Explorer 3
Encyclopedia
Explorer 3 was an artificial satellite
of the Earth
, nearly identical to the first United States
artificial satellite Explorer 1 in its design and mission. It was the second successful launch in the Explorer program
.
, Florida
at 17:31:00 UTC on March 26, 1958, by the Jupiter-C
vehicle.
The Jupiter-C had 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
.
Following the launch of the Soviet Sputnik 1
on October 4, 1957, ABMA was directed to proceed with the launching of a satellite using the Jupiter-C, which had already been flight-tested in nose-cone re-entry tests for the Jupiter IRBM (intermediate-range ballistic missile
). Working closely together, ABMA and JPL completed the job of modifying the Jupiter-C and building the Explorer I in 84 days.
(IGY) by the U.S. Army (Ordinance) into an eccentric
orbit
. The objective of this spacecraft was a continuation of experiments started with Explorer 1. The payload consisted of a cosmic ray
counter (a Geiger-Müller tube
), and a micrometeorite
detector (a wire grid array and acoustic detector). The Explorer 3 spacecraft was spin-stabilized
and had an on-board tape recorder
to provide a complete radiation
history for each orbit. It was discovered soon after launch that the satellite was in a tumbling motion with a period of about 7 seconds. Explorer 3 decay
ed from orbit on June 27, 1958, after 93 days of operation.
by the Explorer satellites was considered to be one of the outstanding discoveries of the IGY.
Explorer 3 was placed in an orbit with a perigee of 186 kilometers and an apogee of 2799 kilometers having a period of 115.7 minutes. Its total weight was 14.1 kilograms, of which 8.4 kg was 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 and a ring of micrometeorite erosion gauges. The Explorer 3 spacecraft was spin-stabilized
and had an on-board tape recorder
to provide a complete radiation
history for each orbit. Data from these instruments was transmitted to the ground by a 60 milliwatt transmitter operating on 108.03 MHz
and a 10 milliwatt transmitter operating on 108.00 MHz.
Transmitting antennas
consisted of two fiberglass
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 3 instrumentation was designed and built with simplicity and high reliability in mind. It was completely successful.
Explorer 3 decayed
from orbit on June 27, 1958, after 93 days of operation.
A replica of the spacecraft is currently located in the Smithsonian Institution
's National Air and Space Museum
, Milestones of Flight Gallery.
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, nearly identical to the first United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
artificial satellite Explorer 1 in its design and mission. It was the second successful launch in the Explorer program
Explorer program
The Explorer program is a United States space exploration program that provides flight opportunities for physics, heliophysics, and astrophysics investigations from space. Over 90 space missions have been launched from 1958 to 2011, and it is still active...
.
Mission
The satellite was launched from Cape Canaveral Air Force StationCape Canaveral Air Force Station
Cape Canaveral Air Force Station is an installation of the United States Air Force Space Command's 45th Space Wing, headquartered at nearby Patrick Air Force Base. Located on Cape Canaveral in the state of Florida, CCAFS is the primary launch head of America's Eastern Range with four launch pads...
, Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
at 17:31:00 UTC on March 26, 1958, by the Jupiter-C
Jupiter-C
The Jupiter-C was an American sounding rocket used for three sub-orbital spaceflights in 1956 and 1957 to test re-entry nosecones that were later to be deployed on the more advanced PGM-19 Jupiter mobile missile....
vehicle.
The Jupiter-C had its origins in the United States Army's Project Orbiter
Project Orbiter
Project Orbiter was a proposed United States spacecraft, an early competitor to Project Vanguard. It was jointly run by the United States Army and United States Navy. It was ultimately rejected by the Ad Hoc Committee on Special Capabilities, which selected Project Vanguard instead...
in 1954. The project was canceled in 1955, however, when the decision was made to proceed with Project Vanguard
Project Vanguard
Project Vanguard was a program managed by the United States Naval Research Laboratory , which intended to launch the first artificial satellite into Earth orbit using a Vanguard rocket as the launch vehicle from Cape Canaveral Missile Annex, Florida....
.
Following the launch of the Soviet Sputnik 1
Sputnik 1
Sputnik 1 ) was the first artificial satellite to be put into Earth's orbit. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957. The unanticipated announcement of Sputnik 1s success precipitated the Sputnik crisis in the United States and ignited the Space...
on October 4, 1957, ABMA was directed to proceed with the launching of a satellite using the Jupiter-C, which had already been flight-tested in nose-cone re-entry tests for the Jupiter IRBM (intermediate-range ballistic missile
Intermediate-range ballistic missile
An intermediate-range ballistic missile is a ballistic missile with a range of 3,000–5,500 km , between a medium-range ballistic missile and an intercontinental ballistic missile...
). Working closely together, ABMA and JPL completed the job of modifying the Jupiter-C and building the Explorer I in 84 days.
Spacecraft design
Explorer 3 was launched in conjunction with the International Geophysical YearInternational Geophysical Year
The International Geophysical Year was an international scientific project that lasted from July 1, 1957, to December 31, 1958. It marked the end of a long period during the Cold War when scientific interchange between East and West was seriously interrupted...
