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.
Space History
Ranger to the Moon
Views of the Solar System Copyright © 1997 by
Calvin J. Hamilton. All rights reserved.
