Telstar and Starfish Prime

The idea of transmitting messages through space came to me suddenly as a result of having read in an Italian electrical journal about the work and experiments of Hertz. My chief trouble was that the idea was so elementary, so simple in logic, that it seemed difficult for me to believe no one else had thought of putting it into practice.

— Guglielmo Marconi

The first transatlantic cable was laid in 1858, reducing the communication time from Europe to the United States from ten days to seconds. By 1965 four hundred telephone channels would link the two continents, available for anyone who cares to pay the $12 for the first three minutes rate ($106 in 2016 dollars). At the time 92.5% of American households had a TV, but a live television signal had never been reliably broadcast across the Atlantic. In fact, it would be just four years between the first television broadcast across the Atlantic and the first broadcast from the Moon. Both would require space travel.

This is not to say that occasional broadcast TV reception didn’t occur across the Atlantic when the conditions were just right. On one night in February 1938 engineers at the RCA Research Station on Long Island were able to receive the BBC signal being broadcast from London. The signal was bouncing off the ionosphere, a phenomenon widely observed by ham radio operators. Those researchers recorded a bit of the broadcast onto 16mm film. Oddly enough no one in Britain actually recorded any of their pre-war programming in a format which survives today, making that film the only surviving recording of British pre-war television.

Providing this reception reliably would be much more difficult however. But that doesn’t mean we didn’t try. Project West Ford was a test conducted by scientists at MIT to create an artificial ionosphere which would exist in every weather condition and at every time of day. In three launches 480 million copper needles, each about a half inch long, were launched into earth orbit. The plan did work, but ultimately it was determined that littering space with millions of sharp specks of metal was perhaps not a great long-term plan.

To communicate with conventional ground-based radios (which can’t transmit around the curvature of the earth) would take a tower 400 miles high. There were transatlantic cables used for telegram and telephone service, but in 1965 there were only 400 telephone channels available. A telephone line has only about 4 KHz of bandwidth, nowhere near the 6 MHz required for an NTSC television channel. In fact, there wasn’t enough bandwidth in all of the available telephone lines crossing the Atlantic combined to send a television signal.

In 1961 Purdue University began a fascinating program of broadcasting educational television from a pair of DC-6 aircraft. These broadcasts allowed schools in areas where educational television signals weren’t available to receive programming. The essential formula was to launch a DC-6 and have it fly in a figure-eight over Montpelier, Indiana for eight hours or so broadcasting prerecorded lessons. This broadcast would cover an area 200 miles in diameter, based on a plane altitude of 23,000 feet. Unfortunately it is rather difficult to get a piston powered aircraft to climb to the many hundreds of miles of altitude required for transatlantic broadcasts.

Moon 🌝

When radio waves bump into solid objects, they are reflected. This is the basic principal behind radar. It also presents a communication opportunity. Rather than launching a technologically advanced communications satellite, what if you could just launch a big-ol hunk of something which would act like a signal reflector in space. Even better what if you knew of a 7.34767309 × 1022 kg reflector already orbiting out there?

Trexler’s Notebook
An entry in James Trexler’s notebook describing the Moon relay.

The first plans to use the Moon as a radio reflector began as an attempt to monitor Soviet radar signals from the United States during the heat of the Cold War. It was quickly realized that the same concept could be used to relay communication signals. A link was ultimately created between Washington DC and Hawaii which successfully transmitted messages for almost a decade.

We also launched passive satellites to use as radio reflectors in the form of giant balloons. Two such balloons were successfully launched (after one failure). Both balloons were composed of a mylar sheet, a material which had only been invented in the previous decade. The larger of the two was 135 feet in diameter and weighed about 200 pounds. The balloons were launched on a Thor-Delta rocket to a 1000mi altitude orbit, where they successfully reflected telephone, radio and television signals.

Echo Horn Antenna
The Horn Antenna used to communicate with the Echo balloons. It was later used to detect the cosmic microwave background radiation signal which won Robert Wilson and Amo Penzias the Nobel Prize.

I would be remiss to not mention one other passive communication relay satellite, if only because it was so cool. The PasComSat was built in 1966 as an evolution of the Echo program. The solar wind played havoc with the Echo satellites orbit and eventually shattered their skin. To solve this the PasComSat was a hexagonal grid of aluminum wire which was embedded in a soft plastic which was designed to dissolve in the presence of solar UV radiation. What was left was the hexagonal grid floating in space.

PasComSat
The PasComSat being pressure tested before launch. Three confused men for scale.

Telstar

Relying on radio reflections bouncing off objects in space is a fundamentally limited tactic however. For satellite communication to truly take off, it was necessary to launch a device which could receive and amplify the signals before sending them back to earth.

