NASA's Juno spacecraft is in orbit around Jupiter after a tense operation July 4. (Reuters)

NASA's Juno spacecraft slipped into orbit around Jupiter to much acclaim in July, but there may be trouble brewing: On Friday, NASA announced that the orbiter's engines seem to be on the fritz. It's not as if Juno is in grave danger, but scientists have opted to delay the next phase of the spacecraft's mission until they can fully investigate the problem.

A set of valves on Juno — part of its fuel pressurization system, and components that help facilitate the firing of the main engine — were a bit sluggish when scientists executed a command sequence last week. “The valves should have opened in a few seconds, but it took several minutes,” Rick Nybakken, Juno project manager at NASA's Jet Propulsion Laboratory, said in a statement. “We need to better understand this issue before moving forward with a burn of the main engine.”

That main engine burn, previously scheduled to occur on Oct. 19, would have brought Juno from a roughly 53-day orbit around Jupiter into a 14-day orbit. For now, Juno's orbit only brings it really close to Jupiter for a few hours at a time every two months or so, then flings it far away to protect it from the planet's violent magnetic field. The first burn of Juno's main engine will bring it into an orbit where it sweeps close to the planet every two weeks.

The next time Juno will be in the right spot for the orbital adjustment is Dec. 11 — the spacecraft will have to complete an entire far-flung orbit before it can start spinning more tightly around the planet. The hope is that the 53-day grace period will give NASA scientists more than enough time to fully understand the problem with the valves. They want to be sure that this engine burn — the first firing of the main engine — won't cause any long-term failures.

In the meantime, they'll be making up for the loss of a couple of close passes by turning on all of Juno's scientific instruments for the spacecraft's Oct. 11 flyby. The team had previously planned on keeping some of them turned off until the orbiter had begun its 14-day flight pattern.

“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,” principal investigator Scott Bolton said in a statement. “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.”

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