Orbiting Solar Observatory (OSO) was a series of stabilized orbiting platforms developed by the Goddard Space Flight Center for observing the Sun and extrasolar sources at ultraviolet, X-ray, and gamma-ray wavelengths. OSO-1 was the first satellite to carry onboard tape recorders for data storage and instruments that could be accurately pointed.

 

The two-section observatory was stabilized because the lower section, the "wheel," spun as a gyroscope at a near constant 30 rpm. The upper fan-shaped section, the "sail," was joined to the wheel by a connecting shaft and remained pointed at the Sun during the OSO daytime. Experiments in the wheel scanned the Sun every two seconds and those in the sail pointed continuously at the Sun.

 

Other results of the OSO series included the first full-disc photograph of the solar corona, the first X-ray observations from a spacecraft of a beginning solar flare and of solar streamers – structures in the corona – and the first observations of the corona in white light and extreme ultraviolet.

 

spacecraft	launch date	launch vehicle	launch site	orbit	mass (kg)
OSO-1	Mar. 7, 1962	Delta	Cape Canaveral	522 × 553 km × 32.8°	208
OSO-2	Feb 3, 1965	Delta C	Cape Canaveral	294 × 306 km × 32.8°	247
OSO-C	Aug 25, 1965	Delta C	Cape Canaveral	launch failure	280
OSO-3	Mar 8, 1967	Delta C	Cape Canaveral	546 × 570 km × 32.8°	281
OSO-4	Oct 15, 1967	Delta C	Cape Canaveral	552 × 555 km × 32.9°	272
OSO-5	Jan 22, 1969	Delta C	Cape Canaveral	538 × 559 km × 33.0°	291
OSO-6	Aug 9, 1969	Delta N	Cape Canaveral	489 × 554 km × 32.9°	290
OSO-7	Sep 29, 1971	Delta N	Cape Canaveral	326 × 572 km × 33.1°	635
OSO-8	Jun 21, 1975	Delta 1914	Cape Canaveral	539 × 553 km × 32.9°	1,066