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<\/p>\nOverall, NASA\u2019s Juno spacecraft in orbit of Jupiter is in good health and good condition as the probe heads toward its two-Earth year anniversary in orbit of the giant planet this July. The spacecraft\u2019s good health was a good sign ahead of NASA\u2019s decision of whether to end the mission this summer or extend it, a decision that was largely understood to be related to how the spacecraft holds up to Jupiter\u2019s intense radiation field. On June 7, the decision was taken to extend the mission.<\/p>\n
Juno overview:<\/b><\/p>\n
Following a flawless launch and cruise to Jupiter, the Juno spacecraft entered orbit of the gas giant on 4 July 2016, entering a 53 day checkout orbit. Juno was supposed to complete two of these checkout orbits before performing an engine burn to reduce the spacecraft\u2019s orbital period and apojove (farthest point in the craft\u2019s orbit of Jupiter) to its planned 14 day science orbit.<\/p>\n
This engine burn, called the Period Reduction Maneuver, was planned for 18 October 2016. However, during the second 53 day checkout orbit and just four days prior to the Period Reduction Maneuver as NASA worked through tests of Juno\u2019s primary engine, engineers saw something in the data that gave them cause for concern.<\/p>\n
At the time, Rick Nybakken, Juno project manager at NASA\u2019s Jet Propulsion Laboratory said, \u201cTelemetry indicates that two helium check valves that play an important role in the firing of the spacecraft\u2019s main engine did not operate as expected during a command sequence that was initiated yesterday. The valves should have opened in a few seconds, but it took several minutes.\u201d<\/p>\n
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Juno performs its critical Orbit Insertion burn at Jupiter on 4 July 2016. Credit: Nathan Koga for NSF\/L2<\/p>\n
The helium valve issue was highly reminiscent of a failure on the Japan Aerospace Exploration Agency\u2019s (JAXA\u2019s) Akatsuki spacecraft which suffered an incomplete engine burn due to faulty helium valves while trying to enter orbit of Venus in 2010.<\/p>\n<\/p>\n
Ultimately, the data on Juno\u2019s helium valves indicated that it was too risky to attempt ignition of the engine, and NASA decided to leave Juno in its 53 day orbit, significantly changing the mission outlook and timing of science operations.<\/p>\n
SpaceX launch tickets (adsbygoogle = window.adsbygoogle || []).push({});<\/p>\n Juno\u2019s 14 day science orbit had been designed to allow the craft to meet its minimum mission success, defined by Juno\u2019s pre-launch criteria as 12 science gathering dives close to Jupiter\u2019s atmosphere, within six months of entering the science orbit. Now, a year-and-a-half after entering orbit of Jupiter, Juno has completed just nine science dives (11 perijoves \u2013 time of closest approach \u2013 overall).<\/p>\n Under the current mission timeline, Juno will not achieve its 12th science dive \u2013 assuming every science instrument continues to function \u2013 until 16 July 2018 during the 14th overall perijove, a far cry from the planned 34 science dive perijoves that were planned to be completed by this month (February 2018) had Juno entered its proper 14 day science orbit.<\/p>\n Current status and mission extension decision:<\/b><\/p>\n Under the originally planned mission timeline, Juno would have completed 37 total orbits of Jupiter, two in the 53 day checkout orbit, 34 science orbits, and one final orbit to send the craft into Jupiter\u2019s atmosphere for a destructive end-of-mission plunge to protect the planet\u2019s potentially life harboring moons.<\/p>\n<\/p>\n