For novel ideas about building embedded systems (both hardware and firmware), join the 30,000+ engineers who subscribe to The Embedded Muse, a free biweekly newsletter. The Muse has no hype and no vendor PR. Click here to subscribe.
Glenn's First Ride
Summary: Half a century ago the USA first put a man in orbit.
Fifty years ago this week I was glued to our black and white TV. My parents kept us (well, the two of us who were old enough to be in school) home that day so we could watch the launch of Friendship 7, the US's first manned orbital mission. I remember the TV images as being grainy, and the rocket's exhaust saturating the camera.
At 2:47 EST, February 20, 1962, John Glenn was hurled aloft by an Atlas booster to complete three orbits in about four hours of elapsed time. Over the course of just another year the Mercury program concluded after three additional flights. At the time Earth was a much bigger hunk of rock than today, as none of these missions got much over 150 miles from the planet, basically just skimming above the atmosphere. It wasn't till 1968 that astronauts first saw Earth as a distinct ball floating in the void.
It's hard to convey the amount of national prestige associated with this flight, after Yuri Gagarin's success a year earlier. America was a very different country then. Only 17 years earlier WWII had ended, which was a historical watershed for a number of reasons, not the least being the country's emergence as a superpower. The USSR had quickly gone from ally to adversary. Just months after Friendship 7's mission we kids were taught to hide under desks in some insanely futile defense against Soviet nuclear weapons. Space was seen as a place to compete, to show our system's advantages over the foe's.
It's also difficult to convey the furious pace the US sustained in our spacefaring efforts. Just seven years after Glenn, Armstrong and Aldrin walked on the moon. In those seven years all of the Mercury orbital missions flew, Gemini began and ended, and Apollo succeeded. In those seven years our missions went from a crude canned astronaut to a pair of spacecraft maneuvering independently a quarter million miles away.
A 1961 paper ("Project Mercury Real-Time Computational And Data-Flow System") describes the data processing systems used on Mercury. A pair of IBM 7090 machines at Goddard Space Flight Center, which were IBM's first commercial transistorized computers, took data downlinked from the Atlas. The data was transmitted to GSFC over "two high-speed 1000 bits per second data circuits." Another 7090 at Cape Canaveral (this was before Kennedy was assassinated) fed GSFC's machines. An IBM 709 in Bermuda assisted with tracking calculations. The 709 was a vacuum-tube computer. With 2000 tubes it could do 42,000 integer calculations per second. And that was pretty much it for automatic computations. Today we can't operate a microwave oven without a processor, and even a telephone has billions of transistors.
According to http://science.ksc.nasa.gov/history/mercury/ma-6/docs/ma-6-results.pdf the spacecraft had 90 channels of telemetry data. A "commutator" (I wonder what technology that used) muxed the signals into a voltage-controlled oscillator whose output fed two-watt UHF FM transmitters.
Friendship 7 did not splash down in the Pacific as was usual in later missions. It hit the Atlantic. 21 ships, 12 helicopters and 16 aircraft were deployed to recover the capsule. Glenn was transferred to a base on Grand Turk Island in the Turks and Caicos, and a model of Friendship 7 is today displayed outside of the airport there.
Friendship 7 is at the Air and Space Museum on the Mall in Washington, DC. It's astonishing to see just how small the spacecraft is.
Published February 20, 2012