When NASA sent a series of commands to the Juno spacecraft’s main engine last October, the spacecraft did not respond properly: two helium check valves that play an important role in its firing opened sluggishly. Those commands had been sent in preparation for a burn of the spacecraft’s Leros 1b engine, which would have brought Juno—a $1.1 billion mission to glean insights about Jupiter—into a significantly shorter orbital period around the gas giant.
Due to concerns about the engine, NASA held off on a “period reduction maneuver” that would shorten Juno’s orbital period from 53.4 to 14 days. When the next chance to do so came in December, again NASA held off. Now the space agency has made it official—Juno will remain in a longer, looping orbit around Jupiter for the extent of its lifetime observing the gas giant.
“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.”
In announcing the decision Friday, space agency scientists took pains to emphasize the benefits of a longer orbit around Jupiter. For example, the “bonus science” will allow Juno to further explore the outer reaches of the Jovian magnetosphere and better understand the interaction of these regions with the solar wind. Spending more time farther away from Jupiter will also lessen the spacecraft’s exposure to the gas giant’s harmful radiation, scientists said.
That being said, longer orbits increase other risks for the spacecraft. NASA had hoped Juno would make 36 close flybys of Jupiter during the next 20 months. Now, making all of those orbits will require nearly four additional years. Whether a spacecraft and its scientific equipment designed for less than two years of observations will be able to hold up for that long remains to be seen.
Operating Juno beyond its designed lifetime comes with a price tag, too. The requested budget for Juno operations in fiscal year 2017 was $39.1 million, which was projected to fall to $14.5 million in 2018 as the mission came to a close. Now, if NASA must come up with an additional $100 to $150 million for an extended mission, those costs will almost certainly harm other missions in the agency’s science directorate.