Juno spacecraft makes Earth flyby

A Jupiter-bound spacecraft swung past Earth Wednesday afternoon in order to get a boost from Earth’s gravity.

NASA’s Juno spacecraft, which launched from Earth toward Jupiter on Aug. 5, 2011, was later yanked back toward the inner solar system by the sun’s gravity. It made its closest approach to Earth at 3:21 p.m. ET, pass about 560 kilometres above South Africa.

Scott Bolton, principal investigator of the Juno mission, said in a statement that the force of Earth’s gravity during the flyby would boost the spacecraft’s speed relative to the Earth from 126,000 kilometres per hour to 140,000 kilometres per hour.

“The gravity assist essentially provides as much propulsion as a second rocket launch.”

Bolton is the director of the space science department at the Southwest Research Institute in San Antonio, Texas. He said Juno, which had a mass of 3.6 tonnes, including fuel and propellant, when it blasted off from Earth, is so big and heavy that “even a larger rocket couldn’t provide enough propulsion to get us all the way to Jupiter.”

Juno, named for the mythological wife and sister of the Roman god Jupiter, is expected to arrive at our solar system’s largest planet on July 4, 2016. After the spacecraft’s arrival, it will circle the planet 33 times from pole to pole. Unlike spacecraft that have visited Jupiter, Juno will be able to see through the gas giant’s dense cloud cover, observing the planet’s magnetic fields, atmosphere and chemical composition.

Its goal is to uncover how Jupiter formed and evolved over its history.

Message to space

During  Wednesday’s close approach, the Juno mission invited amateur radio operators to say “hi” to the spacecraft using Morse code.

“Juno's radio and plasma wave experiment, called Waves, should be able to detect the message if enough people participate,” said a page for the event on the website of NASA’s Jet Propulsion Laboratory at the California Institute of Technology.

During the flyby, Juno was to approach Earth’s sunlit side from deep space, allowing it to take “never-before-seen images of the Earth-moon” from a perspective similar to that of someone on Mars or Jupiter, said Bolton. A movie of the images was expected to be released shortly after the flyby.

The Juno mission team also took the opportunity to check and calibrate the spacecraft’s nine scientific instruments during the flyby.

The mystery of the extra boost

Meanwhile, the European Space Agency planned to measure the spacecraft’s radio signals during the flyby from tracking stations in Argentina and Australia. Its scientists are trying to figure out why some spacecraft pick up or lose an unexpected amount of speed as they swing past the Earth to get a gravity boost.

The variations are very small – so small that in some cases, such as when the NASA’s Cassini and Messenger flew by in 1999 and 2005 respectively, they couldn’t be confirmed. But they have been as large as 13 millimetres per second in the case of NASA’s NEAR spacecraft in 1998.

Daniel Firre, who is responsible for tracking support at the ESA’s European Space Operations Centre, said in a statement that gathering more data is “critical if we are ever to solve this perplexing mystery.”