Pioneer 10 & 11

USA Jupiter/Saturn Flyby & Interstellar Probe
Courtesy of NASA

Pioneer 10 was launched on 2 March 1972, on top of an Atlas/Centaur/TE364-4 launch vehicle. The launch marked the first use of the Atlas-Centaur as a three-stage launch vehicle. The third stage was required to rocket Pioneer 10 to the speed of 51,810 kph needed for the flight to Jupiter. This made Pioneer the fastest manmade object to leave the Earth, fast enough to pass the Moon in 11 hours and to cross the Mars orbit, about 80 million kilometers away, in just 12 weeks.

On 15 July 1972, Pioneer entered the Asteroid Belt, a doughnut shaped area which measures some 280 million kilometers wide and 80 million kilometers thick. The material in the belts travels at speed about 20 km/sec and ranges in size from dust particles to rock chunks as big as Alaska.

After safely traversing the Asteroid Belt, Pioneer 10 headed toward Jupiter. Accelerated by the massive giant to a speed of 132,000 kph, Pioneer 10 passed by Jupiter within 130,354 kilometers of the cloudtops on December 3, 1973. During the passage by Jupiter, Pioneer 10 obtained the first close-up images of the planet, charted Jupiter's intense radiation belts, located the planet's magnetic field, and discovered that Jupiter is predominantly a liquid planet.

Following its encounter with Jupiter, Pioneer 10 is exploring the outer regions of our Solar System, studying energetic particles from our Sun. (solar wind), and cosmic rays entering our portion of the Milky Way. As of February 1996, Pioneer 10 was at a distance of 9.5 billion kilometers from Earth. At that distance, it takes over 8.5 hours for the radio signal (which is traveling at the speed of light) to reach Earth.

Pioneer 11 was launched on 5 April 1973, like Pioneer 10, on top of an Atlas/Centaur/TE364-4 launch vehicle. After safe passage through the asteroid belt on 19 April 1974, the Pioneer 11 thrusters were fired to add another 63.7 m/sec to the spacecraft's velocity. This adjusted the aiming point at Jupiter to 43,000 kilometers above the cloudtops. The close approach also allowed the spacecraft to be accelerated by Jupiter to a velocity 55 times that of the muzzle velocity of a high speed rifle bullet-173,000 kph-so that it would be carried across the Solar System some 2.4 billion kilometers to Saturn.

During its flyby of Jupiter on 2 December 1974, Pioneer 11 obtained dramatic images of the Great Red Spot, made the first observation of the immense polar regions, and determined the mass of Jupiter's moon, Callisto.

Looping high above the ecliptic plane and across the Solar System, Pioneer 11 raced toward its appointment with Saturn on 1 September 1979. Pioneer 11 flew to within 21,000 kilometers of Saturn and took the first close-up pictures of the planet. Instruments located two previously undiscovered small moons and an additional ring, charted Saturn's magnetosphere and magnetic field and found its planet-size moon, Titan, to be too cold for life. Hurtling underneath the ring plane, Pioneer 11 sent back amazing pictures of Saturn's rings. The rings, which normally seem bright when observed from Earth, appeared dark in the Pioneer pictures, and the dark gaps in the rings seen from Earth appeared as bright rings.

Following its encounter with Saturn, Pioneer 11 explored the outer regions of our Solar System, studying energetic particles from our Sun (solar wind), and cosmic rays entering our portion of the Milky Way. In September 1995, Pioneer 11 was at a distance of 6.5 billion kilometers from Earth. At that distance, it takes over 6 hours for the radio signal (which is traveling at the speed of light) to reach Earth.

By September 1995, its power source nearly exhausted, Pioneer 11 could no longer make any scientific observations, and routine mission operations were terminated. There have been no communications with Pioneer 11 since November 1995. The Earth's motion has carried it out of the view of the spacecraft antenna. The spacecraft cannot be maneuvered to point back at the Earth because of the lack of power. It is not known whether the spacecraft is still transmitting a signal. No further tracks of Pioneer 11 are scheduled.

