Mission Overview

The objectives of the OSO satellite series were to perform solar physics experiments above the atmosphere during a complete solar cycle and to map the entire celestial sphere for direction and intensity of UV, X-ray and gamma radiation. The OSO 5 platform consisted of a sail section that pointed two experiments continually toward the sun and a wheel section that spun about an axis perpendicular to the pointing direction of the sail and carried six experiments. Attitude adjustments were performed by gas jets and a magnetic torquing coil. Pointing control permitted the pointed experiments to scan the region of the solar disk in a 40- by 40-arc-min raster pattern. In addition, the pointed section could be commanded to select and scan a 7.5- by 7-arc-min region near the solar disk. Data were simultaneously recorded on tape and transmitted by PCM/PM telemetry. A command system provided for 155 ground-based commands

Launch Date: 1969-01-22 at 16:48:00 UTC
Launch Vehicle: Delta
Launch Site: Cape Canaveral, United States

Type: Orbiter
Central Body: Earth
Epoch start: 1969-01-22 16:48:00 UTC
Orbital Parameters
Periapsis 536.0 km
Apoapsis 561.0 km
Period 95.4800033569336 minutes
Inclination 32.95000076293945°
Eccentricity 0.0018029999919235706

Instrumentation

X-Ray Spectroheliograph

Proportional counters attached to collimators provided eight-channel spectral information as well as the spatial distribution of solar x-ray sources. In the 8- to 18-A region, the collimator was a grazing incidence parabolic reflector that yielded an angular resolution of plus or minus 1 arc-min. In the 3- to 9-A region, two parallel slits collimated the radiation in one dimension only (3.3 arc-min).

Extreme UV Spectroheliograph

Selected solar emission lines (284 A, 304 A, 355 A, 584 A, and 1216 A) were monitored continuously over the entire disk of the sun, using an EUV spectoheliograph. The data were obtained to study the effects of flares and other transient phenomena.

Solar Spectrum Studies

This experiment was designed to observe the whole sun and to record the spectral and time-resolved radiation between 1 and 400 A for a variety of conditions. The instruments consisted of three single Bragg spectrometers (covering 1 to 3 A, 3 to 10 A, and 6 to 25 A), a grazing incidence grating spectrometer covering the range 25 to 400 A, and a pair of ion chambers covering the range 0.5 to 8 A. Useful data were taken while the experiment was pointed toward the center of the sun. Useful data were also recorded when the experiment pointed to the center of the sun in a raster scan of 40- by 40-arc-min. The grating spectrometer began losing sensitivity after 2 months of operation (the grating spectrometer sensitivity can be monitored by observing the 304 A line at various times). The proportional counters in the 1 to 3 A and 3 to 10 A crystal spectrometers were good for about 1 year (their condition may be monitored by comparing the flux for a particular line against the overall flux monitored by the ion chambers). The ion chambers showed no signs of deterioration for over 1 year. The 6 to 25 A spectrometer began losing sensitivity after 6 months of operation. Background levels were usually very small compared to useful signals.

Solar X-Ray Radiation Ion Chamber Photometer

This NRL experiment was designed to monitor the solar X-ray flux in four broad bands between 0.5 and 60 A (0.5 to 3 A, 1 to 8 A, 8 to 16 A, and 44 to 60 A) as part of a long-term project to observe solar X-ray activity with sets of standardized X-ray ion chamber photometers over an entire solar cycle. The instrumentation, mounted in the wheel section of the OSO 5 spacecraft, consisted of four X-ray ion chamber photometers. The 0.5- to 3-A ion chamber had a 50-mm-thick beryllium window and krypton filler gas, the 1- to 8-A ion chamber had a 5-mm-thick beryllium window and argon filler gas, the 8- to 16-A ion chamber had a 0.33-mm-thick aluminum window and nitrogen filler gas, and the 44- to 60-A ion chamber had a 0.25-mm-thick Mylar window and nitrogen filler gas. Each ion chamber photometer had an electrometer amplifier and analog-to-digital converter. The first three bands had automatic range changing capabilities that enabled them to alter their sensitivity in the event of solar flare. The 0.5- to 3-A and 1- to 8-A photometer amplifiers had three sensitivity ranges, and the 8- to 16-A photometer amplifier had two ranges. The ion chamber photometers continuously monitored the incident radiation while a digital sample was taken. The digitizing operation was controlled by two solar cells mounted 90 deg from each other, with one cell facing in the same direction as the four ion chambers. As the satellite wheel rotated, the cell not aligned with the detectors came into view of the sun first and initiated the taking of a seven-bit digital sample of the X-ray background. When the other cell and the X-ray detectors came into view of the sun, the digital sampling of the solar X-ray flux was initiated. The background X-ray reading was subtracted from the solar X-ray reading before readout. An automatic calibration cycle occurred after every 48 readout cycles and consisted of opening the inputs to the amplifiers and performing a normal digitized operation without subtracting the background reading. The experiment functioned properly for over a year, from January 1969 to July 1970. After this time, however, the experiment failed because of undetermined causes and was placed in an inoperable status on September 8, 1971. The data from this experiment were combined with data from a similar experiment on Solrad 9 to provide observational coverage of a major portion of every X-ray solar event that occurred during the period.

