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Ranger 7

Ranger 7

Courtesy of NASA's National Space Science Data Center

 

Launch Date: 1964-07-28
On-orbit dry mass: 361.80 kg
Nominal Power Output: 200.00 W

 

Description

Ranger 7 was designed to achieve a lunar impact trajectory and to transmit high-resolution photographs of the lunar surface during the final minutes of flight. The spacecraft carried six television cameras, an optical earth sensor and high-gain antenna for optimum communications, and solar panels to provide power (as well as additional engineering equipment). The telecommunications equipment converted the composite video signal from the camera transmitters into an RF signal for subsequent transmission through the spacecraft high-gain antenna. Sufficient video bandwidth was provided to allow for rapid framing sequences of both narrow- and wide-angle television pictures. The spacecraft encountered the lunar surface in direct motion along a hyperbolic trajectory, with an incoming asymptotic direction at an angle of -5.57 degrees from the lunar equator. The orbit plane was inclined 26.84 degrees to the lunar equator. After 68.6 hours of flight, impact occurred in an area between Mare Nubium and Oceanus Procellarum (subsequently named Mare Cognitum). Velocity at impact was 2.62 km/sec (1.62 miles per second). The spacecraft performance was excellent. Transmission of over 4,300 photographs occurred during the final 17 minutes of flight, from 1308 UT to 1325 UT on July 31, 1964.

Ranger 7 Impact Television Imaging

The 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. These photographs provided large-scale topographic information needed for the Surveyor and Apollo projects. Vidicons 2.54 centimeters 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 which had independent power distribution networks so that the greatest reliability and probability of obtaining highest quality video pictures would be afforded. The first channel had two full-scan cameras, one wide angle (25-degree field of view and 25-millimeter focal length) designated the A-camera and one narrow angle (8.4 degree field of view and 76-millimeter focal length) B-camera. These cameras utilized an active image area of 11 square millimeter that contained 1150 lines and was scanned in 2.5 seconds. Scan and erase cycles were designed to act alternately resulting in intervals of 5 seconds 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 square millimeters which contained 300 lines and was scanned in 0.2 seconds. The instrument allowed for camera fields of view, ranging from 25 degrees to 2.1 degrees, to overlap and produce a 'nesting' sequence of pictures. 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-millimeter film.

The full-scan camera system began transmitting pictures at 1308 UT on July 31, 1964, 17 minutes, 13 seconds prior to impact. The partial-scan system initiated transmission of pictures at 1312 UT, 13 minutes, 40 seconds prior to impact. The last full-scan transmission occured between 2.5 and 5 seconds before impact, while the last partial-scan picture was taken between 0.2 and 0.4 seconds before impact and achieved resolution to 0.5 meters (1.64 feet). Image motion is more severe in the last pictures. The experiment returned 4,308 photographs of excellent quality.

 

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Views of the Solar System Copyright © 1997 by Calvin J. Hamilton. All rights reserved.