Effects of increased shielding on gamma-radiation levels within spacecraft.

The Shuttle Activation Monitor (SAM) experiment was flown on the Space Shuttle Columbia (STS-28) from 8-13 August, 1989 in a 57 degrees, 300 km orbit. One objective of the SAM experiment was to determine the relative effect of different amounts of shielding on the gamma-ray backgrounds measured with similarly configured sodium iodide (NaI) and bismuth germante (BGO) detectors. To achieve this objective twenty-four hours of data were taken with each detector in the middeck of the Shuttle on the ceiling of the airlock (a high-shielding location) as well as on the sleep station wall (a low-shielding location). For the cosmic-ray induced background the results indicate an increased overall count rate in the 0.2 to 10 MeV energy range at the more highly shielded location, while in regions of trapped radiation the low shielding configuration gives higher rates at the low energy end of the spectrum.     

Analysis of GPS and Loran-C performance for land vehicle navigationin the Canadian Rockies

Loran-C and GPS were assessed for vehicular navigation along selected roads of British Columbia during the winter of 1991. The general topography of this mountainous area is described, together with the specific topographic features and tree coverage characteristics of the 2000 km of roads tested on the mainland and on Vancouver Island. The configuration and characteristics of the Loran C Canadian West Coast chain along the roads used are described. The portable vehicle-mounted system used to collect and analyze the Loran-C and GPS signals along road profiles is described. The performance of Loran-C is analyzed in terms of signal to noise ratios (SNR), field strength, and time-difference distortions, as measured by differential GPS. These distortions, which can reach several hundred meters over distances of less than 20 km, are analyzed in terms of topographic features. The possibility of using these time-independent distortions to calibrate Loran-C for use along the above roads is discussed. Masking of GPS signals due to topographic features and tree coverage along the roads is analyzed. A comparative analysis of both Loran-C and GPS is presented in terms of signal availability and accuracy     

Instrumentenentwicklungen für anwendungsaufgaben der fernerkundung photogrammetrie,geophysik und geodäsie

(Instrument Developments for Applications in Remote Sensing, Photogrammetry, Geophysics and Geodesy) The Modular Optoelectronic Multispectral Seanner MOMS-01, a CCD camera using the push-broom scanner principle, is presented in this paper in its flight configuration. This instrument will be the first European-built spaceborne unaging system for remote sensing applications (launch with Shuttle flight No. 7).Follow-on developments of this initial two-channel version are oriented to an extension of capabilities by a panchromatic high-resolution stereoscopic module for thematic mapping and two additional spectral channels in the reflective IR (up to 2.3 μm) offering a high interpretation potential for future earth resources exploration missions. Furthermore the subjects of advanced laser technology studies are introduced: A picosecond pulse laser system for detection of tectonic motions and for geodetic application, a CO laser for ultra precise range rate determination (Earth potential and Geoid) and a laser range finder for intersatellite distance measurements.     

The statistical properties of coronal mass ejections during 1979–1981

The Solwind coronagraph on the P78-1 earth-orbiting satellite has been monitoring the Sun routinely at 10-minute intervals during the 5-year interval from April, 1979 to the present. In a statistical analysis of about 1000 mass ejections observed through the end of 1981, we find an average occurrence rate of 1.8 mass ejections per day. Histograms of speed, central latitude, angular span, brightness, and other parameters have been constructed, and properties such as shape classification have been tabulated. These characteristics are summarized for these years near sunspot maximum. The average speed and mass estimate are found to be similar to those found at the declining phase of the previous sunspot cycle. The angular span and central latitude distributions are quite different than seen during the declining phase, and are very dependent upon structural class. The fluctuations in the occurrence rate of CMEs does not seem to match the fluctuations in the sunspot number. There is a tendency for high speed CMEs to occur more frequently in 1981 than in 1980, and more frequently in 1980 than in 1979.     

In space, CDs play a new tune

The development of a prototype instrument for biological tests aboard the International Space Station is reviewed. The instrument will employ specially formatted glass and plastic compact disks to conduct tests on biological samples. Special dyes will indicate the presence of proteins, DNA, and other chemicals. One benefit will be the ability to increase the number of trials in an experiment, lending greater validity to the results.     

Which way is the bookstore? A closer look at the judgments of relative directions task

We present a detailed analysis of a widely used assay in human spatial cognition, the judgments of relative direction (JRD) task. We conducted three experiments involving virtual navigation interspersed with the JRD task, and included confidence judgments and map drawing as additional metrics. We also present a technique for assessing the similarity of the cognitive representations underlying performance on the JRD and map-drawing tasks. Our results support the construct validity of the JRD task and its connection to allocentric representation. Additionally, we found that chance performance on the JRD task depends on the distribution of the angles of participants’ responses, rather than being constant and 90 degrees. Accordingly, we present a method for better determining chance performance.     

