Telstar1’s 50th Anniversary

I noticed today an article about the first active communication satellite, Telstar1, which is one of those milestones that enabled the wired world of today. I was a space nut at that time and fully intended to pursue astronautics as a career (until I learned more of the realities of that type of work). I was vaguely aware of Telstar (I was in junior high) but actually not that excited by it. I think few at the time realized the import of active communication satellites; and actually I believe that really sunk into most of the public at the beginning of the first Iraq war, that is, the ability to see events in real-time so distant that only satellite relay could provide the image. It was an ah-ha moment for most of the public even though various aspects of satellite communication had been apparent for decades to “insiders” or implicitly to most of the public.

I really didn’t think much more about communications satellites except for two other interactions. When I had a programming job in the administration of MIT, people from the patent office came to ask me some questions. The first-ever software patent had been issued (through a subterfuge since there was no law for software patents) on a sort algorithm. IIRC, MIT had developed the first digital error correcting codes as part of early (possibly not Telstar) communication satellites (EEC is a vital aspect of communications today) and the patent people saw this opening, created by the sort patent precedent, to attempt to patent ECC, which would have been very valuable (MIT held the patent, though disputed, on core memories and that had produced a large revenue to subsidize both education and research). The challenge to sneak through the patent by subterfuge was to define the “invention”, not as software but as a physical machine and that’s what the patent attorneys wanted my help. Now actually I’d never heard of ECC (parity checking was all I did know about error handling in communications) and MIT’s invention was something similar to CRC (I forget the details) which was very mysterious (binary polynomials?) to me. So I was no help at all and never heard if the attorneys succeeded after getting better advice.

Later in a IBM course on networking I was exposed to the idea why the old communication protocols, particularly bisync, were bad when used on satellites. IBM had just invented SDLC largely to address this. Of course from basic physics courses I knew the speed of light, but I’d never thought about it as applied to communication satellites and translated 186,000 miles/second into the propagation delay for geosynchronous satellites (around a quarter second one-way, so half a second for the up-and-back relay). If you send a data block and then have to wait for the ACK before you can send another, whatever your link bandwidth is, actual thruput is severely reduced. So SDLC introduced the idea of both negative acknowledge only (until a frame count was reached) and also not requiring any acknowledgement before sending the next frame (again, up to a limit, one of the main differences between SDLC and HDLC, which fortunately is what we use today). Even with transmission lines, say as with oceanic cable, the propagation delay is an issue and with today’s huge bandwidth on fiber any of the old protocols would crawl.

So satellite communication issues forced engineers to address many issues in how to structure communications that we might not have faced until later had we just been using wires over relatively short distances with relatively low bandwidths. So to a significant degree the modern Internet is powered by those ideas that arose in the 60s, not to mention that globalization of the Internet was also enabled by satellite communications.

But as a really personal experience another experiment in communication satellites, that predated Telstar1 (12Aug1960), Echo 1, was what excited me. Why? Because I actually saw it! Echo 1 was a large mylar balloon coated with metal, thus making it an excellent reflector of radio waves, but also visible light. So one night (and I have no recollection of how I found out about this), in Billings, Montana, we stood outside at a particular time looking in a particular part of the sky as advised by ??? (TV news?). It took a while to spot it and it moved so slowly across the sky it almost seemed like an illusion. However, by trying to mentally record its position relative to some stars, then look again a few minutes later, the relative motion was quite visible. While the whole experience was a little unreal nonetheless it left me with the excitement that something made by man was now circling over my head, but unlike the few earlier satellites this one I could see and that made it real.

Speaking this triggered a memory recall that was also interesting to me. One night I did an experiment with my old film Nikon, setting it as securely as possible outside pointed at the sky (I had no tripod so had to improvise). Nikons had a “bulb” setting (IIRC, that name) that allowed for arbitrarily long exposures. I had planned some amount of time (say an hour, I forget) but I actually fell asleep waiting on this. Fortunately I awoke before it was light and actually got a good picture (we were far enough out of town the picture wasn’t [badly] washed out due to city glow). When I had the film developed there was exactly what I expected, circular paths of the stars, centered approximately on the north star where I’d aimed the camera. Now, big deal. People have known the path of stars in the night sky for millenia and I certainly knew it as well. BUT, to ACTUALLY capture that motion and be able to SEE it was still very exciting. I know I’d tried to watch stars move before but it’s fairly hard to concentrate your gaze to actually see it. But there is just something exciting about seeing something that you abstractly knew was true. As I’d mentioned in a previous post, now my right brain “knew” what my left brain had believed but without “proof”.

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About dmill96

old fat (but now getting trim and fit) guy, who used to create software in Silicon Valley (almost before it was called that), who used to go backpacking and bicycling and cross-country skiing and now geodashes, drives AWD in Wyoming, takes pictures, and writes long blog posts and does xizquvjyk.
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