Pioneer 11 (also known as Pioneer G) is a NASA robotic space probe launched on April 5, 1973, to study the asteroid belt, the environment around Jupiter and Saturn, the solar wind, and cosmic rays. It was the first probe to encounter Saturn, the second to fly through the asteroid belt, and the second to fly by Jupiter. Later, Pioneer 11 became the second of five artificial objects to achieve an escape velocity allowing it to leave the Solar System. Due to power constraints and the vast distance to the probe, the last routine contact with the spacecraft was on September 30, 1995, and the last good engineering data was received on November 24, 1995.

Mission background

History

Approved in February 1969, Pioneer 11 and its twin probe, Pioneer 10, were the first to be designed for exploring the outer Solar System. Yielding to multiple proposals throughout the 1960s, early mission objectives were defined as:

  • Explore the interplanetary medium beyond the orbit of Mars
  • Investigate the nature of the asteroid belt from the scientific standpoint and assess the belt's possible hazard to missions to the outer planets.
  • Explore the environment of Jupiter.

Subsequent planning for an encounter with Saturn added many more goals:

  • Map the magnetic field of Saturn and determine its intensity, direction, and structure.
  • Determine how many electrons and protons of various energies are distributed along the trajectory of the spacecraft through the Saturn system.
  • Map the interaction of the Saturn system with the solar wind.
  • Measure the temperature of Saturn's atmosphere and that of Titan, the largest satellite of Saturn.
  • Determine the structure of the upper atmosphere of Saturn where molecules are expected to be electrically charged and form an ionosphere.
  • Map the thermal structure of Saturn's atmosphere by infrared observations coupled with radio occultation data.
  • Obtain spin-scan images of the Saturnian system in two colors during the encounter sequence and polarimetry measurements of the planet.
  • Probe the ring system and the atmosphere of Saturn with S-band radio occultation.
  • Determine more precisely the masses of Saturn and its larger satellites by accurate observations of the effects of their gravitational fields on the motion of the spacecraft.
  • As a precursor to the Mariner Jupiter/Saturn mission, verify the environment of the ring plane to find out where it may be safely crossed by the Mariner spacecraft without serious damage.

Pioneer 11 was built by TRW and managed as part of the Pioneer program by NASA Ames Research Center. A backup unit, Pioneer H, is currently on display in the "Milestones of Flight" exhibit at the National Air and Space Museum in Washington, D.C. Many elements of the mission proved to be critical in the planning of the Voyager program.

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File:Pioneer_10_systems_diagram.svg|Pioneer 10 and Pioneer 11 spacecraft diagram

File:NASM-NASM2016-00083.jpg|Reconstructed full-scale mock-up Pioneer 10 / 11 spacecraft at the National Air and Space Museum

File:Pioneer 10 - 11, reconstructed full-scale mock-up - DPLA - 0ee5410618161a495925d68f2fc5e1fb (page 2).jpg|Side view of the spacecraft

File:CAPE KENNEDY, Fla (KSC-73P-0116).jpg|Pioneer 11 during the installation of its protective shroud

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Spacecraft design

The Pioneer 11 bus measures deep and with six panels forming the hexagonal structure. The bus houses propellant to control the orientation of the probe and eight of the twelve scientific instruments. The spacecraft has a mass of 259&nbsp;kilograms.

Attitude control and propulsion

:Orientation of the spacecraft was maintained with six 4.5-N, hydrazine monopropellant thrusters: pair one maintains a constant spin-rate of 4.8 rpm, pair two controls the forward thrust, pair three controls attitude. Information for the orientation is provided by performing conical scanning maneuvers to track Earth in its orbit, a star sensor able to reference Canopus, and two Sun sensors.

Communications

:The space probe includes a redundant system transceivers, one attached to the high-gain antenna, the other to an omni-antenna and medium-gain antenna. Each transceiver is 8 watts and transmits data across the S-band using 2110 MHz for the uplink from Earth and 2292 MHz for the downlink to Earth with the Deep Space Network tracking the signal. Prior to transmitting data, the probe uses a convolutional encoder to allow correction of errors in the received data on Earth.

Power

thumb|SNAP-19 RTG on a Pioneer 10/11 replica

:Pioneer 11 uses four SNAP-19 radioisotope thermoelectric generators (RTGs) (see diagram). They are positioned on two three-rod trusses, each in length and 120 degrees apart. This was expected to be a safe distance from the sensitive scientific experiments carried on board. Combined, the RTGs provided 155 watts at launch, and decayed to 140 W in transit to Jupiter. The spacecraft requires 100 W to power all systems.

Computer

:Much of the computation for the mission was performed on Earth and transmitted to the probe, where it is able to retain in memory, up to five commands of the 222 possible entries by ground controllers. The spacecraft includes two command decoders and a command distribution unit, a very limited form of a processor, to direct operations on the spacecraft. This system requires that mission operators prepare commands long in advance of transmitting them to the probe. A data storage unit is included to record up to 6,144 bytes of information gathered by the instruments. The digital telemetry unit is then used to prepare the collected data in one of the thirteen possible formats before transmitting it back to Earth.

Scientific instruments

Pioneer 11 has one additional instrument more than Pioneer 10, a flux-gate magnetometer.

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! colspan="2" style="text-align: left" | Helium Vector Magnetometer (HVM)

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|Measures the fine structure of the interplanetary magnetic field, mapped the Jovian magnetic field, and provides magnetic field measurements to evaluate solar wind interaction with Jupiter.

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Bibliography

  • Pioneer 11 Profile by NASA's Solar System Exploration
  • Ted Stryk's Pioneer 11 at Saturn page