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NASA's Juno probe is halfway to Jupiter

Paul Sutherland, Feature writer
Aug 14, 2013, 7:00 UTC

Sen—NASA’s latest mission to planet Jupiter has reached the halfway point in its five-year journey.

The probe, called Juno, clocked up the milestone after flying more than 1.4 billion km since it was launched on 5 August 2011.

The mid-point in the spacecraft’s trajectory does not place it midway between Earth and Jupiter however. As is typical for deep space missions, it is following a circuitous route through the Solar System that allows it to gain momentum from inner planets on its flight.

In fact Juno will actually swoop past Earth again in October this year to get a speed boost. The probe was 55.46 million km (34.46 million miles) from Earth when this week’s milestone was reached.

Juno’s project manager, Rick Nybakken of NASA’s Jet Propulsion Laboratory in California, said: “On October 9, Juno will come within 347 miles (559 kilometers) of Earth. The Earth flyby will give Juno a kick in the pants, boosting its velocity by 16,330 mph (about 7.3 kilometers per second). From there, it’s next stop Jupiter.”

The halfway point in the mission was reached on 12 August at 12.25 GMT. Juno’s Principal Investigator Scott Bolton, of the Southwest Research Institute in San Antonio, Texas, said: “Juno’s odometer just clicked over to 9.464 astronomical units. (An astronomical unit, or AU, is approximately equivalent to the distance of the Earth from the Sun and equals 149,597,870.7 km or 879,733,760 miles.)

Bolton added: “The team is looking forward, preparing for the day we enter orbit around the most massive planet in our solar system.”

Juno will arrive at Jupiter on 4 July, 2016. Once there, it will go into a low, elliptical orbit. Unlike NASA’s previous Jupiter probe Galileo, which orbited from 1995 to 2003, Juno will stick close to the planet, circling it from pole to pole.

It will slowly spin as it flies, making it more stable but also giving all eight instruments aboard a chance to scan the planet. In more than 30 orbits, each lasting 11 days, the spacecraft will skim the planet’s cloudtops, coming to within a distance of 5,000 km.


Juno's position on 8 August as it headed back towards Earth. Credit: NASA's Eyes on the Solar System

This orbital pattern, with Jupiter rotating rapidly in a day lasting around 10 hours, will allow Juno to map the whole of the planet’s clouds during its mission and to penetrate deep within them with its onboard instruments.

By hugging the planet, Juno will avoid the regions where Jupiter pumps out its most lethal levels of radiation, particularly a zone around the equator where tiny charged particle of ions and electrons fly about at speeds close to that of light.

Even so, the levels of radiation levels will be equivalent to more than 100 million dental X-rays which would be enough to toast electronics aboard any ordinary spacecraft. The most sensitive electronics will therefore be shielded within a titanium vault a meter wide, with walls a centimeter thick.

A full-colour JunoCam will take photographs of Jupiter’s clouds and promises to deliver spectacular images over seven or so orbits that are the camera’s expected lifetime under the levels of radiation bombardment.

Juno’s main aim will be to learn how Jupiter formed and evolved which will then teach us much about the formation of the Solar System.