An attempt to determine the solar LY alpha flux independently of instrument calibration

Mu is the ratio between radiation pressure and solar gravitation from the Doppler shift between profiles obtained in two opposite directions perpendicular to the ecliptic plane. This parameter is used for both interplanetary hydrogen distribution models and for determination of the absolute value of the Lyman alpha solar flux. The D2A satellite was launched in April 1971 and placed in an orbit whose perigee was 450 km and apogee was 710 km. Measured and calculated angular shifts of the Lyman alpha interplanetary emission profiles were compared, and Mu was found to be equal to 0.62 plus or minus 0.18. The Ly alpha solar flux was also deduced, and was found to be equal to (2.07 plus or minus 0.6) x 10 to the 11th photons/sq cm-sec-A in directions perpendicular to the ecliptic plane for the 1970-1971 period. Both of these values were determined without absolute instrumental calibration. The absolute value obtained for the solar Ly alpha flux represents an increase in accuracy by a factor of two to corresponding OSO 5 measurements.