Orbiting Solar Observatory

The Orbiting Solar Observatory (abbreviated OSO) Program was the name of a series of American space telescopes primarily intended to study the Sun, though they also included important non-solar experiments.

[2] The basic design of the entire series featured a rotating section, the "Wheel", to provide gyroscopic stability.

The critical bearing between the Wheel and the Sail was a major feature of the design, as it had to operate smoothly for months in the hard vacuum of space without normal lubrication.

It also carried both the power from the Sail and the data from the pointed solar instruments to the Wheel, where most of the spacecraft functions were located.

Additional science instruments could also be located in the Wheel, generally looking out on a rotating radius vector which scanned the sky, and also across the Sun, every few seconds.

The failure was suspected to have been caused by a modification to the igniter mechanism in the third stage after some minor technical difficulties experienced on the previous Delta C launch (TIROS 10 on July 2).

Conceived as a polar-orbiting satellite system, these spacecraft would continuously monitor the Sun and surrounding environment with detectors and electronic imaging ranging from x-rays to visual light.