Radar measurements of the planet venus

The Jet Propulsion Laboratory established contact with the planet Venus using a planetary radar system from 10th March to 10th May 1961. Using both velocity and range data, a new value of 149 598 500 km was determined for the astronomical unit which is presently accurate to 500 km. Further data reduction is expected to improve accuracy towards 150 km. The rotation of Venus has been determined by spectral analysis as ~225 days. A super-sensitive receiving system was employed with a 10 kW transmitter operating at 2388 Mc/s. The receiver range capability is a 50 mW signal located on Venus at 30×106 miles. The data received included (1) received signal level, (2) power spectrum of the Venus-reflected signal, (3) Venus-Earth velocity and (4) Venus range. The first two used open- loop receivers; the second two used closed-loop automatic tracking receivers. All significant radio frequencies were derived from an atomic frequency standard.