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Materials were selected for the European TD satellite with a view to avoiding contamination of its stellar ultraviolet telescopes. Materiels were selected using the micro-VCM technique, and some typical cases of materials evaluation are described. The cleanliness of the satellite was monitored during integration and test phases, and in particular during long duration thermal vacuum tests.
The package considered is intended for the channel electron multiplier (CEM) detectors which are to be used for the extreme ultraviolet telescope and helium glow detector instruments of the Apollo-Soyuz test project. In the package design selected, the cone of the CEM is supported at the front end by a silicone rubber ring which is molded in place and self-bonded to both the cone and the housing wall. The helix is supported and insulated from the housing by a fiber glass sleeve which is bonded to the inside of the housing.
Parylene N was selected as a bandpass filter for the extreme-ultraviolet telescope, flown on the Apollo-Soyuz Test Project in July 1975. The telescope measures stellar and diffuse cosmic radiation in the wavelength region from 45 to 170 A. In connection with this application, a systematic study was conducted of the mass absorption coefficient of the Parylene N. The results of the study for the wavelength region from 44 to 2536 A are reported.
During the Apollo-Soyuz Test Project, an extreme-ultraviolet telescope observed the region of the sky from which the interstellar medium approaches the sun. The instrument had a tin filter whose bandpass included the 584-A line of neutral helium. The observations set an upper bound for the number density of neutral helium in the local interstellar medium of 0.004 + or - 0.0022 per cu cm, which is significantly lower than previously reported. The stated error is dominated by the present uncertainty in the solar 584-A flux, which is taken to be approximately 200 million photons/sq cm per sec at earth's orbit. The result is not consistent with previous resonant-scattering Ly-alpha observations of interstellar hydrogen passing through the solar system, which generally yield a hydrogen number density of about 0.1 per cu cm, unless interstellar helium is locally depleted below its cosmic abundance. The result is consistent with cosmic abundances if the much lower average hydrogen densities inferred from recent column-density measurements to nearby hot stars are in fact representative of the immediate solar neighborhood.
Data from the Copernicus satellite's ultraviolet telescope were used to survey column densities of atomic and molecular hydrogen from a large sample of early-type stars; these data have bearing on an eventual understanding of diffuse and dense interstellar clouds. Column densities are derived by fitting damping profiles to the observed spectra, most of which exhibit strong damping lines in the lower rotational levels surveyed. Plots of dust column density, fractional abundance of molecular hydrogen, and the logarithm of fractional abundance versus total gas column density are given for many of the stars; stars with abnormally large or small hydrogen column densities, as well as some distant stars at high galactic latitudes, are considered. Equilibrium and nonequilibrium theories accounting for the abundance of interstellar hydrogen are compared, and support is found in the data for an account which balances hydrogen formation on interstellar grains with destruction through photodissociation. Overall averages for atomic and molecular hydrogen levels in the galactic plane are also calculated.
Observations shortward of the hydrogen Lyman limit provide sensitive determinations of stellar temperatures and interstellar absorption. Such data are of particular value in studies of hot white dwarfs, for which a large fraction of the emission occurs in the extreme-ultraviolet band (100-1000 A). Observations of HZ 43 and Feige 24 have been obtained with the Apollo-Soyuz extreme-ultraviolet telescope; both stars are copious EUV emitters, with four billionths and three billionths erg/sq cm sec in the 170-620-A band, respectively. The EUV data, combined with optical spectrophotometry, allow their temperatures to be estimated as 80,000 and 60,000 K, respectively. The corresponding interstellar neutral hydrogen column densities are about 4 by 10 to the 18th power per sq cm.
