NACA's ECHO 1 TV Satellite

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W2DU:
A few posts back my involvement with the ECHO Spacecraft was mentioned, so I thought a story about my involvement might be of interest to the AM group here. Thus I'm quoting from Reflections 3, Sec 28.3:

Sec 28.3  Echo 1 Spacecraft

     Launched into space on August 8, 1960, Echo 1 was the World’s first attempt to use an Earth-orbiting spacecraft as a means for achieving global TV broadcasting. When inflated after reaching orbit, Echo became a 100-ft spherical balloon made of aluminized mylar film of ½ mil thickness. The aluminized coating on the mylar was used to reflect TV RF signals globally from high-powered transmitters for direct reception to TV receivers on the ground. Although the spacecraft performed correctly while in orbit, its intended use was unsuccessful, because the power required of the TV transmitters was too great to obtain a satisfactory picture on reception after the signal was reflected from the spacecraft.
     However, it is interesting to note that the spacecraft carried two beacon transmitters to verify a successful entry into space after launching from Cape Canaveral. There was concern that it could become lost in clouds, with no way to determine its location thereafter. Hence, the two beacons operating at 108.0 and 108.03 MHz to permit continual radio tracking of the balloon if lost from visual contact.
     The beacon units, mounted at opposite poles of the balloon, included the transmitter, batteries, antenna, and solar cells, were embedded in a plastic disc shaped like a dinner plate, as shown in Photo 28-3.1. The transmitter, shown with and without encasement in Photo 28-3.2, delivered a continuous wave one-hundredth of a watt (ten milliwatts) into the antenna, which produced S9+ signals at the ground stations when the spacecraft was just above the horizon at 1,800 miles distance. Photo 28-3.3 is a view of the bottom side of the unit, showing the transmitter, batteries, and printed circuit connecting the batteries to the solar cells. Photo 28-3.4 shows technicians attaching the beacon to the mylar balloon material with adhesive tape.
    The antenna for Echo 1 was designed by the Author, which by itself brings up an interesting story. The spacecraft was a child of NACA, the forerunner of NASA. RCA’s involvement was to design and build the beacons. However, the engineers at NACA specified emphatically that no wire antenna could be involved due to the possibility of its inadvertently protruding into the skin of the balloon, allowing it to deflate. They strongly suggested that we design the beacon to use a slot antenna by simply making the slot opening in the surface of the balloon. We rejected the slot approach, indicating that while half of the RF energy delivered to the antenna would be radiated outward, the other half would be radiated inward, thus entering the space within the balloon. Inward radiation of RF energy would be disastrous, because the space inside the balloon would form a resonant cavity with extremely high Q. The result would be a highly unstable input impedance for the slot antenna.
     Consequently, we at RCA suggested placing a cavity resonant at the beacon frequency directly behind the slot to prevent inward radiation, and thus all the energy would be radiated outward. However, the NACA engineers were not only skeptical that the high Q of the cavity would cause an unstable impedance for the antenna, but also said building such a cavity behind the slot was impractical. So it became incumbent on RCA to prove the instability of the antenna impedance in the absence of the resonant cavity behind the slot.
     Because it was obviously impractical to take measurements on a balloon 100 feet in diameter, the proof must be found using a scale model for the measurements. As the RF engineer assigned to the antenna development I chose a 100-to-1 scale factor for a measurement model, making the diameter of the model sphere one foot and the measurement frequency 10,800 MHz, or 10.8 GHz. The RCA Laboratories model shop pressed a piece of 1/32″ copper sheeting into a sphere of one foot diameter. (Don't ask me how they did it.)
     A slot with the appropriate dimensions for the 10.8 GHz frequency was cut into the sphere, and fed with RG-55 coaxial cable. As I predicted at the outset, the input impedance of the slot radiator proved to be immeasurable, because the values of SWR exceeded 100:1, varying wildly with small temperature changes in the model. The NACA engineers demanded a demonstration of the measurements performed at their location at Langley Air Force Base, Virginia, which the Author duly performed. The performance convinced the people at Langley that we were correct concerning the instability of the slot impedance without a resonant cavity backing the slot. They finally agreed to allow a stainless steel spring wire antenna after we (RCA) promised to secure the wire embedded in the beacon plate until after the balloon had inflated, to ensure that the wire would not damage the mylar skin of the balloon. Referring to Photo 28-3.1, observe the circular slot near the periphery of the beacon disc, with the wire antenna emerging on the right-hand side. The antenna wire was secured in this slot while the balloon was folded up prior to launch, but when the balloon was inflated the wire was released from the slot, becoming vertical in relation to the surface of the balloon. In addition, a switch at the point where the wire emerged was automatically turned to the ON position when the wire was released, connecting the batteries to the transmitter and thus turning the beacon on.
     Had the NACA engineers believed us concerning the high-Q nature of the space within the balloon, the engineering of the simple quarter-wave vertical antenna mounted over the spherical ground plane supplied by the aluminized coating on the mylar balloon material would have been routine, requiring only designing the mechanical means for preventing the antenna from tearing a hole in the balloon. It seems that it’s sometimes better to keep it simple for government work.

W2DU:
For some reason, Fig 28-3.3 was not permitted on the earlier post with the other three figs.

Walt

Todd, KA1KAQ:
VERY cool story, Walt. That is indeed some interesting history, especially the work-arounds the get the job done with a successful deployment. Having spent over a decade in gov't service, I couldn't agree more about the 'KISS' approach. Unfortunately, the two seem to be at constant odds.

I share your amazement about the copper sheath-into-sphere process. Was a time this type of knowledge and skill was commonplace in most every shop of any size. Try to find it today, anywhere. There are still skilled folks out there, machinists and engineers, who continue to perform the impossible.

Thanks for sharing. And BTW, the reason you couldn't post the final photo is the limit of 3 attachments per post. You worked it out just fine. ;)

N0WVA:
Walt,

I enjoy reading about your pioneering work that we take for granted today. Must have been exciting times back then.

W2XR:
Hi Walt,

Perhaps you may recall a similar series of conversations a few years back, here on the board, pertaining to Echo I. I was fascinated as you recounted your involvement with the program, and your sharing of some of the technology that was involved with Echo.

As a small boy of 6 years old, I can vividly recall my Dad taking me (and several of my young friends) out to the night sky, hoping to catch a glimpse as the highly reflective Echo passed overhead. For a time, that was the big thing in my neighborhood and around the country, at least among the more technically inclined; to watch as Echo made its rapid pass across the night sky.

In 1960, this was pretty heady stuff. The space age was only 3 years old at that point, with the October, 1957 launch of Sputnik. Most of this bordered on the realm of science fiction, at least to those (like my Dad) who may have read about the possibilities of satellites and satellite communications as espoused by the great writer Arthur C. Clarke in the late 1940s. Had I been a radio amateur in 1957, I would have been utterly astounded and amazed, as I am sure many hams of the era were, as I listened to Sputnik transmitting in the 20 Mhz and VHF portions of the radio spectrum.

A quick glimpse of QST magazine of that era reveals the intense interest and coverage of Sputnik within the radio amateur community.

I would never imagine, as a young boy in 1960, and being well aware of Echo at that time, that I would one day be in communication with a former RCA engineer associated with the Echo program. May I state to you that I am honored to do so?

Of possible interest, the company I worked for in the 1980s was a fairly major supplier to RCA Astro of S-level (space-qualified) flight electronics hardware for the TIROS-N and DMSP satellite programs. I found that work fascinating.

73,

Bruce

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