High Energy Astronomy Observatory Research Articles

Optical identification of 4U1907 + 09 using the HEAO-1 scanning modulation collimator position

The paper reports an optical identification of 4U1907 + 09 with a m(v) = 16.4 stellar object in the location determined by the scanning modulation collimator experiment on the first High Energy Astronomy Observatory (HEAO-1). The identification is based on the presence of very strong and broad H-alpha emission. The optical data constrain the distance to be 2-13 kpc, and this gives a range of uncertainty to the typical 2-10 keV luminosity of (1 x 10 to the 35th to 3 x 10 to the 36th) erg/s. The X-ray spectrum and variability is reported, and consideration is given to the hypothesis that the object is an OB supergiant, although its faintness in the blue makes precise spectral classification impossible. It is suggested that this system is an example of a luminous, massive primary emitting a stellar wind which is accreted on the compact object.

Einstein Pictures the X-ray Sky

The second High Energy Astronomy Observatory (HEAO-2, Einstein) is revolutionizing x-ray astronomy just as its namesake revolutionized physics. Earlier x-ray observatories, including HEAO-1, were designed to scan the sky for x-ray emitters. With Einstein, the challenge has shifted from discovering x-ray sources to understanding the processes producing the x-rays. But having 500 times the sensitivity of previous detectors, Einstein makes more than its share of discoveries, too. For example, it sees distant quasars and clusters of galaxies that can barely be detected by the largest optical telescopes.

A survey of the X-ray sky with HEAO A-1

The primary mission of the A-1 instrument aboard the first N. A. S. A. High Energy Astronomical Observatory (HEAO) is to enlarge the catalogue of X-ray sources to about 1000. Seven modules of X-ray proportional counters, having an average effective aperture of about 1700 cm 2 apiece, cover an energy range from 0.25 keV to about 25 keV. Full sky coverage is obtained by spinning the spacecraft at 2 rev. h -1 about the direction to the Sun. The detectors view the sky at right angles to the spin axis, so that 48 great circle sweeps normal to the ecliptic plane are completed each day. As the Earth carries the spacecraft around the Sun, the scan plane rotates 1° in ecliptic latitude each day. The basic scan is obtained with four modules having 1° x 4° collimation, giving 10000 resolution elements on the full sky. Assuming one source detection for every ten resolution elements, the survey should detect about 1000 sources.

Measurements of X-ray source positions by the scanning modulation collimator on HEAO 1

This paper reports preliminary results on the positions of X-ray sources obtained with the modulation collimator on the first NASA High Energy Astronomy Observatory, HEAO 1. Calibration on Sco X-1 establishes the experiment capabilities to be within 7 sec as limited by aspect errors. For the reported X-ray sources certain ambiguities in their positions are resolved and the previous optical identifications of four sources are confirmed, two of which are X-ray bursters and one of which is the black hole candidate Cir X-1. An accurate position for a new transient source is also presented.

High Energy Astronomy Observatory Program

This paper describes the series of three orbiting high energy astronomy observatories that comprise the High Energy Astronomy Observatory (HEAO) program of the National Aeronautics and Space Administration (NASA). The basis and enthusiasm of the scientific community for this program is presented. The HEAO program is a leader in the low cost approach for unmanned scientific investigations and emphasis is given to engineering design and test philosophies being practiced in support of this approach. Several unique designs and the attitude control and determination system (ACDS) used for observatory scan rotation of the first and third missions and for precision pointing on the second mission are described. Finally, preliminary results from the first mission, launched on August 12, 1977, are reviewed.

Survey satellite to map high‐energy sources

The first in a series of High Energy Astronomy Observatory satellites, HEAO‐A, will be inserted in June into a low circular orbit about the Earth from NASA's Kennedy Space Center. The new satellite will spend its six‐month mission lifetime surveying and mapping x‐ray sources throughout the celestial sphere, and also measuring low‐energy gamma‐ray fluxes; its purpose is to amass experimental data related to radio galaxies, neutron stars, pulsars, quasars, stellar explosions and supernovas. The HEAO‐A carries a payload of four experiments. In 1978 and 1979 NASA expects to launch other High Energy Astronomy Observatories to complete the $237‐million, three‐mission HEAO program.

