I'm trying to understand where Juno will pick up most of the slow, cumulative radiation damage within it's orbit.
Currently it is in the higher, 53 day orbit. The original plan was that tomorrow (2016-10-19) it would execute a roughly 395 m/s delta-v burn in order to drop down to a 14 day orbit.
If I understand correctly, most of the radiation that will damage Juno's instruments is associated with Jupiter's magnetic field and lies within a few Jovian diameters of the planet. The 54 day orbit spends slightly less time near jupiter than a 14 day orbit of the same perijove would, but it's a small difference.
If Juno is accumulating most of its radiation damage near the planet, then it should be able to last for 30 or more of these longer period orbits. However, I had just read that Juno would not last for the same number of flybys (over 30) if it remained in this higher orbit, due to accumulated radiation damage.
Here is one example. The lower, 14 day orbit is called the "Science Orbit" in several different articles I've read.
From the Spaceflight 101 article Rocket Burn postponed for NASA’s Juno, to remain in elongated Jupiter Orbit until December
Passing Jupiter on Wednesday, Juno will be outbound again with its next close pass of the planet on December 11 which will be the next opportunity for the Period Reduction Maneuver – pending evaluations of the suspect check valve signature.
The option of a third Capture Orbit has be prepared as part of numerous contingency scenarios worked out for this mission, however, there is some urgency in getting Juno down into the science orbit due to the limited lifetime of the spacecraft in the extreme radiation environment of Jupiter. (my emphasis)
Are my assumptions about the location of the highest damaging parts of the orbit incorrect, and a substantial amount of radiation damage happens far from Jupiter, and thus in each 54 day orbit the accumulated dose is much larger than in each 14 day lower, "Science" orbit?
above: "Capture Orbit Design – Image: NASA/JPL/LASP". From Spaceflight 101
above: sketch of a few of Juno's lower 14-day orbits and illustration of the strongest radiation bands near Jupiter. From the Lost Angeles Times
above: "Animation of Jupiter's Synchrotron Radiation Torus. Credit: NASA/JPL - Caltech". From the Vatican Observatory Blog