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NASA's RELAY Launched Dec 13, 1962




 
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W2DU
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Walt, at 90, Now 92 and licensed 78 years


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« on: January 08, 2011, 04:52:10 PM »

This story is about NASA's early TV repeater in space, called RELAY, launched from Cape Canaveral December 13, 1962. I had two assignments on this project; 1) measuring the radiation patterns of the VHF antenna array that transmitted the telemetry information, while still at RCA prior to shipping to NASA; and 2) Installing UHF TV uplink and downlink dish antennas on the antenna platform at NASA's ground station at Cape Canaveral for communicating with the spacecraft while on the launchpad. This included boresighting the dishes on the spacecraft, three miles away on launch pad 17.

Hope you enjoy this story as much as the previous ones!

Reflections 3

Sec 28.4  The RELAY Communications Spacecraft

How the Author’s Knowledge of Polarization Saved NASA from Scrubbing a Pre-Launch Test of Spacecraft RELAY at Cape Canaveral

     This writing describes the events involving the Author that occurred during a pre-launch test of the RELAY 1 satellite at Cape Canaveral, Florida in December 1962. Although AT&T’s TELSTAR, launched from Cape Canaveral July 10, 1962, was the first active communication satellite capable of relaying transatlantic TV signals, NASA’s RELAY, launched December 13, 1962, became the second such satellite. TELSTAR was built and owned by AT&T, and launched by NASA, but RELAY was owned by NASA and built by the Astro-Electronics Division of RCA (the Author’s employer) after being chosen over AT&T and Hughes. See Photo 28-4.1.
     The NASA platform at Cape Canaveral that supported antennas communicating with various spacecraft on launch pads during pre-launch operations is shown in Photo 28-4.2.

Background

    It should be remembered that in the early 1960’s there was no booster rocket capable of lifting a spacecraft into the geosynchronous orbit altitude of 22,300 miles above the Earth, the altitude required for an orbiting spacecraft to appear stationary with respect to any point on Earth. Consequently, RELAY orbited with a perigee of 820 miles and an apogee of only 4623 miles above the Earth, at an inclination of 47.5°, which made it visible at any one Earth location for a maximum of around 110 minutes a day. (TELSTAR’s perigee was 320 miles and apogee only 1895 miles.)  Therefore, these communications spacecraft were not yet ready for continuous, prime time TV. And further, due to the generic aspect of the name RELAY, the public was never really aware of its existence, or its accomplishments in supporting the early transatlantic TV transmissions. Both TELSTAR and RELAY performed nearly identical missions. However, the name TELSTAR was so exotic at the time that the media referred to the missions of both spacecrafts as TELSTAR, and seldom used the name RELAY. One example of the many times where RELAY performed the task, but for which TELSTAR received the credit, was the transmission of television signals between the US, Europe, and Japan during the 1964 Olympic Games held in Tokyo.
 
