Vela 5B was one of two spin-stabilized, polyhedral satellites that comprised the fifth launch in the Vela program. The orbits of the two satellites on each launch were basically circular at about 17 earth radii, inclined at 60 deg to the ecliptic, and spaced 180 deg apart, thus providing a capability of monitoring opposite sides of the earth. The objectives of the satellites were (1) to study solar and cosmic X rays, extreme ultraviolet radiation (EUV), solar protons, solar wind, and neutrons, (2) to carry out research and development on methods of detecting nuclear explosions by means of satellite-borne instrumentation, and (3) to provide solar flare data in support of manned space missions. Vela 5B, an improved version of the earlier Vela series satellites, had better command capabilities, increased data storage, improved power requirements, better thermal control of optical sensors, and greater experimentation weight. Power supplies of 120 W were provided by 22,500 solar cells mounted on 24 of the spacecraft's 26 faces. A rotation rate of 78 rpm during transfer orbits and 1 rpm after final orbit insertion maintained nominal attitude control. Eight whip antennas and four stub antenna arrays at opposite ends of the spacecraft structure were used for ground command and telemetry.


The wheel of the satellite carried, amongst other experiments, a CsI crystal scintillator. The central crystal was 0.635 cm thick, had a sensitive area of 70 cm2, and was viewed from behind by a pair of photomultiplier tubes. The shield crystal had a wall thickness of 4.4 cm and was viewed by 4 photomultipliers. The field of view was ~ 40 degrees. The energy range covered was 14-254 keV. There were 9 energy channels:the first covering 14-28 keV and the others equally spaced from 28-254 keV. In-flight calibration was done with an 241 Am source. The instrument was designed primarily for observation of solar X-ray bursts. A secondary interest was the measurement of the intensity, spectrum, and spatial distribution of the diffuse cosmic background.

Launch-Orbit Information

Launch Date: 1969-05-23 at 07:57:01 UTC
Launch Vehicle: Titan III-C
Launch Site: Vandenberg AFB, United States
Trajectory Description
Type: Orbiter
Central Body: Earth
Epoch start: 1969-05-23 08:00:00 UTC
Orbital Parameters
Periapsis 110920.0 km
Apoapsis 112283.0 km
Period 6709.0 minutes
Inclination 32.79999923706055°
Eccentricity 0.0057760002091526985