An eye for an i #463 Children

Pioneer 3, a failure with some success

Dressed more like surgeons, these technicians wearing clean room attire inspect the Pioneer 3 probe before shipping it for its launch.   | Photo Credit: NASA Wikimedia Commons

By 1958, scientists knew that ions and electrons could be trapped by the Earth’s magnetic field, even though their existence wasn’t confirmed. It was space scientist James Van Allen and his team of researchers at the University of Iowa who discovered the radiation belts, which are now referred to as the Van Allen Belts.

We now know that there are two belts of radiation circling the Earth and even a third can appear sometimes. These magnetically trapped, highly energetic charged particles surround the Earth in giant doughnut-shaped belts.

Explorers and a Pioneer

Van Allen’s experiments carried aboard Explorer 1, the very first American satellite that was launched on January 31, 1958, and Explorer 3, launched on March 26, 1958, were used by the Iowa group to detect the inner radiation belt. Data provided by instruments carried by Explorer 4, launched July 26, 1958, and Pioneer 3, launched December 6, 1958, established the outer radiation belt encircling the inner belt.

The Pioneer 3 mission was among the first attempts by the U.S. to send a spacecraft to the moon. It was a cone-shaped probe that was 58 cm high and had a base diameter of 25 cm. This cone was composed of a thin fibreglass shell coated with a gold wash. This was done to make it electrically conducting, while it was painted with white stripes to maintain the temperature between 10 and 50 degrees Celsius.

The spin-stabilised probe carried two special six-gm weights that were to be spun out on five-ft wires in order to reduce the spin once the mission got underway. It also carried an optical sensor to test a future imaging system.

Test future imaging system

If this sensor received a beam of light from a source, like the moon, that was wide enough to pass through the lens and fall on two photocells simultaneously, then it would send a signal to switch on the imaging system. Even though this spacecraft did not carry an imaging system, it was a test to see if such a triggering mechanism was workable.

Launched on December 6, 1958, the flight plan of the mission called for the Pioneer 3 probe to pass close to the moon after 33.75 hours and then go into a solar orbit. Premature propellant depletion, however, meant that the main booster engine of the first stage was shut down 3.7 seconds earlier than planned.

Short of escape velocity

Put on its trajectory, it was determined that the Pioneer 3 was about 1,040 km/hour short of the escape velocity required to take it past the Earth orbit. Pioneer 3 reached a maximum altitude of 1,02,322 km before plummeting down, re-entering the Earth’s atmosphere and burning up over Africa on December 7, 38 hours and 6 minutes after launch.

Apart from the fact that Pioneer 3 failed to meet its primary objective of making it to the moon, the de-spin mechanism also failed to operate and hence the optical system could not be tested. The only saving grace came from the Geiger counter that the spacecraft was equipped with to study interplanetary radiation.

Even though the spacecraft was only able to send data for about 25 hours with the remaining 13 hours being blackout periods due to the location of the tracking stations, it turned out to be of significant value. The data from the radiation counter indicated the existence of the outer radiation belt in what is now known as the Van Allen Belts. This turned out to be a major discovery as we have learnt that there are dual bands around the Earth that are actually distinct belts.


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Printable version | Jan 19, 2022 1:10:30 AM | https://www.thehindu.com/children/pioneer-3-a-failure-with-some-success/article37699367.ece

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