3 Orbit Plans
Juno Mission Study of 3 Alternative Orbital Periods for the Main Science Orbits
11-days, 14-days and 20-days
Trajectories provided by JPL have been put into magnetic coordinates and plotted here. The times are in Day Of Year. The blue dot shows perijove and the small red dots are spaced every hour for 5 hours each before and after perijove.
These trajectories were then projected down onto the polar region of the planet (using the usual polar flattening) using 4 magnetic field models. We took spacecraft distances from the center of Jupiter +-10 Rj either side of perijove and used 4 magnetic field models to extrapolate from the spacecraft location down onto the planet and marked when/where the spacecraft is connected to the average main auroral regions for the North and South poles.
Magnetic field models:
Note that because of the precession of the spacecraft orbits, on some of the later orbits the projection goes to the opposite hemisphere – this needs to be fixed. The degree symbol did not convert to .pdf – comes out as a square.
To get a sense of the overall coverage from, say, the first 10 orbits, we have superposed these for north and for south polar regions for the 3 different orbital periods. Note that the coverage is remarkably similar – it’s more about phasing than coverage.
Next we show the North and South poles with all orbits for each case of 11-, 14-, and 20-day periods. Here we just use the Khurana magnetic field model. The local time of the spacecraft footprint on the ionosphere is shown by color. These plots are of the Juno trajectory in a system that is corotating with Jupiter – the System III longitude system. This is a LH system where the (west) longitude increases with time. Looking down on the system from the North, the planet rotates counter-clockwise.
These polar projections of the Juno location using the Khurana magnetic field model onto the polar region of Jupiter – average main auroral oval shown in black. The color coding shows the local time of the spacecraft magnetic foot print on the planet’s ionosphere. The start and end times of the trajectory projections are +-10 RJ from the center of Jupiter.
The consistent pattern is arrival (N) from dawn, perijove near dusk, and departure (S) at dawn. The actual crossings of the auroral are very different from the usual viewing of the aurora – that is, the spacecraft tends to cross the auroral oval most often close to the jovigraphic pole (North: system III 180-300 deg west=LH longitude North, 240-30 deg west=LH longitude South: system III 240-30 deg west=LH longitude) – while Hubble & ground-based observations are of the oval when it is tilted towards Earth – hence seeing the system III west=LH longitudes 140-160 deg North, 30-60 deg South.
Note there are relatively minor differences between the 11-day, 14-day and 20-day orbital alternatives.
For the JADE team we calculated the angle of the magnetic field relative to the spin axis (actually the normal to the spin axis, in the plane that contains the field and spin axis – see diagram in ReadMe file). These show that the greater the precession in local time due to the longer orbit durations (producing a longer mission) result in larger deflection angles towards the end of the mission. More information in this ReadMe file