Telstar
Telstar was the first active communications satellite (launched in 1962), and the first satellite designed to transmit telephone and high-speed data communications.
Launched by NASA aboard a Delta rocket from Cape Canaveral on July 10, 1962, Telstar was the first privately sponsored space launch. A medium-altitude satellite, Telstar was placed in an elliptical orbit (completed once every 2 hours and 37 minutes), revolving at a 45 degree angle above the equator. Because of this, its transmission availability for transatlantic signals was only 20 minutes in each orbit.
Telstar, which had ushered in a new age of the benevolent use of technology, actually became a victim of technology during the Cold War. The day before Telstar was launched, the United States tested a high-altitude nuclear device (called Starfish Prime) which super-energized the Earth's Van Allen Belt where Telstar took orbit. This vast increase in radiation, combined with further increases during subsequent high-altitude blasts, including a Soviet test in October, overwhelmed Telstar's fragile transistors; it went out of service in early December, but was restarted by a workaround in early January of 1963. The additional radiation associated with its return to full sunlight once again caused transistor failure, this time irreparably, and it went out of service on February 21, 1963- but it is still up there.
However I do not know to what you refer - On July 29, 1955, the White House announced that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard. On July 31, the Soviets announced that they intended to launch a satellite by the autumn of 1957.
The first artificial satellite was Sputnik 1, launched by the Soviet Union on 4 October 1957. This triggered the Space Race between the Soviet Union and the United States.
Explorer 1 became the United States' first satellite on January 31, 1958. Explorer-I was placed in an orbit with a perigee of 360 kilometers (224 miles) and an apogee of 2,520 kilometers (1,575 miles) having a period of 114.9 minutes. The total weight was 13.97 kilograms (30.8 lb), of which 8.3 kilograms (18.3 lb) were instrumentation. (In comparison the first Soviet satellite, Sputnik I, weighed 83.6 kg. [184 lbs.]). Explorer I stopped transmission of data on May 23, 1958, when its batteries died, but remained in orbit for more than 12 years. It made a fiery reentry over the Pacific Ocean on March 31, 1970.