Explorer 3
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Photograph of the nearly identical Explorer 1
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| Mission type | Earth science |
|---|---|
| Operator | Army Ballistic Missile Agency (ABMA) |
| Harvard designation | 1958 Gamma 1 |
| SATCAT № | 6 |
| Mission duration | 93 days |
| Spacecraft properties | |
| Manufacturer | Jet Propulsion Laboratory |
| Launch mass | 14.1 kilograms (31 lb) |
| Start of mission | |
| Launch date | March 26, 1958, 17:31 UTC |
| Rocket | Juno I |
| Launch site | Cape Canaveral LC-5 |
| End of mission | |
| Decay date | June 27, 1958 |
| Orbital parameters | |
| Reference system | Geocentric |
| Regime | Medium Earth |
| Semi-major axis | 7,870.7 kilometers (4,890.6 mi) |
| Eccentricity | 0.165894 |
| Perigee | 186 kilometers (116 mi) |
| Apogee | 2,799 kilometers (1,739 mi) |
| Inclination | 33.38 degrees |
| Period | 115.7 minutes |
Explorer 3 (international designation 1958 Gamma) 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. It had the same 33.3 degrees design-orbit inclination as Explorer 1, leading to speculation of Masonic influence.
Mission
The satellite was launched from Cape Canaveral Air Force Station, Florida at 17:31:00 UTC on March 26, 1958, by the Juno I vehicle. The Juno I had its origins in the United States Army's Project Orbiter in 1954. The project was canceled in 1955 when the decision was made to proceed with Project Vanguard.
Following the launch of the Soviet Sputnik 1 on October 4, 1957, Army Ballistic Missile Agency (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 to the Juno I and building the Explorer I in 84 days.
Explorer 3 was launched in conjunction with the International Geophysical Year (IGY) by the U.S. Army (Ordnance) into a highly-eccentric orbit, similar to its sister satellites. 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).
Spacecraft design
The Explorer 3 spacecraft was spin-stabilized using a turntable underneath the final stage. It was discovered soon after launch that the satellite was in a tumbling motion with a period of about 7 seconds. This was caused by the same design flaw as the other similar satellites, spinning about a minor axis of inertia. 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 after final stage burnout
Its total weight was 14.1 kilograms, of which 8.4 kg was instrumentation. 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. 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 was intended to keep 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.
Unlike Explorer 1, the Explorer 3 spacecraft had an on-board tape recorder to provide a complete radiation history for each orbit.
Mission results
The discovery of the Van Allen radiation belt is considered to be one of the outstanding discoveries of the IGY in general and the Explorer satellites in particular. The gaps in the data from the first Explorer were filled in by Explorer 3, which had a specially-built tape recorder to save the data for later transmission.
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. Instrumentation consisted of a cosmic ray detection package (a Geiger counter) and a ring of micrometeorite erosion gauges. 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.
One month after the launch of Explorer 3, a high-altitude_nuclear_explosion, code-named "Yucca", took place. On April 28,1958, a 1.7 kt atomic bomb was exploded at 26.2 km altitude. This may have been the first of its kind. If Explorer 3 was overhead at the time, it may have picked up the radiation signal with its Geiger counter, paving the way for the later experiments.
Explorer 3 ended up in an orbit with a perigee of 186 kilometers and an apogee of 2799 kilometers having a period of 115.7 minutes. Because of the manually-operated ignition sequence and the primitive guidance system, the ship was at an unplanned angle to the horizontal at the apogee of the first stage flight. This caused the final perigee to be much lower than planned, much closer to the sensible atmosphere. The extra drag shortened the lifetime of the satellite. It 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.
See also
References
External links
- Data Sheet, Department of Astronautics, National Air and Space Museum, Smithsonian Institution.
