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{{short description|Series of United States uncrewed lunar and planetary space probes (1958-60; 1965-92)}}
{{distinguish|Pioneers Program}}
{{Infobox space program
| name = 
| image = Pioneer family.jpg
| alt = 
| caption = A family portrait showing (from left to right) ''Pioneers'' 6-9, 10 and 11 and the Pioneer Venus Orbiter and Multiprobe series
| country = United States
| organization = {{Unbulleted list
| [[Air Force Ballistic Missile Division]]
| [[United States Army]]
| [[NASA]]
  }}
| purpose = Lunar and interplanetary exploration
| status = Completed
| cost = 
| duration = {{Unbulleted list
| 1958–1960
| 1965–1992
  }}
| firstflight = [[Pioneer 0]] August 17, 1958
| lastflight = [[Pioneer Venus Multiprobe|Pioneer Venus]] August 1978
| successes = 9
| failures = 10
| partialfailures = 1
| launchsite = [[Cape Canaveral Air Force Station]]
| launcher = {{Unbulleted list
| [[Thor-Able]]
| [[Atlas-Able]]
| [[Juno II]]
| [[Delta E]]
| [[Atlas-Centaur]]
  }}
}}
The '''Pioneer programs''' were two series of [[United States]] lunar and planetary [[space probe]]s. The first program, which ran from 1958 to 1960, unsuccessfully attempted to send spacecraft to orbit the Moon, successfully sent one spacecraft to fly by the Moon, and successfully sent one spacecraft to investigate interplanetary space between the orbits of Earth and Venus. The second program, which ran from 1965 to 1992, sent four spacecraft to measure interplanetary [[space weather]], two to explore [[Jupiter]] and [[Saturn]], and two to explore [[Venus]]. The two outer planet probes, ''[[Pioneer 10]]'' and ''[[Pioneer 11]]'', became the first two of [[List of artificial objects leaving the Solar System|five artificial objects]] to achieve the [[escape velocity]] that will allow them to [[Solar System#Farthest regions|leave the Solar System]], and carried [[Pioneer plaque|a golden plaque]] each depicting a man and a woman and information about the origin and the creators of the probes, in case any [[extraterrestrial life|extraterrestrials]] find them someday.

==Naming==
Credit for naming the first probe has been attributed to Stephen A. Saliga, who had been assigned to the Air Force Orientation Group, Wright-Patterson AFB, as chief designer of Air Force exhibits. While he was at a briefing, the spacecraft was described to him, as, a "lunar-orbiting vehicle, with an infrared scanning device." Saliga thought the title too long, and lacked theme for an exhibit design. He suggested, "Pioneer", as the name of the probe, since "the Army had already launched and orbited the Explorer satellite, and their Public Information Office was identifying the Army, as, 'Pioneers in Space,'" and, by adopting the name, the Air Force would "make a 'quantum jump' as to who, really, [were] the 'Pioneers' in space.'"<ref>
{{cite web | url = https://history.nasa.gov/SP-4402/ch3.htm#88
| title = Origins of NASA Names | access-date = 2006-10-16
| work = NASA History | publisher = www.history.nasa.gov }}</ref>

== Early missions ==
The earliest missions were attempts to achieve Earth's [[escape velocity]], simply to show it was feasible and to study the [[Moon]]. This included the first launch by [[NASA]] which was formed from the old [[National Advisory Committee for Aeronautics|NACA]]. These missions were carried out by the [[Air Force Ballistic Missile Division]], [[United States Army|Army]], and NASA.<ref>{{Cite web|url=https://www.losangeles.spaceforce.mil/?ver=2016-05-02-112846-557|title = Los Angeles Air Force Base > Home}}</ref>

=== Able space probes (1958–1960) ===
[[File:Pioneer I, Reconstructed Replica.jpg|thumb|Reconstructed replica of Pioneer 1]]
[[File:Pioneer IV flight spare 01.jpg |thumb|Lunar flyby spacecraft (Pioneer 3, 4)]]
[[File:Pioneer P-1 P-3 P-30 P-31.jpg|thumb|Pioneer P-1, P-3, 5, P-30, and P-31 probe]]
{| class="wikitable"
! Mission Name !! Alternate Names !! Type !! Outcome !! Date
|-
| [[Pioneer 0]] || Thor-Able 1, Pioneer || Lunar orbiter || Destroyed (Thor failure 77 seconds after launch) || August 17, 1958
|-
| [[Pioneer 1]] || Thor-Able 2, Pioneer I || Lunar orbiter, missed Moon || Third stage partial failure || October 11, 1958
|-
| [[Pioneer 2]] || Thor-Able 3, Pioneer II || Lunar orbiter, reentry || Third stage failure || November 8, 1958
|-
| [[Pioneer P-1]] || Atlas-Able 4A, Pioneer W || Launch vehicle lost ||  || September 24, 1959
|-
| [[Pioneer P-3]] || Atlas-Able 4, Atlas-Able 4B, Pioneer X || Mission failed shortly after launch ||  || November 26, 1959
|-
| [[Pioneer 5]] || Pioneer P-2, Thor-Able 4, Pioneer V ||  ||  || March 11, 1960
|-
| [[Pioneer P-30]] || Atlas-Able 5A, Pioneer Y || Lunar probe || Failed to achieve lunar orbit || September 25, 1960
|-
| [[Pioneer P-31]] || Atlas-Able 5B, Pioneer Z || Lunar probe || Lost in upper stage failure || December 15, 1960
|}

