Gravitational biology and the mammalian circadian timing system.

Mammals have evolved under the influence of many selective pressures. Two of these pressures have been the static force of gravity and the daily variations in the environment due to the rotation of the earth. It is now clear that each of these pressures has led to specific adaptations which influence how organisms respond to changes in either gravity or daily time cues. However, several unpredicted responses to altered gravitational environments occur within the homeostatic and circadian control systems. These results may be particularly relevant to biological and medical issues related to spaceflight. This paper demonstrates that the homeostatic regulation of rat body temperature, heart rate, and activity become depressed following exposure to a 2 G hyperdynamic field, and recovers within 5-6 days. In addition, the circadian rhythms of these same variables exhibit a depression of rhythm amplitude; however, recovery required a minimum of 7 days.     

Dynamic trapping of electrons in the porcupine ionospheric ion beam experiment

Electrons are needed to maintain quasineutrality in a case where positive ions are injected across the magnetic field into a limited volume in a magnetized plasma. In the absence of collisions, a positive potential builds up and traps the electrons which enter the region along the magnetic field. If the added density of ions exceeds the ambient density, large potential differences along the magnetic field can be maintained this way. The process explains several features of the Porcupine xenon ion beam injection experiment, where strong magnetic-field-aligned electric fields were measured in the vicinity of a xenon ion beam which was injected into the ambient ionosphere from a spinning subpayload.     

Non-LTE analysis of a new pulsating PG 1159-type central star detected in the ROSAT XRT all sky survey

We summarize the analysis of a new PG 1159 star, i.e., a hydrogen deficient pre-white dwarf detected in the ROSAT XRT all sky survey /1/. The X-ray source RX J2117.1+3412 is relatively faint (≈0.33 cnt s⁻¹) and was selected for optical identification on the basis of its extreme X-ray softness. With V = 13.2, the counterpart of the X-ray source is in the optical the second brightest member of the PG1159 class. CCD imagery reveals that the star is surrounded by an old highly excited planetary nebula of faint surface brightness. Optical line profiles of HeII, CIV, and OVI and the overall optical and ROSAT PSPC (0.1–2.4 keV) energy distributions are compared to predictions of NLTE model atmospheres. We find an excellent agreement between the atmospheric parameters derived from optical and soft X-ray data. The effective temperature of the star is extremely high (150,000 K). Abundances of He, C and O are found to be consistent with those derived in other PG1159 stars whereas the surface gravity is significantly smaller in RXJ2117.1+3412. New optical spectra presented here show the presence of ultra-high excitation lines of O VIII.     

A demonstration of sub meter GPS orbit determination and highprecision user positioning

High-accuracy orbits have been determined for satellites of the Global Positioning System (GPS), with submeter orbit accuracy demonstrated for two well-tracked satellites. Baselines of up to 2000 km in North America determined with the GPS orbits shows daily repeatability of 0.3-2 parts in 10⁸ and agree with very long baseline interferometry (VLBI) solutions at the level of 1.5 parts in 10 ⁸. Tests used to assess orbit accuracy include orbit repeatability from independent data sets, orbit prediction, ground baseline determination, and formal errors. One satellite tracked for eight hours each day shows RMS errors below 1 m even when predicted more than three days outside of a 1-week data arc. These results demonstrate the powerful relative positioning capability available from differential GPS tracking. Baselines have also been estimated between Florida and sites in the Caribbean region over 1000 km away, with daily repeatability of 1-4 parts in 10⁸. The best orbit estimation strategies included data arcs of 1-2 weeks, process noise models for tropospheric fluctuations, combined processing of GPS carrier phase and pseudorange data, and estimation of GPS solar pressure coefficients     

Programmable ultrawideband signal generator for electromagnetic susceptibility testing

Under Phase I of the Defense Advanced Research Projects Agency (DARPA) Networking in Extreme Environments (NETEX) initiative, Multispectral Solutions, Inc. (MSSI) was tasked with the development of a general-purpose, ultrawideband hardware simulator capable of reproducing a wide variety of ultrawideband (UWB) waveforms. The simulator, with UWB outputs from baseband through millimeter wave, was to be used for the purpose of electromagnetic susceptibility testing of legacy military radio, radar, and positioning systems. The ultimate goal of this portion of the Phase I program was the quantitative determination of those UWB parameters (e.g., frequency, power, pulse rate, pulse shape, dithering, etc.) which had the least impact on the operational performance of legacy designs. This describes the development of the MSSI NETEX UWB simulator (BFP1000).     

Determination of aerosol optical depth from ground measurements

The methods used to determine the aerosol optical depth as a function of wavelength are briefly described and discussed. Some results from the operational network of the World Meteorological Organization and other, more research oriented studies, are reviewed and critically analysed to assess the reliability and accuracy of such determinations and their value as ground truth measurements for space applications.     

A high-altitude barium radial injection experiment

On 16 March 1980 a rocket launched from Poker Flat, Alaska, carried a new type of high-explosive barium shaped charge to 571 km, where detonation injected a thin disk of barium vapor with high velocity nearly perpendicular to the magnetic field. The purpose of the experiment, named “King Crab,” was to advance knowledge of the instabilities, waves, and optical and magnetic effects produced. The TV images of the injection are spectacular, revealing three major regimes of expanding material which showed early instabilities in the neutral gas. The most unusual effect of the injection is a peculiar rayed barium-ion structure lying in the injection plane and centered on a 5 km “black hole” surrounding the injection point. Preliminary computer simulations show a similar rayed structure development due to an electrostatic instability.     

Einstein X-ray observations of cataclysmic variables

Observations with the imaging X-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity X-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars.     

Advanced pointing systems for space astronomy

Requirements on image stability are increasing, often at the same time that instrument external disturbances are increasing. Pointing large diameter optics from the shuttle bay is the prime current example of this situation. In order to achieve cost-effective advanced pointing systems in the face of these problems, a system approach must be taken that encompasses a realistic assessment of requirements, the best possible detector technology, and a broad look at space vehicles and pointing systems that are available. As an example, a rocket instrument for making measurements of the interstellar gas uses a standard pointing system to achieve a spectral resolution of 2 × 10⁵.     

GPS based IPS for ERP vehicles

GPS is an innovative technique for an electronic road pricing (ERP) system. By using GPS technology, ERP systems will be extremely efficient and cost-effective. This paper describes the next generation of ERP in Singapore and proposes a GPS based multisensor positioning system for ERP vehicles. Multisensor fusion algorithms are presented for the integration system. The integrated positioning system (IPS) developed in this paper makes it possible to realize GPS based ERP with a simple composition and low cost