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 (210 ft/sec) to the spacecraft's velocity. This adjusted the aiming point at Jupiter to 43,000 km (26,725 miles) 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 km/hr (108,000 mph) - so that it would be carried across the Solar System some 2.4 billion kilometers (1.5 billion miles) 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.

Pioneer 11

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 13,000 miles 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 km (4 billion miles) 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. However, by September 1995, Pioneer 11 could no longer make any scientific observations. On 30 September 1995, routine daily mission operations were stopped. Intermittent contact continued until November 1995, at which time the last communication with Pioneer 11 took place. There have been no communications with Pioneer 11 since. 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. It is not known whether the spacecraft is still transmitting a signal. No further tracks of Pioneer 11 are scheduled.

Scientific Instruments

The following is a list of scientific instruments on board the Pioneer 11 spacecraft.

• Helium Vector Magnetometer (Eventually Failed)
• Plasma Analyzer
• Charged Particle Instrument
• Cosmic Ray Telescope
• Geiger Tube Telescope
• Trapped Radiation Detector
• Meteoroid Detector (Eventually Failed)
• Asteroid-Meteoroid Experiment (Eventually Failed)
• Ultraviolet Photometer
• Imaging Photopolarimeter
• Infrared Radiometer (Eventually Failed)
• Flux-Gate Magnetometer

As the spacecraft power continued to decline, instruments had to be turned off. By October 1995, none of the instruments could be operated, and the scientific investigations by Pioneer 11 came to an end. Sometime in late 1996, its transmitter will fall silent altogether, and Pioneer 11 will travel forever as a ghost ship in our galaxy.

Source: NASA