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A complex scientific instrument was designed, fabricated, tested, and calibrated for launch onboard OSO-H. This instrument consisted of four spectroheliographs and an X-ray polarimeter. The instrument is designed to study solar radiation at selected wavelengths in the X-ray and the extreme ultraviolet ranges, make observations at the H-alpha wavelength, and measure the degree of polarization of X-ray emissions.
Two Bragg crystal spectrometers were placed on the OSO-4 satellite to study solar flare plasmas by their spectral emissions. The solar flare plasma parameters were measured with these spectrometers, which together covered a total wavelength range of 0.6 to 8.4 A. With these instruments, knowledge could be gained into the mechanisms governing the plasma behavior in the high temperature-low density regime of flare production and in solar evolution and elemental abundances in the sun. However, spacecraft limitations forced many restrictions on the design of the instrument, so the final instrument could not measure all the solar flare plasma state parameters.
A 3 in. x 3 in. NaI(Tl) gamma ray (0.3 to 10 MeV) spectrometer with a CsI(Na) charged particle and anti-Compton shield has been developed for the Orbiting Solar Observatory (OSO-7) which was launched September 30, 1971. The instrument, designed for a rotating wheel compartment, utilizes a 377 channel quadratic PHA with accumulation times of 3, 1, or 0.5 minutes. Quick look and calibration data obtained via a direct data link to a minicomputer allows near real time monitoring and control of the experiment. Various commands changing the operating mode can be executed. The functions which can be commanded include: rotation of the quadrants in which data is collected by 90 deg; gain adjustment of the central detector over a 6:1 range; manual or automatic sequencing of calibrations; variations of accumulation times by telemetering selected channels; and selection of reference directions. A small X-ray detector covering the range 7.5 to 120 keV is also included.
A comparison of surface brightness measurements of the night sky from the OAO-2 and OSO-6 satellites with ground observations shows good agreement between the space experiments but a systematic error in the zero point of the ground observations, indicating an additional atmospheric source of radiation.
The capabilities of the pointed spectroheliograph on board the OSO 7 are discussed. The range and results of the instrument in recording the evolution of solar active regions and solar flares are considered.
The OSO-H solar X-ray instrument monitors X rays from the sun in the energy range 1-300 keV, as well as the charged particle background. The electronics provide accurate logarithmic pulse-height analysis at the high counting rates expected under flare conditions. A high time resolution mode enables tudy the temporal development of a solar flare.
Analysis of images of the sun obtained with the aid of a grazing incidence X-ray telescope on board the OSO IV spacecraft in the 2.5 to 12-A waveband nearly continuously from Oct. 27, 1967, to May 12, 1968. The instrument had sufficient spatial resolution (one and four arc minutes) and temporal resolution (5 to 20 min) to estimate the spatial characteristics of X-ray emitting regions and to monitor the temporal behavior of individual active regions. Variations in the absence of flares of as much as a factor of 10 in the X-ray output of individual regions were observed, with typical durations ranging from several hours to several days. The X-ray time variations are related to observations at optical and radio wavelengths. The results are interpreted under the assumption that the X-ray time variations are caused by temperature changes in the coronal portions of active regions. The contribution of radiative losses to the energy budget of the coronal active region is estimated.
Calculation of the inertial orientation of the OSO-7 spacecraft from the times at which known stars or planets transit planes fixed in the spacecraft. Both the reference planes and the timing information are provided by the star scanner instrument aboard the spacecraft, while the star identification and the statistical estimation of a set of parameters describing the spacecraft attitude are accomplished in a ground station computer facility. A recursive least-squares determination is made of a vector of first-order differential corrections to the attitude state vector. Preliminary analysis indicates the system accuracy to be 3 arc min in each attitude Euler angle.
The performance of the OSO-7 spacecraft during the first twelve months after launch is discussed. A summary description of the spacecraft and experiments is given. Line drawings of the satellite configuration, telemetry subsystem, electronics equipment, pneumatic equipment, and optical equipment are included.
A comprehensive technical description is presented of the Radiation Monitor which is part of the GSFC cosmic X-ray experiment to be flown on the OSO-1 satellite. The theory of operation, fabrication and assembly, and cone angle determination are reported.
