TWENTY FIVE years after its launch, Pioneer 10, the longest lasting and most distant interplanetary explorer, is being retired six billion miles from home.
Pioneer 10's science mission which began on March 2nd, 1972 ends later this month with the craft twice as far from the sun as Pluto, officials at the NASA Ames Research Centre in Mountain View said.
The spacecraft's power sources are quickly degrading, the Pioneer project manager, Mr Larry Lasher, said. While the craft will continue to transmit data for about another 12 months, "we believe the scientific return that we are getting at this point does not justify additional expenditures on the mission", he said.
Pioneer 10 is so far away that its radio signal, travelling at the speed of light, or 186,000 miles per second, takes more than nine hours to reach the Earth.
Built by TRW Space & Electronics Group, a unit of Cleveland based TRW Inc, Pioneer JO was launched in the same year Hewlett Packard introduced the world's first hand held calculator.
"By present standards, the instruments [aboard Pioneer 10] were low tech," said Prof James Van Allen, of the University of Iowa, and one of the principal investigators on the Pioneer 10 mission.
Its mission was intended to last just 21 months. But to the surprise of many scientists, it survived to become one of NASA's most prolific interplanetary explorers. "It has been a success beyond any of the original objectives," Prof Van Allen said.
Pioneer 10 was the first spacecraft to travel through the asteroid belt and explore the outer solar system, the first spacecraft to visit Jupiter, the first to use a planet's gravity to change its course and to reach solar system escape velocity, and the first to pass beyond the known planets.
On June 13th, 1983, more than 11 years after launch, Pioneer 10 became the first man made object to leave the solar system.
"It paved the way opened the door for all the of the missions," said Mr Lasher of Ames, which pilots Pioneer 10 and collects its data.
At the age of 25, Pioneer, travelling at 28,000 mph is still recording the intensity of galactic cosmic rays in the outer heliosphere, a region still under the influence of the sun, as it races toward the heliopause, the true outer boundary of the solar system.
Six of its original 11 instruments are functional, but the energy produced by its generators can only operate two of them. In the coming months the craft's power sources will continue to degrade.
Prof Van Allen said he would try to pressure NASA to continue collecting at least some data from Pioneer until the end of 1997.
Once Pioneer 10's radio signal dies out, the ghost ship will coast silently through deep space on its own momentum.