An X-ray redshift measure for clusters of galaxies up to Z not less than 1

Correlated measurements of redshifted iron line emission and apparent surface brightness are suggested for unambiguously defining intrinsic X-ray characteristics for clusters of galaxies up to z not less than 1. If some of the weak unidentified high-galactic-latitude X-ray sources are clusters at z roughly equal to 1-3, then such correlated measurements should be feasible within the complement of instruments aboard the HEAO-B orbiting X-ray telescope observatory. In addition, those clusters at z less than 1 would require spectral data from broader bandwidth experiments, such as the all-sky survey to be provided by the proportional counters aboard the first mission of the High Energy Astronomy Observatory (HEAO-A).

A Diagnostic Emulator for HEAO software development

Diagnostic Emulation is the application of microprogramming to the emulation of an operational computer to support software development and verification for that computer. A conventional technique, Interpretive Computer Simulation (ICS), has been used for many years in support of such software development and verification efforts. The ICS method is becoming less cost effective. For the development of attitude control software for NASA's High Energy Astronomical Observatory (HEAO) diagnostic emulation was considered as an alternative. This paper describes the motivation for using an ICS or diagnostic emulator to validate command and control software, the potential advantages of microprogramming, and the analysis which led to the development of the HEAO Diagnostic Emulator rather than the use of conventional techniques. Also discussed are the emulator implementation tradeoff analysis, the resulting program design, and the interface between the microprogram and the assembly language modules. The results to date are described, including the capability, speed, and reliability of the program and initial user response.

Design of the HEAO Main Bus Shunt Regulator

The High Energy Astronomy Observatory (HEAO) main bus regulator contains a redundant error amplifier (REA) and a 12-section sequenced shunt transconductance amplifier (STA) in which not more than three and not less than one shunt section are in an active control mode regardless of a failure in any one of the twelve sections. The part of the work concerned with the shaping of the frequency response of the REA and STA minor feedback loops and of the teolator major feedback loop is described. Emphasis is on the application of a general design technique embodying a "design-analyze-measure iteration loop," in which a first-cut design and analysis is corrected ard improved after experimental observation of discrepancies and deficiencies. In particular, an incipient high-frequency oscillation was thereby reliably eliminated. It is demonstrated that analysis techniques involving a minimum of algebra can provide full quantitative information on an efficient and reliable system design.

Test Evaluation of a High Performance Pulse Rebalanced Gyro for Strapdown IMU Applications

Recent mission requirements in the strapdown Inertial Measurement Unit (IMU) field have emphasized the need for inertial sensors which combine the capability of providing precision attitude reference with long mission life. The single-axis hydrodynamic-spin-bearing gyroscope operated with pulse-rebalance servo electronics is a prime candidate sensor for these missions. This paper provides a summary of recent test results and analytical evaluation for a high-performance instrument of this type. The sensor parameters and performance test results summarized in this paper are based on an extensive evaluation program of the 64 PM RIG gas-bearing gyro. The 64 PM RIG design base is the 64 AC RIG (25 IRIG), which was initially developed by MIT, with the primary difference between the two instruments being the use of a permanent magnet DC torquer (rather than an AC torquer) in the 64 PM RIG. The 64 AC RIG was originally developed and produced in large quantities for an inertially-stabilized platform used in a missile application and has since been used as an inertial sensor on several spacecraft programs (OSO-7 and ATS-6). A single-degree-of-freedom gyro, the 64 PM RIG utilizes a hydrodynamic gas bearing, a microsyn pickoff, a magnetic suspension, and a permanent-magnet torquer, and is fully floated to minimize error torques about its sensitive axes. Sensor drift data is summarized which demonstrates the bias variability over a 15 hour period to be less than 0.001 deg/hr. The specific strapdown IMU performance areas which are addressed include sensor scale factor linearity and stability, the noise output of the sensor as characterized by its power spectral density, the attitude reference error buildup as a function of the interval between bias updates, and performance of the sensor in the dynamic environment typically encountered during vehicle maneuvers. The pulse-rebalance technique implemented is binary (forced-limit-cycle), and uses quantized pulse-width modulation of the gyro torquing signal. A dual-scale design of the pulse-rebalanced sensor has been implemented and evaluated. The pulse-rebalanced sensor has a demonstrated capability of maintaining an attitude reference within 1.0 arc-second for time periods exceeding 30 minutes. Test data demonstrating scale factor non-linearity of less than 40 PPM and scale factor stability below a PPM/day is presented. The 64 PM RIG sensor is being incorporated into two strapdown IMUs which will provide the primary attitude reference for the International Ultraviolet Explorer (IUE) and the High Energy Astronomy Observatory (HEAO) spacecrafts. The six-sensor IUE/IMU and the modular two-sensor HEAO/IMU are discussed from the packaging (size, weight, power) and functional viewpoints. Included is a brief description of the hybridized pulse-rebalance servo electronics used for the two programs.

