On This Day: Transit 1, the Granddaddy of GPS.

On this date in 1960 the Transit 1B was launched becoming the first successful navigation satellite.  The earlier Transit 1A, launched in September 1959 failed to reach orbit.

The program got its start shortly after the Soviets launched Sputnik 1 in 1957.  Scientists were able to determine its orbit using doppler shift of its radio signals during a single pass.  They theorized that if the orbit of a satellite was known and predictable, they could work backwards from the same information and determine the position a station receiving those signals and they proposed a satellite system to implement this principle.

The Transit 1B was launched on April 13, 1960 on a Thor-AbleStar rocket.  The rocket consisted of a Thor missile first stage and an “Ablestar” second stage.  This class of rocket was able to put up to 330 lbs into Low Earth Orbit.

The system was successfully tested in 1960.

After the first tests, the decision was made to switch from the Thor-Ablestar launcher to the Scout, solid fueled launcher.  This presented a significant challenge as the solid fueled Scout had both a lower payload capacity and subjected the payload to higher vibration during launch.  Smaller and more rugged electronics were successfully designed and the successfully  orbited went into orbit in December 1962.  The first of these new satellites Transit 5A-1 had problems with its power supply.  A second, launched in April 1963 failed to achieve orbit.  A third had various electronics problems including oscillator instability which meant it could not be used for navigation but it did successfully demonstrate gravity gradient stabilization (the ancestor of the “tether” concept).

These early “teething” problems were overcome and the Navy started using the system for navigation in 1964.  Surveyors used the system for making accurate benchmark measurements by averaging multiple Transit readings.

The system was rendered obsolete by the Global Positioning System satellites.  The last Transit satellite was launched in 1988, and remained in service until 1996, through the early days of GPS.

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