The extreme-ultraviolet telescope on the Apollo-Soyuz Test Project Mission observed several nearby stars of spectral type earlier than B3 in search of thermal emission from possible hot circumstellar plasma. The stars studied in the 45-185 and 114-185 A passbands of the instrument included Lambda Sco, Nu Sco, Beta CMa, Beta Cen, Sigma Sgr, and Alpha Pav. Diffuse emission around these stars in excess of about 1 billionth erg/sq cm/sec per sr/eV in the 45-185 A band and about 1 hundred-millionth erg/sq cm/sec per sr/eV in the 114-185 A band was not detected. The experimental data have been used to place upper limits on the emission measure of the plasma and the stellar-wind luminosity, using standard models. The data rule out the existence of sizable bubbles of hot plasma around any of the stars surveyed. In all cases the electron density in these regions, if they exist, may not exceed about 0.2 electron/cu cm.
An upper bound for the number density of neutral helium in the local interstellar medium of 0.004 + or - 0.0022 per cu cm was previously reported, based on extreme-ultraviolet telescope observations at 584 A made during the 1975 Apollo-Soyuz Test Project. A variety of evidence is found which indicates that the 584-A sensitivity of the instrument declined by a factor of 2 between the last laboratory calibration and the time of the measurements. The upper bound on the helium density is therefore revised to 0.0089 + or - 0.005 per cu cm.
Using the Apollo-Soyuz mission's extreme ultraviolet telescope, it proved possible to observe the equatorial aurora on four different occasions. The observations were made from 220 km in quiet geomagnetic conditions. In all cases, signals were well above ambient background in the 50 to 150 A, 114 to 150 A, 170 to 600 A, and 500 to 780 A bands. The existence of a strong feature in the 50 to 150 A region may be an indication that other elements besides helium - possibly oxygen and nitrogen - contribute to the enhancement.
The extreme ultraviolet telescope on the Apollo-Soyuz mission observed the equatorial aurora from an altitude of 220 km on four separate occasions in July 1975, in quiet geomagnetic conditions (Ap = 6). In all cases signals well above ambient background in the 50-150, 114-150, 170-600, and 500-780 A bands were recorded as the spacecraft moved across the equator and the instrument viewed the atmosphere below it. The observed emissions are confined to a band roughly 10 to 20 deg in width with the peak emission occurring in the range -15 to +2 deg magnetic latitude. No enhancement on the 1350-1550 A channel was noted. The observed signals are interpreted as recombination radiation of energetic helium and, possibly, oxygen ions originating in the terrestrial ring current.
The design of a suitable coalignment system (CAS) for the Solar Extreme Ultraviolet Telescope and Spectrometer (SEUTS) is presented. The CAS provides offset adjustment capabilities to SEUTS which will be mounted on a single large pointing system with other devices. The suitability of existing designs is determined and modifications are suggested.
Data from the 1350-1550 A bandpass channel of the 2.5-deg angular resolution extreme-ultraviolet telescope on the Apollo-Soyuz mission have been analyzed for stellar and airglow radiation contributions for the galactic latitude range above 30 deg. At intermediate latitudes, the resulting diffuse background is found to be correlated with the neutral hydrogen column density as determined by 21 cm radio data. This result, together with the observed anisotropy and mean intensity of the radiation field, is consistent with the hypothesis that scattering of galactic-plane starlight off dust grains having an albedo of 0.5 and a phase function coefficient of 0.5 is the primary source of the observed radiation field at the intermediate latitudes. The background intensity near the poles is, however, higher than expected from the H I column density and extinction measurements.
A three-dimensional polar orbit exploration of the sun and solar-related phenomena in the heliosphere through the International Solar Polar Mission (ISPM) is discussed. The characteristics of the out-of-the-ecliptic mission are mentioned and a detailed list of the scientific objectives is given: properties of the solar corona, the solar wind, the structure of the sun-wind interface, the heliospheric magnetic field, solar and non-solar cosmic rays, solar radio bursts and plasma waves, and the interstellar/interplanetary neutral gas and dust. Measurements of the Jovian magnetosphere during the Jupiter flyby phase and interplanetary physics investigations during the initial earth-Jupiter phase are pointed out as secondary objectives. The Nasa spacecraft with a sun-pointing despun platform on which the White Light Coronagraph/X-Ray and Extreme Ultraviolet Telescope (CXX), and the Mass Separating Ion Instrument are mounted, is detailed. The operational configuration of EASA, a spin stabilized spacecraft, is given and characteristics of special features such as the large paraboloidal high gain antenna, the radio-isotope thermoelectric generator, the radial boom and the central equipment compartment are described and shown in a diagram. The mission design and launch parameters block diagrams are given.
