Stubborn valves leave Juno hanging

When it comes to orbiting planets, there are more hospitable places to ply your trade than our solar system's resident gas giant. Ions and electrons whizz around Jupiter's equator at the speed of light, threatening to fry any unsuspecting spacecraft electronics in their path. Through a meticulously planned orbit, NASA's Juno probe has now circled Jupiter and evaded its harmful radiation for more than four months, but just as the spacecraft was to swing in for a closer look, an unexpected engine complication has resulted in a first, and hopefully minor, setback.

Since pulling off a correction burn and slipping into orbit around Jupiter on July 4, Juno has circled our solar system's largest planet twice, once every 53.5 days. Because Juno ventures closer to Jupiter than any spacecraft before it, mission planners had to be quite careful about how they had the probe make its approach.

This is described as a highly elliptical polar orbit and has Juno make huge sweeping passes of Jupiter that actually see it spend most of its time in outer space, beyond the destructive clutches of its radiation. This has allowed the team to turn on craft's science instruments for performance checks and calibration in the Jupiter environment (and snap a few pics along the way), before entering a tighter 14-day orbit, where the bulk of the Juno's science will be collected.

Juno was all set to make its move on October 19, during the part of its orbit that brings it closest to the planet. Its shift to a 14-day orbit will be facilitated by a burn of its main rocket motor, in what is called a period-reduction maneuver, the last of its scheduled burns. But during a command sequence in the lead-up to the event, the mission control team found things weren't exactly going to plan.

"Telemetry indicates that two helium check valves that play an important role in the firing of the spacecraft's main engine did not operate as expected during a command sequence that was initiated yesterday," said Rick Nybakken, Juno project manager at NASA's Jet Propulsion Laboratory. "The valves should have opened in a few seconds, but it took several minutes. We need to better understand this issue before moving forward with a burn of the main engine."

So while NASA works out what the deal is with those misfiring valves, Juno will continue on another 53.5-day long path around Jupiter. And because the best time for Juno to make the burn is when it is closest to the planet, this means that it won't zero in on its primary science phase until December 11, if all goes to plan.

While only time will tell how the setback impacts the Juno mission's overall success, there is an immediate upside. Originally, only three science instruments were going to be operational during the upcoming period-reduction maneuver, but NASA will now take the opportunity to fire up the craft's full gamut of planet-scoping weaponry to gather as much data as possible when it zooms by on October 19.

"It is important to note that the orbital period does not affect the quality of the science that takes place during one of Juno's close flybys of Jupiter," said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. "The mission is very flexible that way. The data we collected during our first flyby on August 27th was a revelation, and I fully anticipate a similar result from Juno's October 19th flyby."

Source: NASA