After 1.7 billion miles Juno nails its Jupiter orbit to within tens of miles

Traveling at a speed of 165,000mph toward a swirling gas giant Monday night, the Juno spacecraft would have no second chances. Had its Leros 1b engine burned too long, Jupiter would have swallowed Juno into its gaseous maw. If the British-made engine burned too short, the spacecraft would have zipped onward into space, lost into the inky blackness forever. But Juno needed no second chance late on the night of July 4th as its hardy little engine fired for a total of 2,102 seconds, perfect to within one second, inserting the spacecraft neatly into orbit around Jupiter.

Back on Earth engineers at the Jet Propulsion Laboratory in California cheered heartily. During the last five years a team of 300 engineers have guided Juno along its path. Another 900 built and launched the spacecraft. Moments after the orbital insertion Scott Bolton, the mission’s principal investigator, saluted the team of engineers, telling them they were the “best ever.” In his euphoria, Bolton added, “You just did the hardest thing NASA's ever done."

Perhaps not, but it is no small thing to spend the better part of a decade building a spacecraft to survive the harsh radiation of Jupiter, launch it across 1.7 billion miles of space over five years, and then drop it precisely where you want around a planet 2.5 times more massive than all the other planets in the solar system—combined. At the end of the day Juno hit a keyhole a few tens of miles across.

In reality, NASA also now sentenced its $1.1 billion (~£850M) spacecraft to die. Mission managers hope to get 37 orbits out of Juno over the next 20 months before radiation slowly breaks down its electronics and propulsion system. Even though a 1cm-thick wall of titanium encases the spacecraft’s electronics to provide some protection, a few of its nine instruments may begin to fail in as few as eight or 10 orbits. Before the spacecraft fails entirely engineers will place Juno into a slowly degrading orbit that will eventually force it to plunge into the planet. This is so that none of its potentially life bearing moons, such as Europa, might be contaminated.

Because of Juno’s limited lifespan, the science mission begins almost immediately. The spacecraft’s instruments will come online about two days from now, when Juno embarks upon its first elongated orbit, spanning 53 days. As it travels into Jupiter’s intense radiation belts Juno will not send data back to Earth, so scientists will have to wait until the end of August to begin getting large amounts of information about the planet. Shorter, closer-in orbits will follow in 2017.

Jupiter, of course, has been surveyed extensively before by NASA’s Galileo probe, which studied both the stormy, colorful gas giant and its extensive system of moons beginning about two decades ago. Juno will seek to probe more deeply into the interior of Jupiter with two magnetometers, which will allow scientists to map the planet’s magnetic field. They hope to understand precisely how that intense magnetic field is generated, and how hydrogen behaves at the very high pressures at the center of the planet. Other instruments on board will measure Jupiter’s gravitational field, the structure of its clouds, and the amount of water in Jupiter’s atmosphere.

And now, thanks to Monday's night's precise maneuvers, Juno will get a chance to deliver on the promise of its hefty science mission. “Tonight Juno sang to us, and it was a song of perfection," said Rick Nybakken, Juno's project manager at the Jet Propulsion Laboratory, during a late night news conference.

As much of the United States celebrated the 240th anniversary of the US Declaration of Independence, in its own way NASA offered a tribute to the country of Washington, Jefferson, and Lincoln. Once again NASA had made it look easy, but it certainly was not. No other country has ever sent a spacecraft into orbit around Jupiter, and now America has done it twice. A happy birthday, indeed.

Listing image by NASA