Explorer 1

Launch data: Designation 00004 / 1958Alpha 1 / 58001A Launch date 01 Feb 1958 - 3:47:56 UT Launch site CC, LC26A Launch vehicle Jupiter C (Juno 1 from the US Army) s/n° RS-29 Mission Scientific: ionosphere study Earth orbit on 1 Feb - 04:49 (.20) Perigee/Apogee 356 x 2548 km Eccentricity  0.140 Inclination 33.24° Period 114,80 min

1e US satellite:

Technicians installing Explorer 1

The Explorer I satellite perched on top of its Juno I launcher

Explorer 1 on top rocket

Description

• Explorer 1 was the first successfully launched U. S. spacecraft. Launched late on 31 January 1958 (10:48 p.m. EST, or 03:48 UTC on 01 February) on an adapted Jupiter-C rocket, Explorer 1 carried instrumentation for the study of cosmic rays, micrometeorites, and for monitoring of the satellite's temperature.
• The Jupiter-C launch vehicle consisted of four propulsive stages. The first stage was an upgraded Redstone liquid-fueled rocket. The second, third, and fourth stage rockets consisted of eleven, three, and one (respectively) Sergeant motors. The rocket was realized by Wernher von Braun's team, a german engineer from Peenemünde. He had been working since 1953 at the Redstone Arsenal (Huntsville, Alabama) to design a balistic missile with the help of the Army Ballistic Missile Agency and the Jet Propulsion Laboratory.
  The satellite itself was the fourth stage of the Jupiter-C rocket. It was cylindrical, 2.03 m long and 0.152 m in diameter. Four whip antennas were mounted symmetrically about the mid-section of the rocket. The spacecraft was spin stabilized.
• The 4.82 kg instrumentation package was mounted inside of the forward section of the rocket body. A single Geiger-Mueller detector was used for the detection of cosmic rays. Micrometeorite detection was accomplished using both a wire grid (arrayed around the aft section of the rocket body) and an acoustic detector (placed in contact with the midsection). Data from the instruments were transmitted continuously, but acquisition was limited to those times when the spacecraft passed over appropriately equipped ground receiving stations. Assembly of data proceeded slowly also due to the fact that the satellite's spin-stabilized attitude transitioned into a minimum kinetic energy state, that of a flat spin about its transverse axis. This was deduced from the modulation of the received signal, which produced periodic fade-outs of the signal.
• Explorer I, made an outstanding scientific discovery. The satellite determined that the earth was surrounded by a series of radiation belts formed by the earth’s magnetic field. They were named after Dr. James Van Allen, who was one of the principal investigators. The Sputniks had also detected higher radiation at different altitudes, but the Russians did not properly analyze the data until after Van Allen announced his discovery.
• Explorer I also determined that the threat from micro-meteors was less than some scientists anticipated and should not pose a threat to most satellites. Explorer I was the just the first in the longest series of American satellites, which included 55 Explorers. The first five Explorers were similar to Explorer I.
• Explorers 3 and 4 were successfully orbited by Juno I launchers while Explorers 2 and 5 failed to achieve orbit. The Explorer series included over 20 major variants launched by an array of Junos, Jupiters, Thors, Scouts and Deltas. Explorer 55 was launched on Nov. 20, 1975, more than 17 years after Explorer I. The Explorer series produced many important discoveries about the magnetosphere, meteorites, and atmospheric physics in addition to the detection of the Van Allen belts.