Read out Pioneer 10 - a satellite is revolutionizing planetary science. The space probe had paved the way for the astronomers to the outer planets. Meanwhile, the spaceflight veteran is over ten billion kilometers away from us - and is still broadcasting. December 3, 1973: NASA's tight control room in Mountain View, California, has crackling tension. About 50 scientists and engineers gaze fixedly at the endless rows of numbers on the screens. They come from Pioneer 10, the first man-made probe that has ventured far into the outer solar system and is now facing its most severe test: will it withstand the concentrated radiation bombardment of planetary giant Jupiter? The most dramatic moments of the entire mission are imminent.

The radiation dose near Jupiter exceeds all expectations. Electrically charged particles from the solar wind are caught in the powerful magnetic field of the planet and accelerated to high speeds. They could mean the end of Pioneer 10. The radiation exceeds the earthly values ​​by a thousandfold. With a top speed of 36 kilometers per second, the probe shoots 131, 000 kilometers high above the outermost clouds of ammonia ice. Then Pioneer 10 disappears behind the planet.

The radio connection is interrupted for 40 minutes. Now even the cooler minds are getting restless: Would the signals reappear, or had the radiation belt destroyed the electronics of the measuring instruments? Everything was fine. Almost everything. Although Pioneer 10 reported back on schedule, some instruments seemed to receive ghostly signals and played crazy.

The radiation field had faked them false messages. "We had to tell Pioneer everything, switch every instrument on and off, set the order of measurements, regulate sensitivities, and so on. On some days we sent the probe 2, 000 to 3, 000 commands behind it. "Richard Fimmel, who was responsible for some of the scientific instruments on board and had been in charge of the mission from the start, is still amazed at this technical pioneering achievement when he designed the from the Californian company TRW Space and Technology built probe with their more modern successors Voyager and Galileo compares. display

The effort for Pioneer 10 was worth it. Numerous observations, including over 300 photos with a resolution of up to 500 kilometers, came to Earth. For the first time, the turbulent atmosphere of the gas giant could be observed up close and its enormous magnetic field measured. More importantly, Pioneer 10 has paved the way for all later and more accurate explorations of the outer solar system. Without this pioneering effort, the mission of the two Voyager spacecraft launched in late summer 1977 would not have been possible. Companies."

In the meantime, Pioneer 10's energy resources are so exhausted that only one scientific instrument can be operated: alternately the Geiger counter to detect the cosmic rays and the UV spectrometer, which measures the radiation reflected by the hydrogen between the stars. At the end of this or the beginning of the next year, the probe will be completely silent.

NASA officially terminated the mission on April 1, 1997. The $ 500, 000 annual operating costs were out of all proportion to the scientific output. The Silver Jubilee for the 25th anniversary of Pioneer 10, which was celebrated on March 2 of this year at the headquarters of NASA, was also a farewell party. The data also benefits young academics. "The Pioneer program got about 50 students to the doctoral degree, " smiled Charlie Hall, Pioneer 10's first project manager, at the ceremony. NASA has not completely abandoned its probe. Approaching flight controllers will fire them for a while and sporadically overhear their last whispers.

By contrast, Pioneer 11 has been silent since November 1995, when it was 6.6 billion kilometers from the Sun. The radio antenna could no longer be aligned with the earth: the power from the batteries had dried up. In just under four million years, Pioneer 11 will fly past the star Lambda in the constellation of Adler and will continue to drive further and further towards the center of the Milky Way.

Pioneer 10 is now over 10 billion kilometers (67 AU) away from us - almost twice as far as Pluto. Every hour, their distance increases by another 45, 000 kilometers. Never before has an earthly spaceship penetrated deeper into space. In February 1998, however, the probe will have to relinquish that record to Voyager 1, who shoots faster in the opposite direction.

Pioneer 10 will be on its way for at least 10, 000 years before it passes the alleged cradle of long-period comets: the Oort cometary cloud, which surrounds the solar system like a spherical shell. And in 33000 years she will fly past the dwarf star Ross 248 - at the stately distance of 3.3 light years, always in the direction of the constellation Taurus. About every million years, she'll pass more stars, "a ghost ship silently drifting through the dark room, " Larry Lasher says.

The probe will still intersect between the stars when there is no one on earth who could remember them. But even Pioneer's journey does not last forever. At some point, but only in billions of years, the interstellar matter, which rubs like the finest emery paper on the metal ghost ship, will destroy the probe. Their dust will spread in the boundless space between the stars.

=== Rüdiger Vaas

© science.de

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