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[MIAMI] A US$1.1 billion Nasa spacecraft called Juno must dodge debris and extreme radiation Monday as it attempts to orbit Jupiter on a high-stakes mission to probe the solar system's origin.
Juno is expected to arrive late Monday in the vicinity of the largest planet in our cosmic neighborhood, five years after the unmanned solar-powered observatory launched from Cape Canaveral, Florida.
"We are barreling down on Jupiter really quick," said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio, Texas.
As Nasa counted down to Juno's arrival, he admitted to being "nervous" and "scared" about the fate of the spacecraft, which is traveling at a speed of more than 130,000 miles per hour (209,200 kilometers per hour) toward what he called "the king of the solar system."
A key concern is that the spacecraft must survive radiation levels as high as one hundred million X-rays in the course of a year, explained Heidi Becker, senior engineer on radiation effects at Nasa's Jet Propulsion Laboratory.
Those high-energy electrons, moving at the speed of light, "will go right through a spacecraft and strip the atoms apart inside your electronics and fry your brain if you don't do anything about it," she said.
"So we did a lot about it," she added, describing the half-inch-thick layer of titanium that protects the electronics in a vault to bring the radiation dose down.
Still, she described the close approach as going "into the scariest part of the scariest place... part of Jupiter's radiation environment where nobody has ever been." Juno must also avoid debris as it speeds through a belt of dust and meteorites surrounding Jupiter.
"If it gets hit - even by a big piece of dust, even by a small piece of dust - it can do very serious damage," Mr Bolton said.
On approach, the engine doors are open, leaving the nozzle vulnerable, he said.
"If any dust is in our way and hits that nozzle, it will knock a hole right through the coating that protects that nozzle and allows the engine to burn uninterrupted," he told reporters.
"That is one of the big gambles." After that, a tricky, fully automated orbit maneuver must go well as the engine fires to slow it down enough to be captured by Jupiter's orbit.
This "burn," or orbit insertion, begins at 11:18 pm (0318 GMT) and should last around 35 minutes.
The spacecraft must then re-orient itself toward the Sun in order to power the solar arrays.
If it fails to enter orbit, Juno may shoot past Jupiter, bringing a mission 15 years in the making to a swift end some 540 million miles (869 million kilometers) from Earth.
Scientists hope to find out more about how much water Jupiter holds and the makeup of its core in order to figure out how the planet - and others in the neighbourhood, including Earth - formed billions of years ago.
The solar system's most massive planet is fifth from the sun.
With an atmosphere of hydrogen and helium, it's known for its Great Red Spot, a storm bigger than Earth that has been raging for hundreds of years.
The first mission designed to see beneath Jupiter's clouds, Juno is named after the Roman goddess who was the wife of Jupiter, the god of the sky in ancient mythology.
She was said to be able to see through the clouds with which Jupiter veiled himself to hide his mischief.
The Nasa mission aims to orbit Jupiter from pole to pole, sampling its charged particles and magnetic fields for the first time and revealing more about the auroras in ultraviolet light that can be seen around the planet's polar regions.
Juno should circle the planet 37 times before finally making a death plunge in 2018, to prevent the spacecraft from causing damage to any of Jupiter's icy moons, which Nasa hopes to explore one day for signs of life.
Although Juno will not be the first spacecraft to circle Jupiter, Nasa says its orbit will bring it closer than its predecessor, Galileo, which launched in 1989.
That spacecraft found evidence of subsurface saltwater on Jupiter's moons Europa, Ganymede and Callisto before making a final plunge into Jupiter in 2003.
Nasa says Juno should be able to get closer than Galileo - this time within 3,100 miles (5,000 kilometers) above the cloud tops.
"We have done everything humanly possible to make this mission a success," said Nasa's director of planetary science, Jim Green.
However, "it is still a cliffhanger for me, too."