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Friday, February 1, 2008

It Was Fifty Years Ago Today. . .

On February 1st, 1958 at 03:48 UTC, Explorer I, the United States' first Earth satellite, was launched from Cape Canaveral, Florida on a Juno I rocket. (The launch occurred at 22:48 local time on January 31st at the launch site, so the anniversary is often commemorated on that date; since satellite ephemerides are recorded in Universal Time, I'll use that convention.)

Here are four videos showing contemporary film of the development of the satellite and its launch, and here is another from the Army's The Big Picture (remember seeing these on tee-vee in the Fifties?). Note that back then they counted down to “X” instead of “T”—I suppose there were, indeed, a lot more unknowns in a rocket launch of that epoch. Also, zero was the time when the firing signal was given, which initiated tank pressurisation and the ignition sequence, not the time of liftoff, which was about 16 seconds later. Of course, Redstone-class rockets simply sat on a launch table; there were no hold-downs, so there wasn't the concept of “launch commit” as on fancier boosters.

In all of these videos, the launch vehicle is referred to as a Jupiter-C. This is how I recall it being described at the time, but this is not strictly correct: the rocket was renamed Juno I, perhaps to obscure its derivation from the Jupiter-C, a testbed for nosecone technology for the Jupiter medium-range ballistic missile. Although the first stages of the Jupiter-C and Juno I (which were identical—the launchers differed only in their solid fuel upper stages) were derived from and bore a strong resemblance to the Redstone, there were significant differences, The propellant tanks were stretched, and the Jupiter-C and Juno used a higher energy fuel: a mix of unsymmetrical dimethylhydrazine and diethylenetriamine instead of the ethanol/water mixture used in the Redstone.

Explorer I remained in orbit until March 31st, 1970, by which time four humans had walked on the Moon.

Posted at February 1, 2008 00:11