Let’s Get Technical

    During the time an active spacecraft is atop the launching rocket on the launch pad it is necessary to be in constant communication with it to perform housekeeping chores, such as monitoring various voltages and component temperatures, plus activating the cameras and tape recorders to verify their state of readiness. In other words, communications that will continue during the launch phase and on into the operational phase after orbit is achieved. To accommodate the communications for these satellites during the pre-launch testing and launch- phase operations, a ground station containing the complementary instrumentation was established approximately three miles from the launch pad complex, which in this case, the launch pads using the Delta rockets was Complex 17. A 20’ x 60’ platform supported by wooden poles at approximately 40 feet above ground was built at the ground station to mount the antenna arrays aimed toward the spacecraft on the launch pad, shown in Photo 28-4.2. Yagi, and various other antenna arrays mounted on the right-hand end of the platform were used to communicate at the VHF frequencies that involve reception of telemetry signals and transmission of command signals. The dish antennas on the left-hand end of the platform provided the UHF video links to the spacecraft, the large dish providing the uplink frequency of 1725 MHz and the small dish providing the downlink frequency of 4169.7 MHz.
      On the appointed day the initial pre-launch testing of RELAY 1 was in progress. The first portion of the test was performed with the gantry in place around the spacecraft, and all tests went well. However, as the gantry was being moved away the command signal from the ground station began fading at the input of the receiver in the spacecraft. When the gantry was completely away from the spacecraft the signal at the receiver was zero. With no way to further command the spacecraft with the gantry moved away, the launch director thought he had no alternative but to scrub the test for the day to allow the problem to be analyzed and repaired. Enter Author Maxwell, who had just finished installing the video-link dishes. Immediately sensing the cause of the signal failure he persuaded the launch director to take a short break in the test procedure to allow him to analyze and fix the problem. The director agreed. (Maxwell was knowledgeable concerning the RELAY antenna systems, because he had measured their antenna radiation patterns during the development phase of the spacecraft, in addition to measuring the final patterns proving that their performance conformed to the NASA specifications.)
     Maxwell reasoned that the problem was due to cross polarization between the command transmitting antenna at the ground station and the receiving antenna on the spacecraft. The receiving antenna was vertically polarized, so Maxwell reasoned correctly that the wrong polarization was being used at the ground station. He and the NASA engineers at the ground station checked the patch panel that contained the connections to the RF coaxial cables leading to the antennas mounted on the platform. The indications inside the ground station were that the command transmitter was indeed correctly connected to the port labeled VERTICAL POLARIZATION TRANSMIT. Maxwell still insisted that the active antenna was horizontally polarized, and further insisted on checking the cable routings on the platform. It took some very diplomatic persuasion to get the NASA RF engineers to agree that the cables on the platform could be connected to the wrong antenna. However, he and the NASA engineers climbed onto the platform to investigate the problem and found the coaxial cable labeled VERTICAL POLARIZATION TRANSMIT was indeed connected to a horizontally-polarized antenna array, as Maxwell predicted.
     That cable was quickly disconnected from the horizontal array and re-connected to a vertical array, when voila, the signal level at the command receiver in the spacecraft returned to normal. The launch director was delighted, giving Maxwell a hearty congratulation for saving his test from being scrubbed until another day.
     It’s now quite reasonable to ask, “How could the Author be so certain that the problem was one of cross polarization?” To answer this question we must go back in time to December 1959 at Cape Canaveral. After completing the development of the antenna system for the spacecraft TIROS 1, he was assigned the task of designing, constructing, and installing the antennas at the ground station to be used for the pre-launch operations of the TIROS spacecraft at Cape Canaveral, which was launched April 1, 1960. After installing those antennas he proceeded to the twelfth-story level of the gantry at launch pad 17A to take field strength measurements at the point where the spacecraft would be positioned. These measurements were necessary to determine the power needed at the ground station to communicate successfully with the spacecraft on the launch pad. The data obtained from these measurements revealed a surprising phenomenon. Because the girders used in the construction of the gantry were so tightly connected at each joint, the RF currents induced in them from the signals radiated from the antennas at the ground station flowed uniformly in both the vertical and horizontal girders regardless of the polarization radiated from the antennas at the ground station. Consequently, no matter which polarization was radiating from the antennas at the ground station, the field strength received by the test antenna at the spacecraft location within the confines of the gantry was identical, no matter which polarization of the test antenna—horizontal, vertical, or any angle in between. In other words, within the gantry the incoming linearly-polarized waves were being converted to circular polarization, due to the girder construction of the gantry. This then, is the reason the vertically-polarized RELAY receiving antenna within the gantry received a normal level signal with the transmitting antenna radiating horizontally-polarized waves, but which dropped to zero signal when the gantry was removed. A perfect example of loss of signal due to cross polarization—problem solved!



* Photo 28-4.2a.JPG (131.37 KB, 843x910 - viewed 649 times.)

* Photo 28-4.1a.jpg (73.58 KB, 780x996 - viewed 669 times.)
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« Reply #1 on: January 10, 2011, 12:05:22 AM »

Another great story, Walt, thnks!

I wasn't aware of the RELAY satellite... seems like the term TELSTAR almost became generic in its usage.
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« Reply #2 on: January 10, 2011, 01:39:06 AM »

Another great story, Walt

Makes me want to go outside and check the polarization on my antennas.

But, on second thought, I think I'll just wait till Spring.

Fred
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