(IGY) by the U.S. Army (Ordinance) into an eccentric
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
. The objective of this spacecraft was a continuation of experiments started with Explorer 1. The payload consisted of a cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
counter (a Geiger-Müller tube
Geiger-Müller tube
A Geiger–Müller tube is the sensing element of a Geiger counter instrument that can detect a single particle of ionizing radiation, and typically produce an audible click for each. It was named for Hans Geiger who invented the device in 1908, and Walther Müller who collaborated with Geiger in...
), and a micrometeorite
Micrometeoroid
A micrometeoroid is a tiny meteoroid; a small particle of rock in space, usually weighing less than a gram. A micrometeor or micrometeorite is such a particle that enters the Earth's atmosphere or falls to Earth.-Scientific interest:...
detector (a wire grid array and acoustic detector). The Explorer 3 spacecraft was spin-stabilized
Spin-stabilized satellite
A spin-stabilized satellite is a satellite which has the motion of one axis held fixed by spinning the satellite around that axis, using the gyroscopic effect.The attitude of a satellite or any rigid body is its orientation in space...
and had an on-board tape recorder
Tape recorder
An audio tape recorder, tape deck, reel-to-reel tape deck, cassette deck or tape machine is an audio storage device that records and plays back sounds, including articulated voices, usually using magnetic tape, either wound on a reel or in a cassette, for storage...
to provide a complete radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
history for each orbit. It was discovered soon after launch that the satellite was in a tumbling motion with a period of about 7 seconds. Explorer 3 decay
Orbital decay
Orbital decay is the process of prolonged reduction in the altitude of a satellite's orbit.This can be due to drag produced by an atmosphere due to frequent collisions between the satellite and surrounding air molecules. The drag experienced by the object is larger in the case of increased solar...
ed from orbit on June 27, 1958, after 93 days of operation.
Mission results
The discovery of the Van Allen radiation beltVan Allen radiation belt
The Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is named after its discoverer, James...
by the Explorer satellites was considered to be one of the outstanding discoveries of the IGY.
Explorer 3 was placed in an orbit with a perigee of 186 kilometers and an apogee of 2799 kilometers having a period of 115.7 minutes. Its total weight was 14.1 kilograms, of which 8.4 kg was instrumentation. The instrument section at the front end of the satellite and the empty scaled-down fourth-stage rocket casing
MGM-29 Sergeant
The MGM-29 Sergeant was an American short-range, solid fuel, surface-to-surface missile developed at the Jet Propulsion Laboratory. Activated by the US Army in 1962 to replace the MGM-5 Corporal it was deployed overseas by 1963, carrying the W52 nuclear warhead or alternatively one of high explosives...
orbited as a single unit, spinning around its long axis at 750 revolutions per minute.
Instrumentation consisted of a cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
detection package and a ring of micrometeorite erosion gauges. The Explorer 3 spacecraft was spin-stabilized
Spin-stabilized satellite
A spin-stabilized satellite is a satellite which has the motion of one axis held fixed by spinning the satellite around that axis, using the gyroscopic effect.The attitude of a satellite or any rigid body is its orientation in space...
and had an on-board tape recorder
Tape recorder
An audio tape recorder, tape deck, reel-to-reel tape deck, cassette deck or tape machine is an audio storage device that records and plays back sounds, including articulated voices, usually using magnetic tape, either wound on a reel or in a cassette, for storage...
to provide a complete radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
history for each orbit. Data from these instruments was transmitted to the ground by a 60 milliwatt transmitter operating on 108.03 MHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
and a 10 milliwatt transmitter operating on 108.00 MHz.
Transmitting antennas
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
consisted of two fiberglass
Fiberglass
Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...
slot antennas in the body of the satellite itself and four flexible whips forming a turnstile antenna
Turnstile antenna
A turnstile antenna is a set of two dipole antennas aligned at right angles to each other and fed 90 degrees out-of-phase. The name reflects that the antenna looks like a turnstile when mounted horizontally. When mounted horizontally the antenna is nearly omnidirectional on the horizontal plane...
. 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
Trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...
, orbit, and inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
.
Electrical power was provided by nickel-cadmium chemical batteries
Nickel-cadmium battery
The nickel–cadmium battery ' is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes....
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 3 instrumentation was designed and built with simplicity and high reliability in mind. It was completely successful.
Explorer 3 decayed
Orbital decay
Orbital decay is the process of prolonged reduction in the altitude of a satellite's orbit.This can be due to drag produced by an atmosphere due to frequent collisions between the satellite and surrounding air molecules. The drag experienced by the object is larger in the case of increased solar...
from orbit on June 27, 1958, after 93 days of operation.
A replica of the spacecraft is currently located in the Smithsonian Institution
Smithsonian Institution
The Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...
's National Air and Space Museum
National Air and Space Museum
The National Air and Space Museum of the Smithsonian Institution holds the largest collection of historic aircraft and spacecraft in the world. It was established in 1976. Located in Washington, D.C., United States, it is a center for research into the history and science of aviation and...
, Milestones of Flight Gallery.
External links
- Data Sheet, Department of Astronautics, National Air and Space MuseumNational Air and Space MuseumThe National Air and Space Museum of the Smithsonian Institution holds the largest collection of historic aircraft and spacecraft in the world. It was established in 1976. Located in Washington, D.C., United States, it is a center for research into the history and science of aviation and...
, Smithsonian InstitutionSmithsonian InstitutionThe Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...
.