The scientists and engineers running the Juno mission to Jupiter have decided to keep the spacecraft in its 53-day orbit for the rest of its mission rather than fire its engines to lower the orbit to its planned 14 days duration.
The original Juno flight plan envisioned the spacecraft looping around Jupiter twice in 53-day orbits, then reducing its orbital period to 14 days for the remainder of the mission. However, two helium check valves that are part of the plumbing for the spacecraft’s main engine did not operate as expected when the propulsion system was pressurized in October. Telemetry from the spacecraft indicated that it took several minutes for the valves to open, while it took only a few seconds during past main engine firings. “During a thorough review, we looked at multiple scenarios that would place Juno in a shorter-period orbit, but there was concern that another main engine burn could result in a less-than-desirable orbit,” said Rick Nybakken, Juno project manager at NASA’s Jet Propulsion Laboratory in Pasadena, California. “The bottom line is a burn represented a risk to completion of Juno’s science objectives.”
There are both pros and cons for using this longer orbit, detailed at the link, with.the most important being that doing nothing avoids losing the mission entirely.