The Moon: We Look Before We Leap - Ranger 6
January 24, 1964 Electronics Magazine

January 24, 1964 Electronics [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Electronics, published 1930 - 1988. All copyrights hereby acknowledged.

Congress was breathing hard down the neck of NASA while Ranger 6 was being prepared for its surveillance mission to the lunar surface. In 1962, Ranger 3, the first to carry a TV camera, went into orbit around the sun after missing the moon. Ranger 4 (dubbed "Brainless I") impacted the moon but did not send back any data. And Ranger 5 lost power after launch and missed the moon by about 450 miles. Time was running out to collect data for use in fulfilling the challenge issues by President John F. Kennedy on May 25, 1961, to "...commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth." That challenge was successfully met by the Apollo 11 mission partially on July 21st, 1969 by landing Neil Armstrong and Buzz Aldrin on the moon, and then fully on July 24th when they (Armstrong, Aldrin and Michael Collins) returned safely to Earth. Ranger 6 unfortunately ended in failure on February 2nd, 1964, when its TV camera did not return any images prior to the planned crash landing. Finally, on July 31st, 1964, Ranger 7 managed to transmit pictures back to Mission Control.

Ranger 6 Moon Mission

Close-up pictures from Ranger 6 will aid later Apollo flights

By Joel A. Strasser

Assistant Editor

Hightstown, N. J. - Next week, another Ranger space probe is scheduled to go on a one-way trip to the moon. If Ranger 6 succeeds in sending close-up TV pictures back to earth as it crash lands, it will have accomplished a job that three previous Rangers failed to do. And it will have set a new record for TV transmission - 239,000 miles.

Ranger 6, scheduled for launch by NASA January 30 from Cape Kennedy, stands a better chance of achieving its goals. Bernard P. Miller, RCA's Ranger project manager, told Electronics. This confidence stems from the following improvements that have been built into the new Ranger:

• Number of TV cameras has been raised to six, to increase the number of detailed pictures transmitted in the 10 minutes before impact. A unique sequencing arrangement schedules their transmission.

• Transmitter output power has been raised to 60 W, the most power ever transmitted by a spacecraft. This compares with 3 W in previous Ranger one-camera systems.

• Completely redundant systems characterize spacecraft electronics. Ranger's six-camera TV subsystem has two independent channels.

• Reliability on both booster and TV subsystem has been tightened up through more rigorous testing and more careful component selection.

• Electronics are "right on the state of the art," according to Miller. Power amplifiers and the dummy load have been pressurized to counter the breakdown phenomena. These include both the partial pressure type of breakdown and "multipactor" - AC or RF breakdown that occurs only in hard vacuum as a result of secondary emission. Video combiner, previously a coaxial type, is now a solid-state device.

• Passive thermal control system, completely independent of JPL's, is built into the RCA portion of the electronics. The body of the TV sub-system is used as a heat sink.

Ranger 6 is, however, "still a high risk type of shot" because of its difficult midcourse and terminal maneuvers, according to Miller. RCA built the TV subsystem for Ranger under contract to Jet Propulsion Laboratory. The systems are identical for Rangers 6 through 9.

Plans are to transmit a warm-up signal to the cameras 15 min before hard impact on the moon. The picture-taking sequence will start 10 min before Ranger impacts at 6,000 mph.

As Ranger falls toward the moon, area coverage is traded for increasing resolution. Some 3,000 pictures covering 101 nautical miles on a side from about 700 nautical miles from the surface down to pictures covering 123 ft on a side from about 2,000 to 3,000 feet up should result.

Before 6 - 1, 2, 3, 4, 5 Rangers 1 and 2, launched in 1961, went into low earth orbits, rather than their programmed deep-space orbits, but achieved their primary objectives - testing the spacecraft.

In 1962, Ranger 3, the first to carry a TV camera, went into orbit around the sun after missing the moon. Ranger 4 (dubbed "Brainless I") impacted the moon but did not send back any data. And Ranger 5 lost power after launch and missed the moon by about 450 miles. Primary mission of these three was to obtain seismic data - TV was secondary.

On Ranger 6, TV Is the Primary Mission

Television Subsystem - The six TV cameras (three are 1-inch wide-angle types and three 3-inch narrow-angle types) are mounted at slightly different angles.

Two cameras (one of each size) provide a full-scan of 800 resolution lines, and are in the F-channel (see diagram). Four cameras (two of each size) provide partial-scan (P-channel) coverage of 200 resolution lines of the 800-line picture.

Each channel's transmitter chain provides 60-w output. Of the 120 w fed to a four-port hybrid, a directional antenna gets 60 w and the dummy load dissipates 60 w. Center frequency of the F-channel is 959.52 Mc, and of the P-channel, 960.58 Mc. TV bandwidth is 200 kc.

Cameras are adjusted to a lighting range of 20 to 2,600 foot-lamberts - comparable to average lighting conditions on earth at 3 p.m. If the lunar surface is darker than expected, a low signal-to-noise ratio would result. If it's brighter than expected, some loss of the gray scale could occur from saturation.

Picture Sequencing - To squeeze as many pictures as possible into those valuable 10 min before impact, the pictures are sequenced for transmission.

Full-scan pictures will take 2.5 seconds to scan and 2.5 see to prepare. With both cameras operating at the same frequency, one camera will be constantly preparing while the other is scanning.

On the P-channel, the scanning time is 0.2 sec and the preparation time is 0.6 sec. The first partial-scan camera will scan for 0.2 sec. When this is completed, the second will begin scanning, while the first begins its 0.6-sec preparation period. In short, when the fourth partial-scan camera completes scanning, the first has completed one 0.2-sec scan and one 0.6-sec preparation cycle; the second has completed one 0.2-sec scan and 0.4-sec of its preparation cycle; and the third has completed one 0.2-sec scan and 0.2 sec of its preparation cycle.

The use of different frequencies as well as different chains permit complete independence between F and P channels. Both operate simultaneously, but one can operate alone if the other malfunctions.

Posted November 5, 2018