Explorer I

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. Explorer 1 - Americas first satellite (NASA illustration) This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... The Army Ballistic Missile Agency (ABMA) is the part of the US Army which, in the 1950s, designed the Jupiter-C IRBM and Jupiter IRBM. The Saturn I was also conceived by the ABMA. At this time the ABMA was headed by Doctor Wernher von Braun. ... The NASA Jet Propulsion Laboratory (JPL), in La Cañada Flintridge, near Los Angeles, California, USA, builds and operates unmanned spacecraft for the National Aeronautics and Space Administration (NASA). ... Earth science (also known as geoscience, the geosciences or the Earth Sciences), is an all-embracing term for the sciences related to the planet Earth. ... Earth (IPA: , often referred to as the Earth, Terra, the World or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ... February 1 is the 32nd day of the year in the Gregorian Calendar. ... 1958 (MCMLVIII) was a common year starting on Wednesday of the Gregorian calendar. ... Coordinated Universal Time (UTC) is a high-precision atomic time standard. ... The Jupiter-C Intermediate Range Ballistic Missile (IRBM) was designed by the Army Ballistic Missile Agency (ABMA) The vehicle consists of a modified Redstone ballistic missile with three solid-propellant upper stages. ... March 31 is the 90th day of the year in the Gregorian Calendar (91st in Leap years), with 275 days remaining. ... 1970 (MCMLXX) was a common year starting on Thursday (the link is to a full 1970 calendar). ... Unsolved problems in physics: What causes anything to have mass? Mass is a property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... The elements of an orbit are the parameters needed to specify that orbit uniquely, given a model of two ideal masses obeying the Newtonian laws of motion and the inverse-square law of gravitational attraction. ... In geometry, the semi-major axis (also semimajor axis) a applies to ellipses and hyperbolas. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... Inclination in general is the angle between a reference plane and another plane or axis of direction. ... MILSTAR:A communication satellite A satellite is any object that orbits another object (which is known as its primary). ... for North America see also: Atlantic Standard Time Zone and Eastern Daylight Time Categories: Time zones ... January 31 is the 31st day of the year in the Gregorian calendar. ... February 1 is the 32nd day of the year in the Gregorian Calendar. ... For alternate meanings of GMT, see GMT (disambiguation). ... 1958 (MCMLVIII) was a common year starting on Wednesday of the Gregorian calendar. ... The International Geophysical Year or IGY was an international scientific effort that lasted from July 1, 1957, to December 31, 1958. ... Cape Canaveral Air Force Station Launch Compex 26 (LC-26) was a launch site at Merritt Island, Florida. ... The Bumper V-2 was the first missile launched at Cape Canaveral on July 24, 1950. ... This article or section does not cite its references or sources. ... The Jupiter-C Intermediate Range Ballistic Missile (IRBM) was designed by the Army Ballistic Missile Agency (ABMA) The vehicle consists of a modified Redstone ballistic missile with three solid-propellant upper stages. ...

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. Motto: Пролетарии всех стран, соединяйтесь! (Transliterated: Proletarii vsekh stran, soedinyaytes!) (Russian: Workers of the world, unite!) Anthem: The Internationale (1922-1944) Hymn of the Soviet Union (1944-1991) Capital (and largest city) Moscow None; Russian de facto Government Federation of Soviet Republics  - Last President Mikhail Gorbachev  - Last Premier Ivan Silayev Establishment October Revolution   - Declared... Sputnik 1 was the first artificial satellite to be launched into orbit, on October 4, 1957. ... October 4 is the 277th day of the year (278th in leap years) in the Gregorian Calendar. ... 1957 (MCMLVII) was a common year starting on Tuesday of the Gregorian calendar. ... Titan II rockets launched 12 U.S. Gemini spacecraft in the 1960s. ... The NASA Jet Propulsion Laboratory (JPL), in La Cañada Flintridge, near Los Angeles, California, USA, builds and operates unmanned spacecraft for the National Aeronautics and Space Administration (NASA). ... The Jupiter-C Intermediate Range Ballistic Missile (IRBM) was designed by the Army Ballistic Missile Agency (ABMA) The vehicle consists of a modified Redstone ballistic missile with three solid-propellant upper stages. ... The Army Ballistic Missile Agency (ABMA) is the part of the US Army which, in the 1950s, designed the Jupiter-C IRBM and Jupiter IRBM. The Saturn I was also conceived by the ABMA. At this time the ABMA was headed by Doctor Wernher von Braun. ... The Jupiter-C Intermediate Range Ballistic Missile (IRBM) was designed by the Army Ballistic Missile Agency (ABMA) The vehicle consists of a modified Redstone ballistic missile with three solid-propellant upper stages. ... Sputnik 2 (Russian: , Satellite 2) was the second spacecraft launched into Earth orbit, on November 3, 1957, and the first to carry a living animal - a dog. ... November 3 is the 307th day of the year (308th in leap years) in the Gregorian Calendar, with 58 days remaining. ...

