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Explorer 1

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This article is about the U.S. satellite. For other uses, seeExplorer One (disambiguation).
For other uses, seeExplorer (disambiguation).

Explorer 1
Explorer 1 in its orbital configuration, with the launch vehicle's fourth stage attached
NamesExplorer I
1958 Alpha 1
Mission typeEarth science
OperatorJPL/Army Ballistic Missile Agency
Harvard designation1958 Alpha 1
COSPAR ID1958-001AEdit this at Wikidata
SATCATno.00004
Mission duration120 days (planned)
111 days (achieved)
Spacecraft properties
SpacecraftExplorer I
Spacecraft typeScience Explorer
BusExplorer 1
ManufacturerJet Propulsion Laboratory
Launch mass13.97 kg (30.8 lb)
Dimensions203 cm (80 in) length
15.2 cm (6.0 in) diameter
Power60watts
Start of mission
Launch date1 February 1958, 03:47:56GMT
RocketJuno I(RS-29)
Launch siteAtlantic Missile Range,LC-26A
ContractorArmy Ballistic Missile Agency
Entered service1 February 1958
End of mission
Last contact23 May 1958
Decay date31 March 1970
Orbital parameters
Reference systemGeocentric orbit[1]
RegimeMedium Earth orbit
Perigee altitude358 km (222 mi)
Apogee altitude2,550 km (1,580 mi)
Inclination33.24°
Period114.80 minutes
Revolutionno.58402
Instruments
Cosmic-Ray Detector
Micrometeorite Detector
Resistance Thermometers
Satellite Drag Atmospheric Density
Explorer program

Explorer 1was the first satellite launched by the United States in 1958 and was part of the U.S. participation in theInternational Geophysical Year(IGY). The mission followed the first two satellites, both launched by the Soviet Union during the previous year,Sputnik 1andSputnik 2.This began aSpace Raceduring the Cold War between the two nations.

Explorer 1 was launched on 1 February 1958 at 03:47:56 GMT (or 31 January 1958 at 22:47:56 Eastern Time) atop the firstJunobooster fromLC-26Aat theCape Canaveral Missile Test Centerof the Atlantic Missile Range (AMR), in Florida. It was the first spacecraft to detect theVan Allen radiation belt,[2]returning data until its batteries were exhausted after nearly four months. It remained in orbit until 1970.

Explorer 1 was given Satellite Catalog Number 00004 and the Harvard designation 1958 Alpha 1,[3]the forerunner to the modernInternational Designator.

Background[edit]

The U.S. Earth satellite program began in 1954 as a joint U.S. Army and U.S. Navy proposal, called Project Orbiter, to put a scientific satellite into orbit during theInternational Geophysical Year.The proposal, using a military Redstone missile, was rejected in 1955 by the Eisenhower administration in favor of the Navy'sProject Vanguard,using a booster advertised as more civilian in nature.[4][5]Following the launch of the Soviet satelliteSputnik 1on 4 October 1957, the initialProject Orbiterprogram was revived as the Explorer program to catch up with the Soviet Union.[6]

Explorer 1 was designed and built by the Jet Propulsion Laboratory (JPL), while aJupiter-Crocket was modified by the Army Ballistic Missile Agency (ABMA) to accommodate a satellite payload; the resulting rocket known as theJuno I.The Jupiter-C design used for the launch had already been flight-tested in nose cone reentry tests for theJupiterintermediate-range ballistic missile (IRBM), and was modified into Juno I. Working closely together, ABMA and JPL completed the job of modifying the Jupiter-C and building Explorer 1 in 84 days. However, before work was completed, the Soviet Union launched a second satellite,Sputnik 2,on 3 November 1957. The U.S. Navy attempted to put the first U.S. satellite into orbit, but failed with the launch of theVanguard TV-3on 6 December 1957.[7]

Spacecraft[edit]

The satellite Explorer 1 is mated to its booster at LC-26.

Explorer 1 was designed and built byCalifornia Institute of Technology's JPL under the direction of Dr.William H. Pickering.It was the second satellite to carry a mission payload (Sputnik 2 was the first).

The total mass of the satellite was 13.97 kg (30.8 lb), of which 8.3 kg (18 lb) were instrumentation. In comparison, the mass of the first Soviet satellite Sputnik 1 was 83.6 kg (184 lb). 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.

