# Did Juno do a plane change circa October 2019? If so, by how much?

There are several reports in the news that the Juno spacecraft executed a very long propulsive maneuver so that it wouldn't pass through Jupiter's shadow. Apparently it would be in dark so long that the batteries would die before it returned to sunlight, and that was considered somewhere between risky and fatal.

Last time I checked which is about two years ago, Juno was in a highly elliptical, near-polar orbit.

So how did this maneuver allow Juno to avoid Jupiter's shadow (presumably at apoapsis?) Was it basically a plane-change, rotating the vertical orbital plane from one side of the shadow to the other, or was it something more interesting?

Either way, if it's possible say "by how much" the orbit was changed in some way circa October 2019, that would be good to know.

• The image in that article appears to imply that the orbit is still polar, which should indeed imply a plane change. But I'm not confident without actual data or statements. Oct 3, 2019 at 10:39
• Alternately it could have changed the eccentricity, changing the orbital period, and so missing it that way, but the plane change is far more likley
– user20636
Oct 3, 2019 at 15:57

Juno indeed performed a plane change circa October 2019.

Using trajectory data available on JPL's SSD Horizons System I turned state vectors into Keplerian elements (because the Horizons output of orbital elements is not very spreadsheet friendly):

The change in inclination is about 5°.

Edit: Stumbled upon Pavlak et al. "Juno Trajectory Redesign Following PRM Cancellation," 2017 which states:

For the 53-day trajectory, solar eclipse avoidance is achieved via a series of apojove maneuvers – up to and including APO-21 – to ensure that the spacecraft does not enter eclipse inbound to PJ-22. Then, at APO-22, a large, 50-60 m/s, maneuver is leveraged to change the orbital plane geometry – including an inclination increase of 4-5 degrees – and avoid eclipse entry inbound to PJ-23.

The change in inclination is about 5° and the maneuver cost 50-60 m/s of $$\Delta V$$ (nominal 52.95 m/s).

• i.stack.imgur.com/pKQb1.png Horizons also provides osculating orbital elements, (the Keplerian elements of the instantaneous motion of an object If the reference body where the only gravitational body that exists). If you choose Jupiter as the reference, it should give essentially the same thing as your analysis of the state vectors referenced to Jupiter. (you can choose any body as the reference for osculating elements; if you chose Mars as a reference for Juno you'd get numbers, but they wouldn't mean much since Juno is primarily responding to Jupiter's gravity)
– uhoh
Oct 29, 2021 at 20:23
• @uhoh I am aware, but I dislike how it outputs in a CSV format (one data point spread over multiple rows AND columns!!!) Oct 29, 2021 at 22:19
• Spreading one time point over multiple rows (rather than one row per point) sounds like some kind of bug somewhere, or at least a problem that can be easily solved. I haven't tried the new Horizons interface yet, but I never had a problem with the old one. Of course I always use Python to read the downloaded text files rather than Excel.
– uhoh
Oct 30, 2021 at 0:23
• I clicked the CSV box and did a quick download and opened in my Excel and it seems okay to me i.stack.imgur.com/WiJTJ.jpg
– uhoh
Oct 30, 2021 at 0:30
• @uhoh works now (of course!), thanks! Oct 30, 2021 at 17:21