Trapped particle radiation levels on several OSO missions were calculated for nominal trajectories using improved computational methods and new electron environment models. Temporal variations of the electron fluxes were considered and partially accounted for. Magnetic field calculations were performed with a current field model and extrapolated to a later epoch with linear time terms. Orbital flux integration results, which are presented in graphical and tabular form, are analyzed, explained, and discussed.
The primary objective of this experiment is to utilize proportional counters of multi-anode multi-layer construction to obtain the spectra of X-ray sources and the diffuse background over the 2 to 60 keV band. Possible broad emission lines, absorption, and spectral breaks in both discrete sources and the diffuse background will be investigated. A schematic representation of this experiment as configured for the OSO-1 wheel and characteristic parameters are summarized.
Solar flares in three broad EUV spectral bands have been observed from OSO-5 with a grating spectrophotometer. Results are given for three large flares of Mar. 12, Mar. 21 and Apr. 21, 1969. In general, the time dependence of the flare intensity in each band is characterized by a slowly varying component with impulsive bursts superimposed. Bands 2 (465 to 630 A) and 3 (760 to 1030 A) are quite similar in their time variations, but band 1 (280 to 370 A) shows less impulsive structure, and declines more slowly. Absolute EUV intensities for the flares are estimated, and a comparison is made with the 2800 mc/sec radio emission. A flare model is proposed to account for the EUV time variations during a large flare.
The X-ray source Her X-1, identified as a pulsating, eclipsing X-ray source, was observed by the UCSD X-ray telescope on the OSO-7 satellite. A three-point spectrum for Her X-1 was determined on the basis of data obtained when the source was in its high-intensity state. Errors in the UCSD result due to uncertainties in the gain and in converting counts per second to photon flux are about 20%.
The seventh Orbiting Solar Observatory, OSO-7, carries an X-ray detector for measuring the positions, spectra, and time variations of X-ray sources in the energy range from 1 to 60 keV. The instrument has operated successfully since the launch on 1971 September 29. The purpose of this paper is to describe the instrument and to report a measurement of the spectrum of Tau X-1 based on data covering the widest energy range that has so far been observed in a single experiment.
The UCSD solar X-ray instrument on the OSO-7 satellite observes X-ray bursts in the 2- to 300-keV range with 10.24-sec time resolution. Spectra obtained from the proportional counter and scintillation counter are analyzed for the event of Nov. 16, 1971, at 0519 UT in terms of thermal (exponential spectrum) and nonthermal (power law) components. The energy content of the approximately 20,000,000 K thermal plasma increased with the 60-sec duration hard X-ray burst, which entirely preceded the 5-keV soft X-ray maximum. If the hard X-rays arise by thick target bremsstrahlung, the nonthermal electrons above 10 keV have sufficient energy to heat the thermally emitting plasma. In the thin target case the collisional energy transfer from nonthermal electrons suffices if the power law electron spectrum is extrapolated below 10 keV, or if the ambient plasma density exceeds 4 x 10 to the 10th power per cu cm.
An externally occulted Lyot coronagraph employing a digitized SEC vidicon detection system is a prime experiment aboard the NASA Orbiting Solar Observatory 7 (OSO 7). Continuing daily operation since the 29 September 1971 launch has produced more than 2200 pictures of the solar white light corona covering the region between 3 R and 10 R. Important advantages of the SEC vidicon in this application are its ability to integrate an electron image and store it for long periods prior to readout. Special applications of digital techniques are employed in stepping and pulsing the readout electron beam, thereby realizing the detector's inherent qualities of high resolution and large dynamic range.
The Thermal Control Coatings Experiment flown on OSO 3 in the near-earth space environment was designed to measure changes in the solar absorptance and IR emittance of selected test coatings. The present work describes results obtained from four years in orbit. Changes in solar absorptance of the coatings are illustrated as a function of equivalent sun hours, and it is seen that five of eleven coatings considered exhibit no change in solar absorptance over four years or 7500 equivalent sun hours. The effects of micrometeoroids on polished metal surfaces are judged to be negligible for a near-earth mission of four years.