Data from the scientific instruments was transmitted to the ground by two antennas. A 60 milliwatt transmitter fed adipole antennaconsisting of two fiberglassslot antennasin the body of the satellite operating on 108.03 MHz, and four flexible whips forming aturnstile antennawere fed by a 10 milliwatt transmitter operating on 108.00 MHz.[8][9]

Because of the limited space available and the requirements for low weight, the payload instrumentation was designed and built with simplicity and high reliability in mind, using germanium and silicon transistors in its electronics.[10]A total of 20 transistors were used in Explorer 1, plus additional ones in the Army's micrometeorite amplifier. Electrical power was provided bymercury chemical batteriesthat made up approximately 40% of the payload weight.

The external skin of the instrument section was sandblasted stainless steel with white stripes. Several other color schemes had been tested, resulting in backup articles, models, and photographs showing different configurations, including alternate white and green striping and blue stripes alternating with copper. The final color scheme was determined by studies of shadow–sunlight intervals based on firing time, trajectory, orbit, and inclination.

Explorer 1 schematic

Science payload[edit]

Universal Newsreelabout the satellite

The Explorer 1 payload consisted of the IowaCosmic RayInstrument without a tape data recorder which was not modified in time to make it onto the spacecraft. The real-time data received on the ground was therefore very sparse and puzzling showing normal counting rates and no counts at all. The later Explorer 3 mission, which included a tape data recorder in the payload, provided the additional data for confirmation of the earlier Explorer 1 data.

The scientific instrumentation of Explorer 1 was designed and built under the direction of Dr.James Van Allenof theUniversity of Iowacontaining:[8]

  • Five temperature sensors (one internal, three external and one on the nose cone);
  • Acoustic detector (crystaltransducerand solid-stateamplifier) to detectmicrometeorite(cosmic dust) impacts. It responded to micrometeorite impacts on the spacecraft skin in such a way that each impact would be a function of mass and velocity. Its effective area was 0.075 m2and the average threshold sensitivity was 2.5×10−3g cm/s;[12][13]
  • Wire grid detector, also to detect micrometeorite impacts. It consisted of 12 parallel connected cards mounted in a fiberglass supporting ring. Each card was wound with two layers of enamelednickel alloywire with a diameter of 17 μm (21 μm with the enamel insulation included) in such way that a total area of 1 × 1 cm (0.39 × 0.39 in) was completely covered. If a micrometeorite of about 10 μm impacted, it would fracture the wire, destroy the electrical connection, and thus record the event.[12][13]

Flight[edit]

Explorer 1 launch control console on display at Huntsville Space museum
Explorer 1 launch control console on display at Huntsville Space and Rocket Center. The red arrow points to the manually turned launch key switch.

After a jet stream-related delay on 28 January 1958, at 03:47:56 GMT on 1 February 1958[14]theJuno Irocket was launched, putting Explorer 1 into orbit with aperigeeof 358 km (222 mi) and anapogeeof 2,550 km (1,580 mi) having a period of 114.80 minutes, and aninclinationof 33.24°.[1][15]Goldstone Tracking Stationcould not report after 90 minutes as planned whether the launch had succeeded because the orbit was larger than expected.[14]At about 06:30 GMT, after confirming that Explorer 1 was indeed in orbit, a news conference was held in the Great Hall at the National Academy of Sciences in Washington, D.C. to announce it to the world.[16]

Hand drawn Explorer 1 mission plot.
Hand drawn Explorer 1 mission plot.

The original expected lifetime of the satellite beforeorbital decaywas three years.[14]Mercury batteriespowered the high-power transmitter for 31 days and the low-power transmitter for 105 days. Explorer 1 stopped transmission of data on 23 May 1958,[17]when its batteries died, but remained in orbit for more than 12 years.[18]It reentered the atmosphere over the Pacific Ocean on 31 March 1970 after more than 58,400 orbits.

