Descent Imaging on the Lunar Ranger Missions

The Ranger spacecraft were the "ultimate" in descent camera systems--their entire mission was simply to take pictures as the spacecraft fell toward the lunar surface. No attempt was made to safely land the Rangers---they simply crashed into the Moon at full flight velocity.

The Ranger television system consisted of a six slow-scan vidicon TV cameras capable of transmitting high-resolution, close-up television pictures of the lunar surface during the final minutes of flight before the spacecraft impacted the lunar surface.

Vidicons 2.54 cm (1 inch) in diameter with an antimony-sulfide oxy-sulfide (ASOS) photoconductor target were used for image sensing in all six cameras. There were two camera channels with independent power distribution networks to increase reliability. The first channel had two full-scan cameras, one wide angle "A camera" with 25 degree field of view and 25-mm focal length), and one narrow angle "B camera" with 8.4 degree field of view and 76-mm focal length. These cameras utilized an active image area of 11 sq mm that contained 1150 lines and was scanned in 2.5 sec. Scan and erase cycles were designed to alternate resulting in intervals of 5 sec between consecutive pictures on a particular camera.

The other channel had four partial-scan "P cameras", two narrow angle and two wide angle. The image area of these four cameras was 2.8 sq mm which contained 300 lines and was scanned in 0.2 sec. The instrument allowed for camera fields of view, ranging from 25 deg to 2.1 deg, to overlap and produce a 'nesting' sequence of pictures.

The video data were transmitted to Earth in analog form. The video transmissions were recorded on both kinoscope film recorders and magnetic tape recorders. A cathode-ray tube reconstructed the original image, which was then photographed on 35-mm film.

When the Ranger pictures were transmitted to Earth, television viewers for the first time saw in their homes the words "LIVE FROM THE MOON" across their screens. The Ranger missions marked the start of an exciting time of exploration that culminated in the Apollo missions which landed 12 men on the Moon between 1969 and 1972.