Description

Vela 3A and Vela 3B were two polyhedral satellites comprising the third in a series of six Vela launches. The orbits of the two satellites on each launch were basically circular at a radial distance of about 17 earth radii and spaced 180 deg apart. The satellites were spin stabilized at about 2 rps and had their spin axes inclined at about 60 deg to the ecliptic. Data acquisition was mainly real time and averaged 25% (1 out of every 4 h) coverage per day. Data coverage was increased for special events. The satellite operated well during the period of major data coverage, i.e., from launch until the April 1967 launch of the Vela 4 satellites. After this time, data acquisition from the Vela 3 satellites became increasingly sporadic.

 

Instrumentation

X-Ray/Charged Particle
No Information

Gamma-Ray/Charged Particle
No Information

Neutron Detectors
The neutron detector was designed to monitor neutron signals from nuclear explosions in space and to establish background characteristics for neutron detectors exposed to neutrons and showers produced in the spacecraft by cosmic rays. The detector used a large polyethylene moderator to thermalize incident neutrons, the thermal neutrons were detected in two helium 3-filled proportional counters. Each counter had its own power supply and amplifier to afford greater reliability. Neutrons in the approximate range 1 - 100 MeV were counted and read out each second. The detector also reacted to (but did not distinguish) protons greater than 25 MeV in energy, thus it provided a simple indication of solar proton activity. The experiment worked well over the period of major data coverage.

Electrostatic Analyzer and GM Tubes
This experiment consisted of two Geiger counters and a hemispherical electrostatic analyzer. The instruments were designed to study the intensity, energy spectrum, and angular distributions of solar wind and magnetospheric particles. The Geiger counters measured electrons with energies greater than 45 keV. Particles were accepted from a cone of 35-deg half-angle. One counter was mounted so that the axis of the acceptance cone was perpendicular to the spin axis. The other counter had the field of view shifted 30 deg relative to the spin axis. The counters were operated only in real time (i.e., only 25% of the time), and a measurement was taken once each second. The electrostatic analyzer was mounted on the spacecraft equatorial plane and had a field of view of about 5 deg in spacecraft longitude and about 90 deg in spacecraft latitude. In the real-time mode, the electrostatic analyzer measured the ion or electron (polarity was selected by ground command) flux in 64 logarithmically spaced energy-per-charge channels covering the range 0.2 to 18 keV/Q. A complete 64-point energy spectrum was taken centered on each of the following directions in the spacecraft equatorial plane and relative to the spacecraft-sun line: -11, -5, 1, 7, 14, 89, 190, and 291 deg (minus signs indicate angles to the left (east) of the sun). This set of angles could be rotated (by ground command) by +30 deg for Vela 3A and -30 deg for Vela 3B. In the real-time mode, a complete set of measurements (64-point spectra in each of eight directions) was taken every 256 s and repeated continuously. In the store mode, the analyzer took a 16-point energy spectrum at the angles 1 and 190 deg every 512 s. The instruments worked well over the period of major data coverage of the spacecraft.

lM-S Background Radiation Detector
No information available.

Solid State Detector
No information available.

Solid State Detector
The purpose of this experiment was to study the intensity, spatial distribution, time variations, and energy spectra of the electrons in the transition region and in the tail of the earth's magnetosphere. The sensor consisted of a gold, surface-barrier semiconductor detector. This detector was shielded from sunlight by two layers of nickel foil. The energy loss in these foils by electrons with energy greater than about 40 keV was almost negligible. The instrument responded to electrons between 30 and 475 keV and protons between 180 and 570 keV. The energy spectrum was measured in steps by successive stepping of a pulse-height analyzer giving eight points on the integral energy spectrum. Electrons and protons could be distinguished by comparison of this detector and the Geiger-Mueller experiment (NSSDC 65-058A-07) count rates. This experiment worked well over the period of major data coverage of the satellite.

Geiger Tubes
This experiment was used in the analysis of particle events where electrons and protons of comparable energy were simultaneously incident upon the semiconductor electron detector (experiment NSSDC 65-058A-06). The detector consisted of a single Geiger counter with an electron threshold of 45 keV. This experiment worked well over the period of major data coverage of the spacecraft.

Search Coil Magnetometer
The magnetic field experiments on the Vela 3A spacecraft, part of the U.S. program for the detection of nuclear weapons explosions in space, consisted of a single axis induction magnetometer oriented transverse to the spin axis of the spacecraft. The sensor's output was linearly extended over the range 0 to 100 nT. The sampling rate was 0.5 Hz and the instrument bypass was 1.87 to 2.12 Hz. The data have been used to study fluctuations of the magnetic field near the bow shock and magnetosheath.

EUV Detector
No information available.

Launch-Orbit Information

Launch Date: 1965-07-20
Launch Vehicle: Atlas
Launch Site: Cape Canaveral, United States
Mass: 150.0 kg

Summary