Vela 2A and Vela 2B were two spin-stabilized (2 rev/sec) 144-kg satellites comprising the second launch in a series of six Vela launches. The orbits of the two satellites on each launch were basically circular at about 17 earth radii and were spaced 180 deg apart. Their objectives were to monitor nuclear weapons explosions in space and to study x-rays, gamma-rays, neutrons, magnetic fields, and charged particles over a wide range of energies from solar wind to cosmic ray as the satellites passed through interplanetary space, the bow shock, the magnetosheath, and the magnetotail. The satellite operated in either a real-time mode (one data frame/sec) or a memory store mode (one data frame every 256 sec). The spacecraft operated in the real-time mode about 40 percent of the time and in the store mode for the rest of the time unitl the next Vela launch. At this time, tracking priority was given to the new spacecraft, and the older spacecraft operated in the store mode only. There had been less and less data coverage of these satellites with each succeeding launch.



X-Ray/Charged Particle
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Gamma-Ray/Charged Particle
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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.

Electron-Proton Spectrometer
This experiment consisted of one Geiger counter and one hemispherical electrostatic analyzer. They were designed to study the intensity energy spectrum and angular distributions of solar wind and magnetospheric particles. The Geiger counter measured electrons with energies greater than 45 keV. Particles were accepted from a cone of 35 deg half angle. The counter was mounted so that the axis of the acceptance cone was perpendicular to the spin axis. The counter was operated only in real 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 16 logarithmically spaced energy per charge channels covering the range 0.3 to 20 keV. A complete 16 point energy spectrum was taken centered on each of the following directions in the spacecraft equatorial plane and relative to the spacecraft - sun line -12 deg, -6 deg, 0 deg, 6 deg, 12 deg, 90 deg, 180 deg and 270 deg (minus signs indicate angles to the left (East of the sun). In the real time mode a complete 128 point spectrum was taken every 128 sec. Very little information was obtained in the memory store mode. The instruments worked well over the period of major coverage of the spacecraft.

lM-S Background Radiation Detector
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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 sensor was shielded from sunlight by two layers of nickel foil. The energy loss in these foils by electrons with energy greater than about 40 meV was almost negligible. The instrument responded to electrons between 45 and 430 keV and protons between 180 and 570 keV. The energy spectrum was measured in steps by successive stepping of the pulse height analyzer giving seven points on the integral energy sprectum. Electrons and protons could be distinguished by comparison of this detector and the Geiger-Mueller experiment (NSSDC 64-040A-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 64-040A-06). The detectors were two Geiger counters, one with an electron threshold of 46 keV for electrons and the other with an electron threshold of 125 keV. The experiment worked well over the period of major data coverage of the spacecraft.

Search Coil Magnetometer
The magnetic field experiment on the Vela 2A spacecraft, part of the USA 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 logarithmically extended over the dynamic range of 0-36 gamma. The sampling rate was 1 Hz and the instrument bandpass was 1.75 - 2.25 Hz. The presence of a large and variable spacecraft generated field at the spin frequency of the satellites contaminated the magnetometer data.

Launch-Orbit Information

Launch Date: 1964-07-17
Launch Vehicle: Atlas-Agena D
Launch Site: Cape Canaveral, United States
Mass: 150.0 kg