### Description of the Spacecraft

Measured from its farthest ends, from the horn of the medium-gain antenna to the tip of the omnidirectional antenna, the Pioneer spacecraft is 2.9 meters long. Its widest cross-wise dimension, exclusive of the booms, is the 2.7-meter diameter high gain antenna. Pioneer weighs 270 kilograms. The spacecraft is spin-stabilized, spinning about the axis of the high gain dish antenna at approximately 5 rpm. Six Hydrazine thrusters provide velocity, attitude and spin-rate control.

Electrical power is provided by four radioisotope thermoelectric generators (RTG), each providing 40 watts of power at launch. Two three-rod trusses, 120 degrees apart, project from the equipment compartment to deploy the RTG power sources about 10 feet from the center of the spacecraft. A third boom, 120 degrees from the others, projects from the experiments compartment and positions the helium vector magnetometer sensor 20 feet from the spacecraft center.

Pioneer 10 carries 11 instruments, only 5 of which are still in use. Pioneer 11 carries 12 instruments, only 3 of which were still in use when communications ended in late 1995.

As the first two spacecraft to leave our solar system, Pioneer 10 & 11 carry a graphic message in the form of a 6- by 9-inch gold anodized plaque bolted to the spacecraft's main frame.

### About the Launch Vehicle

Launch of Pioneer 10

The Atlas vehicle has a total thrust of 186,979 kilograms, consisting of two 79,473-kilogram-thrust booster engines; one 27,416-kilogram thrust sustainer engine, and two vernier engines, each developing 307 kilograms thrust. Propellants are liquid oxygen and RP1.

The Centaur second stage has two engines having a total thrust of 13,273 kilograms. This engine carries insulation panels which are jettisoned just before the vehicle leaves the Earth's atmosphere and are used to prevent heat or air friction from causing boil-off of liquid hydrogen during flight through the atmosphere. Propellant is liquid hydrogen and liquid oxygen.

The solid-fueled TE364-4 third stage develops approximately 6,820 kilograms of thrust. This stage also spins the spacecraft up to 60 rpm.

### Scientific Instruments

The following is a list of scientific instruments on board the Pioneer 10 & 11 spacecraft. Some instruments are no longer used, either because they have failed (F), or because they were only used during Jupiter or Saturn encounter (ENC). As the available spacecraft power is continuing to decline, other instruments can no longer be used because of power limitations (P/L).

#### Pioneer 10 Instruments

- Helium Vector Magnetometer (F)
- Plasma Analyzer (P/L)
- Charged Particle Instrument
- Cosmic Ray Telescope
- Geiger Tube Telescope
- Trapped Radiation Detector (P/L)
- Meteoroid Detector (ENC)(F)
- Asteroid-Meteoroid Experiment (ENC)(F)
- Ultraviolet Photometer
- Imaging Photopolarimeter (ENC) (P/L)
- Infrared Radiometer (F)

The Pioneer 11 instruments are the same as the Pioneer 10 instruments, except that a Flux-Gate Magnetometer was added. Instruments on the spacecraft were gradually turned off as power levels declined. The spacecraft is no longer in communication with Earth.

### Pioneer Plaque

On the plaque a man and woman stand before an outline of the spacecraft. The man's hand is raised in a gesture of good will. The physical makeup of the man and woman were determined from results of a computerized analysis of the average person in our civilization.

The key to translating the plaque lies in understanding the breakdown of the most common element in the universe - hydrogen. This element is illustrated in the left-hand corner of the plaque in schematic form showing the hyperfine transition of neutral atomic hydrogen. Anyone from a scientifically educated civilization having enough knowledge of hydrogen would be able to translate the message. The plaque was designed by Dr. Carl Sagan of Cornell University and drawn by his wife, Linda Salzman Sagan.

### Mission Management

The Pioneers are managed by the Ames Research Center, Mountain View, Calif., for NASA's Office of Space Science. The spacecraft were built by TRW Space & Technology Group, Redondo Beach, Calif. under contract with NASA, Ames Research Center.

Space History

##### Views of the Solar System Copyright © 1997 by Calvin J. Hamilton. All rights reserved.