After NASA’s Juno spacecraft fired up its engine Monday, letting it slow down and settle into Jupiter’s orbit, it ultimately arrived off schedule – by a second.
That is to say, an unmanned probe departed from Earth five years ago, traveled 1.7 billion miles through the solar system and reached its destination within a tick of scientists’ prediction.
Even NASA was a bit surprised.
“We hit our burn targets within one second,” said Rick Nybakken, Juno project manager. “On a target that was just tens of kilometers large. Isn’t that incredible?”
Also incredible: NASA only needed to fine-tune Juno's trajectory once in its years-long journey for the probe to arrive as planned.
That only course correction, called a trajectory correction maneuver, took place February 3. NASA had another course correction planned for May 31.
But Juno’s navigators didn’t need it.
“With Jupiter they were able to target it a long time ago, and they were just able to anticipate every possible influence on the spacecraft so well that the last time adjusted anything was back in February and they still hit it that precisely,” Nybakken told USA TODAY.
To navigate deep space with such accuracy, Juno relied on several tools. The spacecraft has four star trackers, as NPR’s Joe Palca explains, camera-like devices able to scan and recognize the stars around Juno. The stars’ coordinates tell Juno how it’s oriented and whether it’s pointed in the right direction.
Additionally, three large radio antennas on earth – in Spain, Australia and California – pick up radio signals that scientists used to measure Juno's location and speed.
The process behind such a voyage is complex, but ask Nybakken how Juno hit its target with near perfection and he’ll put it simply: “These guys are just really good.”
“They’re able to look at the effects of the sun versus the effects of Jupiter versus solar wind,” he said. “Anything that might be a perturbation. Every time we’ve done a maneuver, they’ve nailed it.”
Follow Josh Hafner on Twitter: @joshhafner