A survey of a region of the sky around the antisolar direction in the earth's shadow was surveyed by the extreme ultraviolet telescope on the Apollo-Soyuz mission, whose 170-620 A channel is primarily sensitive to the H II, 304-A and He I, 584-A resonance. A sharp decrease in intensity was found as the line of sight sweeps into the shadow region. Once the line of sight is contained within the shadow, a residual signal above instrumental background was observed that was independent of view direction and spacecraft position. An upper limit at the 2sigma confidence level to a possible He II, 304-A component that can escape detection by the instrument corresponds to 0.002 R, or to a column density of 10 to the 9th ions/sq cm scattering at line center. The brightest possible sources for such emissions are multiple scattering from plasmaspheric He(+) in the shadow and scattering from He(+) created by the photoionization of the interstellar wind neutral helium.
High sensitivity and spatial resolution observations of the He II 304-A emission line intensity in the earth's nightglow have been carried out by the extreme ultraviolet telescope on the Apollo-Soyuz mission in July, 1975. The data, obtained over a wide range of plasmasphere parameters, are compared to the predictions of a kinetic equilibrium model of plasmaspheric ion density. Excellent agreement between observation and theory is found using as inputs a temperature model, solar flux and H(+) and O(+) number densities determined by extrapolating nearly simultaneous Atmospheric Explorer C measurements at 300 km. The observations in the Northern Hemisphere are well fit by a model having 285 He(+) ions/cu cm at 500 km independent of latitude or longitude, while those in the south require 430 He(+) ions/cu cm at the same altitude. This result is consistent with available information on the interhemispheric asymmetry of He(+) observed by a mass spectrometer on Explorer 32 and on the winter neutral helium bulge.
The Pinhole/Occulter Facility concept uses a remote occulting mask to provide high resolution observations of the solar corona and of astronomical X-ray sources. With coded-aperture and Fourier-transform techniques, the Pinhole/Occulter makes images at a resolution of 0.2 arc sec for 2-120 keV X-rays, using a 50-m boom erected from the payload bay of the Space Shuttle or mounted on a free-flying platform. The remote occulter also creates a large shadow area for solar coronal observations; the Pinhole/Occulter concept includes separate optical and ultraviolet telescopes with 50-cm apertures. These large telescopes will provide a new order of resolution and sensitivity for diagnostic observations of faint structures in the solar corona. The Pinhole/Occulter is a powerful and versatile tool for general-purpose X-ray astronomy, with excellent performance in a broad spectral band complementary to that accessible with AXAF. The large collecting area of 1.5 sq m results in a 5 sigma detection threshold of about 0.02 microJy for the 2-10 keV band.
The Thermal Radiation Analysis System (TRASYS) and the Simplified Shuttle Payload Analyzer (SSPTA) are applied for the purpose of comparison to the Solar Maximum Repair Mission (SMRM) and Astro-1/UVT (Ultraviolet Telescope), making use also of the System Improved Numerical Differencing Analyzer (SINDA). The majority of radiation conductances obtained from the TRASYS and SSPTA computer codes are shown to be within + or - 20 percent of each other, though the interchange factors associated with some crucial components of the system are located beyond this region. A sample model is also considered, which consists of an outer and an inner boxes with emisivities of 0.32 and 0.80 respectively. It is concluded that a thorough, methodical comparison between the two codes is necessary.
Strategy and algorithm produce well-balanced timetable that accommodates many constraints. Strategy for scheduling star observations on Space Shuttle astronomy missions ensures best use of three future ultraviolet telescopes. Strategy, described in report, takes into account such diverse factors as maneuvers of Space Shuttle orbiter, interference by Moon, occultation by Earth, reflections, unstaffed periods during crew rotation, encounters with South Atlantic anomaly, and obscuration during dispersal of ejected water.