Gravity science (Juno)
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The Gravity Science experiment and instrument set aboard the Juno Jupiter orbiter is designed to monitor Jupiter's gravity.[1][2][3] It maps Jupiter's gravitational field, which will allow the interior of Jupiter to be better understood.[3] It uses special hardware on Juno, and also on Earth,[1] including the high-gain K-band and X-band communication systems of the Deep Space Network as well as Juno's Ka-band Translator System (KaTS).[1][4] These components work together to detect minute changes in radio frequency (Doppler shift) to measure the spacecraft's velocity over time.[5] The KaTS box was funded by the Italian Space Agency and overseen by professor Luciano Iess from University La Sapienza in Rome.[4] KaTS detects signals coming from the DSN on Earth, and then sends replies in a very precise way that allows the velocity of Juno to be determined to within 0.001 millimeters per second.[4] The spacecraft receives a tone signal on the Ka band and then replies using the X-band radio.[1]
As the spacecraft traverses the space near Jupiter, the planet, and even variations in the planets interior, cause a variation in Juno velocity.[6] The gravity science experiment measures these velocity changes using a combination of hardware on Earth and the spacecraft, which allows the effect of gravity to be measured, and thereby mass variations in Jupiter's interior.[6]
- Deep Space Network 25 sends a tone signal at 32.5 GHz (Ka-Band)
- Juno KaTS sends tone signal at 35 GHz (X-Band)
Juno launched in 2011 and arrived at Jupiter orbit in July 2016.[7]
The GS was planned out to be used on orbits 4, orbit 9, and orbits 10 through 32.[8] When GS operates it must point its antenna at Earth, and is not operated simultaneously with the Microwave Radiometer instrument on Juno.[8] The parameters of the GS experiment were adjusted to account for a 53-day orbit the Juno spacecraft ended up being in.[9]
The GS experiment uses Deep Space Network's DSS-25 antenna which is equipped with simultaneous dual X- and Ka-band transmitters and receivers, as well as the spacecraft which also has X and Ka-band radio systems.[9]