages greater than -350 V and plasma densities near or greater than 10(exp 5)/cm(exp -3). AS expected according to theory, arcing was more prevalent when array temperatures were cold (based on biasing in eclipse).

Guidice, Donald A.↗
NASA NTRS1995

STS-74 Flight Day 1

On this first day of the STS-74 mission, the flight crew, Cmdr. Kenneth Cameron, Pilot James Halsell, and Mission Specialists William McArthur, Jerry Ross, and Chris Hadfield, are shown in prelaunch and launch activities. This mission is the second of seven Mir-Space Shuttle hook-ups. Major objectives of this mission are to include a docking between Mir and the Space Shuttle and the transfer of a Russian docking module, water, supplies, and two solar arrays to the Mir space station. This mission highlights the first time that astronauts from Canada, Russia, the U.S. and the European Space Agency (ESA) will be onboard a single spacecraft in space at the same time. Additional experimental payloads onboard the shuttle are the GLO-4 PASDE Payload (GPP) experiment and the Photogrammetric Appendage Structural Dynamics Experiment (PASDE).

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NASA NTRS1995

STS-74 Flight Day 4

On this fourth day of the STS-74 mission, the flight crew, Cmdr. Kenneth Cameron, Pilot James Halsell, and Mission Specialists William McArthur, Jerry Ross, and Chris Hadfield, perform a successful docking between the space shuttle and the Mir space station using the Russian-made docking module that had been previously installed on the third day of the mission. The astronauts and the Mir 20 cosmonauts, Cmdr. Yuri Gidzenko, Flight Engineer Gergei Avdeyev, and Cosmonaut-Researcher (ESA) Thomas Reiter, are shown greeting each other from inside the docking module and an in-orbit interview between the crews and NASA is conducted in both English and Russian.

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NASA NTRS1995

STS-74 Flight Day 5

On this fifth day of the STS-74 mission, the flight crew, Cmdr. Kenneth Cameron, Pilot James Halsell, and Mission Specialists William McArthur, Jerry Ross, and Chris Hadfield, were awakened to the theme from the movie '2001: A Space Odyssey.' The Mir 20 cosmonauts, Cmdr. Yuri Gidzenko, Flight Engineer Sergei Avdeyev, and Cosmonaut-Researcher (ESA) Thomas Reiter, and shuttle astronauts are shown giving each other plaques and presents to commemorate their historic docking event and the start towards the development of the International Space Station. There is a press conference from Moscow by a one of the officers of the Russian Space Agency with both flight crews and an additional separate press interview of the crews by Canadian reporters. There is video footage of the two docked spacecraft taken from various angles.

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NASA NTRS1995

STS-74 Flight Day 6

On this sixth day of the STS-74 mission, the flight crew, Cmdr. Kenneth Cameron, Pilot James Halsell, and Mission Specialists William McArthur, Jerry Ross, and Chris Hadfield and the Mir 20 cosmonauts, Cmdr. Yuri Gidzenko, Flight Engineer Sergei Avdeyev, and Cosmonaut-Researcher (ESA) Thomas Reiter, were greeted and briefly interviewed by the Secretary General of the United Nations, Boutros Boutros-Ghali, on the 50th anniversary of the United Nations via a radio satellite hookup. An additional interview with other journalists from different areas of the United States and Canada was also presented.

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NASA NTRS1996

Definition of exobiology experiments for future Mars missions

During the past year we have concentrated on two objectives. The first objective is ongoing and is to define the experimental parameters that are necessary to conduct autonomously a mineralogical analysis of the Martian surface in situ using differential thermal analysis coupled with gas chromatography (DTA/GC). The rationale in support of this objective is that proper interpretation of the mineralogical data from the DTA/GC can be used to better describe the present and past environments of Mars, leading to a better assessment of the probability of life evolving on Mars. To meet these objectives we have analyzed a number of samples collected from nature using the DTA/GC. One of the more significant findings was that in samples of desert varnish we detected magnetite and maghemite that may serve as potential biomarkers applicable to DTA/GC analyses of Martian surface material during landed missions. The second objective follows from the first and is to better understand microbe-environment interactions by determining the response of microbes to changes in their environment, including extreme desiccation and solar UV-radiation. The rationale behind this is to develop hypotheses regarding what may have happened to life that may have arose on Mars, and microbial life that may get to the surface of Mars via spacecraft, or meteors from Earth. To accomplish this objective we have exposed microbes, collected from NaCl and gypsum-halite crystals, to the space environment aboard the ESA-German Biopan facility for 15 days. The most significant finding was that these microbes survived the exposure better than others.

