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 light and X-ray and gamma radiation. The OSO 2 platform consisted of a sail section, which pointed two experiments continuously toward the sun, and a wheel section, which spun about an axis perpendicular to the pointing direction of the sail and carried six experiments. Attitude adjustment was performed by gas jets. A pointing control system permitted the pointed experiments to scan the region of the sun in a 40- by 40-arc-min raster pattern. Data were simultaneously recorded on tape and transmitted by PCM/PM telemetry. A command system provided for 70 ground-based commands. The spacecraft performed normally until the pitch gas supply neared exhaustion on November 6, 1965. The spacecraft was then placed in a stowed condition. The transmitter was commanded on intermittently until March 3, 1966, and then on a weekly schedule until June 1, 1966, when it ceased operation. For more information, see A. W. L. Ball, Spaceflight, v. 12, p. 244, 1970.

Launch Date: 1965-02-03 at 16:33:00 UTC
Launch Vehicle: Delta
Launch Site: Cape Canaveral, United States
Decay Date: 1989-08-09

Type: Orbiter
Central Body: Earth
Epoch start: 1965-02-03 16:33:00 UTC

Orbital Parameters
Periapsis: 435 km
Apoapsis: 466 km
Period: 93.6 minutes
Inclination 32.9°
Eccentricity 0.00227

Instrumentation

Solar X-ray Bursts

This experiment was designed (1) to measure solar X-ray bursts in three wavelength bands (2 to 8 A, 8 to 20 A, and 44 to 60 A), the 2- to 8-A background radiation, and X-ray emissions from solar prominences high above the solar limb, and (2) to map X-ray sources on the sun in two wavelength intervals (2 to 8 A and 44 to 60 A). The experiment, located in the sail section of the satellite, had two operational modes--pointed and raster. The pointed mode used five GM tube counters (three were used as burst detectors, one as a background detector, and one as a prominence detector) and was designated the solar X-ray telescope. The raster mode, called the X-ray spectroheliograph, used two of the burst detectors. This, however, failed to function. In the pointed mode, the burst detectors were pointed directly at the sun to within plus or minus 1 arc-min of the center of the apparent solar disk and continuously monitored the solar X-ray flux except during telemetry readout of the satellite tape recorder and spacecraft night. The background detector was pointed away from the sun and provided a basis for correcting the data for counts caused by particle radiation. The prominence detector looked at the region around the sun by means of an X-ray detector equipped with an occulting disk that artificially eclipsed the sun. The intensity measurements for the burst portion of the experiment were accurate to 7% for short time intervals (8 s) and had better than 7% accuracy for long time intervals (8 min). The experiment produced about 1 month of X-ray data.

Corona White Light

The instrumentation for this experiment, located in the solar-oriented 'sail' section of the satellite, operated in a pointed mode and a raster mode. The pointed mode measured the intensity of the white light corona by means of an externally occulted white light lyot coronagraph, which was aimed to within plus or minus 1 arc-min of the center of the apparent solar disk. The coronal light was detected on an end window-like photomultiplier. Data were obtained, with a 1 arc-min resolution, from which the corona can be reproduced between r/r sub s=3.5 and 7-- There was too much stray light for r/r sub s values between 7 and 10 for any useful data reduction. The raster mode, designated as the EUV spectroheliograph, scanned over a 40 arc-min by 40 arc-min area only when the coronagraph was turned off and the raster scan 'execute' command was transmitted to the pointed section of the satellite. The scan, which included the entire solar disk and part of its corona, formed images of the sun in hydrogen Lyman-Alpha (1216 A), he II (304 A), and a region near 584 A. The resolution of these images was 1 arc-min. Data were received from February 1965 to November 1965 and were of good quality.

Zodiacal Light Monitor

The purpose of this experiment was to investigate the direction and intensity of polarized zodical light. Experiment apparatus carried in the rotating wheel section measured the intensity of polarized light along the spin axis. To do this, photomultipliers covered with sheets of poloroid were mounted on the top and bottom of the wheel section. The photomultipliers had a 10 degree field of view and measured both visible and infrared light. Rotation of the polaroid sheet with the wheel section produced an alternating signal of 0.5 cps, which was a direct measure of the intensity of the polarized light. During the design of this experiment, it was realized that the equipment could also be used for airglow observations. Examination of experiment data unexpectedly yielded useful measurements of terrestrial lightning and radiation.

Cosmic Gamma (100-1000 MeV) Detector

This experiment measured the direction of arrival and energies of primary cosmic gamma-ray radiation in the energy range of approximately 100 MeV to 1 BeV. The primary purpose of this experiment was to locate discrete sources of radiation and to determine their energy spectra inthe range mentioned above. Energy resolution was expected to be about 30 percent, and directional accuracies were measured to within plus or minus 10 deg. The individual counters were a lead-glass Cerenkov counter, a lucite Cerenkov counter, and a plastic scintillator.

Gamma Ray

This experiment was designed to detect gamma rays from the sun and from other sources in space, and to analyze their energy spectra from 01. to 0.7 MeV. Of particular interest was the ability to detect the 0.511 MeV electron-positron annihilation line and to study any possible temporal variations. The detector consisted of a 5.08-cm (2-in) long by 2.54-cm (1-in) diameter csi (TL) crystal viewed by a single photomultiplier tube together with a 22.23-cm (8.75-in) long by 14.61 cm (5.75-in) diameter csi (TL) crystal viewed by four photomultiplier tubes. The small crystal was inserted into a well of the larger crystal, the output of the smaller crystal being run in anticoincidence with the large crystal. This output was fed into a pulse height analyzer. This detector and its mode of operation provided a gamma-ray spectrometer which had angular collimation, low background sensitivity, suppression of the Compton continuum, and relatively high photopeak efficiency.

Solar UV Spectrometer

No Information Available

Thermal Radiation Emissivity

No Information Available

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