The first such satellite to be launched was a seventy-one pound sphere covered in solar cells called the Telstar 1. At the ‘equator’ of the sphere was two rings of cavity antennas, small cavities to receive 4 GHz signals from earth, and large cavities to send those signals back down to earth at 6 GHz.

Telstar

The satellite was rotationally symmetric because it didn’t have the necessary thrusters or inertia wheels which would be required to have it hold a constant orientation. Instead it was spin-stabilized, inheriting the 200 rpm or so spin from the final stage of the Thor-Delta rocket which launched it. (Like all other rockets of the era, the Thor-Delta system was a repurposed ballistic missile with a couple smaller rockets tacked on top to give it a second and third stage).

Thor-Delta Launch
Thor-Delta launch of the Telstar 1

While the satellite’s control system used transistors (which had been invented in the same Bell Labs who built the satellite), transistors were not yet a viable way to work with very high frequency signals. Instead the actual amplification of the signal was done with a Traveling Wave Tube, a type of vacuum tube. Thus, the first true communications satellite was fundamentally analog, linking a set of receiving antennas to a vacuum tube amplifier and releasing it through a set of transmitting antennas to create one ‘communication channel’. Anyone who could broadcast a signal at the right corner of space as the satellite passed by would find their signal rebroadcast.

On July 23 1962 the Telstar relayed the first live transatlantic television signal which was aired simultaneously by Eurovision in Europe and all three major networks in the United States. President Kennedy was scheduled to make some statements, but he wasn’t ready when the satellite was acquired. Of course, when you’re not ready the first impulse is to think about baseball. A clip of a Phillies and Cubs game was aired while the President prepared. Ultimately he was able to give his address before the satellite orbited out of view to the east.

The satellite also allowed for time to be synchronized between the United States and Europe to a standard previously impossible. It takes a signal roughly 30ms to travel a transatlantic cable, making time synchronization more accurate than about 2ms challenging. A satellite however provides a third position which is at a location known by both parties. By observing the phase of a signal sent by the satellite, it’s possible to get timing accuracy within one microsecond (0.001 ms). This principle would lead to the development of the GPS technology we use today.

Two of the base stations communicated with the Telstar using 177 ft ‘horn antennas’. Each antenna weighted almost 750,000 lbs and was housed in a 14-story building. To work properly these antennas had to be aimed at the satellite with an accuracy of less than 0.06 degrees. Even then, the orbit of the satellite wasn’t geosynchronous, meaning it would only be over the Atlantic where communication between the stations was possible for twenty minutes every two and a half hour orbit.

Horn Antenna

(You can read more than you ever thought you’d need to know about the radome enclosing the antennas here.)

Decline

The U.S. tests, already carried out successfully, undoubtedly constitute the greatest geophysical experiment ever conducted by man.

— James Van Allen 1959

On July 9th, 1962 an American 1.4 megaton-yield nuclear bomb detonated above the Johnston Atoll, just west of Hawaii. The blast, known as the Starfish Prime test, was an experiment conducted by the American government to better understand what happened if you blew up a giant bomb in the upper atmosphere.

The test was instrumental in redefining our understanding of the electromagnetic pulse (EMP) created by a nuclear blast. That’s a fancy way of saying the scientists had no idea how much damage it would do. Over three hundred streetlights were knocked out in Hawaii 900 miles away. Burglar alarms were set off all over town and the microwave link which connected telephone calls from Kauai to the other islands was damaged.

Honolulu Fallout
The explosion painted the sky red and created a momentary second sun over Honolulu.

The damage wasn’t limited to devices on the ground. The explosion released beta particles which formed radiation belts around the earth (known as the Christofilos effect). The radiation eventually destroyed one-third of the satellites in low Earth orbit at the time, including the Telstar and the UKs first satellite the Ariel 1. The effects on radio transmissions were measured as far away as Lexington, Massachusetts.

Fall

Report

The radiation gradually damaged the solar cells and the transistors in the Telstar. As the radiation damage accumulated the satellite gradually became uncontrollable. By November of 1962 the command channel was ignoring most commands sent to it. Through some Apollo 13 level brainstorming the engineers were able to get it to fail in an ‘on’ state allowing the satellite to continue to relay transmissions for a time. Ultimately it fully failed on February 21st 1963. Satellites of the day were launched with multi-year timers designed to disable the transmitter after a prescribed amount of time to prevent old or failed satellites from consuming precious radio frequencies indefinitely. There was no provision for deorbiting the satellite however, it continues to orbit to this day. As I write this it’s passing directly over Minneapolis, Minnesota, 5261 km above the ground.

For more, take a look at the excellent history of satellite communication produced by NASA in 1995.


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