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). The Jupiter-C Intermediate Range Ballistic Missile (IRBM) was designed by the Army Ballistic Missile Agency (ABMA) The vehicle consists of a modified Redstone ballistic missile with three solid-propellant upper stages. ... Project Orbiter was a proposed spacecraft, an early competitor to Project Vanguard. ... Project Vanguard was the name of the United States program that was to have launched the first artificial satellite of the Earth. ... A nose cone that contained one of the Voyager spacecraft is seen here as it is mounted on top of a Titan III/Centaur launch vehicle. ... Atmospheric reentry is the process by which vehicles that are outside the atmosphere of a planet can enter that atmosphere and reach the planetary surface intact. ... Jupiter IRBM mobile missile The PGM-19 Jupiter was an intermediate-range ballistic missile of the United States Air Force. ... An intermediate-range ballistic missile (IRBM) is a ballistic missile with a range of 3000-3500 km. ...

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. The NASA Jet Propulsion Laboratory (JPL), in La Cañada Flintridge, near Los Angeles, California, USA, builds and operates unmanned spacecraft for the National Aeronautics and Space Administration (NASA). ... The California Institute of Technology (commonly referred to as Caltech)[1] is a private, coeducational university located in Pasadena, California, in the United States. ... Willam H. Pickering, JPL/NASA Photo Sir William Hayward Pickering ONZ KBE (December 24, 1910—March 15, 2004) was a New Zealand-American who headed Pasadena, Californias Jet Propulsion Laboratory (JPL) for 22 years, retiring in 1976. ... James Van Allen at National Air & Space Museum (NASM), 1981, Photo courtesy of NASM. Explorer I model and Pioneer H probe in background James Alfred Van Allen (September 7, 1914 – August 9, 2006) was an American space scientist at the University of Iowa. ... The University of Iowa is a major national research university located on a 1,900-acre campus in Iowa City, Iowa, USA, on the Iowa River in East Central 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. Modern geiger counter. ... Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ... Old Cap or Old Capitol Building, Iowas first state capitol building and a university landmark. ... To help compare different orders of magnitude this page lists lengths between 106 and 107 m (1,000 and 10,000 km). ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... Mission Description Explorer-III was nearly identical to Explorer I in design and mission. ... The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ... Van Allen radiation belts The Van Allen Radiation Belt is a torus of energetic charged particles (plasma) around Earth, trapped by Earths magnetic field. ...

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. Van Allen belts The Van Allen radiation belt is a torus of energetic charged particles around Earth, trapped by Earths magnetic field. ...

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. MGM-29 Sergeant in flight The MGM-29 Sergeant was an American short-range, solid fuel, surface-to-surface missile. ...

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. MegaHertz (MHz) is the name given to one million (106) Hertz, a measure of frequency. ...

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. A yagi antenna Most simply, an antenna is an electronic component designed to send or receive radio waves. ... The composite Rutan VariEze, a home-build light aircraft Glass-reinforced plastic (GRP), is a composite material or fiber-reinforced plastic made of a plastic reinforced by fine fibers made of glass. ...

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. From top to bottom â€” Gumstick, AA, and AAA nickel-cadmium (NiCd) batteries. ...

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. May 23 is the 143rd day of the year in the Gregorian calendar (144th in leap years). ... 1958 (MCMLVIII) was a common year starting on Wednesday of the Gregorian calendar. ... March 31 is the 90th day of the year in the Gregorian Calendar (91st in Leap years), with 275 days remaining. ... 1970 (MCMLXX) was a common year starting on Thursday (the link is to a full 1970 calendar). ... The Explorer program was the United Statess first successful attempt to launch an artificial satellite . ...

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. The Smithsonian Institution Building or Castle on the National Mall serves as the Institutions headquarters. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

Reference

• Data Sheet, Department of Astronautics, National Air and Space Museum, Smithsonian Institution.

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Explorer I