Pioneer 4

Pioneer 4

Pioneer 4flight spare
Mission type	Lunarflyby
Operator	NASA
Harvard designation	1959 Nu 1
COSPAR ID	1959-013A
SATCATno.	113
Mission duration	3 days, 10 hours and 29 minutes
Spacecraft properties
Manufacturer	Jet Propulsion Laboratory
Launch mass	6.08 kg
Start of mission
Launch date	3 March 1959, 05:10:56 GMT
Rocket	Juno II
Launch site	Cape Canaveral,LC-5
Contractor	Chrysler
End of mission
Last contact	6 March 1959, 15:40:00 GMT
Orbital parameters
Reference system	Heliocentric
Semi-major axis	1.1015 AU
Eccentricity	0.07109
Perihelion altitude	0.98 AU
Aphelion altitude	1.13 AU
Inclination	1.5°
Period	398.0 days
Epoch	3 March 1959
Flyby ofMoon
Closest approach	4 March 1959, 22:25 GMT
Distance	58,983 kilometres (36,650 mi)
Pioneer program

Pioneer 4was an Americanspin-stabilizeduncrewed spacecraftlaunched as part of thePioneer programon alunar flybytrajectory and into aheliocentric orbitmaking it the first probe of theUnited Statesto escape from the Earth's gravity. Launched on March 3, 1959, it carried a payload similar toPioneer 3:a lunar radiation environment experiment using aGeiger–Müller tubedetector and a lunar photography experiment. It passed within 58,983 km (36,650 mi) of theMoon's surface. However,Pioneer 4did not come close enough to trigger itsphotoelectric sensor.The spacecraft was still insolar orbitas of 1969.It was the only successfullunar probelaunched by the U.S. in 12 attempts between 1958 and 1963; only in 1964 wouldRanger 7surpass its success by accomplishing all of its mission objectives.

After the SovietLuna 1probe conducted the first successful flyby of the Moon on 3 January 1959, the pressure felt by the US to succeed with a lunar mission was enormous, especially since American mission failures were entirely public while the Soviet failures were kept a secret.

Spacecraft design

Pioneer 4was a cone-shaped probe 51 cm high and 23 cm in diameter at its base. The cone was composed of a thinfiberglassshell coated with a gold wash to make it electrically conducting and painted with white stripes to maintain the temperature between 10 and 50 °C. At the tip of the cone was a small probe which combined with the cone itself to act as an antenna. At the base of the cone, a ring ofmercury batteriesprovided power. Aphotoelectric sensorprotruded from the center of the ring. The sensor was designed with twophotocellswhich would be triggered by the light of the Moon when the probe was within about 30,000 km of the Moon. At the center of the cone was a voltage supply tube and twoGeiger–Müller tubes.The Laboratory's Microlock system, used for communicating with earlier Explorer satellites, did not have sufficient range to perform this mission. Therefore, a new radio system called TRAC(E)Tracking And Communication (Extraterrestrial)was designed. TRAC(E) was an integral part of theGoldstone Deep Space Communications Complex.A transmitter with a mass of 0.5 kg delivered aphase modulatedsignal of 0.1 W at a frequency of 960.05 MHz. The modulated carrier power was 0.08 W and the total effective radiated power 0.18 W. A despin mechanism consisted of two 7 gram weights which spooled out to the end of two 150 cm wires when triggered by a hydraulic timer 10 hours after launch. The weights were designed to slow the spacecraft spin from 400 rpm to 6 rpm, and then weights and wires were released. Pioneer 4 received a few small modifications over its predecessor, namely added lead shielding around the Geiger tubes and modifications to the telemetry system to improve its reliability and signal strength. The probe hadS/N#4, with probe #3 recalled from launch due to technical issues.

Launch vehicle

Pioneer 4was launched with aJuno IIlaunch vehicle, which also launchedPioneer 3.Juno II closely resembled theJuno I(Jupiter-Cbased) vehicle that launchedExplorer 1.Its first stage was a 19.51 m elongatedJupiterIRBMmissile that was used by theU.S. Army.On top of the Jupiter propulsion section was a guidance and control compartment that supported a rotating tub containing the rocket stages 2, 3 and 4.Pioneer 4was mounted on top of stage 4.

Mission

At 05:10:56 GMT on the night of 3 March 1959, Pioneer 4 lifted off from LC-5 atCape Canaveral.This time, the booster performed almost perfectly so thatPioneer 4achieved its primary objective (an Earth-Moon trajectory), returned radiation data and provided a valuable tracking exercise. A slightly longer than nominal second stage burn, however, was enough to induce small trajectory and velocity errors, so that the probe passed within 58,983 km of theMoon's surface (7.2° E, 5.7° S) on 4 March 1959 at 22:25 GMT (5:25 p.m. EST) at a speed of 7230 km/h. The distance was not close enough to trigger the photoelectric sensor. This scanning device was being tested for use in future probes to activate either a film or vidicon camera. The probe continued transmitting radiation data for 82.5 hours, to a distance of 658,000 kilometres (409,000 mi),and reached perihelion on 18 March 1959 at 01:00 GMT. The cylindrical fourth stage casing (173 cm long, 15 cm diameter, 4.65 kg) went into orbit with the probe. The communication system had worked well, and it was estimated that signals could have been received out to 1,000,000 kilometres (620,000 mi) had there been enough battery power.

• 
  The Pioneer 4 probe is inspected by (left to right) Dr. Wernher von Braun, payload engineer John Casani and Dr. James Van Allen.
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  Pioneer 4
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  Pioneer IV flight spare
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  Launch ofPioneer 4
• Universal newsreel about the launch

See also

• Luna 1– a similarSoviet space programmission launched 2 January 1959, several weeks beforePioneer 4.

External links

• NASA JPLPioneer 3and4
• NSSDC Master Catalog: SpacecraftPioneer 4