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The decision, made in response to some technical difficulties with the plumbing for the spacecraft's main engine, cuts down the number of science orbits Juno can make from about 32 to 12. But in many ways the change might actually allow for better science, mission team members said.
“Sometimes you make lemonade when you have lemons — or when you appear to have lemons,” said Rick Nybakken, Juno’s project manager at
Juno entered Jovian orbit last year after a five-year journey through space. The mission's goal: to probe the many mysteries of the solar system's most massive planet, from the composition of its core to the behavior of its powerful magnetosphere.
The answers to such questions could offer unprecedented insight into the composition and evolution of the early solar system.
The spacecraft began circling Jupiter in long, 53-day orbits, and was set to push itself into shorter two-week orbits soon after. This would allow it to fly close over the surface (about 2,600 miles) more frequently during the relatively short mission, originally set to end in February 2018.
But two helium check valves for the main engine had started to respond too slowly. This meant that if the team tried to push the spacecraft into the two-week orbit, they could risk sending it off-course.
After reviewing their options, Nybakken said, the team decided that attempting the maneuver wasn't worth the risk to the mission overall.
The longer orbits won't hurt the science, said Scott Bolton, Juno's principal investigator from Southwest Research Institute. In fact, they might actually come with added benefits. With these longer orbits, the spacecraft will now be able to study the more distant parts of Jupiter's magnetosphere in a way that it could not have before. And because of eventual changes in its relative orientation to Earth over time, the spacecraft should be able to get more precise measurements of Jupiter's gravitational field — which should help them better map out the planet's core (if it does indeed have one).
"You have everything that you had in the original mission, and you have all these additional things that you didn't have before," Bolton said. "So that's just a bit of luck."
As a bonus, the longer orbits actually end up causing less radiation damage to the spacecraft than the short two-week orbits do. This means that the spacecraft doesn't necessarily need to be crashed into Jupiter by early 2018, as originally planned — a move that was designed to keep the satellite from falling into and contaminating potentially life-friendly worlds such as the icy moon Europa.
Juno's current plan allows it to operate through July 2018 — which would allow for only 12 science orbits instead of the more than 30 in the original plan. However, with less fear of radiation damage, it's possible that the spacecraft could end up making many more orbits around the gas giant.
But that decision is up to NASA, Nybakken said, and at a later date. For now, the team is looking forward to Juno's next close pass above the gas giant, on March 27.
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