''Pioneer 6'', ''7'', ''8'', and ''9'' were

space probe A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; or ent ...

s in the Pioneer program, launched between 1965 and 1969. They were a series of solar-orbiting, spin-stabilized, solar cell- and battery-powered satellites designed to obtain measurements on a continuing basis of interplanetary phenomena from widely separated points in space. They were also known as Pioneer A, B, C, and D. The fifth (Pioneer E) was lost in a launch accident, and therefore did not receive a numerical designation.

Purpose

''Pioneers 6'', ''7'', ''8'', and ''9'' were created to make the first detailed, comprehensive measurements of the

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...

, solar

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

and

cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

s. They were designed to measure large scale magnetic phenomena and particles and fields in

interplanetary space Interplanetary may refer to: *Interplanetary space, the space between the planets of the Solar System *Interplanetary spaceflight, travel between planets *The interplanetary medium, the material that exists in interplanetary space *The InterPlanet ...

. Data from the vehicles have been used to better understand stellar processes and the structure and flow of the solar wind. The vehicles also acted as the world's first space-based solar weather network, providing practical data on

solar storm A solar storm is a disturbance on the Sun, which can emanate outward across the heliosphere, affecting the entire Solar System, including Earth and its magnetosphere, and is the cause of space weather in the short-term with long-term patterns comp ...

s which affect communications and power on Earth. The experiments studied the positive

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s (cations) and

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

s in the solar wind, the interplanetary electron density (

radio propagation Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affecte ...

experiment), solar and galactic cosmic rays, and the

Interplanetary Magnetic Field The interplanetary magnetic field (IMF), now more commonly referred to as the heliospheric magnetic field (HMF), is the component of the solar magnetic field that is dragged out from the solar corona by the solar wind flow to fill the Solar Syst ...

. The spacecraft were important collectors of

heliophysics Heliophysics (from the prefix " helio", from Attic Greek ''hḗlios'', meaning Sun, and the noun "physics": the science of matter and energy and their interactions) is the physics of the Sun and its connection with the Solar System. NASA define ...

and

space weather Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the time varying conditions within the Solar System, including the solar wind, emphasizing the space surrounding the Earth, including conditions in the ma ...

data. In conjunction with other spacecraft these, for the first time, enabled spaceborne observations to be combined with terrestrial observations on the ground and from sounding balloons. Pioneer 9 in early August 1972 recorded significant observations of one of the most potent solar storms ever recorded, and the most hazardous to

human spaceflight Human spaceflight (also referred to as manned spaceflight or crewed spaceflight) is spaceflight with a crew or passengers aboard a spacecraft, often with the spacecraft being operated directly by the onboard human crew. Spacecraft can also be ...

during the

Space Age The Space Age is a period encompassing the activities related to the Space Race, space exploration, space technology, and the cultural developments influenced by these events, beginning with the Sputnik_1#Launch_and_mission, launch of Sputnik 1 ...

Vehicle description

Each craft was identical. They were spin-stabilized diameter × tall cylinders with a long

magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, o ...

boom and solar panels mounted around the body. The main

antenna Antenna ( antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two collid ...

was a high-gain directional antenna. The spacecraft were spin-stabilized at about 60 RPM, and the spin

axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis * Axis (mathematics), a designator for a Cartesian-coordinat ...

was

perpendicular In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It can ...

to the

ecliptic plane The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...

and pointed toward the south

ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...

pole. Instruments: * Solar Wind Plasma Faraday Cup (6, 7) * Cosmic-Ray Telescope (6, 7) * Electrostatic Analyzer (6, 7, 8) * Superior Conjunction Faraday Rotation (6, 7) * Spectral Broadening (6) * Relativity Investigation (6) * Uniaxial Fluxgate Magnetometer (6) * Cosmic-Ray Anisotropy (6, 7, 8, 9) * Celestial Mechanics (6, 7, 8, 9) * Two-Frequency Beacon Receiver (6, 7, 8, 9) * Single-Axis Magnetometer (7, 8) * Cosmic Dust Detector (8, 9) * Cosmic Ray Gradient Detector (8, 9) * Plasma Wave Detector (8) * Triaxial Magnetometer (9) * Solar Plasma Detector (9) * Electric Field Detector (9)

Communications

By ground command, one of five

bit rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...

