Juice's precise Earth flyby leaves more propellant for Jupiter's icy moons, ESA says

The six in that count were opportunities: windows ESA set aside in the four weeks before the pass for adjusting Juice's approach ^[4]. The one that was used, a tiny nudge, put the spacecraft on the trajectory that made the most of Earth's gravity ^[4]. The other five went unused ^[1]. Operators have tracked Juice with extra care since 17 August and will keep doing so until 10 October ^[5].

"The flyby required ultra-precise navigation in real time. Thanks to our very careful planning, we used only a small amount of the propellant reserved for this flyby," said Angela Dietz, Juice's spacecraft operations manager ^[7]. "This gives us more to use at Jupiter to carry out observations of the planet's icy moons," she said ^[8].

That account comes from the operators themselves. ESA did not say how much propellant was left over, or how it converts into observing time at Jupiter. I think the single nudge is good evidence of careful navigation on the way in. As evidence about the science budget at Jupiter it is weaker, until ESA puts a figure on the reserve.

The instrument work took months to plan. Teams from ESA's spacecraft operations, science operations and technical centres worked with the external teams behind Juice's 10 science instruments to decide which to switch on and when ^[10]. "Juice's journey to Jupiter provides only a few opportunities to calibrate and validate the instruments under well-understood environmental conditions," said Claire Vallat, the Juice project scientist who led that effort ^[11].

Power forced some of the choices. Instrument activities "sometimes have to be prioritised, for example when Juice was in Earth's shadow this morning, and relying on battery power alone," Vallat said ^[12]. On this flyby, she said, calibration activities "were prioritised based on their relevance to preparing the instruments for their work at Jupiter, while also considering whether an opportunity is unique or can be scheduled later in the journey" ^[13].

ESA describes an Earth flyby as relatively straightforward next to the 35 flybys of Jupiter's giant moons, among them Ganymede and Europa, that Juice will make later ^[14]. Discussions on instrument operations for the Europa passes started 10 years ago and will continue until Juice flies past Europa in the early 2030s ^[15].