Unify mission range and distance variable names

[jkirk5]

Desired capability or behavior.

Dynamic.Mission.RANGE and Dynamic.Mission.DISTANCE have the same meaning in Aviary. We should choose one and rename throughout Aviary.
The difference is probably a holdover from the LEAPS2 and GASPy codes.

@johnjasa: We only need one of them. I'd say distance is probably most clear?
@ehariton: My preference is to go with Mission.Dynamic.Range since Distance could be interpreted as vertical or horizontal, but Range has a stronger connection with horizontal movement. We should leave an alias reference so people familiar with one can see that we've changed the var name.

Is your feature request related to a problem? Please describe.

No response

Associated Bug Report

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[jkirk5]

I have a strong preference for ground_distance for a couple reasons. Range and distance are definitely distinct concepts that sometimes (but not always) overlap. Range is always discussed in the context of a prescribed mission - this can differ from actual ground distance traveled - a military jet, for example, has a "range" that is half of it's actual flight distance (it has to return to the same place).

Having "range" as the integrated value in dymos doesn't make much sense to me - it doesn't seem intuitive to refer to a point halfway along the mission as some kind of "partial range" state (try describing a specific point of a mission as "at a range of XXX nmi" - it sounds like you're referring to an entirely different mission with a new target range. Repeat but with "at a distance of XXX nmi" and it is much more clear you're referring to a point along the mission profile).

Ground distance alleviates any possible confusion on which distance is being referred to. IMO, this isn't quite as important as the range vs. distance dichotomy, as I've never seen anyone care about "true" flight distance, or length of the actual flight path arc through space.

[xjjiang]

There is no Dynamic.Mission.RANGE but Dynamic.Mission.DISTANCE. So, it is likely that it is done already. BTW, there is Mission.Landing.GROUND_DISTANCE. So, ground_distance may not be the best name.