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Explorer I

2007 Schools Wikipedia Selection. Related subjects: Space transport

                                                       CAPTION: Explorer I

                                        Explorer 1
                               Organization: Army Ballistic Missile Agency
                          Major contractors:     Jet Propulsion Laboratory
                               Mission type:                 Earth Science
                               Satellite of:                         Earth
                                     Launch: February 1, 1958 at 03:48 UTC
                             Launch vehicle:                        Juno I
                                      Decay:                March 31, 1970
                           Mission duration:                      111 days
                                       Mass:                    13.9703 kg
                                   NSSDC ID:                     1958-001A
                                    Webpage:                          NASA
                                                         Orbital elements
                             Semimajor axis:                    7,832.2 km
                               Eccentricity:                       .139849
                                Inclination:                        33.24°
                             Orbital period:                 114.8 minutes
                                     Apogee:                      2,550 km
                                    Perigee:                        358 km
                                     Orbits:                       ~56,000
                                                              Instruments
                   Geiger-Mueller detector :      Detection of cosmic rays
                           Wire grid array :      Micrometeorite detection
                         Acoustic detector :      Micrometeorite detection

   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 10:48pm EST on January 31 (03:48 on 1 February
   in GMT), 1958, 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 onboard a Juno I rocket.

Mission

   Following the launch of the Soviet satellite Sputnik I on October 4,
   1957, there was a frenzied effort by the United States to launch a
   satellite of its own, beginning the Space Race. Explorer-I was designed
   and built by the Jet Propulsion Laboratory (JPL), while the Jupiter-C
   rocket was modified by the Army Ballistic Missile Agency (ABMA) to
   accommodate a satellite payload, the resulting rocket becoming known as
   the Juno I. Working closely together, ABMA and JPL completed the job of
   modifying the Jupiter-C and building the Explorer-I in 84 days. Before
   work was completed, however, the Soviet Union launched a second
   satellite, Sputnik 2, on November 3, 1957.

Launch vehicle

   Explorer-I's launch vehicle, the Juno I, has its origins in the United
   States Army's Project Orbiter in 1954. The project was canceled in
   1955, however, when the decision was made to proceed with Project
   Vanguard. The Jupiter-C used for the launch had already been
   flight-tested in nose cone reentry tests for the Jupiter IRBM).

Spacecraft design

   Explorer-I was designed and built by the Jet Propulsion Laboratory of
   the California Institute of Technology under the direction of Dr.
   William H. Pickering. The satellite instrumentation of Explorer-I was
   designed and built by Dr. James Van Allen of the University of Iowa.

   Explorer-I was the second satellite to carry a mission payload (Sputnik
   II was the first). Most notably, it was equipped with a geiger counter
   for the purposes of detecting cosmic rays. Sometimes the
   instrumentation would report the expected cosmic-ray count (~30 counts
   per second) but sometimes it would show a peculiar 0 counts per second.
   The Iowa group (under Van Allen) noted that all of the 0 counts per
   second reports were from an altitude of 2000+ km over South America,
   while passes at 500 km would show the expected level of cosmic rays.
   After Explorer III, it was decided that the original geiger counter had
   been overwhelmed by strong radiation coming from a belt of charged
   particles trapped in space by the Earth's magnetic field, now known as
   a Van Allen radiation belt.

Mission results

   The discovery of the Van Allen Belts by the Explorer satellites was
   considered to be one of the outstanding discoveries of the
   International Geophysical Year.

   Explorer-I was placed in an orbit with a perigee of 360 kilometers (224
   miles) and an apogee of 2520 kilometers (1575 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. The instrument section at
   the front end of the satellite and the empty scaled-down fourth-stage
   rocket casing orbited as a single unit, spinning around its long axis
   at 750 revolutions per minute.

   Instrumentation consisted of a cosmic-ray detection package, an
   internal temperature sensor, three external temperature sensors, a
   nose-cone temperature sensor, a micrometeorite impact microphone, and a
   ring of micrometeorite erosion gauges. Data from these instruments were
   transmitted to the ground by a 60-milliwatt transmitter operating on
   108.03 megahertz and a 10 milliwatt transmitter operating on 108.00
   MHz.

   Transmitting antennas consisted of two fibreglass slot antennas in the
   body of the satellite itself and four flexible whips forming a
   turnstile antenna. The rotation of the satellite about its long axis
   kept the flexible whips extended.

   The external skin of the instrument section was painted in alternate
   strips of white and dark green to provide passive temperature control
   of the satellite. The proportions of the light and dark strips were
   determined by studies of shadow-sunlight intervals based on firing
   time, trajectory, orbit, and inclination.

   Electrical power was provided by nickel-cadmium 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.

   Because of the limited space available and the requirements for low
   weight, the Explorer-I instrumentation was designed and built with
   simplicity and high reliability in mind. It was completely successful.

   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. Explorer I was
   the first of the long-running Explorer program, which as of November
   2004 has launched 83 Explorer probes.

   The identically-constructed flight backup of Explorer I is currently
   located in the Smithsonian Institution's National Air and Space Museum,
   Milestones of Flight Gallery.
   Retrieved from " http://en.wikipedia.org/wiki/Explorer_I"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
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   Documentation License. See also our Disclaimer.