Results[edit]

Explorer 1 changed rotation axis after launch. The elongated body of the spacecraft had been designed to spin about its long (least-inertia) axis but refused to do so, and instead startedprecessingdue to energydissipationfrom flexible structural elements. Later it was understood that on general grounds, the body ends up in the spin state that minimizes the kinetic rotational energy for a fixed angular momentum (this being the maximal-inertia axis). This motivated the first further development of theEuleriantheory of rigid body dynamics after nearly 200 years – to address this kind of momentum-preserving energy dissipation.[19][20]

Sometimes the instrumentation reported the expected cosmic ray count (approximately 30 counts per second) but other times it would show a peculiar zero counts per second. The University of Iowa (underJames Van Allen) observed that all of the zero counts per second reports were from an altitude of more than 2,000 km (1,200 mi) over South America, while passes at 500 km (310 mi) would show the expected level of cosmic rays. Later, afterExplorer 3,it was concluded that the original Geiger counter had been overwhelmed ( "saturated" ) by strong radiation coming from a belt of charged particles trapped in space by the Earth's magnetic field. This belt of charged particles is now known as theVan Allen radiation belt.The discovery was considered to be one of the outstanding discoveries of theInternational Geophysical Year.

The acoustic micrometeorite detector detected 145 impacts of cosmic dust in 78,750 seconds. This calculates to an average impact rate of 8.0−3impacts per second per square meter, or 29 impacts per hour per square meter, over the twelve-day period.[21]

Legacy[edit]

Explorer 1 was the first of the long-running Explorers program. Four follow-up satellites of the Explorer series were launched by theJuno Ilaunch vehicle in 1958, of these, Explorer 3 and 4 were successful, while Explorer 2 and 5 failed to reach orbit. The final flight of the Juno I booster, the satelliteBeacon-1,also failed.[22]The Juno I vehicle was replaced by theJuno IIlaunch vehicle in 1959.

A follow-up to the first mission, Explorer-1 [PRIME], was successfully launched aboard aDelta IIlaunch vehicle in late October 2011. The PRIME was built using modern satellite construction techniques. The orbiting satellite was a backup, because the initial Explorer-1 PRIME, launched on 4 March 2011, did not reach orbit due to a launch vehicle failure.[23]

An identically constructed flight backup of Explorer 1 is on display in theSmithsonian Institution'sNational Air and Space Museum,Milestones of Flight Gallery in Washington, D.C.LC-26was deactivated in 1963, and was designated for use as a museum in 1964, theAir Force Space and Missile Museum.[24]Here too, a full-scale Explorer 1 is on display, but this one is a mockup.[25]

Gallery[edit]

See also[edit]

References[edit]