s, one of four data formats, and one of four operating modes could be selected. The five-bit rates were 512, 256, 64, 16, and 8 bit/s. Three of the four data formats contained primarily scientific data and consisted of 32 seven-bit words per frame. One scientific data format was for use at the two highest bit rates. Another was for use at the three lowest bit rates. The third contained data from only the

experiment. The fourth data format contained mainly engineering data. The four operating modes were: real-time, telemetry store, duty cycle store, and memory readout. In the real-time mode, data were sampled and transmitted directly (without storage) as specified by the data format and bit rate selected. In the telemetry store mode, data were stored and transmitted simultaneously in the format and at the bit rate selected. In the duty-cycle store mode, a single frame of scientific data was collected and stored at a rate of 512 bit/s. The time interval between the collection and storage of successive frames could be varied by ground command between 2 and 17 min to provide partial data coverage for periods up to 19 hours, as limited by the bit storage capacity. In the memory readout mode, data was read out at whatever bit rate was appropriate to the satellite distance from Earth.

Time line and current status

As stated by JPL, "The Pioneer 6–9 program has been touted as one of the least expensive of all NASA spacecraft programs in terms of scientific results per dollar spent." Although the four spacecraft have not been regularly tracked for science data return in recent years, a successful telemetry contact with Pioneer 6 was made on December 8, 2000 to celebrate 35 years of continuous operation since launch. Its original design life expectancy was only 6 months. Although NASA described ''Pioneer 6'' as "extant" , there has been no contact since December 8, 2000. At this time ''Pioneer 6'' had operated for 12,758 days, making it the oldest operating space probe until it was surpassed by ''

Voyager 2 ''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, ''Voyager 1'', on a ...

'' on August 13, 2012. It is also believed that contact is still possible with ''Pioneer 7'' and ''8''; only ''Pioneer 9'' is definitely not working.

''Pioneer 6''

December 16, 1965 Launched at 07:31:00 UTC from Cape Canaveral to a circular solar orbit with a mean distance of 0.8 AU. December 1995 The prime Traveling-wave tube ( TWT) failed sometime after December 1995. July 1996 Spacecraft commanded to the backup TWT. October 6, 1997 Tracked with the 70 meter Deep Space Station 43 in Australia. The MIT and ARC Plasma Analyzers, as well as the cosmic ray detector from the University of Chicago, were turned on and working. December 8, 2000 Successful telemetry contact for about two hours.

''Pioneer 7''

August 17, 1966 Launched from Cape Canaveral into solar orbit with a mean distance of 1.1 AU. March 20, 1986 Flew within 12.3 million kilometers of

Halley's Comet Halley's Comet or Comet Halley, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–79 years. Halley is the only known short-period comet that is regularly visible to the naked eye from Earth, and thus the o ...

and monitored the interaction between the cometary hydrogen tail and the solar wind. It discovered He+ plasma produced by charge exchange of solar wind He++ with neutral cometary material. March 31, 1995 Tracked successfully. The spacecraft and one of the science instruments were still functioning.

''Pioneer 8''

December 13, 1967 Launched at 14:08:00 UTC from Cape Canaveral into solar orbit with a mean distance of 1.1 AU from the Sun. August 22, 1996 The spacecraft commanded to switch to the backup TWT. Downlink signal was re-acquired, one of the science instruments again functioning.

''Pioneer 9''

November 8, 1968 Launched at 09:46:00 UTC from Cape Canaveral into solar orbit with a mean distance of 0.8 AU. 1983 Final contact. 1987 Contact was attempted, but failed.

Pioneer E

August 27, 1969 Launched at 21:59:00 UTC from Cape Canaveral. The launch vehicle was destroyed by

range safety In the field of rocketry, range safety may be assured by a system which is intended to protect people and assets on both the rocket range and downrange in cases when a launch vehicle might endanger them. For a rocket deemed to be ''off course'' ...

after hydraulics in the first stage failed.

References

External links

Pioneer Project Page

''Pioneer 6'' Profile
b
NASA's Solar System Exploration

''Pioneer 7'' Profile
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NASA's Solar System Exploration

''Pioneer 8'' Profile
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NASA's Solar System Exploration

''Pioneer 9'' Profile
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NASA's Solar System Exploration

''Pioneer E'' Profile
b
NASA's Solar System Exploration

NSSDC Master Catalog: Spacecraft ''Pioneer 6''

NSSDC Master Catalog: Spacecraft ''Pioneer 7''

NSSDC Master Catalog: Spacecraft ''Pioneer 8''

NSSDC Master Catalog: Spacecraft ''Pioneer 9''

NSSDC Master Catalog: Spacecraft Pioneer-E
{{NASA space program Pioneer 06 Missions to the Sun Derelict space probes Derelict satellites in heliocentric orbit