Low-Energy Gamma-Ray Experiment

This experiment was designed to detect gamma rays from the sun and from other sources in space, and to analyze their energy spectra in the 2 to 200 keV range. The solar phase of the experiment, which was the primary phase, emphasized observation of hard solar x-ray bursts as well as a search for a constantly present activity-dependent, hard x-ray flux. The detector was a descendant of the anticoincidence-shielded gamma-ray detector in the GSFC experiment on OSO 2, which operated in the 100 to 700 keV range. The experiment equipment had a 80 sq cm aperture approximately 2-sec time resolution, nine-channel pulse-height analysis and in-flight calibration.

Measurement of the Self-Reversal of the Solar Lyman-Alpha Line

This flight instrument was designed for studying the line shape of the solar Lyman-alpha line summed over the entire solar disk. It made use of the optical resonance of hydrogen and deuterium gases. A grating and mirror system converted the incident solar radiation into a beam of Lyman-alpha light (1216 A) with a bandwidth of 100 A, which entered two resonance cells. One cell was filled with molecular hydrogen and the other cell was filled with molecular dueterium gas. Each cell had a photomultiplier mounted at its exit window to measure the total intensity of the solar spectrum in the 100-A bandwidth. In addition, each cell had a photomultiplier mounted at right angles to the cell (i.e., at right angles to the incident beam) that measured the intensity of the light scattered by the cell. Heated filaments in these cells dissociated some of the gas, and different concentrations of atomic species in the cells were obtained by varying filament voltage. The signal on the right angle detectors was proportional to the intensity of the incident light at 1215.664 A for the hydrogen cell (0.015 A bandwidth) and at 1215.335 A for the deuterium cell (0.011 A). Scanning was accomplished by a doppler shift due to approaching and receding velocity of the spacecraft with relation to the sun at orbit morning and evening. An internal calibration lamp was included in the experiment. The experiment operated 1 h every 2 calendar days.

Zodiacal Light Monitor

This experiment, a modified version of an OSO 2 experiment (65-007A-04), was designed to measure the intensity and degree of polarization of zodiacal light as a function of ecliptic latitude and to search for changes in zodiacal light resulting from solar disturbances. It was also intended to study the intensity of the airglow continuum layer and to study the distribution of nighttime lightning storms. Six photomultiplier/filter photometers were used with various apertures and orientations. These photometers were PM-1, PM-2, PM-3, PM-4, PM-5, and PM-6. PM-1 was oriented parallel to the spin axis with a 9.25- by 57-deg field of view (FOV) and a red/visual passband. PM-2 was oriented antiparallel to the spin axis with a 9.25- by 57-deg FOV and a blue (3500 to 5000 A) passband. PM-3 was oriented parallel to the spin axis with an 11-deg-diameter conical FOV and a blue (3500 to 5000 A) passband. PM-4 was oriented parallel to the spin axis with a 10.5-deg offset, a 9.5-deg-diameter conical FOV, and a blue (3500 to 5000 A) passband. PM-5 was oriented antiparallel to the spin axis with a 9-deg-diameter conical FOV and a red (6000 to 8500 A) passband. PM-6 was oriented antiparallel to the spin axis with a 9-deg offset, a 9.5-deg-diameter FOV, and a visual/red passband. These photometers measured light intensity up to about 1000 times that of a tenth magnitude star, on a scale from 0 to 4096. In addition, two photodiodes, each with a sensitivity about one-sixteenth that of the photometers, functioned as monitor eyes and were sampled once every 5 s. Eye-1 was oriented parallel to the spin axis with a 10.5-deg offset and had a 21-deg-diameter conical FOV. Eye-2 was oriented antiparallel to the spin axis, was offset by 5 deg, and had a 17.5-deg-diameter FOV.

Solar Extreme Ultraviolet Monitor

This experiment was designed to (1) observe temporal variations of solar UV intensity in three broad bands between 280 A and 1030 A (280 to 370 A, 465 to 630 A, and 760 to 1030 A), (2) observe variations in intensity in these bands during solar flares, (3) make estimates for the three UV bands of active and quiet region contributions and limb brightening as a result of measurements made during solar eclipses, and (4) make an approximate determination of the differences in temperature and constituent number densities of the earth's upper atmosphere between sunrise and sunset. The instrumentation, located in the wheel section of the OSO 5 spacecraft, consisted of a single Rowland-mounted, concave, grazing-incidence, grating spectrophotometer, which dispersed the radiation into the three bands, and three Bendix resistance-strip-type photomultipliers, which detected the radiation in each band. Counts from each band were obtained during every revolution of the satellite (about 2 s) during the daylight portion of the orbit, including sunrise and sunset. The count range was from 100 to 20,000, but variations of more than 5% caused by pitch changes or interference were sometimes present. Inflight calibration, namely a check on the grating reflectivity and photomultiplier response, was made at regular intervals for the first few weeks of operation but was discontinued because of a malfunction of the calibration lamp. A background reading was also taken periodically while the instrument was looking away from the sun. Because of the calibration lamp malfunction, the instrument was deactivated by ground command in May 1969.

Science

Summary