Explorer 1

Explorer 1 was the first satellite successfully launched by the United States. It was launched on February 1, 1958, as part of the nation's participation in the International Geophysical Year and in direct response to the launch of Sputnik 1 by the Soviet Union. The satellite's primary scientific achievement was the discovery of the Van Allen radiation belt, a zone of charged particles trapped by Earth's magnetic field. This historic mission was developed and built by the Jet Propulsion Laboratory under the direction of Dr. William H. Pickering and carried a cosmic ray detector designed by Dr. James Van Allen of the University of Iowa.

Background and development

The project was initiated under immense political and scientific pressure following the Soviet Union's successful launches of Sputnik 1 and Sputnik 2 in late 1957. The United States Department of Defense authorized the United States Army Ballistic Missile Agency, led by Dr. Wernher von Braun, to attempt a satellite launch using a modified Redstone missile. The satellite design and construction were entrusted to the Jet Propulsion Laboratory, then operated by the California Institute of Technology. The scientific payload, a cosmic ray experiment proposed by Dr. James Van Allen, was selected to make fundamental observations of the space environment. This rapid development effort, known as Project Orbiter, competed with the United States Navy's Project Vanguard, which had suffered a very public launch failure in December 1957.

Mission and launch

Explorer 1 was launched from Cape Canaveral Launch Complex 26 atop a Juno I four-stage rocket, a derivative of the Jupiter-C sounding rocket. The launch occurred at 03:48 UTC on February 1, 1958, placing the satellite into an elliptical Medium Earth orbit. The Juno I launch vehicle was developed by the team at the Army Ballistic Missile Agency in Huntsville, Alabama. Initial telemetry confirmed the satellite was alive and transmitting data, with signals received by ground stations including the Minitrack network. The successful orbit was a major victory for the United States in the early Space Race, coming just four months after the Sputnik 1 launch.

Design and instrumentation

The satellite was cylindrical, approximately 2 meters long and 0.15 meters in diameter, and weighed 13.97 kilograms. Its primary structure was made of a strong but lightweight stainless steel alloy. The payload section was designed to separate from the burned-out fourth-stage rocket motor in orbit. The sole scientific instrument was a cosmic ray detection package designed by Dr. James Van Allen's team at the University of Iowa. This instrument consisted of a Geiger-Müller tube and associated electronics to measure the flux of energetic particles. Other components included two transmitters operating at 108.00 and 108.03 MHz, powered by mercury batteries, and external sensors to measure micrometeorite impacts and satellite skin temperature.

Scientific results and legacy

The data returned by the cosmic ray detector led to the monumental discovery of the Van Allen radiation belt. Scientists noted that the instrument counts dropped to zero at certain orbital altitudes, which Dr. James Van Allen correctly interpreted as the sensor being saturated by an intense, previously unknown band of radiation. This discovery was announced to the public and the scientific community, fundamentally altering the understanding of Earth's magnetosphere. The mission proved the viability of using relatively small, instrumented satellites for major scientific discovery. Explorer 1's success cemented the roles of the Jet Propulsion Laboratory and the Army Ballistic Missile Agency in the nascent NASA, which was formed later in 1958.

Post-mission

The satellite's transmitters ceased operation on May 23, 1958, after 111 days, when its batteries were depleted. Explorer 1 remained silently in orbit for over twelve years. Its orbit gradually decayed due to atmospheric drag, and it re-entered Earth's atmosphere over the Pacific Ocean on March 31, 1970. A full-scale replica of the satellite is on permanent display at the National Air and Space Museum in Washington, D.C.. The success of the mission directly led to the long-running and highly productive Explorer program, which has launched over 90 missions to date. The original flight spare, Explorer 3, which confirmed the radiation belt findings, is preserved at the Smithsonian Institution.

Category:Explorer program Category:1958 in spaceflight Category:Artificial satellites orbiting Earth Category:International Geophysical Year satellites