Mancinelli, Rocco L.↗
NASA NTRS1995

Solar wind research with the Large Angle Spectroscopic Coronagraph (LASCO) experiment onboard the Solar and Heliospheric Observatory (SOHO) satellite

The ESA-NASA satellite, to be launched in October 1995, carries three nested coronagraphs, which will image the solar corona from 1.1 R(solar mass) to 30 R(solar mass). Super polished mirrors have been developed for the design of a mirror Lyot coronagraph which has a straylight level comparable with the coronal intensity from 1.1 R, to 30 R(solar mass) Coronal details can be imaged with a spatial resolution of 6 arc seconds. A Fabry Perot interferometer with a spectral resolution of 0.7 A at the wavelength of the green coronal emission line will allow the simultaneous construction of spectra over the entire field of view of 10(exp 6) pixels. The middle coronagraph (1.5 R(solar mass) - 6 R(solar mass)) and the outer coronagraph (3 R(solar mass) - 30 R(solar mass)) are externally occulted lens Lyot coronagraphs. Their straylight level 10(exp -11) B(solar mass) and 10(exp -12) B(solar mass) respectively is an order of magnitude smaller than the intensity of the corona. The sensitivity of LASCO to distinguish between different solar wind acceleration mechanisms will be discussed as well as its ability to discern different CME models.

Brueckner, G. E.↗
NASA NTRS1994

An Analytical Tool for Fracture Control

The structural integrity of critical NASA space flight hardware is ensured through a damage tolerance program which is dictated in the fracture control requirements. The goal of a fracture control program is to ensure proper material selection and control, control of working stress levels, use of fracture resistant design concepts, manufacturing process control, and the use of qualified inspection procedures. The damage tolerance philosophy assumes that all components contain initial defects and the damage accumulation process is thus entirely crack propagation. The service capability of fracture critical components is determined by analysis and/or test. A large percentage of NASA fracture critical hardware is certified by analysis only and it is therefore imperative that the analysis code utilized contain the latest state of the art technology. Not all space contractors and vendors are able to develop and maintain an analysis code which meets this requirement. A response to this need has been fulfilled by the development of the NASA/FLAGRO (NASGRO) fracture mechanics code here at the Johnson Space Center. The NASGRO code is based primarily in Linear Elastic Fracture Mechanics (LEFM) and is continually updated to meet to needs of the user community. Development assistance comes from other NASA centers as well as the European Space Agency (ESA). The code currently has a vast materials data file (over 350 different entries) which defines the material strength, fracture toughness, crack growth rate, and crack growth threshold. The code also allows for user defined inputs of data from other sources. The code also provides a large library of stress intensity factor solutions for numerous geometries and loading conditions.

Patin, Raymond M.↗
NASA NTRS1995

Mobile satellite business networks: A part of the European mobile system

The European Space Agency (ESA) is presently procuring an L-band payload EMS, to be embarked on the ITALSAT-2 satellite due for launch in early 1996, in order to promote a regional European mobile system. One of the Land Mobile Communication systems supported by EMS is the MSBN (Mobile Satellite Business Network) voice and data system which will offer the services of a business network on a seamless European coverage. This paper will first recall the characteristics of the MSBN system, which is based on quasi-synchronized CDMA (Code Division Multiple Access) techniques in both directions, and then describe the CDMA receivers implementation. Main validation test results will also be reported confirming predicted performances.

deMateo, M. L.↗
NASA NTRS1995

Aeronautical Satellite Data Link System (SDLS) for high-density air-traffic areas