  1. ^ab"Trajectory: Explorer-1 1958-001A".NASA. 14 May 2020.Retrieved12 February2021.Public DomainThis article incorporates text from this source, which is in thepublic domain.
  2. ^Paul Dickson,Sputnik: The Launch of the Space Race,Toronto: MacFarlane Walter & Ross, 2001, p. 190
  3. ^Yost, Charles W. (1963).Registration data for United States Space Launches(PDF).United Nations Office for Outer Space Affairs.Retrieved19 February2009.
  4. ^Matt Bille and Erika Lishock, The First Space Race: Launching the World's First Satellites, Texas A&M University Press, 2004, Chapter 5
  5. ^"Project Vanguard – Why It Failed to Live Up to Its Name".Time.21 October 1957. Archived fromthe originalon 15 May 2008.Retrieved12 February2008.
  6. ^"Sputnik and the Dawn of the Space Age".NASA History.NASA.Retrieved13 February2008.Public DomainThis article incorporates text from this source, which is in thepublic domain.
  7. ^McLaughlin Green, Constance; Lomask, Milton (1970)."Chapter 11: from Sputnik I to TV-3".Vanguard, A History.NASA. Archived fromthe originalon 7 October 2018.Retrieved13 February2008.Public DomainThis article incorporates text from this source, which is in thepublic domain.
  8. ^ab"Explorer-I and Jupiter-C".NASA.Retrieved9 February2008.Public DomainThis article incorporates text from this source, which is in thepublic domain.
  9. ^Williams, W.E. Jr. (April 1960). "Space Telemetry Systems".Proceedings of the Institute of Radio Engineers.48(4): 685–690.doi:10.1109/JRPROC.1960.287448.S2CID51646193.
  10. ^"The First Transistors in Space – Personal Reflections by the Designer of the Cosmic Ray Instrumentation Package for the Explorer I Satellite".A Transistor Museum Interview with Dr. George Ludwig.The Transistor Museum.Retrieved25 February2008.
  11. ^"Cosmic-Ray Detector".NASA. 14 May 2020.Retrieved12 February2021.Public DomainThis article incorporates text from this source, which is in thepublic domain.
  12. ^ab"Micrometeorite Detector".NASA. 14 May 2020.Retrieved12 February2021.Public DomainThis article incorporates text from this source, which is in thepublic domain.
  13. ^abManring, Edward R. (January 1959). "Micrometeorite Measurements from 1958 Alpha and Gamma Satellites".Planetary and Space Science.1(1): 27–31.Bibcode:1959P&SS....1...27M.doi:10.1016/0032-0633(59)90019-4.
  14. ^abcLey, Willy (October 1968)."The Orbit of Explorer 1".Galaxy Science Fiction.pp. 93–102.
  15. ^"Solar System Exploration Explorer 1".NASA. Archived fromthe originalon 8 January 2008.Retrieved6 February2008.Public DomainThis article incorporates text from this source, which is in thepublic domain.
  16. ^McDonald, Naugle (2008). "Discovering Earth's Radiation Belts: Remembering Explorer 1 and 3".NASA History.89(39). NASA: 361–363.Bibcode:2008EOSTr..89..361M.doi:10.1029/2008EO390001.Public DomainThis article incorporates text from this source, which is in thepublic domain.
  17. ^Zadunaisky, Pedro E. (October 1960). "The Orbit of Satellite 456 Alpha (Explorer 1) during the First 10500 Revolutions".SAO Special Report.50.Bibcode:1960SAOSR..50.....Z.
  18. ^Ley, Willy(October 1968)."The Orbit of Explorer-1".For Your Information.Galaxy Science Fiction.Vol. 27, no. 3. pp.93–102.[T]he original estimate of the lifetime of Explorer-1, made a week or so after firing, was three years. It has been orbiting for ten years by now and the estimate of its remaining lifetime is again three years, but this time surrounded by careful explanations about the factors we don't know.
  19. ^Efroimsky, Michael (August 2001). "Relaxation of wobbling asteroids and comets – theoretical problems, perspectives of experimental observation".Planetary and Space Science.49(9): 937–955.arXiv:astro-ph/9911072.Bibcode:2001P&SS...49..937E.CiteSeerX10.1.1.256.6140.doi:10.1016/S0032-0633(01)00051-4.S2CID14114765.
  20. ^Efroimsky, Michael (March 2002). "Euler, Jacobi, and missions to comets and asteroids".Advances in Space Research.29(5): 725–734.arXiv:astro-ph/0112054.Bibcode:2002AdSpR..29..725E.CiteSeerX10.1.1.192.380.doi:10.1016/S0273-1177(02)00017-0.S2CID1110286.
  21. ^Dubin, Maurice (January 1960)."IGY Micrometeorite Measurements"(PDF).Space Research – Proceedings of the First International Space Science Symposium.1(1): 1042–1058.Bibcode:1960spre.conf.1042D.Retrieved9 February2023.
  22. ^J. Boehm, H.J. Fichtner, and Otto A. Hoberg,EXPLORER SATELLITES LAUNCHED BY JUNO 1 AND JUNO 2 VEHICLES,NASAPublic DomainThis article incorporates text from this source, which is in thepublic domain.
  23. ^Evelyn Boswell (23 October 2011)."MSU's twin satellite to launch October 28 on NASA rocket".Space Science and Engineering Laboratory.Archived fromthe originalon 5 October 2013.Retrieved1 October2013.
  24. ^Launch Complex 26 BlockhouseArchived25 April 2016 at theWayback MachinePublic DomainThis article incorporates text from this source, which is in thepublic domain.
  25. ^Explorer IArchived26 May 2016 at theWayback MachinePublic DomainThis article incorporates text from this source, which is in thepublic domain.
  26. ^Nemiroff, R.; Bonnell, J., eds. (31 January 2008)."The First Explorer".Astronomy Picture of the Day.NASA.Retrieved3 February2008.Public DomainThis article incorporates text from this source, which is in thepublic domain.
  27. ^"NASA / JPL - Ground Antenna".NASA.Retrieved30 March2012.Public DomainThis article incorporates text from this source, which is in thepublic domain.

Bibliography[edit]

West, Doug (2017).Dr Wernher von Braun: A Short Biography.U.S.ISBN978-1-9779279-1-0.{{cite book}}:CS1 maint: location missing publisher (link)

External links[edit]

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