By Jove! NASA's Juno prepares to slip into orbit around Jupiter

The big red button has already been pushed on the risky manoeuvre to date

Photo credit: NASA/Aubrey Gemignani

NASA's Juno spacecraft is set to enter its most critical stage as it attempts to fly into Jupiter’s orbit.

At 4:18am BST, NASA’s Juno spacecraft will begin its orbital insertion burn, a move that will decelerate its velocity – slow enough to be captured by Jupiter’s gravitational field.

The burn will initiate when the spacecraft is at its closest approach to the gas giant and will last 35 minutes. It has to be perfectly executed. All other instruments will be turned off to prevent any malfunctions that could interfere with the burn.

NASA's missions rarely fail, but there have been instances when orbital insertion fails. In 1999, the Mars Climate Orbiter lost communication with Earth during its orbital burn. Scientists later discovered that it had passed too close to the planet and disintegrated in the Red Planet's atmosphere.

The oxidiser and fuel valves in Juno's British-built Leros-1b engine will open automatically. The propellant, which is MON/hydrazine – a mix of nitrous oxide and dinitrogen tetroxide – will flow into the combustion chamber where it will be ignited as fuel.

The burn should change Juno’s velocity by 1,212 miles per hour (542 metres a second) on average. If the burn fires at the wrong time or duration, there is a chance that the spacecraft will fly straight past Jupiter and fail its mission worth £800m. There are no second chances.

Jupiter is a giant gas ball – 11 times wider and 300 times more massive than Earth. It is unknown if the planet has a solid core so Juno will not be landing on any surface. Instead, if the spacecraft successfully enters Jovian orbit, it will be descending into its fluffy clouds.

The goal is to understand how the planet formed and its role within the Solar System. Planetary scientists believe that it was one of the earliest planets to form and was originally much closer to the Sun. Its huge mass means that its gravitational field is strong and has a bigger impact on other planets. Scientists believe Jupiter may have scattered the icy planets into the furthest reaches of the Solar System when it and Saturn became gravitationally excited.

The orbital insertion burn is not the only danger, however, and the spacecraft will have to battle its way through Jupiter’s hostile magnetosphere. It has to be able to withstand the onslaught of electrically charged particles whipped up by the planet’s powerful magnetic field in order to measure that field and study Jupiter’s auroras.

Juno will also be looking for water and ammonia in the atmosphere. Its Gravity Space experiment will be probing beneath Jupiter’s atmosphere to map the planet’s gravitational field and study its internal structure to find out if the planet has a solid core.

Whether Juno makes it to its destination is now out of the scientists’ hands. Last Thursday evening, mission controllers launched “ji4040” – a command that launched the spacecraft into autopilot mode.

The spacecraft is roughly the size of a basketball court and will be powered by sunlight throughout its mission. It will orbit Jupiter 37 times before it enters its final deorbit phase, where it will descend deeper into the planet’s atmosphere and burn up in February 2018. ®

Watch the mission trailer here.

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