The European Space Agency has recently commissioned a study to investigate the feasibility of a low-cost aeronautical Satellite Data Link System (SDLS) to provide for the needs of Air Traffic Services, i.e. safety related communications over continental areas with high air-traffic density. This study is placed in today's context which sees the first generation of Aeronautical Mobile Satellite System (AMSS) being gradually but restrictively put into service in oceanic airspaces with low air-traffic density. This paper first discusses the case of ATS dedicated versus mixed (ATS and commercial) Comms service provision and identifies the specific ATS comms requirements context. Specific emphasis is put on the ICAO (International Civil Aviation Organization) standardization framework for both the ATN (Aeronautical Telecommunication Network) and the SSR (Secondary Surveillance Radar) Mode S specific services. An architectural system and network design for a future SDLS is then proposed, such as to meet the ATS comms requirements within the realm of existing technologies. To minimize development risk and cost, consideration is given to re-use the ESA-developed Land Mobile Communication Technology, known as MSBN (Mobile Satellite Business Network) featuring distinct subnetworks. It is particularly suited to an ATM (Air Traffic Management) decentralized architecture made of independent ATC (Air Traffic Control) Centers. Finally the study follow-on phase is introduced, which is intended to cover system design and development leading to a demonstration program, as a first step towards proposals for international standardization and acceptance.

Alain Delrieu↗
NASA NTRS1995

Key design issues for user terminals operating with HEO satellites

Coverage of high-latitude areas in the northern hemisphere using geostationary satellites can not be achieved with good elevation angles, and highly inclined elliptical orbits (HEO) present one possible way to overcome this problem. The high elevation angles they achieve and the relative motion of the satellites across the sky, including satellite hand-over, present a specific set of requirements for the design of user terminals, be they for communication or broadcast-reception purposed. This paper reviews key design issues for user terminals operating with satellites in highly inclined elliptical orbits. While all aspects of user terminal design are broadly covered, special emphasis is given to the antenna and RF front-end design. The types of terminals discussed include communications terminals: the hand-held, the notebook, and the vehicle-mounted types, as well as the vehicle-mounted digital audio broadcasting (DAB) receiver terminal. A number of solutions are outlined, based on tradeoffs with respect to the most significant system interface parameters such as G/T and equivalent isotropically radiated power (EIRP). Candidate antenna and front-end configurations were studied, in particular patch and helical antennas with the principal aim of deriving low cost, yet effective solutions. Issues related to achieving best EIRP for the communications terminals are presented, taking into account radiation safety limits. The differences in the design of receive only versus receive/transmit RF front-ends for HEO system terminals are highlighted and solutions for both proposed. This paper summarizes the results of internal ESTEC studies and external ESA-sponsored work concerning major user terminal parameters and design aspects performed for Archimedes -- a HEO satellite constellation for multimedia broadcasting and communications.

Stojkovic, I.↗
NASA NTRS1996

STS-76 Flight Day 1

On this first day of the STS-76 mission, the flight crew, Cmdr. Kevin P. Chilton, Pilot Richard A Searfoss, and Mission Specialists Shannon W. Lucid, Linda M. Godwin, Michael R. Clifford, and Ronald M. Sega, are shown performing prelaunch and launch activities for the night launch of the Space Shuttle Atlantis. The primary objective of this mission is the third docking between the Mir Space Station and Atlantis and a crew transfer. Lucid will remain onboard the Mir for about four months. Other activities include an EVA by Godwin and Clifford, logistics operations, and scientific research with a SPACEHAB module, some middeck experiments, and a Get Away Special (GAS) canister. Also, almost a ton of equipment and supplies will be transferred to the Mir. Experiments include the Mir Electric Field Characterization (MEFC), European Space Agency (ESA) Biorack life sciences experiment, Queens University Experiment in Liquid Diffusion (QUELD), Optizone Liquid Phase Sintering Experiment (OLIPSE), and a Naval Research Laboratory (NRL) GAS payload Trapped Ions in Space (TRIS), which will measure low-energy particle radiation in the inner magnetosphere. This mission also will include a KidSat, a prototype of Earth viewing cameras and instruments, that allow students in grades K-12 to see and direct the capture of pictures from space. Footage from Mission control is also included.

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