Explorer 1

Explorer 1 was the first artificial Earth satellite of the United States (1958) and the world's third after the two satellite Sputnik 1 and 2 of the Soviet Union.

Geophysics and missile technology

Explorer 1 was the first satellite of the Explorer program, which was the first and most comprehensive program of satellites and space probes of the United States. Most of them ( about 80) have been extremely successful and were used for the study of the ionosphere, the geography ( remote sensing) and astronomy.

The scientific reason for Explorer 1 was the Polar Ionospheric respectively and the (first ) International Geophysical Year 1957 / 58th The launch was announced by the U.S. President in July 1955 ( four days this was followed by a similar announcement by the Soviet Union, then the United States before the first satellite launched ).

But even military-technical reasons played a role ( Cold War, ICBMs ).

Explorer 1 as a replacement for Vanguard

The launch of Explorer 1 was made on February 1, 1958 at 3:48 UTC (31 January at 22:48 clock time) from launch pad 26 of the Cape Canaveral Air Force Station. The launch window was four hours between 3:30 UTC and 7:30 UTC, opened.

Originally, the satellite should be two days previously brought into space - the launch had to be postponed twice due to bad weather conditions ( Jetstream ) but. Even on launch day was not sure if the wind speeds would subside.

They started " Explorer 1" with the four-stage launch vehicle of the type Juno 1, a slight modification of the medium-range missile Jupiter C. The launch pad was in the vicinity of Cape Canaveral on the long peninsula on the Atlantic coast of Florida.

Explorer 1 consisted of a 205 cm long cylinder with a diameter of 16 cm and reached an elliptical orbit between about 360 km and 2530 km altitude. With a total mass of 13.9 kg accounted for 8.3 kg of payload. Explorer was equipped with telemetry antennas and geophysical instruments - among others those magnetometers with which the Van Allen radiation belt was detected around the Earth.

For political reasons, was originally built by a U.S. Navy probe - the small Vanguard 1 - be the first artificial satellite of the United States. ( Been the three-stage launch vehicle was not tested yet) After a false start on December 6, 1957, Wernher von Braun at his urging granted permission to launch a satellite into orbit.

Explorer 1 was significantly smaller and lighter than the Soviet Sputnik, but provided numerous measurement data via the ionosphere, the ( later named the Van Allen belt ) to a radiation belts were around close around the Earth. With later Explorer launches the radiation belt was - and a second lying outside - further explored and proved to be dangerous for human spaceflight, the preliminary plans were running for some time.

Planning and construction of the satellite was carried out by the Jet Propulsion Laboratory (JPL ) of the California Institute of Technology (Caltech under Dr. William H. Pickering ). The measurement instruments developed by Dr. James Van Allen, the Jupiter rocket was a modification of the medium-range missile type Redstone. She came out of the workshops of the ABMA (Army Ballistic Missile Agency) under the direction of Wernher von Braun, the former German rocket pioneer in Peenemünde. The Jupiter -C was a direct " descendant " of the German A4 (V2) and was developed in 1955-56.

Slow decrease of the orbit

Over time, the web dropped slowly because of the braking action of the uppermost layers of air ( exosphere ) - average of 30 km per year. It was - as well as from the first Soviet satellite - already 1958/59 model of the high atmosphere to be improved. The air density assumed to date had been scheduled by several times too low. After 12 years in space explorer burned up on March 31, 1970 in about 100 km altitude.