=== Juno II lunar probes (1958–1959) ===
* [[Pioneer 3]]  – Lunar flyby, missed Moon due to launcher failure December 6, 1958
* [[Pioneer 4]]  – Lunar flyby, achieved Earth [[escape velocity]], launched March 3, 1959

== Later missions (1965–1978) ==
[[File:NASM-NASM2016-00083.jpg|thumb|''Pioneer'' 10 / 11]]
Five years after the early Able space probe missions ended, [[NASA Ames Research Center]] used the Pioneer name for a new series of missions, initially aimed at the [[inner Solar System]], before the flyby missions to [[Jupiter]] and [[Saturn]]. While successful, the missions returned much poorer images than the [[Voyager program]] probes would five years later. In 1978, the end of the program saw a return to the inner Solar System, with the [[Pioneer Venus Orbiter]] and [[Pioneer Venus Multiprobe|Multiprobe]], this time using orbital insertion rather than flyby missions.

The new missions were numbered beginning with Pioneer 6 (alternate names in parentheses).

=== Interplanetary weather ===
The spacecraft in Pioneer missions [[Pioneer 6, 7, 8, and 9|6, 7, 8, and 9]] comprised a new interplanetary [[space weather]] network:
* Pioneer 6 (Pioneer A) – launched December 1965
* Pioneer 7 (Pioneer B) – launched August 1966
* Pioneer 8 (Pioneer C) – launched December 1967
* Pioneer 9 (Pioneer D) – launched November 1968 (''inactive since 1983'')
* Pioneer E – lost in launcher failure August 1969
Pioneer 6 and Pioneer 9 are in solar orbits with 0.8 [[Astronomical unit|AU]] distance to the Sun. Their orbital periods are therefore slightly shorter than Earth's. Pioneer 7 and Pioneer 8 are in solar orbits with 1.1 AU distance to the Sun. Their orbital periods are therefore slightly longer than Earth's. Since the probes' orbital periods differ from that of the Earth, from time to time, they face a side of the Sun that cannot be seen from Earth. The probes can sense parts of the Sun several days before the Sun's rotation reveals it to ground-based Earth orbiting observatories.

=== Outer Solar System missions ===
[[File:Outersolarsystem-probes-4407b.svg|thumb|400px|Map showing location and trajectories of the ''Pioneer 10'' (blue), ''Pioneer 11'' (green), ''[[Voyager 1]]'' (purple) and  ''[[Voyager 2]]'' (red) spacecraft, as of April 4, 2007]]
[[File:Pioneer10-plaque.jpg|thumb|right|The [[Pioneer plaque]] attached to Pioneers ''10'' and ''11'']]
* ''[[Pioneer 10]]'' (Pioneer F) –  [[Jupiter]], [[interstellar medium]], launched March 1972
* ''[[Pioneer 11]]'' (Pioneer G) –  [[Jupiter]], [[Saturn]], [[interstellar medium]], launched April 1973
* [[Pioneer H]]  – proposed out-of-[[ecliptic]] mission for 1974, never launched. Would have used flight spare for Pioneers 10 and 11.<ref>{{cite web |title= Pioneer H, Jupiter Swingby Out-of-the-Ecliptic Mission Study |url= https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930073120_1993073120.pdf |date= 20 August 1971 |access-date= 7 July 2017 |archive-date= 14 May 2010 |archive-url= https://web.archive.org/web/20100514075504/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930073120_1993073120.pdf |url-status= dead }}</ref>

=== Venus project ===
{{Main|Pioneer Venus project}}
* [[Pioneer Venus Orbiter]] (Pioneer Venus 1, Pioneer 12) – launched May 1978
* [[Pioneer Venus Multiprobe]] (Pioneer Venus 2, Pioneer 13) – launched August 1978
** Pioneer Venus Probe Bus – transport vehicle and upper atmosphere probe
** Pioneer Venus Large Probe – 300&nbsp;kg parachuted probe
** Pioneer Venus North Probe – 75&nbsp;kg impactor probe
** Pioneer Venus Night Probe – 75&nbsp;kg impactor probe
** Pioneer Venus Day Probe – 75&nbsp;kg impactor probe

== See also ==
* [[Mariner program]]
* [[Pioneer anomaly]]
* [[Ranger program]]
* [[Surveyor program]]
* [[Timeline of Solar System exploration]]
* [[Voyager program]]

== References ==
{{Reflist}}

== External links ==
{{Commons category}}
* [https://web.archive.org/web/20071017210114/http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Pioneer_Moon Pioneer (Moon) Program Page] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [http://www.nap.edu/books/0309090504/html/ Mark Wolverton's ''The Depths of Space'' online]
* [https://web.archive.org/web/20020228155848/http://www.astronautix.com/lvs/thorable.htm Thor Able – Encyclopedia Astronautica]
* [http://www.sdfo.org/stl/ Space Technology Laboratories Documents Archive]
* [http://spacecrafts3d.org/models/pioneer.html WebGL-based 3D artist's view of Pioneer @ SPACECRAFTS 3D]

{{Pioneer program | before=''None, see contemporaneous program [[Mariner program|Mariner]]'' | after=[[Voyager program|Voyager]] }}
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{{Jupiter}}
{{NASA planetary exploration programs}}
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{{Use American English|date=January 2014}}

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