Molecular oxygen absorption of solar Lyman- alpha observed by Interkosmos-1

The satellite Interkosmos-1, was launched on October 14, 1969, into an orbit with perigee height 260 km, apogee height 640 km and an inclination of 48.4 degrees. A Lyman- alpha photometer, was mounted on the observing platform of the satellite, and directed towards the Sun with an accuracy of +or-1 degree. During the period of observation, October 15-23, 1969, the measured absolute values of solar Lyman- alpha flux varied between 3.7 and 4.7 ergs cm-2 s-1, with a mean value of 4.1 ergs cm-2 s-1. One purpose of the experiment was to measure the height-dependent absorption of Lyman- alpha in the upper atmosphere when the satellite entered the Earth's shadow ('satellite sunset').