Pioneer Saturn voyage.
Encounter trajectory.
On September 1, 1979, the spacecraft, now designated Pioneer Saturn, reached Saturn after 6 years in flight. It passed through the ring plane outside the edge of Saturn’s A-ring and then swung in under the rings from 2,000 to 10,000 km below them. At the point of closest approach, it attained a speed of 114,100 km/h (71,900 mi/h) and came within 21,400 km of the planet’s cloud tops. While it was approaching, encountering, and leaving Saturn, the spacecraft took the first closeup pictures of the planet, showing 20 to 30 times more detail than the best pictures taken from Earth, and made the first close measurements of its rings and several of its moons, including the largest moon, the planet-sized Titan. Titan, along with Mars, has been considered by many scientists to be the most likely place to find life in the solar system.
Pioneer Saturn unraveled many mysteries. It determined that Saturn has a magnetic field and trapped radiation belts, measured the mass of Saturn and some of its moons, and studied the character of Saturn’s interior. It confirmed the presence and determined the magnitude of an internal heat source for Saturn. Its instruments studied the temperature distribution, composition, and other properties of the clouds and atmospheres of Saturn and Titan, and took photometric and polarization measurements of Iapetus, Rhea, Dione, and Tethys. Pioneer may also have discovered a previously unknown moon of Saturn. The spacecraft measured the mass, structure, and other characteristics of Saturn’s rings, and passed safely through the outer E-ring, which posed a potential hazard for Pioneer. It also discovered new rings. One of these rings, called the F-ring by the Pioneer team, lies just outside the A-ring. The gap between the F-ring and the A-ring has been tentatively designated the Pioneer Division. The other new ring has been called the G-ring, which lies well outside the F-ring.
Pioneer carries a scientific payload of 11 operating instruments; another instrument, the asteroid/meteoroid detector, was turned off in 1975. Two other experiments, celestial mechanics and S-band occultation of Saturn, use the spacecraft radio to obtain data. Pioneer Saturn is a spinning spacecraft, which gives its instruments a full-circle scan 7.8 times a minute. It uses a nuclear source for electric power because the sunlight at Jupiter and beyond is too weak for a solar-powered system.
Two booms project from the spacecraft to deploy the nuclear power source about 3 meters from the sensitive spacecraft instrumentation. A third boom positions the magnetometer sensor about 6 meters from the spacecraft. Six thrusters provide velocity, attitude, and spin-rate control. A dish antenna is located along the spin axis and looks back at Earth throughout the mission, adjusting its view by changes in spacecraft attitude as the spacecraft and Earth move in their orbits around the sun.
Tracking facilities of NASA’s Deep Space Network, located at Goldstone, California, and in Spain and Australia, supported Pioneer Saturn during interplanetary flight and encounter. Pioneer’s radio signals, traveling at the speed of light, took 85 minutes to reach Earth from Saturn, a round-trip time of almost 3 hours, somewhat complicating ground control of the spacecraft. Almost 10,000 commands were sent to the spacecraft in the 2-week period before closest approach. Continued communications should be possible through at least the mid 1980’s.
After the spacecraft passed Saturn, it headed out of the solar system, traveling in the direction the solar system moves with respect to the local stars in our galaxy and in approximately an opposite direction from its sister spacecraft, Pioneer 10. Both spacecraft have plaques attached to them which contain a message from Earth for any intelligent species that may intercept the spacecraft during their endless journeys through interstellar space.
| Pioneer Saturn Scientific Instruments | ||
|---|---|---|
| Instrument | Principal Investigator | Experiment Objective |
| Helium vector magnetometer | Edward J. Smith Jet Propulsion Laboratory | Magnetic fields |
| Fluxgate magnetometer | Mario Acuña Goddard Space Flight Center | Magnetic fields |
| Plasma analyzer | John H. Wolfe Ames Research Center | Solar plasma |
| Charged particle | John A. Simpson University of Chicago | Charged particle composition |
| Cosmic ray telescope | Frank B. McDonald Goddard Space Flight Center | Cosmic ray energy spectra |
| Geiger tube telescope | James A. Van Allen University of Iowa | Charged particles |
| Trapped radiation detector | R. Walker Fillius University of California, San Diego | Trapped radiation |
| Asteroid/meteoroid detector[1] | Robert K. Soberman General Electric Co. and Philadelphia Drexel University | Asteroid/meteoroid astronomy |
| Meteoroid detector | William H. Kinard Langley Research Center | Meteoroid detection |
| Radio transmitter and DSN | John D. Anderson Jet Propulsion Laboratory | Celestial mechanics |
| Ultraviolet photometer | Darrell L. Judge University of Southern California Los Angeles | Ultraviolet photometry |
| Imaging photopolarimeter | Tom Gehrels University of Arizona, Tucson | Photo imaging and polarimetry |
| Infrared radiometer | Andrew Ingersoll California Institute of Technology | Infrared thermal structure |
| Radio transmitter and DSN | Arvydas J. Kliore Jet Propulsion Laboratory | S-band occultation |