NASA’s Juno mission to Jupiter have decided to postpone the upcoming burn of its main rocket motor originally scheduled for Oct. 19

Juno’s orbital period reduction delayed

After two orbits of 53.4 days around the gas giant since its orbital insertion on July 4th, NASA’s Juno spacecraft was planned to move to a 14 day-orbit set, named “science orbits”. Juno is programmed to travel a total of 33 of these ‘short’ science orbits before the planned end of the mission.

The transition from the 53.4 orbit to the science orbit was supposed to take place on Wednesday October 19th, but a set of valves that are part of the spacecraft’s fuel pressurization system did not work properly. “The valves should have opened in a few seconds after a command sent on October 13, but it took several minutes”, said Rick Nybakken, Juno project manager at JPL, “We need to better understand this issue before moving forward with a burn of the main engine”.

Juno science orbits — Image: NASA/JPL/Caltech/LASP

After consulting with Lockheed Martin Space Systems of Denver and NASA Headquarters, Washington, the project decided to delay the PRM maneuver (which stays for “period reduction maneuver”) at least one orbit. Juno’s Period Reduction Maneuver, in its general architecture, is thought to be very similar to the Jupiter Orbit Insertion Burn: Juno will point away from the sun and Earth, begin sending status tones, face its engine towards the direction of travel and fire to slow the spacecraft down. Shorter in duration than JOI, the PRM will slow Juno enough to bring down the apojove altitude and reduce the orbital period to 14 days — 13 days, 23 hours and 41 minutes to be precise.

The most efficient time to perform such a burn is when the spacecraft is at the part of its orbit which is closest to the planet. The next window for the burn would therefore be during Juno’s close flyby of Jupiter on Dec. 11.

Juno Orbit Timeline — Image: NASA/JPL/Caltech/LASP

The first clean science orbit was supposed to start on November 16, 2016 and the last on February 6, 2018 (#36, Extra Orbit), but this PRM delay will consequently move forward all the rest of the mission.

The good news is that in the close flyby with a PRM included, all the instruments of Juno were planned to be shut down, but now, with the period reduction maneuver postponed, all of the spacecraft’s science instruments will be gathering data during the upcoming flyby next Wednesday, so we can expect a new awesome set of very close views of Jupiter.

Scott Bolton, principal investigator of the Juno mission, underlined that the orbital period does not affect the quality of the science that takes place during one of Juno’s close flybys of Jupiter. The mission is luckily very flexible. The incoming 14-day orbits after a successful PRM will be filled with activities such as science data acquisition and regularly performed communications sessions with Earth and that will take place during the delay period as well.

More information on the Juno mission is available at

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