Description

The purpose of the OGO 3 spacecraft, the third of a series of six Orbiting Geophysical Observatories, was to conduct many diversified geophysical experiments to obtain a better understanding of the earth as a planet. OGO 3 consisted of a main body that was parallelepipedal in form, two solar panels, each with a solar-oriented experiment package (SOEP), and two orbital plane experiment packages (OPEP). One face of the main body was designed to be earth pointing (Z axis), and the line connecting the two solar panels (X axis) was intended to be perpendicular to the earth-sun-spacecraft plane. The solar panels were able to rotate about the X axis. The OPEPs were mounted on, and could rotate about, an axis which was parallel to the Z axis and attached to the main body. Due to a failure in the attitude control subsystem on July 23, 1966, the spacecraft was put into a permanent spin mode about the Z axis. Both the orientation of the spin axis and the spin period were variable, the latter usually in the range 90 s to 125 s.

At launch, the local time of apogee was 2300 h. OGO 3 carried 21 experiments. Thirteen of these were particle studies, and two were magnetic field studies. In addition, there was one each of the following types of experiments: interplanetary dust, VLF, Lyman-alpha, gegenschein, atmospheric composition, and radio astronomy. Real-time data were transmitted at 1, 8, or 64 kbs depending on the distance from the spacecraft to earth. Playback data were tape recorded at 1 kbs and transmitted at 64 kbs. Two wideband transmitters, one feeding into an omnidirectional antenna and the other feeding into a directional antenna, were used to transmit data. A special purpose telemetry system, feeding into either antenna, was also used to transmit wideband data in real time only. Tracking was accomplished by using radio beacons and a range and range-rate S-band transponder. Routine spacecraft operation was discontinued on December 1, 1969, after which only data from Heppner's experiment (E-11) was acquired. All spacecraft support terminated on February 29, 1972. By March 1971 spacecraft perigee had increased to 16,400 km and the inclination had increased to 75.8 deg.

Instrumentation

There were 4 cosmic ray instruments (1 of which included a gamma-ray spectrometer), 4 plasma, 2 trapped radiation, 2 magnetic fields, 5 ionosphere, 3 radio/optical, and 1 micrometeoroid detectors. Again, the GSFC positron search and gamma-ray spectrometer was included. The experiment was essentially identical to what was flown on OGO 1, with the PMTs being replaced by an improved variety.

Experiments

Solar Cosmic Rays
Cosmic-Ray Isotopic Abundance
Cosmic-Ray Spectra and Fluxes
Positron Search and Gamma-Ray Spectrometer
Electrostatic Plasma Analysis (Protons .1-20keV)
Plasma Probe, Faraday Cup
Low Energy Proton Measurement
Low-Energy Proton and Electron Differential Energy Analyzer (LEPEDEA)
Trapped Radiation Scintillation Counter
Magnetic Survey using Two Magnetometers
Triaxial Search-Coil Magnetometer
Spherical Ion and Electron Trap
Planar Ion Electron Trap
Positive Ion Concentration
Radio Propagation
VLF Noise and Propagation
Radio Astronomy
Geocoronal Lyman-Alpha Scattering
Gegenschein Photometry
Interplanetary Dust Particles
Electron Spectrometer
Ionization Chamber

Launch-Orbit Information

Launch Information

Launch Date: 1966-06-07 at 02:55:00 UTC
Launch Vehicle: Atlas-Agena B
Launch Site: Cape Canaveral, United States
Mass: Mass: 514.8 kg

Type: Orbiter

Central Body: Earth

Epoch start: 1966-06-07 02:55:00 UTC

Periapsis Apoapsis Period Inclination Eccentricity
295 km 122,219 km 2,913 minutes 31.4째 0.90127
Science

This time, the experiment was successful in achieving all of its objectives. OGO 3 maintained 3-axis stabilization for 46 days. At that point, an attitude controller failed and the spacecraft was put into a spin on 23 July 1966. The spin period varied from 90-125 seconds. By June 1969, data acquisition was limited to 50% of the orbital path. Routine operation was discontinued on 1 December 1969, and complete termination occurred on 29 February 1972.

Summary