Half a century ago, NASA's Pioneer 10 visited Jupiter, then just kept going

And going and going until the probe squeaked its last in 2003

It is 50 years since Pioneer 10, NASA's first all-nuclear electrical powered spacecraft, got up close and personal with our solar system's largest planet, Jupiter.

Pioneer 10, the first of NASA's probes into the outer solar system, was launched from Cape Canaveral on March 3, 1972. The spacecraft was powered by radioisotope thermoelectric generators (RTGs) running on plutonium-238 because solar power was insufficient at the distance of Jupiter from the Sun. The primary goal of the probe was to observe the gas giant, assuming it got through the asteroid belt and survived the intense radiation around the planet.

Many of the lessons learned from Pioneer 10 would go on to inform the design of its successors, including the Voyager probes.

On December 4, 1973, Pioneer 10 made its closest approach to Jupiter. According to NASA, the spacecraft came within 81,000 miles (130,354 km) of the planet's surface and passed at approximately 78,000 miles per hour (126,000 kilometers/hour).

Between November 6 and December 31, 1973, the spacecraft took about 500 pictures of Jupiter's atmosphere with the highest resolution of approximately 200 miles (320 km), clearly showing landmarks such as the Great Red Spot.

However, it was touch and go. Scientists speculated that Pioneer 10 might be dashed to pieces, or at least disabled, by debris in the asteroid belt. It survived, recording far fewer impacts than expected and paving the way for future missions into the outer solar system. Then there was the radiation – would Pioneer 10's electronics function as the probe flew through the harsh environment around Jupiter? Again, the spacecraft survived as it endured its closest encounter with the gas giant and experienced peak intensities of electrons more than 10,000 times that of Earth.

As it transpired, the intense radiation caused only one glitch to occur – a command corruption meant that photography of Io and some of Jupiter did not go as expected. However, the fact that the spacecraft's computer survived is a testament to the engineers who designed the electronics.

Pioneer 10's imaging system was basic compared to those launched on more modern probes. The Imaging Photopolarimeter (IPP) relied on the spacecraft's spin to build up an image in strips only 0.3 degrees wide. The strips captured red and blue light and were used to build up an image, with green derived from the red and blue.

Although the images were stunning for scientists used to observing Jupiter from Earth, the probe carried other instruments for measuring magnetic fields, temperature, radiation, and micrometeoroids. Although the encounter with Jupiter was declared over as 1974 dawned, Pioneer 10 sailed on through the solar system, crossing the orbits of Saturn and Neptune, and eventually losing its crown as the most distant human-made object when it was overtaken by Voyager 1 in 1998.

In 1997, routine contact with the probe was axed due to budgetary constraints, although some instruments, including the Geiger tube telescope, were still collecting data. By 2000, the spacecraft was still transmitting a faint signal, indicating that all was normal onboard. Its last telemetry data was received in 2002, and the last signal from the probe was heard in 2003. By then, it took more than 11 hours for the signal to reach Earth, and the spacecraft's fading power source had decayed to the point where the radio transmitter could barely be powered.

A final attempt was made to contact the probe in 2006, but there was no response. More than 30 years into a mission that was supposed to last less than two, Pioneer 10 was confirmed dead – or at least too weak to be heard.

Pioneer 10 was a mission packed with firsts – the first to cross the asteroid belt, the first to visit Jupiter, the first to leave the solar system, and the first to include a message for intelligent extraterrestrial life. While the Voyager probes impressed with the science collected and their astonishing longevity, it is important to remember the trailblazer that went before. ®

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