Paula Cleggett-Haleim
Headquarters, Washington, D.C                                            
June 11, 1993
(Phone:  202/358-0883)

Peter Waller 
Ames Research Center, Mountain View, Calif.
(Phone:  415//604-3938)

RELEASE:  93-11

0PIONEER CELEBRATES 10 YEARS BEYOND THE KNOWN SOLAR PLANETS

   The most distant manmade object, Pioneer 10, on Sunday 
celebrates the 10th anniversary of becoming the first spacecraft 
to explore beyond the orbit of Pluto, currently the most distant 
solar system planet discovered.

   Pioneer 10 continues to send back science data to Earth even 
though the spacecraft is 5 1/2 billion miles from its home planet.  
It takes more than 8 hours for Pioneer 10's radio signal to make 
the trip to Earth.

   Pioneer 10 left all the known planets behind on June 13, 1983.  
Launched in 1972, the 570-pound spacecraft had a design life of 21 
months.  More than two decades later, it continues to hurtle 
through deep space at close to 30,000 miles per hour.  

   Five of the 11 instruments aboard are still sending back data 
through the spacecraft's 7 1/2 watt radio signal, about the 
strength of a home nightlight.  Pioneer 10 has transmitted more 
than 170 billion bits of science data.  By the time its signal 
reaches the football-field-sized antennas of NASA's Deep Space 
Network, the signal has the strength of 4-billionths of a 
trillionth of a watt.

   During its long life, Pioneer 10 has scored a number of firsts 
-- the first spacecraft to cross the asteroid belt; to fly by 
Jupiter and return pictures; to chart Jupiter's intense radiation 
belts; to measure the mass of its four planet-sized moons; to 
locate the giant planet's magnetic field and to discover that 
Jupiter is predominantly a liquid planet.

   As it plows through unexplored space, Pioneer 10 continues to 
seek the boundary between the solar wind and true interstellar 
space, to search for evidence of a possible 10th planet and for 
gravity waves confirming Einstein's Theory of Relativity.  
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   Events such as collisions between entire galaxies would 
"rattle" the actual structure of space itself, producing gravity 
waves.  The waves may be relatively easy to detect in the long 
wavelengths (1 billion to 5 billion miles).

   "Pioneer 10 and its sister ship, Pioneer 11, have been two of 
the greatest scientific successes of the Space Age,"  said Dr. 
James Van Allen of the University of Iowa, a Pioneer principal 
investigator.

   Perhaps Pioneer 10's most important finding about the outer 
solar system is the extent of the sun's atmosphere, originally 
thought to have ended at the orbit of Jupiter or Pluto.  Pioneer 
10 is now almost 10 times that far and still within the solar 
atmosphere.  Many scientists now say that the solar wind boundary 
interface with the cosmic interstellar gas might be as far away as 
9.3 billion miles, compared to Earth's distance from the sun of 93 
million miles.

   "Pioneer 10's exploration of the outer heliosphere (sun's 
atmosphere) and its interface with the interstellar gas is of 
fundamental scientific importance," said Dr. Frank B. McDonald of 
the University of Maryland, Principal Investigator for the cosmic 
ray telescope.  "By lasting so long, Pioneer 10 has in essence 
created a new science mission and represents a triumph for 
American technology and industry."

   "We still take science data from it daily and will probably 
continue to do so until at least 1998.  That's an 
out-of-this-world record of accomplishment," said Richard Fimmel, 
Ames' Pioneer 10 Project Manager.

   Pioneer 10 is managed by NASA's Ames Research Center, Mountain 
View, Calif., and was built by TRW, Redondo Beach, Calif.

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