A main engine burn on the Juno spacecraft scheduled for Wednesday October 19 has been postponed until Juno completes another orbit around Jupiter, a trip that currently takes 53.4 days. The engine burn was intended to accelerate the spacecraft so it could orbit Jupiter in just 14 days, after which the main science phase of the mission was going to begin and the majority of the data taken.
According to NASA, the Juno mission team decided to postpone the burn after two valves on the spacecraft's main engine failed to properly open. The spacecraft needs to be at its closest to Jupiter for the engine burn to achieve the proper acceleration and trajectory, so the team will have to wait until December 11, when Juno completes a full orbit at its current speed, to attempt to fire the engine again and insert into its trajectory for its main science mission.
"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, in a NASA press release. "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."
It is not clear how the delay will affect Juno's overall mission going forward, considering the bombardment of radiation from Jupiter puts a hard limit on the spacecraft's lifetime. The mission is currently scheduled to end by impacting Juno into Jupiter in February 2018, and any delays to the main data-gathering portion of the mission could result in less information ultimately gleaned from the orbiter.
The engine malfunction isn't all bad, however. The spacecraft was origionally scheduled to shut down most of its science instruments for the engine burn, but now it will be able to gather data as it makes a close pass of Jupiter on Wednesday. As Scott Bolton, principal investigator for the Juno mission, points out, "the mission is very flexible" due to the fact that the close flybys are when the spacecraft is expected to learn the most.
"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," he says. "The data we collected during our first flyby on August 27 was a revelation, and I fully anticipate a similar result from Juno's October 19 flyby."
It is still unclear what exactly caused the engine's helium check valves to open more slowly than anticipated, but hopefully the issue is not systemic of a larger problem on the big Jovian orbiter.