Juno salutes its home planet and heads to Jupiter

by Harvey Leifert
Wednesday, December 11, 2013

Thanks to orbital mechanics, a spacecraft heading to Jupiter must go most of the way there, then loop around the sun, zoom back close to Earth, and finally head out again on its mission to the largest planet in the solar system. That's the story of Juno, launched by NASA on Aug. 5, 2011, and due to arrive at Jupiter on July 4, 2016. Its journey required a boost in velocity, relative to the sun, which it received when it flew as close as 559  kilometers above Earth on Oct. 9, 2013. Juno’s flyby of its home planet took it over several continents, with its lowest approach occurring over Cape Town, South Africa.

But these technical requirements gave scientists the opportunity to do some really cool experiments on the way.

As Juno sped toward Earth at high speed, mission scientists, led by principal investigator Scott Bolton of the Southwest Research Institute in San Antonio, Texas, devised several novel ways to test its instruments, while at the same time arousing public interest in the spacecraft and its mission. They reported their findings Tuesday, Dec. 10, at the annual meeting of the American Geophysical Union in San Francisco, Calif.

One of the key instruments on Juno is a small camera, designed to take high speed, but low resolution, images of faint stars once it is in orbit around Jupiter. As Juno rotates every 30 seconds about its axis, the camera will help determine its orientation at any moment. John Jørgensen of the Danish Technical University in Copenhagen reported that colleagues decided to test the camera by taking images of Earth and the moon, one image every fifth rotation of the spacecraft, starting from 3.5 million kilometers away. The result is a unique movie, showing lunar revolutions and an eclipse of Earth, from its outer space perspective.

Another experiment tested Juno’s Waves instrument, designed to study Jupiter’s magnetosphere. Bill Kurth of the University of Iowa in Iowa City described an experiment in which some 1,400 amateur radio operators around the world were mobilized to transmit the word “hi” at the same time, to see if Juno could receive their individually faint transmissions. In Morse code, "hi" is four “dits,” followed by two “dits,” but for the experiment, each “dit” was extended to 30 seconds. Although the signal to noise ratio was low, Waves did capture and record a series of “hi"s, greetings from the planet to which it will never return.

Once at Jupiter, Juno will make 33 revolutions of the planet, providing the first ever views of its poles and probe beneath the thick cloud cover to learn about its origins, internal structure, atmosphere and magnetosphere.

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