Daytime VHF amplitude scintillations recorded at an Indian low-latitude station,Waltair (17.7°N, 83.3°E) during 1997–2003

In this research, it is presented the daytime amplitude scintillations recorded at VHF frequency (244 MHz) at an Indian low-latitude station, Waltair (17.7°N, 83.3°E) during seven continuous years (1997–2003). Contrary to the nighttime scintillation seasonal trends, the occurrence of daytime scintillations maximizes during summer followed by winter and the equinox seasons. The fade depths, scintillation indices and the patch durations of daytime scintillations are meager when compared with their nighttime counterparts. A co-located digital high frequency (HF) ionosonde radar confirms the presence of sporadic (Es) layers when daytime scintillations are observed. The presence of daytime scintillations is evident when the critical frequency of the Es-layer (foEs) is ≥4 MHz and Es-layers are characterized by a highly diffuse range spread Es echoes as can be seen on ionograms. It is surmised that the gradient drift instability (GDI) seems to be the possible mechanism for the generation of these daytime scintillations. It is quite likely that the spread Es-F-layer coupling is done through polarization electric fields (Ep) that develop inside the destabilized patches of sporadic E layers, which are mapped up to the F region along the field lines as to initiate the daytime scintillations through the GDI mechanism. Further, the presence of additional stratification of ionosphere F-layer, popularly known as the F3-layer, is observed on ionograms once the Es-layers and daytime scintillations are ceased.     

Correlation of IRTAM and FPMU data confirming the application of IRTAM to support ISS Program safety

A “Real-Time” plasma hazard assessment process was developed to support International Space Station (ISS) Program real-time decision-making providing solar array constraint relief information for Extravehicular Activities (EVAs) planning and operations. This process incorporates real-time ionospheric conditions, ISS solar arrays’ orientation, ISS flight attitude, and where the EVA will be performed on the ISS. This assessment requires real-time data that is presently provided by the Floating Potential Measurement Unit (FPMU) which measures the ISS floating potential (FP), along with ionospheric electron number density (Ne) and electron temperature (Te), in order to determine the present ISS environment. Once the present environment conditions are correlated with International Reference Ionosphere (IRI) values, IRI is used to forecast what the environment could become in the event of a severe geomagnetic storm. If the FPMU should fail, the Space Environments team needs another source of data which is utilized to support a short-term forecast for EVAs. The IRI Real-Time Assimilative Mapping (IRTAM) model is an ionospheric model that uses real-time measurements from a large network of digisondes to produce foF2 and hmF2 global maps in 15?min cadence. The Boeing Space Environments team has used the IRI coefficients produced in IRTAM to calculate the Ne along the ISS orbital track. The results of the IRTAM model have been compared to FPMU measurements and show excellent agreement. IRTAM has been identified as the FPMU back-up system that will be used to support the ISS Program if the FPMU should fail.     

Regolith X-Ray Imaging Spectrometer (REXIS) Aboard the OSIRIS-REx Asteroid Sample Return Mission

The Regolith X-ray Imaging Spectrometer (REXIS) is the student collaboration experiment proposed and built by an MIT-Harvard team, launched aboard NASA’s OSIRIS-REx asteroid sample return mission. REXIS complements the scientific investigations of other OSIRIS-REx instruments by determining the relative abundances of key elements present on the asteroid’s surface by measuring the X-ray fluorescence spectrum (stimulated by the natural solar X-ray flux) over the range of energies 0.5 to 7 keV. REXIS consists of two components: a main imaging spectrometer with a coded aperture mask and a separate solar X-ray monitor to account for the Sun’s variability. In addition to element abundance ratios (relative to Si) pinpointing the asteroid’s most likely meteorite association, REXIS also maps elemental abundance variability across the asteroid’s surface using the asteroid’s rotation as well as the spacecraft’s orbital motion. Image reconstruction at the highest resolution is facilitated by the coded aperture mask. Through this operation, REXIS will be the first application of X-ray coded aperture imaging to planetary surface mapping, making this student-built instrument a pathfinder toward future planetary exploration. To date, 60 students at the undergraduate and graduate levels have been involved with the REXIS project, with the hands-on experience translating to a dozen Master’s and Ph.D. theses and other student publications.     

Efficiency Estimation of Electrothermal Thrusters Use in the Control System of the Technological Spacecraft Motion

The influence of various control systems of the orbital motion of a technological spacecraft on the level of microacceleration of its internal environment is simulated. Conclusions are drawn about the effectiveness of control systems with different actuators for realization of certain gravitationally sensitive processes onboard a spacecraft.