NASA holds up work on High Energy Astronomy Observatory

NASA holds up work on High Energy Astronomy Observatory

A Position-Sensitive X-Ray Detector for the HEAO-A Satellite

A position-sensitive, low-energy proportional counter system is described which will be used on the High-Energy Astronomical Observatory, Mission A, spacecraft. The associated system incorporates the capability to employ pulse-shape discrimination for background rejection and interpolation circuitry to locate the centroid of an X-ray event with an accuracy of approximately one eighth the cathode-wire spacing.

ADVANCED X-RAY OBSERVATORIES

Since the discovery of the first X-ray sources in 1962 by the use of modest instruments flown on sounding rockets Giacconi et al. (1962), observations of cosmic X-rays have continued to provide a steady flow of information that has affected our view of virtually all astronomical phenomena. Correspondingly, an increasing share of the resources devoted to space sciences of many nations has been allocated to this new observing window. Within the past year the first satellite devoted to X-ray astronomy, UHURU, was launched by NASA followed by a second satellite launched by the Naval Research Laboratories. Within the next several years a number of small satellites devoted largely to X-ray astronomy SAS-C by NASA, UK-IV by Great Britain, and the ANS by the Netherlands will be flown, as well as individual experiments on such satellites as OSO. In 1975, NASA is planning to begin its High Energy Astronomy Observatory (HEAO) series based on the use of the Titan-3C launch

Design of a Celestial Thomson-Scattering X-Ray Polarimeter

A general discussion of the scientific importance and status of stellar x-ray polarimetry is presented. A stellar x-ray polarimeter designed to fit into the bottom half of the NASA Orbiting Solar Observatory-I (OSO-I) wheel compartment or other similar spacecraft is described. In this design, the linear polarization is obtained as a function of energy. The sensitivity of the polarimeter in the 4 - 24 keV energy range was optimized with the aid of a Monte Carlo simulation computer program and is given for several important celestial x-ray sources. Estimates of sensitivity thresholds for a much larger polarimeter, suitable for flight in the NASA High-Energy Astronomy Observatory (HEAO), are also given. The minimum detectable polarization for several x-ray sources is given. For example, the minimum detectable polarization at the 99% confidence level for the Crab nebula in a 24-h observation time is 1.4% for an OSO polarimeter in a compartment (50 × 30 × 30) cm and 0.27% for a HEAO polarimeter in a compartment (100 × 100 × 30) cm. These satellite experiments are feasible and will yield significant polarization results which will have an important bearing on our understanding of x-ray source mechanisms.

Lockheed space system will put observatory into circular orbit

A Lockheed circularizing system called the Orbiting Adjust Stage (OAS), will help place a High Energy Astronomy Observatory (HEAO) in a 200‐nautical‐mile circular orbit. The OAS fits atop the Titan IIID primary booster, and above the Orbit Adjust Stage is the observatory spacecraft. The OAS and its motor will remain attached to the observatory and will put it into a virtually perfect circular orbit, with a variance of less than two miles.

A New Instrument Concept for Gamma Ray Astronomy

A new instrument concept that utilizes the principle of the Total Absorption Shower Cascade (TASC) detector is proposed for gamma ray astronomy in space. Using the TASC detector to measure the gamma ray energy and wire chamber arrays to measure the incident angle, an instrument package designed to measure gamma rays having energies greater than 100 MeV is being proposed for a large satellite such as NASA's proposed High Energy Astronomy Observatory. The proposed instrument has a minimal flux sensitivity of 2 × 10-10 photons/cm2 sr sec which will allow gamma rays with energies up to 104 GeV to be measured. An energy resolution (FWHM) for the TASC detector of ~l percent at 10 GeV has been measured and an angular resolution of ~1 degree appears to be obtainable for the wire chamber arrays.