NASA has revealed that its Juno probe has developed engine trouble as it orbits Jupiter, leading to a delay in part of the mission.
A statement from the US space agency said that the probe developed a fault in a set of valves that make up part of the craft's fuel pressurisation system.
"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 in Pasadena, California.
"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."
The probe was scheduled to fire the engines on 19 October to decrease its 'orbital period', the time it takes to orbit the gas giant, from 53.4 to 14 days.
This engine burn can happen only at certain times, however, if it is to be efficient. NASA explained that the best time to perform such a burn is when the craft is at the part of its orbit which is closest to the planet. The next opportunity for the burn will be during a close flyby of Jupiter on 11 December.
Before the engine problems had been discovered, the plan was for this part of the mission to use only some of the probe's scientific instruments, but perhaps fearing further failures NASA has now decided that all instruments will be used to examine Jupiter after the next engine burn.
Experts remain hopeful that the mission will still prove successful.
"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 27 August was a revelation, and I fully anticipate a similar result from Juno's 19 October flyby."
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