January 31, 1958 –
Explorer-I, officially Satellite 1958 Alpha (and sometimes referred to as Explorer 1), was the first Earth satellite of the United States, having been launched at 10:48 pm EST on this date, as part of the United States program for the International Geophysical Year.
The satellite was launched from LC-26 at Cape Canaveral Air Force Station in Florida, on board a Juno I rocket. Although it carried a number of instruments, Explorer I was relatively small, weighing just 30 lbs (13 kg).
Electrical power was provided by mercury chemical batteries that made up approximately 40 percent of the payload weight. These provided power that operated the high power transmitter for 31 days and the low-power transmitter for 105 days.
(This is on the test.)
The Haus of Dcaligari 